Publications by authors named "Michael M Lell"

48 Publications

3D-Visualization of Neurovascular Compression at the Ventrolateral Medulla in Patients with Arterial Hypertension.

Clin Neuroradiol 2021 Jun 27;31(2):335-345. Epub 2020 May 27.

Department of Neurosurgery, Friedrich-Alexander University, Erlangen-Nuremberg (FAU), Erlangen, Germany.

Purpose: Controversy exists on the association of arterial hypertension (HTN) and neurovascular compression (NVC) at the ventrolateral medulla (VLM). No standardized and reproducible technique has been introduced yet for detection of NVC in HTN. This study aimed to generate, analyze and compare different results of exact reproducible anatomical 3D-representations of the VLM in patients with HTN, based on magnetic resonance imaging (MRI).

Methods: A 3T scanner provided MRI (T2-constructive interference in steady state (CISS) high resolution imaging and three-dimensional Time-of-flight (3D-TOF) angiography) from the posterior fossa of 44 patients with clinical treatment-resistant HTN. Image processing consists of segmentation of the CISS data, registration and fusion of the CISS and TOF data and visualization. For each patient two 3D-visualizations (before and after fusion) were obtained. The reproduction quality of the vessels, flow-related signal variability and pulsation artifacts were analyzed and compared, using a ranking score.

Results: Integrating vascular information from TOF into CISS data reduced artifacts in 3D-visualizations of exclusively processed CISS data. The quality of 3D-visualization of the vessels near the brain stem was significantly improved (p = 0.004). The results were reproducible and reliable. The quality of the 3D-presentations of neurovascular relationships at the VLM improved significantly (p < 0.001).

Conclusion: The 3D-visualization of fused image data provides an excellent overview of the relationship between cranial nerves and vessels at the VLM and simplifies the detection of NVC in HTN. It provides a powerful tool for future clinical and scientific research. Although microvascular decompression (MVD) in treatment resistant HTN is not a standard procedure, it can be discussed in selected patients with intractable severe HTN.
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http://dx.doi.org/10.1007/s00062-020-00916-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8211615PMC
June 2021

Recent and Upcoming Technological Developments in Computed Tomography: High Speed, Low Dose, Deep Learning, Multienergy.

Invest Radiol 2020 01;55(1):8-19

Division of X-ray Imaging and CT (E025), German Cancer Research Center (DKFZ), Heidelberg, Germany.

The advent of computed tomography (CT) has revolutionized radiology, and this revolution is still going on. Starting as a pure head scanner, modern CT systems are now able to perform whole-body examinations within a couple of seconds in isotropic resolution, single-rotation whole-organ perfusion, and temporal resolution to fulfill the needs of cardiac CT. Because of the increasing number of CT examinations in all age groups and overall medical-driven radiation exposure, dose reduction remains a hot topic. Although fast gantry rotation, broad detector arrays, and different dual-energy solutions were main topics in the past years, new techniques such as photon counting detectors, powerful x-ray tubes for low-kV scanning, automated image preprocessing, and machine learning algorithms have moved into focus today.The aim of this article is to give an overview of the technical specifications of up-to-date available CT systems and recent hardware and software innovations for CT systems in the near future.
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http://dx.doi.org/10.1097/RLI.0000000000000601DOI Listing
January 2020

Evaluation of ventricular septal defects using high pitch computed tomography angiography of the chest in children with complex congenital heart defects below one year of age.

J Cardiovasc Comput Tomogr 2019 Jul - Aug;13(4):226-233. Epub 2019 Feb 1.

University Hospital Erlangen, Department of Radiology, Maximiliansplatz 1, 91054, Erlangen, Germany; Imaging Science Institute Erlangen, Ulmenweg 18, 91054, Erlangen, Germany. Electronic address:

Background: Aim of this study was to assess the accuracy of ventricular septal defects (VSD) using high pitch computed tomography angiography (CTA) of the chest in children below 1 year of age, compared to the intraoperative findings and echocardiography.

Methods: Out of 154 patients that underwent Dual-Source CTA of the chest using a high-pitch protocol at low tube voltages (70-80 kV), 55 underwent surgical repair of a VSD (median age 8 days, range 1-348 days). The margins of the VSDs and their relation to the surrounding structures were reproduced by en-face views using multiplanar reformations (MPR). Absolute diameter, normalized area and relative area compared to the aortic valve annulus were used for discrimination between restrictive and non-restrictive defects. Localization was classified into four subtypes. The results were compared to two-dimensional echocardiography and intraoperative findings.

Results: Median absolute size of VSDs did not differ significantly between CTA-measurements (10.8 mm, range 2.8-18.1 mm) and intraoperative findings (12.0 mm, 3.0-25.0 mm, p = 0.09). Echocardiographic values were significantly lower (9.6 mm, 3.0-18.5 mm, both p < 0.01). The classification of the location and orientation matched the intraoperative situs in 96.4% of all cases using CT and in 87.3% using echocardiography. Echocardiography missed the relation to valves in 11% of all cases. Pre-interventional sensitivity and specificity for detection of a VSD were 97.2/98.9% compared to echocardiography. Median radiation dose was 0.32 mSv (range 0.12-2.00 mSv) and differed significantly between second and third generation Dual-Source CT (0.43 vs. 0.22 mSv, p = 0.003).

Conclusion: Size and subtype of VSDs can be accurately assessed by CTA of the chest in patients with complex congenital heart defects at a very low radiation dose.
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http://dx.doi.org/10.1016/j.jcct.2019.01.023DOI Listing
February 2020

Impact of Contrast Media Concentration on Low-Kilovolt Computed Tomography Angiography: A Systematic Preclinical Approach.

Invest Radiol 2018 05;53(5):264-270

Objectives: Low peak kilovoltage (kVp) protocols in computed tomography angiography (CTA) demand a review of contrast media (CM) administration practices. The aim of this study was to systematically evaluate different iodine concentrations of CM in a porcine model.

Materials And Methods: Dynamic 70 kVp CTA was performed on 7 pigs using a third-generation dual-source CT system. Three CM injection protocols (A-C) with an identical total iodine dose and iodine delivery rate (150 mg I/kg, 12 s, 0.75 g I/s) differed in iodine concentration and flow rate (protocol A: 400 mg I/mL, 1.9 mL/s; B: 300 mg I/mL, 2.5 mL/s; C: 150 mg I/mL, 5 mL/s). All protocols were applied in a randomized order and compared intraindividually. Arterial enhancement at different locations in the pulmonary artery, the aorta, and aortic branches was measured over time. Time attenuation curves, peak enhancement, time to peak, and bolus tracking delay times needed for static CTA were calculated. The reproducibility of optimal parameters was tested in single-phase CTA.

Results: The heart rates of the pigs were comparable for all protocols (P > 0.7). The injection pressure was significantly higher for protocol A (64 ± 5 psi) and protocol C (55 ± 3 psi) compared with protocol B (39 ± 2 psi) (P < 0.001). Average arterial peak enhancement in the dynamic scans was 359 ± 51 HU (protocol A), 382 ± 36 HU (B), and 382 ± 60 HU (C) (A compared with B and C: P < 0.01; B compared with C: P = 0.995). Time to peak enhancement decreased with increasing injection rate. The delay time for bolus tracking depended on the injection rate as well and was highest for protocol A (4.7 seconds) and lowest for protocol C (3.9 seconds) (P = 0.038). The peak enhancement values of the dynamic scans highly correlated with those of the single-phase CTA scans.

