Publications by authors named "Erik M Pedersen"

24 Publications

  • Page 1 of 1

MRI-based contouring of functional sub-structures of the lower urinary tract in gynaecological radiotherapy.

Radiother Oncol 2020 04 10;145:117-124. Epub 2020 Jan 10.

Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.

Introduction: Research in radiation-induced urinary morbidity is limited by lack of guidelines for contouring and dose assessment of the lower urinary tract. Based on literature regarding anatomy, physiology and imaging of the lower urinary tract, this study aimed to provide advice on contouring of relevant sub-structures, reference points and reference dimensions for gynaecological radiotherapy.

Material And Methods: 210 MRIs for Image-Guided Adaptive Brachytherapy (IGABT) were analysed in 105 locally advanced cervical cancer patients treated with radio(chemo)therapy. Sub-structures (trigone, bladder neck and urethra) were contoured and trigone height (TH) and width (TW) were measured. Internal urethral ostium (IUO) and Posterior inferior border of pubic symphysis-urethra (PIBS-U) points were used to identify proximal and middle/low urethra, respectively. Urethra reference length (URL) was defined as IUO and PIBS-U distance. TH, TW and URL were also quantified on 54 MRIs acquired for External Beam Radiotherapy (EBRT).

Results: Median absolute differences in volumes and dimensions between first and second IGABT fraction were 0.7 cm, 4.3 cm, 0.2 cm, 0.3 cm and 0.2 cm for trigone, bladder neck, TH, TW and URL, respectively. Mean(±SD) TH and TW were 2.7(±0.4)cm and 4.4(±0.4)cm, respectively, with no significant difference (p = 0.15 and p = 0.06, respectively) between IGABT and EBRT. URL was significantly shorter in EBRT than in IGABT MRIs (p < 0.001).

Conclusions: This study proposed relevant urinary sub-structures and dose points and showed that standardized contouring is reproducible. Trigone reference dimensions are robust despite different bladder filling and treatment conditions. Standardized contouring and reference points may improve understanding of urinary morbidity.
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http://dx.doi.org/10.1016/j.radonc.2019.12.011DOI Listing
April 2020

An iliopsoas plane block does not cause motor blockade-A blinded randomized volunteer trial.

Acta Anaesthesiol Scand 2020 03 13;64(3):368-377. Epub 2019 Nov 13.

Department of Clinical Medicine, Faculty of Health, Aarhus University, Aarhus, Denmark.

Background: A femoral nerve block relieves pain after total hip arthroplasty, but its use is controversial due to motor paralysis accompanied by an increased risk of fall. Assumedly, the iliopsoas plane block (IPB) targets the hip articular branches of the femoral nerve without motor blockade. However, this has only been indicated in a cadaver study. Therefore, we designed this volunteer study.

Methods: Twenty healthy volunteers were randomly allocated to blinded paired active vs. sham IPB (5 mL lidocaine 18 mg/mL with epinephrine vs saline). The primary outcome was reduction of maximal force of knee extension after IPB compared to baseline. Secondary outcomes included reduction of maximal force of hip adduction, and the pattern of injectate spread assessed with magnetic resonance imaging.

Results: Mean (confidence interval) change of maximal force of knee extension from baseline to after IPB was -9.7 N (-22, 3.0) (P = .12) (n = 14). The injectate was consistently observed in an anatomically well-defined closed fascial compartment between the intra- and extra-pelvic components of the iliopsoas muscle anterior to the hip joint.

Conclusion: We observed no significant reduction of maximal force of knee extension after an IPB. The injectate was contained in a fascial compartment previously shown to contain all sensory branches from the femoral nerve to the hip joint. The clinical consequence of selective anesthesia of all sensory femoral nerve branches from the hip could be a reduced risk of fall compared to a traditional femoral nerve block. Registration of Trial: The trial was prospectively registered in EudraCT (Reference: 2018-000089-12, https://www.clinicaltrialsregister.eu/ctr-search/search?query=2018-000089-12).
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http://dx.doi.org/10.1111/aas.13498DOI Listing
March 2020

Diffusion gradient nonlinearity bias correction reduces bias of breast cancer bone metastasis ADC values.