Conclusions: In 70 kVp CTA, 300 mg I/mL iodine concentrations showed to be superior to high-concentration CM when keeping the iodine delivery rate constant. Besides, iodine concentrations as low as 150 mg I/mL can be administered without compromising vascular enhancement. This opens up new possibilities in CM administration.
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http://dx.doi.org/10.1097/RLI.0000000000000437DOI Listing
May 2018

Myocardial adaption to HI(R)T in previously untrained men with a randomized, longitudinal cardiac MR imaging study (Physical adaptions in Untrained on Strength and Heart trial, PUSH-trial).

PLoS One 2017 7;12(12):e0189204. Epub 2017 Dec 7.

Department of Radiology and Nuclear Medicine, Hospital of Nuremberg, Paracelsus Medical University, Nuremberg, Bavaria, Germany.

Objective: Although musculoskeletal effects in resistance training are well described, little is known about structural and functional cardiac adaption in formerly untrained subjects. We prospectively evaluated whether short term high intensity (resistance) training (HI(R)T) induces detectable morphologic cardiac changes in previously untrained men in a randomized controlled magnetic resonance imaging (MRI) study.

Materials And Methods: 80 untrained middle-aged men were randomly assigned to a HI(R)T-group (n = 40; 43.5±5.9 years) or an inactive control group (n = 40; 42.0±6.3 years). HI(R)T comprised 22 weeks of training focusing on a single-set to failure protocol in 2-3 sessions/week, each with 10-13 exercises addressing main muscle groups. Repetitions were decreased from 8-10 to 3-5 during study period. Before and after HI(R)T all subjects underwent physiologic examination and cardiac MRI (cine imaging, tagging).

Results: Indexed left (LV) and right ventricular (RV) volume (LV: 76.8±15.6 to 78.7±14.8 ml/m2; RV: 77.0±15.5 to 78.7±15.1 ml/m2) and mass (LV: 55.5±9.7 to 57.0±8.8 g/m2; RV: 14.6±3.0 to 15.0±2.9 g/m2) significantly increased with HI(R)T (all p<0.001). Mean LV and RV remodeling indices of HI(R)T-group did not alter with training (0.73g/mL and 0.19g/mL, respectively [p = 0.96 and p = 0.87]), indicating balanced cardiac adaption. Indexed LV (48.4±11.1 to 50.8±11.0 ml/m2) and RV (48.5±11.0 to 50.6±10.7 ml/m2) stroke volume significantly increased with HI(R)T (p<0.001). Myocardial strain and strain rates did not change following resistance exercise. Left atrial volume at end systole slightly increased after HI(R)T (36.2±7.9 to 37.0±8.4 ml/m2, p = 0.411), the ratio to end-diastolic LV volume at baseline and post-training was unchanged (0.47 vs. 0.47, p = 0.79).

Conclusion: 22 weeks of HI(R)T lead to measurable, physiological changes in cardiac atrial and ventricular morphologic characteristics and function in previously untrained men.

Trial Regristration: The PUSH-trial is registered at the US National Institutes of Health (ClinicalTrials.gov), NCT01766791.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0189204PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5720775PMC
December 2017

Image quality, diagnostic accuracy, and potential for radiation dose reduction in thoracoabdominal CT, using Sinogram Affirmed Iterative Reconstruction (SAFIRE) technique in a longitudinal study.

PLoS One 2017 5;12(7):e0180302. Epub 2017 Jul 5.

Department of Radiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany.

Objective: To step-wise evaluate image quality of sinogram-affirmed iterative reconstruction (SAFIRE) in reduced-dose (RD) thoracoabdominal computed tomography (CT) compared to full-dose (FD) and RD filtered back projection (FBP) in a longitudinal study.

Materials And Methods: 122 patients were included in this prospective study. 49 patients (14 men: mean age ± SD, 56±0.4 years; 35 women: 58±1.3 years) completed FD, RD1 (80%-dose) and RD2 (60%-dose) thoracoabdominal CT. Each CT dataset was reconstructed with FBP and SAFIRE. For quantitative image analysis image noise was measured in defined tissue regions. Qualitative image evaluation was performed according to the European Guidelines on Quality criteria for CT. Additionally artifacts, lesion conspicuity, and edge sharpness were assessed.

Results: Compared to FD-FBP noise in soft tissue increased by 12% in RD1-FBP and 27% in RD2-FBP reconstructions, whereas SAFIRE lead to a decrease of 28% (RD1) and 17% (RD2), respectively (all p <0.001). Visually sharp reproduction, lesion conspicuity, edge sharpness of pathologic findings, and overall image quality did not differ statistically significant between FD-FBP and RD-SAFIRE datasets. Image quality decreased in RD1- and RD2-FBP compared to FD-FBP, reaching statistically significance in RD2 datasets (p <0.001). In RD1- and RD2-FBP (p <0.001) streak artifacts were noted.

Conclusion: Using SAFIRE the reference mAs in thoracoabdominal CT can be reduced by at least 30% in clinical routine without loss of image quality or diagnostic information.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0180302PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5498038PMC
October 2017

Relationship between low tube voltage (70 kV) and the iodine delivery rate (IDR) in CT angiography: An experimental in-vivo study.

PLoS One 2017 20;12(3):e0173592. Epub 2017 Mar 20.

MR and CT Contrast Media Research, Bayer Healthcare, Berlin, Germany.

Objective: Very short acquisition times and the use of low-kV protocols in CTA demand modifications in the contrast media (CM) injection regimen. The aim of this study was to optimize the use of CM delivery parameters in thoraco-abdominal CTA in a porcine model.

Materials And Methods: Six pigs (55-68 kg) were examined with a dynamic CTA protocol (454 mm scan length, 2.5 s temporal resolution, 70 s total acquisition time). Four CM injection protocols were applied in a randomized order. 120 kV CTA protocol: (A) 300 mg iodine/kg bodyweight (bw), IDR = 1.5 g/s (flow = 5 mL/s), injection time (ti) 12 s (60 kg bw). 70 kV CTA protocols: 150 mg iodine/kg bw: (B) IDR = 0.75 g/s (flow = 2.5 mL/s), ti = 12 s (60 kg bw); (C) IDR = 1.5 g/s (flow = 5 mL/s), ti = 12 s (60 kg bw); (D) IDR = 3.0 g/s (flow = 10 mL/s), ti = 3 s (60 kg bw). The complete CM bolus shape was monitored by creating time attenuation curves (TAC) in different vascular territories. Based on the TAC, the time to peak (TTP) and the peak enhancement were determined. The diagnostic window (relative enhancement > 300 HU), was calculated and compared to visual inspection of the corresponding CTA data sets.

Results: The average relative arterial peak enhancements after baseline correction were 358.6 HU (A), 356.6 HU (B), 464.0 HU (C), and 477.6 HU (D). The TTP decreased with increasing IDR and decreasing ti, protocols A and B did not differ significantly (systemic arteries, p = 0.843; pulmonary arteries, p = 0.183). The delay time for bolus tracking (trigger level 100 HU; target enhancement 300 HU) for single-phase CTA was comparable for protocol A and B (3.9, 4.3 s) and C and D (2.4, 2.0 s). The scan window time frame was comparable for the different protocols by visual inspection of the different CTA data sets and by analyzing the TAC.

Conclusions: All protocols provided sufficient arterial enhancement. The use of a 70 kV CTA protocol is recommended because of a 50% reduction of total CM volume and a 50% reduced flow rate while maintaining the bolus profile. In contrast to pulmonary arterial enhancement, the systemic arterial enhancement improved only slightly increasing the IDR from 1.5 g/s to 3 g/s because of bolus dispersion of the very short bolus (3s) in the lungs.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0173592PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5358883PMC
August 2017

Radiation dose reduction in parasinus CT by spectral shaping.

Neuroradiology 2017 Feb 16;59(2):169-176. Epub 2017 Jan 16.