J Magn Reson Imaging 2020 03 16;51(3):904-911. Epub 2019 Jul 16.

The Department of Radiology, Aarhus University Hospital, Aarhus N, Denmark.

Contract Grant Sponsor: Health Research Fund of Central Denmark Region.

Background: Diffusion gradient nonlinearity (DGNL) bias causes apparent diffusion coefficient (ADC) values to drop with increasing superior-inferior (SI) isocenter offset. This is a concern when performing quantitative diffusion-weighted imaging (DWI).

Purpose/hypothesis: To investigate if DGNL ADC bias can be corrected in breast cancer bone metastases using a clinical DWI protocol and an online correction algorithm.

Study Type: Prospective.

Subjects/phantom: A diffusion phantom (Model 128, High Precision Devices, Boulder, CO) was used for in vitro validation. Twenty-three women with bone-metastasizing breast cancer were enrolled to assess DGNL correction in vivo.

Field Strength/sequence: DWI was performed on a 1.5T MRI system as single-shot, spin-echo, echo-planar imaging with short-tau inversion recovery (STIR) fat-saturation. ADC maps with and without DGNL correction were created from the b50 and b800 images.

Assessment: Uncorrected and DGNL-corrected ADC values were measured in phantom and bone metastases by placing regions of interest on b800 images and copying them to the ADC map. The SI offset was recorded.

Statistical Tests: In all, 79 bone metastases were assessed. ADC values with and without DGNL correction were compared at 14 cm SI offset using a two-tailed t-test.

Results: In the diffusion phantom, DGNL correction increased SI offset, where ADC bias was lower than 5%, from 7.3-13.8 cm. Of the 23 patients examined, six had no metastases in the covered regions. In the remaining patients, bias of uncorrected bone metastasis ADC values was 19.1% (95% confidence interval [CI]: 15.4-22.9%) at 14 cm SI offset. After DGNL correction, ADC bias was significantly reduced to 3.5% (95% CI: 0.7-6.3%, P < 0.001), thus reducing bias due to DGNL by 82%.

Data Conclusion: Online DGNL correction corrects DGNL ADC value bias and allows increased station lengths in the SI direction.

Level Of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:904-911.
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http://dx.doi.org/10.1002/jmri.26873DOI Listing
March 2020

Ga-PSMA-PET/CT in comparison with F-fluoride-PET/CT and whole-body MRI for the detection of bone metastases in patients with prostate cancer: a prospective diagnostic accuracy study.

Eur Radiol 2019 Mar 21;29(3):1221-1230. Epub 2018 Aug 21.

Department of Radiology, Copenhagen University Hospital Herlev and Gentofte, Herlev Ringvej 75, DK-2730, Herlev, Denmark.

Objectives: To determine the diagnostic accuracy of gallium prostate-specific membrane antigen (PSMA)-based positron emission tomography/computed tomography (PET/CT) in comparison with F-fluoride-based PET/CT (NaF-PET/CT) and whole-body magnetic resonance imaging (WB-MRI) for the detection of bone metastases in patients with prostate cancer.

Methods: Sixty patients with prostate cancer were included in the period May 2016 to June 2017. The participants underwent three scans (index tests) within 30 days: a NaF-PET/CT, a WB-MRI and a PSMA-PET/CT. Experienced specialists assessed the scans. In the absence of a histological reference standard, the final diagnosis was determined as a panel diagnosis. Measures of the diagnostic performances of the index tests were calculated from patient-based dichotomous outcomes (0 or ≥ 1 bone metastasis) and pairwise compared (McNemar test). For each index test, the agreement with the final diagnosis with regard to the number of bone metastases detected (0, 1-5, > 5) and the inter-reader agreement was calculated (kappa coefficients).

Results: Fifty-five patients constituted the final study population; 20 patients (36%) were classified as having bone metastatic disease as their final diagnosis. The patient-based diagnostic performances were (sensitivity, specificity, overall accuracy) PSMA-PET/CT (100%, 100%, 100%), NaF-PET/CT (95%, 97%, 96%) and WB-MRI (80%, 83%, 82%). The overall accuracy of PSMA-PET/CT was significantly more favourable compared to WB-MRI (p = 0.004), but not to NaF-PET/CT (p = 0.48). PSMA-PET/CT classified the number of bone metastases reliably compared to the final diagnosis (kappa coefficient 0.97) and with an "almost perfect" inter-reader agreement (kappa coefficient 0.93).

Conclusions: The overall accuracy of PSMA-PET/CT was significantly more advantageous compared to WB-MRI, but not to NaF-PET/CT.

Key Points: • PSMA-PET/CT assessed the presence of bone metastases correctly in all 55 patients • PSMA-PET/CT was more advantageous compared to WB-MRI • No difference was found between PSMA-PET/CT and NaF-PET/CT.
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http://dx.doi.org/10.1007/s00330-018-5682-xDOI Listing
March 2019

Needle migration and dosimetric impact in high-dose-rate brachytherapy for prostate cancer evaluated by repeated MRI.

Brachytherapy 2018 Jan - Feb;17(1):50-58. Epub 2017 Sep 19.

Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.

Purpose: To quantify needle migration and dosimetric impact in high-dose-rate brachytherapy for prostate cancer and propose a threshold for needle migration.

Methods And Materials: Twenty-four high-risk prostate cancer patients treated with an HDR boost of 2 × 8.5 Gy were included. Patients received an MRI for planning (MRI1), before (MRI2), and after treatment (MRI3). Time from needle insertion to MRI3 was ∼3 hours. Needle migration was evaluated from coregistered images: MRI1-MRI2 and MRI1-MRI3. Dose volume histogram parameters from the treatment plan based on MRI1 were related to parameters based on needle positions in MRI2 or MRI3. Regression was used to model the average needle migration per implant and change in D90 clinical target volume, CTV. The model fit was used for estimating the dosimetric impact in equivalent dose in 2 Gy fractions for dose levels of 6, 8.5, 10, 15, and 19 Gy.

Results: Needle migration was on average 2.2 ± 1.8 mm SD from MRI1-MRI2 and 5.0 ± 3.0 mm SD from MRI1-MRI3. D90 CTV was robust toward average needle migration ≤3 mm, whereas for migration >3 mm D90 decreased by 4.5% per mm. A 3 mm of needle migration resulted in a decrease of 0.9, 1.7, 2.3, 4.8, and 7.6 equivalent dose in 2 Gy fractions for dose levels of 6, 8.5, 10, 15, and 19 Gy, respectively.

Conclusions: Substantial needle migration in high-dose-rate brachytherapy occurs frequently in 1-3 hours following needle insertion. A 3-mm threshold of needle migration is proposed, but 2 mm may be considered for dose levels ≥15 Gy.
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http://dx.doi.org/10.1016/j.brachy.2017.08.005DOI Listing
July 2018

Dosimetric impact of contouring and needle reconstruction uncertainties in US-, CT- and MRI-based high-dose-rate prostate brachytherapy treatment planning.

Radiother Oncol 2017 04 8;123(1):125-132. Epub 2017 Mar 8.

Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark; Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.

Background And Purpose: The purpose was to evaluate the dosimetric impact of target contouring and needle reconstruction uncertainties in an US-, CT- and MRI-based HDR prostate BT treatment planning.

Material And Methods: US, CT, and MR images were acquired post-needle insertion in 22 HDR-BT procedures for 11 consecutive patients. Dose plans were simulated for an US-, CT- and MRI-based HDR-BT treatment planning procedure. Planning uncertainties in US- and CT-based plans were evaluated using MRI-based planning as reference. Target (CTV) was re-contoured on MRI. Dose results were expressed in total equivalent dose given in 2Gy fractionation dose for EBRT (46Gy) plus 2 HDR-BT fractions.

Results: Uncertainties in US- and CT-based planning caused the planned CTV-D to decrease with a mean of 2.9±5.0Gy (p=0.03) and 2.9±2.9Gy (p=0.001), respectively. The intra-observer contouring variation on MRI resulted in a mean variation of 1.6±1.5Gy in CTV-D. Reconstruction uncertainties on US resulted in a dose variation of±3Gy to the urethra, whereas data for CT were not available for this.