Department of Radiology, University Hospital Erlangen, Maximiliansplatz 1, 91054, Erlangen, Germany.

Introduction: Spectral shaping aims to narrow the X-ray spectrum of clinical CT. The aim of this study was to determine the image quality and the extent of radiation dose reduction that can be achieved by tin prefiltration for parasinus CT.

Methods: All scans were performed with a third generation dual-source CT scanner. A study protocol was designed using 100 kV tube voltage with tin prefiltration (200 mAs) that provides image noise levels comparable to a low-dose reference protocol using 100 kV without spectral shaping (25 mAs). One hundred consecutive patients were prospectively enrolled and randomly assigned to the study or control group. All patients signed written informed consent. The study protocol was approved by the local Institutional Review Board and applies to the HIPAA. Subjective and objective image quality (attenuation values, image noise, and contrast-to-noise ratio (CNR)) were assessed. Radiation exposure was assessed as volumetric CT dose index, and effective dose was estimated. Mann-Whitney U test was performed for radiation exposure and for image noise comparison.

Results: All scans were of diagnostic image quality. Image noise in air, in the retrobulbar fat, and in the eye globe was comparable between both groups (all p > 0.05). CNR did not differ significantly between both groups (p = 0.7). Radiation exposure (1.7 vs. 2.1 mGy, p < 0.01) and effective dose (0.055 vs. 0.066 mSv, p < 0.01) were significantly reduced in the study group.

Conclusion: Radiation dose can be further reduced by 17% for low-dose parasinus CT by tin prefiltration maintaining diagnostic image quality.
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http://dx.doi.org/10.1007/s00234-016-1780-0DOI Listing
February 2017

Reaching for better image quality and lower radiation dose in head and neck CT: advanced modeled and sinogram-affirmed iterative reconstruction in combination with tube voltage adaptation.

Dentomaxillofac Radiol 2017 Jan 8;46(1):20160131. Epub 2016 Sep 8.

1 Department of Radiology, University Hospital Erlangen, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Germany.

Objectives: The aim of this study was to evaluate image quality and radiation dose in low-dose head and neck CT comparing two different commercially available iterative reconstruction algorithms: sinogram-affirmed iterative reconstruction (SAFIRE) and advanced modeled iterative reconstruction (ADMIRE) with fixed and automated tube voltage adaptation (TVA).

Methods: CT examinations of 103 patients were analysed. 58 patients were examined on a single-source CT at fixed tube voltage of 120 kV and reconstructed with filtered back projection (FBP) and SAFIRE (Strength Level 3). 45 patients were examined in a single-source mode on a dual-source CT with automated TVA and reconstructed with FBP and ADMIRE (Strength Levels 2 and 3). Image noise was calculated in seven anatomical volumes of interest. Subjective evaluation of the CT images was performed using a four-grade scale.

Results: Mean CT numbers of FBP and the corresponding iterative reconstruction did not differ significantly (p = 0.74-0.99). Image noise was lower with both iterative reconstruction techniques than with FBP (SAFIRE 3: -22.3%; ADMIRE 2: -14.9%; ADMIRE 3: -24.2%; all p < 0.05); hence, the signal-to-noise ratio and the contrast-to-noise values were higher. Subjective image quality revealed a more favourable result for the iterative reconstruction. ADMIRE 3 in combination with automated TVA showed 14.4% (p < 0.05) less image noise with a 7.5% lower radiation dose than SAFIRE 3 with fixed tube voltage.

Conclusions: Higher image quality at lower radiation dose can be achieved using ADMIRE in combination with automated TVA.
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http://dx.doi.org/10.1259/dmfr.20160131DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5595050PMC
January 2017

Dose reduction potential of iterative reconstruction algorithms in neck CTA-a simulation study.

Dentomaxillofac Radiol 2016 Oct 19;45(8):20160228. Epub 2016 Aug 19.

1 Institute of Radiology, University Hospital Erlangen-Nuernberg, University of Erlangen-Nuernberg, Erlangen, Germany.

Objectives: This study aimed to determine the degree of radiation dose reduction in neck CT angiography (CTA) achievable with Sinogram-affirmed iterative reconstruction (SAFIRE) algorithms.

Methods: 10 consecutive patients scheduled for neck CTA were included in this study. CTA images of the external carotid arteries either were reconstructed with filtered back projection (FBP) at full radiation dose level or underwent simulated dose reduction by proprietary reconstruction software. The dose-reduced images were reconstructed using either SAFIRE 3 or SAFIRE 5 and compared with full-dose FBP images in terms of vessel definition. 5 observers performed a total of 3000 pairwise comparisons.

Results: SAFIRE allowed substantial radiation dose reductions in neck CTA while maintaining vessel definition. The possible levels of radiation dose reduction ranged from approximately 34 to approximately 90% and depended on the SAFIRE algorithm strength and the size of the vessel of interest. In general, larger vessels permitted higher degrees of radiation dose reduction, especially with higher SAFIRE strength levels. With small vessels, the superiority of SAFIRE 5 over SAFIRE 3 was lost.

Conclusions: Neck CTA can be performed with substantially less radiation dose when SAFIRE is applied. The exact degree of radiation dose reduction should be adapted to the clinical question, in particular to the smallest vessel needing excellent definition.
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http://dx.doi.org/10.1259/dmfr.20160228DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5595027PMC
October 2016

Dual-Energy Computed Tomography Angiography of the Head and Neck With Single-Source Computed Tomography: A New Technical (Split Filter) Approach for Bone Removal.

Invest Radiol 2016 10;51(10):618-23

From the *Department of Radiology, University Hospital Erlangen-Nuremberg, Erlangen; and †Siemens AG, Healthcare Sector, Forchheim, Germany.

Objectives: Dual-energy computed tomographic angiography (DE-CTA) has been demonstrated to improve the visualization of the head and neck vessels. The aim of this study was to test the potential of split-filter single-source dual-energy CT to automatically remove bone from the final CTA data set.

Materials And Methods: Dual-energy CTA was performed in 50 consecutive patients to evaluate the supra-aortic arteries, either to grade carotid artery stenosis or to rule out traumatic dissections. Dual-energy CTA was performed on a 128-slice single-source CT system equipped with a special filter array to separate the 120-kV spectrum into a high- and a low-energy spectrum for DE-based automated bone removal. Image quality of fully automated bone suppression and subsequent manual optimization was evaluated by 2 radiologists on maximum intensity projections using a 4-grade scoring system. The effect of image reconstruction with an iterative metal artifact reduction algorithm on DE postprocessing was tested using a 3-grade scoring system, and the time demand for each postprocessing step was measured.

Results: Two patients were excluded due to insufficient arterial contrast enhancement; in the remaining 48 patients, automated bone removal could be performed successfully. The addition of iterative metal artifact reduction algorithm improved image quality in 58.3% of the cases. After manual optimization, DE-CTA image quality was rated excellent in 7, good in 29, and moderate in 10 patients. Interobserver agreement was high (κ = 0.85). Stenosis grading was not influenced using DE-CTA with bone removal as compared with the original CTA. The time demand for DE image reconstruction was significantly higher than for single-energy reconstruction (42.1 vs 20.9 seconds).

Conclusions: Our results suggest that bone removal in DE-CTA of the head and neck vessels with a single-source CT is feasible and can be performed within acceptable time and moderate user interaction.
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http://dx.doi.org/10.1097/RLI.0000000000000290DOI Listing
October 2016

Feasibility of Respiratory-gated High-pitch Spiral CT:: Free-breathing Inspiratory Image Quality.

Acad Radiol 2016 Apr 4;23(4):406-12. Epub 2016 Feb 4.