Conclusions: Uncertainties related to contouring and reconstruction in US- and CT-based HDR-BT treatment plans resulted in a systematic overestimation of the prescribed target dose. Inter-modality uncertainties (US and CT versus MR) were larger than MR intra-observer uncertainties.
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http://dx.doi.org/10.1016/j.radonc.2017.01.007DOI Listing
April 2017

The potential of MRI-guided online adaptive re-optimisation in radiotherapy of urinary bladder cancer.

Radiother Oncol 2016 Jan 26;118(1):154-9. Epub 2015 Nov 26.

Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom.

Background And Purpose: Adaptive radiotherapy (ART) using plan selection is being introduced clinically for bladder cancer, but the challenge of how to compensate for intra-fractional motion remains. The purpose of this study was to assess target coverage with respect to intra-fractional motion and the potential for normal tissue sparing in MRI-guided ART (MRIGART) using isotropic (MRIGARTiso), an-isotropic (MRIGARTanIso) and population-based margins (MRIGARTpop).

Materials And Methods: Nine bladder cancer patients treated in a phase II trial of plan selection underwent 6-7 weekly repeat MRI series, each with volumetric scans acquired over a 10 min period. Adaptive re-planning on the 0 min MRI scans was performed using density override, simulating a hypo-fractionated schedule. Target coverage was evaluated on the 10 min scan to quantify the impact of intra-fractional motion.

Results: MRIGARTanIso reduced the course-averaged PTV by median 304 cc compared to plan selection. Bladder shifts affected target coverage in individual fractions for all strategies. Two patients had a v95% of the bladder below 98% for MRIGARTiso. MRIGARTiso decreased the bowel V25 with 15-46 cc compared to MRIGARTpop.

Conclusion: Online re-optimised ART has a considerable normal tissue sparing potential. MRIGART with online corrections for target shift during a treatment fraction should be considered in ART for bladder cancer.
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http://dx.doi.org/10.1016/j.radonc.2015.11.003DOI Listing
January 2016

Intra-fractional bladder motion and margins in adaptive radiotherapy for urinary bladder cancer.

Acta Oncol 2015 27;54(9):1461-6. Epub 2015 Aug 27.

a Department of Medical Physics , Aarhus University/Aarhus University Hospital , Aarhus , Denmark.

Background: The bladder is a tumour site well suited for adaptive radiotherapy (ART) due to large inter-fractional changes, but it also displays considerable intra-fractional motion. The aim of this study was to assess target coverage with a clinically applied method for plan selection ART and to estimate population-based and patient-specific intra-fractional margins, also relevant for a future re-optimisation strategy.

Material And Methods: Nine patients treated in a clinical phase II ART trial of daily plan selection for bladder cancer were included. In the library plans, 5 mm isotropic margins were added to account for intra-fractional changes. Pre-treatment and weekly repeat magnetic resonance imaging (MRI) series were acquired in which a full three-dimensional (3D) volume was scanned every second min for 10 min (a total of 366 scans in 61 series). Initially, the bladder clinical target volume (CTV) was delineated in all scans. The t = 0 min scan was then rigidly registered to the planning computed tomography (CT) and plan selections were simulated using the CTV_0 (at t = 0 min). To assess intra-fractional motion, coverage of the CTV_10 (at t = 10 min) was quantified using the applied PTV. Population-based margins were calculated using the van Herk margin recipe while patient-specific margins were calculated using a linear model.

Results: For 49% of the cases, the CTV_10 extended more than 5 mm outside the CTV_0. However, in 58 of the 61 cases (97%) CTV_10 was covered by the selected PTV. Population-based margins of 14 mm Sup/Ant, 9 mm Post and 5 mm Inf/Lat were sufficient to cover the bladder. Using patient-specific margins, the overlap between PTV and bowel-cavity was reduced from 137 cm(3) with the plan selection strategy to 24 cm(3).

Conclusion: In this phase II ART trial, 5 mm isotropic margin for intra-fractional motion was sufficient even though considerable intra-fractional motion was observed. In online re-optimised ART, population-based margin can be applied although patient-specific margins are preferable.
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http://dx.doi.org/10.3109/0284186X.2015.1062138DOI Listing
January 2016

Assessment of radiation doses to the para-aortic, pelvic, and inguinal lymph nodes delivered by image-guided adaptive brachytherapy in locally advanced cervical cancer.