Department of Radiology, University of Erlangen, Maximiliansplatz 1, Erlangen, Germany; Imaging Sciences Institute (ISI), Ulmenweg 18, Erlangen, Germany. Electronic address:

Rationale And Objectives: This study aimed to develop and implement a respiratory-gated setup for dual-source computed tomography (CT) at high pitch to examine patients in a reproducible inspiratory phase.

Materials And Methods: Twenty-one patients underwent free-breathing respiratory-gated chest CT using a high-pitch scan mode no more than 6 months after inspiratory breath-held nongated CT, which serves as reference. Scan parameters were as follows: pitch = 3.4, 128 × 0.6 mm collimation, 0.28 s gantry rotation time, and 150 ref.mAs per tube at 120 kV. The examinations were triggered using the tidal wave provided by a respiratory-gating system as input signal. Image quality was assessed focusing on artifacts and delineation of the anatomical and pathological structures. Lung volumes were measured on both free-breathing and reference examinations.

Results: All examinations were performed without complications. Image quality was high with both protocols. Significantly less motion artifacts were recorded with the high-pitch mode compared to the reference (P = 0.02). Most of the artifacts were located in the peripheral parts of the lower lobes for the study group and in the central part of the left lower lobe for the reference. Average total lung volume was 4.5 ± 1.5 L in respiratory-gated examinations and 5.8 ± 0.9 L in examinations with breath-hold in inspiration.

Conclusions: High-pitch chest CT scanning during free breathing minimizes motion artifacts, improving image quality in patients with limited breath-holding abilities. To assure scanning in an inspiratory phase, data acquisition should be triggered with a respiratory-gating system.
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http://dx.doi.org/10.1016/j.acra.2015.12.018DOI Listing
April 2016

A Novel Pairwise Comparison-Based Method to Determine Radiation Dose Reduction Potentials of Iterative Reconstruction Algorithms, Exemplified Through Circle of Willis Computed Tomography Angiography.

Invest Radiol 2016 May;51(5):331-9

From the *Institute of Radiology, University of Erlangen-Nuremberg, Erlangen; and †Siemens Healthcare, Forchheim, Germany.

Objectives: The aim of this study was to determine the dose reduction potential of iterative reconstruction (IR) algorithms in computed tomography angiography (CTA) of the circle of Willis using a novel method of evaluating the quality of radiation dose-reduced images.

Materials And Methods: This study relied on ReconCT, a proprietary reconstruction software that allows simulating CT scans acquired with reduced radiation dose based on the raw data of true scans. To evaluate the performance of ReconCT in this regard, a phantom study was performed to compare the image noise of true and simulated scans within simulated vessels of a head phantom. That followed, 10 patients scheduled for CTA of the circle of Willis were scanned according to our institute's standard protocol (100 kV, 145 reference mAs). Subsequently, CTA images of these patients were reconstructed as either a full-dose weighted filtered back projection or with radiation dose reductions down to 10% of the full-dose level and Sinogram-Affirmed Iterative Reconstruction (SAFIRE) with either strength 3 or 5. Images were marked with arrows pointing on vessels of different sizes, and image pairs were presented to observers. Five readers assessed image quality with 2-alternative forced choice comparisons.

Results: In the phantom study, no significant differences were observed between the noise levels of simulated and true scans in filtered back projection, SAFIRE 3, and SAFIRE 5 reconstructions.The dose reduction potential for patient scans showed a strong dependence on IR strength as well as on the size of the vessel of interest. Thus, the potential radiation dose reductions ranged from 84.4% for the evaluation of great vessels reconstructed with SAFIRE 5 to 40.9% for the evaluation of small vessels reconstructed with SAFIRE 3.

Conclusions: This study provides a novel image quality evaluation method based on 2-alternative forced choice comparisons. In CTA of the circle of Willis, higher IR strengths and greater vessel sizes allowed higher degrees of radiation dose reduction.
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http://dx.doi.org/10.1097/RLI.0000000000000243DOI Listing
May 2016

Third-generation dual-source 70-kVp chest CT angiography with advanced iterative reconstruction in young children: image quality and radiation dose reduction.

Pediatr Radiol 2016 Apr 6;46(4):462-72. Epub 2016 Jan 6.

Department of Radiology, University Hospital Erlangen, Maximiliansplatz 1, 91054, Erlangen, Germany.

Background: Many technical updates have been made in multi-detector CT.

Objective: To evaluate image quality and radiation dose of high-pitch second- and third-generation dual-source chest CT angiography and to assess the effects of different levels of advanced modeled iterative reconstruction (ADMIRE) in newborns and children.

Materials And Methods: Chest CT angiography (70 kVp) was performed in 42 children (age 158 ± 267 days, range 1-1,194 days). We evaluated subjective and objective image quality, and radiation dose with filtered back projection (FBP) and different strength levels of ADMIRE. For comparison were 42 matched controls examined with a second-generation 128-slice dual-source CT-scanner (80 kVp).

Results: ADMIRE demonstrated improved objective and subjective image quality (P < .01). Mean signal/noise, contrast/noise and subjective image quality were 11.9, 10.0 and 1.9, respectively, for the 80 kVp mode and 11.2, 10.0 and 1.9 for the 70 kVp mode. With ADMIRE, the corresponding values for the 70 kVp mode were 13.7, 12.1 and 1.4 at strength level 2 and 17.6, 15.6 and 1.2 at strength level 4. Mean CTDIvol, DLP and effective dose were significantly lower with the 70-kVp mode (0.31 mGy, 5.33 mGy*cm, 0.36 mSv) compared to the 80-kVp mode (0.46 mGy, 9.17 mGy*cm, 0.62 mSv; P < .01).

Conclusion: The third-generation dual-source CT at 70 kVp provided good objective and subjective image quality at lower radiation exposure. ADMIRE improved objective and subjective image quality.
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http://dx.doi.org/10.1007/s00247-015-3510-xDOI Listing
April 2016

Imaging Hepatocellular Carcinoma with Dynamic CT Before and After Transarterial Chemoembolization: Optimal Scan Timing of Arterial Phase.

Acad Radiol 2015 Dec 26;22(12):1516-21. Epub 2015 Sep 26.

Department of Radiology, University of Erlangen-Nuremberg, Erlangen, Germany.

Rationale And Objectives: The aim of this study was to determine the optimal arterial phase delay for computed tomography imaging of hepatocellular carcinoma (HCC) before and after transarterial chemoembolization (TACE) using a low iodine dose protocol.

Materials And Methods: A total of 39 patients with known HCC were imaged with dynamic computed tomography of the liver (40-second scan duration, 60 mL of contrast medium), both on the same day before TACE and 1 day after TACE. Time attenuation curves of vessels, nonmalignant liver parenchyma, and 62 HCCs were normalized to a uniform aortic contrast arrival and analyzed.

Results: Maximal arterial phase HCC to liver contrast was reached between 13 and 17 seconds after aortic contrast arrival, both before and after TACE.

Conclusions: Using our low iodine dose protocol, arterial phase imaging of HCC should be performed between 13 and 17 seconds after aortic contrast arrival, both before and after TACE.
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http://dx.doi.org/10.1016/j.acra.2015.08.021DOI Listing
December 2015

Evolution in Computed Tomography: The Battle for Speed and Dose.

Invest Radiol 2015 Sep;50(9):629-44

From the *Department of Radiology, University Hospital Erlangen, Erlangen, Germany; †Department of Radiology and Nuclear Medicine, Maastricht University Medical Center, Maastricht, the Netherlands; ‡Institute for Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich, Switzerland; §Department of Medical Physics, University of Crete, Iraklion, Crete, Greece; and ∥X-Ray Imaging and CT, German Cancer Research Center (DKFZ), Heidelberg, Germany.

The advent of computed tomography (CT) has revolutionized radiology. Starting as head-only scanners, modern CT systems are now capable of performing whole-body examinations within a couple of seconds in isotropic resolution. Technical advancements of scanner hardware and image reconstruction techniques are reviewed and discussed in their clinical context. These improvements have led to a steady increase of CT examinations in all age groups for a number of reasons. On the one hand, it is very easy today to obtain whole-body data for oncologic staging and follow-up or for trauma imaging. On the other hand, new examinations such as cardiac imaging, virtual colonoscopy, gout imaging, and whole-organ perfusion imaging have widened the application profile of CT. The increasing awareness of risks associated with radiation exposure triggered the development of a variety of dose reduction techniques. Effective dose values below 1 mSv, less than the annual natural background radiation (3.1 mSv/year on average in the United States), are now routinely possible for a number of dedicated examinations, even for coronary CT angiography.
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http://dx.doi.org/10.1097/RLI.0000000000000172DOI Listing
September 2015

Computed Tomography Angiography of Carotid Arteries and Vertebrobasilar System: A Simulation Study for Radiation Dose Reduction.

Medicine (Baltimore) 2015 Jul;94(26):e1058

From the Institute of Radiology (MK, SE, AE, FK, MSM, JFB, MU, MML), University of Erlangen-Nuremberg, Maximiliansplatz 1, Erlangen, Germany; and Siemens Healthcare (TA), Forchheim, Germany. MK and SE contributed equally to this work.

Computed tomography angiography (CTA) of carotid arteries and vertebrobasilar system is a standardized procedure with excellent image quality, but radiation exposure remains a matter of concern. The aim of this study is to examine to what extent radiation dose can be lowered in relation to a standard protocol by simulating examinations with lower tube currents applying a dedicated software.Lower tube current was simulated by a dedicated noise insertion and reconstruction software (ReconCT). In a phantom study, true scans were performed with different dose protocols and compared to the results of simulated dose reductions of the same degree, respectively. In a patient study, 30 CTAs of supra-aortic vessels were reconstructed at a level of 100%, 75%, 50%, and 25% of the initial dose. Objective and subjective image analyses were performed.No significant noise differences between true scans and simulated scans of mimicked contrasted vessels were found. In the patient study, the quality scores of the 4 dose groups differed statistically significant; this difference vanished for the comparison of the 100% and 75% datasets after dichotomization into the categories of diagnostic and nondiagnostic image quality (P = .50).This study suggests an easy-to-implement method of simulating CTAs of carotid arteries and vertebrobasilar system with lower tube current for dose reduction by artificially adding noise to the original raw data. Lowering the radiation dose in a moderate extent to 75% of the original dose levels does not significantly alter the diagnostic image quality.
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http://dx.doi.org/10.1097/MD.0000000000001058DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4504529PMC
July 2015

Influence of Different Antioxidants on X-Ray Induced DNA Double-Strand Breaks (DSBs) Using γ-H2AX Immunofluorescence Microscopy in a Preliminary Study.

PLoS One 2015 21;10(5):e0127142. Epub 2015 May 21.

Department of Radiology, University Hospital Erlangen-Nuremberg, Erlangen, Germany.

Background: Radiation exposure occurs in X-ray guided interventional procedures or computed tomography (CT) and γ-H2AX-foci are recognized to represent DNA double-strand breaks (DSBs) as a biomarker for radiation induced damage. Antioxidants may reduce the induction of γ-H2AX-foci by binding free radicals. The aim of this study was to establish a dose-effect relationship and a time-effect relationship for the individual antioxidants on DSBs in human blood lymphocytes.

Materials And Methods: Blood samples from volunteers were irradiated with 10 mGy before and after pre-incubation with different antioxidants (zinc, trolox, lipoic acid, ß-carotene, selenium, vitamin E, vitamin C, N-acetyl-L-cysteine (NAC) and Q 10). Thereby, different pre-incubation times, concentrations and combinations of drugs were evaluated. For assessment of DSBs, lymphocytes were stained against the phosphorylated histone variant γ-H2AX.

Results: For zinc, trolox and lipoic acid regardless of concentration or pre-incubation time, no significant decrease of γ-H2AX-foci was found. However, ß-carotene (15%), selenium (14%), vitamin E (12%), vitamin C (25%), NAC (43%) and Q 10 (18%) led to a significant reduction of γ-H2AX-foci at a pre-incubation time of 1 hour. The combination of different antioxidants did not have an additive effect.

Conclusion: Antioxidants administered prior to irradiation demonstrated the potential to reduce γ-H2AX-foci in blood lymphocytes.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0127142PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4440758PMC
February 2016

Myocardial adaptation to high-intensity (interval) training in previously untrained men with a longitudinal cardiovascular magnetic resonance imaging study (Running Study and Heart Trial).

Circ Cardiovasc Imaging 2015 Apr;8(4)

From the Departments of Radiology (M.S., A.S., M.S.M., W.W., M.U., M.M.L.), Medical Physics (W.K., S.v.S.), and Cardiology (S.A.), Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany.

Background: To prospectively evaluate whether short-term high-intensity (interval) training (HI(I)T) induces detectable morphological cardiac changes in previously untrained men in cardiovascular magnetic resonance imaging.

Methods And Results: Eighty-four untrained volunteers were randomly assigned to a HI(I)T group (n=42; 44.1±4.7 years) or an inactive control group (n=42; 42.3±5.6 years). HI(I)T focused on interval runs (intensity: 95%-105% of individually calculated heart rate at the anaerobic threshold). Before and after 16 weeks, all subjects underwent physiological examination, stepwise treadmill test with blood lactate analysis, and contrast-enhanced cardiovascular magnetic resonance imaging (cine, tagging, and delayed enhancement). Indexed left ventricular (LV) and right ventricular (RV) volume (LV, 77.1±8.5-83.9±8.6; RV, 80.5±8.5-86.6±8.1) and mass (LV, 58.2±6.4-63.4±8.1; RV, 14.8±1.7-16.1±2.1) significantly increased with HI(I)T. Changes in LV and RV morphological parameters with HI(I)T were highly correlated with an increase in maximal aerobic capacity (VO2max) and a decrease in blood lactate concentration at the anaerobic threshold. Mean LV and RV remodeling index of HI(I)T group did not alter with training (0.76 ±0.09 and 0.24±0.10 g/mL, respectively [P=0.97 and P=0.72]), indicating balanced cardiac adaptation. Myocardial circumferential strain decreased after HI(I)T within all 6 basal segments (anteroseptal, P=0.01 and anterolateral, P<0.001). There was no late gadolinium enhancement in any of the participants before or post HI(I)T.

Conclusions: Sixteen weeks of HI(I)T lead to measurable changes in cardiac atrial and ventricular morphology and function in previously untrained men. This correlates with improvements in parameters of endurance capacity.

Clinical Trial Registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01406730.
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http://dx.doi.org/10.1161/CIRCIMAGING.114.002566DOI Listing
April 2015

Automated tube voltage selection in thoracoabdominal computed tomography at high pitch using a third-generation dual-source scanner: image quality and radiation dose performance.

Invest Radiol 2015 May;50(5):352-60

From the *Department of Radiology, University of Erlangen; and †Imaging Science Institute, Erlangen, Germany.

Objectives: The objective of this study was to evaluate the radiation dose and image quality performance of thoracoabdominal examinations with an automated tube voltage selection (tube voltage adaptation), tube current modulation, and high pitch using a third-generation dual-source computed tomography (CT) compared intraindividually with 120-kV examinations with tube current modulation with special attention on clinically relevant lesions in the liver, the lungs, and extrahepatic soft tissues.

Materials And Methods: This study was approved by the institutional review board. Computed tomography of the body was performed using a third-generation dual-source system in 95 patients (mean body mass index, 25 kg/m²; range, 18-35 kg/m²). For 49 of these patients, all calculated tube settings and resulting dose values were recorded for each of the 12 gradual contrast weightings of the tube voltage adaptation algorithm. Spiral CT was performed for all patients with an intermediate weighting (grade 7) in a portal venous phase at 120 reference kV, 180 reference mAs, and pitch of 1.55. Objective image quality was assessed on the basis of contrast-to-noise ratio. Subjective image quality was assessed on the basis of clarity and sharpness of anatomical and pathological structures as well as interfering beam hardening and spiral and motion artifacts (heart, lungs, diaphragm). Previous examinations on a 64-slice scanner served as reference.

Results: All examinations were rated good or excellent for clinical diagnosis. Automated tube voltage selection resulted in significantly lower effective radiation dose (9.5 mSv) compared with the reference (12.0 mSv; P < 0.01). Contrast-to-noise ratio and image quality of soft tissue lesions were significantly increased (P < 0.01). Motion artifacts were significantly reduced (P < 0.01).

Conclusions: Automated tube voltage adaptation combined with high-pitch protocols allows for a substantial radiation dose reduction while substantially increasing the image quality, even at large-volume exposure.
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http://dx.doi.org/10.1097/RLI.0000000000000133DOI Listing
May 2015

Optimizing contrast media injection protocols in state-of-the art computed tomographic angiography.

Invest Radiol 2015 Mar;50(3):161-7

From the *Department of Radiology, University of Erlangen; †Imaging Science Institute Erlangen, Erlangen; ‡MR and CT Contrast Media Research, Bayer Healthcare, Berlin; §Siemens Healthcare, Forchheim; and ∥Department of Radiology, University of Marburg, Marburg, Germany.

Objective: Very short acquisition times and the increasing use of low-kilovolt protocols in standard computed tomographic (CT) angiography (CTA) examinations demand modifications in the contrast media (CM) injection regimen. The aim of this study was to optimize the use of tube voltage-adjusted CM delivery parameters, especially injection duration and iodine delivery rate (IDR), in thoracoabdominal CTA in a porcine model.

Materials And Methods: Eight pigs (53-72 kg) were examined with a third-generation dual-source CT system with a dynamic CTA protocol (4-dimensional spiral, 454-mm scan length, 2.5-second temporal resolution, 70-second total acquisition time). Six CM injection protocols were applied in randomized order and intraindividually compared. The standard CTA protocol was performed at 120 kV, with an injection of 300 mg iodine/kg body weight and a flow of 5 mL/s (IDR, 1.5 g/s). On the basis of phantom measurements for the low-kilovolt CTA protocols, the iodine dosage was adjusted to 150 mg iodine/kg (70 kV) and 210 mg iodine/kg (90 kV). Therefore, either the IDR was kept constant and the injection time was reduced, or the injection time was kept constant and the IDR was reduced by modifying the CM flow or concentration. Time attenuation curves, time to peak, and peak enhancement were calculated for different locations within the aorta, renal arteries, and large veins.

Results: The heart rates were comparable among the different injection protocols (66.9-78.1 beats per minute). The average injection peak pressure depended on the flow rate and CM concentration and ranged from 42.9 to 114.7 psi. The average arterial peak enhancement was comparable for protocols with identical injection times and reduced IDR (362.4 HU [standard 120-kV protocol; 300 mg iodine/kg; IDR, 1.5 g/s], 360.0 HU [70 kV; 150 mg iodine/kg; IDR, 0.75 g/s], 365.4 HU [70 kV; 150 mg iodine/kg; IDR, 0.75 g/s; CM, 150 mg iodine/mL], 344.3 HU [90 kV; 210 mg iodine/kg; IDR, 1.1 g/s]). Higher peak enhancements could be achieved by applying protocols with identical IDR and a reduced injection time (502.5 HU [70 kV; 150 mg iodine/kg; IDR, 1.5 g/s] and 394.6 HU [90 kV; 210 mg iodine/kg; IDR, 1.5 g/s]).

Conclusions: By adjusting the IDR, low-kilovolt CTA is able to achieve comparable aortic enhancement with a significant reduction in CM dosage. A shorter injection time at constant IDR results in higher enhancement and a narrower scan window and might be preferable for fast CTA acquisition techniques.

Clinical Relevance/application: The optimization of CM injection protocols is mandatory to achieve state-of the art CTA at low kilovolt and can reduce CM doses to patients.
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http://dx.doi.org/10.1097/RLI.0000000000000119DOI Listing
March 2015

Contrast medium application in pediatric high-pitch cardiovascular CT angiography: manual or power injection?

J Cardiovasc Comput Tomogr 2014 Jul-Aug;8(4):315-22. Epub 2014 May 22.

Department of Radiology, University of Erlangen-Nuremberg, Maximiliansplatz 1, Erlangen 91054, Germany.

Background: Dual-source CT offers accurate depiction of cardiac structures in children with congenital heart disease. For cardiac CT, optimal enhancement of the cardiovascular structures is essential. There is considerable controversy about the administration of contrast medium (CM) in infants and small children, with either a power injector or a manual (hand) injection.

Objective: The aim of this study was to compare image quality with power injection of CM (study group) and manual injection (control group).

Methods: Thirty-four patients (study group, 6.8 ± 9.6 months and control group, 4.6 ± 8.9 months, nonrandomized) underwent dual-source CT angiography of the chest using a prospective electrocardiography-triggered high-pitch spiral mode (pitch, 3.4; 80 kV). In the study group (17 patients), a power injector was used, and in the control group (17 patients, historical group), manual CM injection had been performed. To assess image quality, both subjective and objective parameters were evaluated independently by 2 experienced radiologists.

Results: Subjective overall image quality, signal-to-noise ratio, and contrast-to-noise ratio were significantly higher using power injection compared with manual injection (P < .05). However, depiction of cardiovascular structures did not differ significantly between both groups in all evaluated regions except the superior vena cava and the coronary arteries.

Conclusion: In infants and small children with congenital heart disease, both manual and power injector protocols allowed for diagnostic imaging of cardiac and extracardiac structures. However, image quality and vascular attenuation were superior using a power injector.
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http://dx.doi.org/10.1016/j.jcct.2014.05.002DOI Listing
May 2015

Automated tube voltage adaptation in head and neck computed tomography between 120 and 100 kV: effects on image quality and radiation dose.

Neuroradiology 2014 Sep 25;56(9):797-803. Epub 2014 Jun 25.

Department of Radiology, University Hospital Erlangen, Maximiliansplatz 1, 91054, Erlangen, Germany,

Introduction: Low tube voltage allows for computed tomography (CT) imaging with increased iodine contrast at reduced radiation dose. We sought to evaluate the image quality and potential dose reduction using a combination of attenuation based tube current modulation (TCM) and automated tube voltage adaptation (TVA) between 100 and 120 kV in CT of the head and neck.

Methods: One hundred thirty consecutive patients with indication for head and neck CT were examined with a 128-slice system capable of TCM and TVA. Reference protocol was set at 120 kV. Tube voltage was reduced to 100 kV whenever proposed by automated analysis of the localizer. An additional small scan aligned to the jaw was performed at a fixed 120 kV setting. Image quality was assessed by two radiologists on a standardized Likert-scale and measurements of signal- (SNR) and contrast-to-noise ratio (CNR). Radiation dose was assessed as CTDIvol.

Results: Diagnostic image quality was excellent in both groups and did not differ significantly (p = 0.34). Image noise in the 100 kV data was increased and SNR decreased (17.8/9.6) in the jugular veins and the sternocleidomastoid muscle when compared to 120 kV (SNR 24.4/10.3), but not in fatty tissue and air. However, CNR did not differ statistically significant between 100 (23.5/14.4/9.4) and 120 kV data (24.2/15.3/8.6) while radiation dose was decreased by 7-8%.

Conclusions: TVA between 100 and 120 kV in combination with TCM led to a radiation dose reduction compared to TCM alone, while keeping CNR constant though maintaining diagnostic image quality.
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http://dx.doi.org/10.1007/s00234-014-1393-4DOI Listing
September 2014

Dose reduction of the female breast in chest CT.

AJR Am J Roentgenol 2014 May;202(5):W447-52

1 Department of Radiology, University Erlangen-Nuremberg, Maximiliansplatz 1, Erlangen 91054, Germany.

Objective: Organ-based tube current modulation has been shown to significantly reduce the radiation dose to the female breast in phantom studies. We sought to assess the proportions of female breast and glandular tissues that are within the range of organ-based tube current modulation in different age groups and whether these proportions could be optimized by clothing. The secondary objective of our study was to determine whether metal parts of brassieres cause artifacts that impair the diagnostic value.

Subjects And Methods: Five hundred seventy-eight female patients undergoing chest CT were included in this study. Two hundred nine patients were prospectively examined wearing a brassiere (group A), and the control patients (group B; n = 369) were scanned according to our previous standard without wearing a brassiere during CT. The two groups were subdivided according to cup size (A-E). For CT data acquisition, an angle-dependent tube current modulation, which reduces the tube current for anterior tube position to minimize direct exposure to anteriorly located organs, was used. The proportion of breast tissue and glandular tissue located within and outside the region of tube current reduction was assessed.

Results: The results showed that 60.4% of total breast tissue and 67.1% of glandular tissue was inside the region of tube current reduction in group B; the proportions were significantly improved, to an average of 91.3% and 96%, respectively, in group A. Diagnostically relevant artifacts were introduced in none of the patients. Patients' age correlated with this effect, with higher rates of improvement in the older patient group. Angle-dependent tube current modulation was most effective in patients with cup size A while wearing a brassiere. In this group, 97.5% of breast tissue and 98.1% of glandular tissue was inside the region of tube current reduction. Women with a cup size of E had the largest effect of wearing a brassiere, increasing the rate of breast tissue that was affected by angle-dependent tube current modulation from 30.0% to 83.3% and that of glandular tissue from 31.8% to 90.0%.

Conclusion: We show that wearing a brassiere increases the percentage of breast tissue within the region of reduced tube current and, therefore, improves the performance of angle-dependent tube current modulation technique.
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http://dx.doi.org/10.2214/AJR.13.10541DOI Listing
May 2014

Stent evaluation in low-dose coronary CT angiography: effect of different iterative reconstruction settings.

J Cardiovasc Comput Tomogr 2013 Sep-Oct;7(5):319-25. Epub 2013 Sep 26.

Radiological Institute, Friedrich-Alexander-University-Erlangen-Nuremberg, Maximiliansplatz 1, 91054 Erlangen, Germany.

Background: Different iterative reconstruction (IR) techniques compensate increased noise from lower tube current-time product settings, yet the differences between IR settings remain unclear.

Objective: Aim of this study was to test whether different IR settings have a clinically relevant influence on image quality and on the diagnostic accuracy of low-dose CT angiography in patients with a stent.

Methods: Forty-two patients with 73 coronary stents were prospectively enrolled. Data were acquired with dual-source CT, and images were reconstructed with standard filtered back projection (FBP) and raw data-based IR with different settings (I3, I4, I5). Quantitative parameters, including CT-attenuation, noise, signal-to-noise ratio, contrast-to-noise ratio, as well as the presence of in-stent stenosis > 50% were determined. All patients had invasive angiography as reference standard.

Results: Mean effective dose was 0.32 ± 0.02 mSv. Image noise decreased significantly compared with FBP (I3 = 29%; I4 = 38% and I5 = 45%), whereas signal-to-noise and contrast-to-noise ratios increased significantly (all IR settings P < .01). Subjective image quality was superior with all IR settings (P < .01). FBP sensitivity, specificity, positive predictive value, and negative predictive value were 83%, 71%, 36%, and 96% per stent compared with 100%, 76%, 44%, and 100%, respectively, in IR reconstructions independent of the IR setting applied.

Conclusion: In low-dose coronary CT angiography, higher IR settings significantly improved subjective and objective image quality but had no effect on accuracy.
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http://dx.doi.org/10.1016/j.jcct.2013.08.012DOI Listing
July 2014

Attenuation-based automatic kilovolt (kV)-selection in computed tomography of the chest: effects on radiation exposure and image quality.

Eur J Radiol 2013 Dec 30;82(12):2386-91. Epub 2013 Aug 30.

Department of Radiology, University Erlangen, Germany.

Objectives: To evaluate an automated attenuation-based kV-selection in computed tomography of the chest in respect to radiation dose and image quality, compared to a standard 120 kV protocol.

Materials And Methods: 104 patients were examined using a 128-slice scanner. Fifty examinations (58 ± 15 years, study group) were performed using the automated adaption of tube potential (100-140 kV), based on the attenuation profile of the scout scan, 54 examinations (62 ± 14 years, control group) with fixed 120 kV. Estimated CT dose index (CTDI) of the software-proposed setting was compared with a 120 kV protocol. After the scan CTDI volume (CTDIvol) and dose length product (DLP) were recorded. Image quality was assessed by region of interest (ROI) measurements, subjective image quality by two observers with a 4-point scale (3--excellent, 0--not diagnostic).

Results: The algorithm selected 100 kV in 78% and 120 kV in 22%. Overall CTDIvol reduction was 26.6% (34% in 100 kV) overall DLP reduction was 22.8% (32.1% in 100 kV) (all p<0.001). Subjective image quality was excellent in both groups.

Conclusion: The attenuation based kV-selection algorithm enables relevant dose reduction (~27%) in chest-CT while keeping image quality parameters at high levels.
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http://dx.doi.org/10.1016/j.ejrad.2013.08.043DOI Listing
December 2013

Comparison of lesion detection and quantitation of tracer uptake between PET from a simultaneously acquiring whole-body PET/MR hybrid scanner and PET from PET/CT.

Eur J Nucl Med Mol Imaging 2013 Jan 6;40(1):12-21. Epub 2012 Oct 6.

Clinic of Nuclear Medicine, University Hospital Erlangen, Ulmenweg 18, Erlangen, Germany.

Purpose: PET/MR hybrid scanners have recently been introduced, but not yet validated. The aim of this study was to compare the PET components of a PET/CT hybrid system and of a simultaneous whole-body PET/MR hybrid system with regard to reproducibility of lesion detection and quantitation of tracer uptake.

Methods: A total of 46 patients underwent a whole-body PET/CT scan 1 h after injection and an average of 88 min later a second scan using a hybrid PET/MR system. The radioactive tracers used were (18)F-deoxyglucose (FDG), (18)F-ethylcholine (FEC) and (68)Ga-DOTATATE (Ga-DOTATATE). The PET images from PET/CT (PET(CT)) and from PET/MR (PET(MR)) were analysed for tracer-positive lesions. Regional tracer uptake in these foci was quantified using volumes of interest, and maximal and average standardized uptake values (SUV(max) and SUV(avg), respectively) were calculated.

Results: Of the 46 patients, 43 were eligible for comparison and statistical analysis. All lesions except one identified by PET(CT) were identified by PET(MR) (99.2 %). In 38 patients (88.4 %), the same number of foci were identified by PET(CT) and by PET(MR). In four patients, more lesions were identified by PET(MR) than by PET(CT), in one patient PET(CT) revealed an additional focus compared to PET(MR). The mean SUV(max) and SUV(avg) of all lesions determined by PET(MR) were by 21 % and 11 % lower, respectively, than the values determined by PET(CT) (p < 0.05), and a strong correlation between these variables was identified (Spearman rho 0.835; p < 0.01).

Conclusion: PET/MR showed equivalent performance in terms of qualitative lesion detection to PET/CT. The differences demonstrated in quantitation of tracer uptake between PET(CT) and PET(MR) were minor, but statistically significant. Nevertheless, a more detailed study of the quantitative accuracy of PET(MR) and the factors governing it is needed to ultimately assess its accuracy in measuring tissue tracer concentrations.
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http://dx.doi.org/10.1007/s00259-012-2249-yDOI Listing
January 2013

Attenuation-based automatic kilovolt selection in abdominal computed tomography: effects on radiation exposure and image quality.

Invest Radiol 2012 Oct;47(10):559-65

Department of Radiology, University Erlangen, Erlangen, Germany.

Objectives: Dose reduction has become a major issue in computed tomography (CT). The benefit of kilovolt (kV) reduction has been demonstrated in CT angiography. We sought to evaluate an attenuation-based fully automated kV-selection and milliampere second-adaption algorithm for CT and to assess radiation dose and image quality in comparison with a standard 120 kV protocol in contrast-enhanced (CE) portal-venous thoracoabdominal imaging.

Materials And Methods: One hundred patients (mean age, 58.4 ± 5.7 years; mean body mass index [BMI], 26.1 ± 5.1 kg/m(2)) underwent CE CT using automated selection of the tube potential (80-140 kV) with milliampere second adaption based on the attenuation profile of the scout scan. The estimated CT dose index was recorded for the proposed scan setting and standard 120-kV protocol. Regions of interest measurements were performed at different locations for objective assessment of image quality. Signal-to-noise ratio and contrast-to-noise ratio (CNR) were calculated. The subjective image quality was assessed by 2 observers with a 4-point scale using previous CT examinations with the 120-kV standard protocol as the reference for comparison.

Results: The kV-selection algorithm could be applied in all examinations without problems. Image quality was high, and there were no significant differences compared with previous examinations of the patients performed at 120 kV. Eighty kilovolts was used in 9% of examinations (mean BMI, 22.8 ± 2.8 kg/m(2)); 100 kV, in 75% (mean BMI, 23.7 ± 4.7 kg/m(2)); 120 kV, in 16% (mean BMI, 30 ± 3.3 kg/m(2)); and 140 kV, in a single case (BMI, 49.4 kg/m(2)). The average estimated CT dose index reduction was 25.3% in the 80-kV group, 14.5% in the 100-kV group, and 11.4% overall. The CNR did not differ significantly, whereas the signal-to-noise ratio was significantly higher in the 80- and 100-kV examinations.

Conclusion: The attenuation-based kV-selection algorithm was demonstrated to be applicable in clinical routine of CE thoracoabdominal CT, to keep CNR constant, and to result in a significant dose reduction while preserving image quality.
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http://dx.doi.org/10.1097/RLI.0b013e318260c5d6DOI Listing
October 2012

Acute stroke: a comparison of different CT perfusion algorithms and validation of ischaemic lesions by follow-up imaging.

Eur Radiol 2012 Dec 21;22(12):2559-67. Epub 2012 Jun 21.

Institute of Radiology, University Hospital Erlangen, Erlangen, Germany.

Objectives: To compare ischaemic lesions predicted by different CT perfusion (CTP) post-processing techniques and validate CTP lesions compared with final lesion size in stroke patients.

Methods: Fifty patients underwent CT, CTP and CT angiography. Quantitative values and colour maps were calculated using least mean square deconvolution (LMSD), maximum slope (MS) and conventional singular value decomposition deconvolution (SVDD) algorithms. Quantitative results, core/penumbra lesion sizes and Alberta Stroke Programme Early CT Score (ASPECTS) were compared among the algorithms; lesion sizes and ASPECTS were compared with final lesions on follow-up MRI + MRA or CT + CTA as a reference standard, accounting for recanalisation status.

Results: Differences in quantitative values and lesion sizes were statistically significant, but therapeutic decisions based on ASPECTS and core/penumbra ratios would have been the same in all cases. CTP lesion sizes were highly predictive of final infarct size: Coefficients of determination (R (2)) for CTP versus follow-up lesion sizes in the recanalisation group were 0.87, 0.82 and 0.61 (P < 0.001) for LMSD, MS and SVDD, respectively, and 0.88, 0.87 and 0.76 (P < 0.001), respectively, in the non-recanalisation group.

Conclusions: Lesions on CT perfusion are highly predictive of final infarct. Different CTP post-processing algorithms usually lead to the same clinical decision, but for assessing lesion size, LMSD and MS appear superior to SVDD.

Key Points: Following an acute stroke, CT perfusion imaging can help predict lesion evolution. Delay-insensitive deconvolution and maximum slope approach are superior to delay-sensitive deconvolution regarding accuracy. Different CT perfusion post-processing algorithms usually lead to the same clinical decision. CT perfusion offers new insights into the evolution of stroke.
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http://dx.doi.org/10.1007/s00330-012-2529-8DOI Listing
December 2012

Normalized metal artifact reduction in head and neck computed tomography.

Invest Radiol 2012 Jul;47(7):415-21

Department of Radiology, University of Erlangen, Erlangen, Germany.

Objective: Artifacts from dental hardware affect image quality and the visualization of lesions in the oral cavity and oropharynx in computed tomography (CT). Therefore, magnetic resonance imaging is considered the imaging modality of choice in this region. Standard methods for metal artifact reduction (MAR) in CT replace the metal-affected raw data by interpolation, which is prone to new artifacts. We developed a generalized normalization technique for MAR (NMAR) that aims to suppress algorithm-induced artifacts and validated the performance of this algorithm in a clinical trial.

Material And Methods: A 3-dimensional forward projection identifies the metal-affected raw data in the original projections after metal is segmented in the image domain by thresholding. A prior image is used to normalize the projections before interpolation. The original raw data are divided pixel-wise by the projection data of the prior image and, after interpolation, are denormalized again. Data from 19 consecutive patients with metal artifacts from dental hardware were reconstructed with standard filtered backprojection (FBP), linear interpolation MAR (LIMAR), and NMAR. The image quality of slices containing metal was analyzed for the severity of artifacts and diagnostic value; magnetic resonance imaging performed the same day on a 3-T system served as a reference standard in all cases.

Results: A total of 260 slices containing metal dental hardware were analyzed. A total of 164 slices were nondiagnostic with FBP, 157 slices with LIMAR, and 87 slices with NMAR. The mean (SD) number of slices per patient with severe artifacts was 10.1 (3.7), 9.6 (4.6), and 5.4 (3.6) and the mean (SD) number of slices with artifacts affecting diagnostic confidence was 3.3 (1.7), 4.9 (2.9), and 3.7 (1.9) for FBP, LIMAR, and NMAR, respectively (P < 0.001). Pairwise comparison did not show significant differences between FBP and LIMAR (P = 0.40), but there were significant differences between FBP and NMAR as well as LIMAR and NMAR (both P < 0.001). Interobserver agreement was excellent (κ = 0.974). Two malignant lesions were unmasked with NMAR image reconstructions. No algorithm-related artifacts were detected in regions that did not contain metal in NMAR images.

Conclusion: Normalized MAR has the potential to improve image quality in patients with artifacts from dental hardware and to improve the diagnostic accuracy of CT of the oral cavity and oropharynx.
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http://dx.doi.org/10.1097/RLI.0b013e3182532f17DOI Listing
July 2012
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