Brachytherapy 2015 Jan-Feb;14(1):56-61. Epub 2014 Aug 28.

Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark; Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark.

Purpose: This study evaluated the dose delivered to lymph nodes (LNs) by brachytherapy (BT) and the effect of BT image-guided optimization on the LN dose.

Methods And Materials: Twenty-five patients with locally advanced cervical cancer were retrospectively analyzed, 16 patients of them had LN involvement. The patients received whole pelvis intensity-modulated radiation therapy (45-50 Gy/25-30 fx) to whole pelvis and two fractions of MRI pulsed-dose-rate BT. The delineated LN groups were para-aortic, inguinal, common iliac (CI), external iliac, internal iliac, obturator, and presacral. For each LN group, D98%, D50%, and D2% (the dose that covers 98%, 50%, and 2% of the volume, respectively) were evaluated for optimized and standard BT plans. The correlation between total reference air kerma (TRAK) and D50% of the LN groups was evaluated.

Results: BT contributed considerable dose (mean D50% was 3.8-6.2 Gy equivalent total dose in 2-Gy fractions) to the pelvic LN (external iliac, internal iliac, obturator, and presacral) in optimized plans, whereas less-dose contribution to CI, para-aortic, and inguinal (mean D50% was 0.5-1.9 Gy equivalent total dose in 2-Gy fractions) was observed. Optimized plans delivered less dose to the LNs as compared with standard plans, although differences only amounted to a mean of 0.2-0.9 Gy (D50%). TRAK showed a significant correlation with LN D50% for all LN groups except CI, although only 19-38% of the dose variation could be explained by the TRAK.

Conclusions: BT contributes considerable dose to pelvic LNs and should be considered in the evaluation of total LN doses.
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http://dx.doi.org/10.1016/j.brachy.2014.07.005DOI Listing
June 2015

Correction of diffusion-weighted magnetic resonance imaging for brachytherapy of locally advanced cervical cancer.

Acta Oncol 2014 Aug 14;53(8):1073-8. Epub 2014 Jul 14.

Department of Clinical Engineering, Aarhus University Hospital , Aarhus , Denmark.

Background: Geometrical distortion is a major obstacle for the use of echo planar diffusion-weighted magnetic resonance imaging (DW-MRI) in planning of radiotherapy. This study compares geometrical distortion correction methods of DW-MRI at time of brachytherapy (BT) in locally advanced cervical cancer patients.

Material And Methods: In total 21 examinations comprising DW-MRI, dual gradient echo (GRE) for B₀ field map calculation and T2-weighted (T2W) fat-saturated MRI of eight patients with locally advanced cervical cancer were acquired during BT with a plastic tandem and ring applicator in situ. The ability of B0 field map correction (B₀M) and deformable image registration (DIR) to correct DW-MRI geometric image distortion was compared to the non-corrected DW-MRI including evaluation of apparent diffusion coefficient (ADC) for the gross tumor volume (GTV).

Results: Geometrical distortion correction decreased tandem displacement from 3.3 ± 0.9 mm (non-corrected) to 2.9 ± 1.0 mm (B₀M) and 1.9 ± 0.6 mm (DIR), increased mean normalized cross-correlation from 0.69 ± 0.1 (non- corrected) to 0.70 ± 0.10 (B₀M) and 0.77 ± 0.1 (DIR), and increased the Jaccard similarity coefficient from 0.72 ± 0.1 (non-corrected) to 0.73 ± 0.06 (B₀M) and 0.77 ± 0.1 (DIR). For all parameters only DIR corrections were significant (p < 0.05). ADC of the GTV did not change significantly with either correction method.

Conclusion: DIR significantly improved geometrical accuracy of DW-MRI, with remaining residual uncertainties of less than 2 mm, while no significant improvement was seen using B₀ field map correction.
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http://dx.doi.org/10.3109/0284186X.2014.938831DOI Listing
August 2014

Feasibility of applying a single treatment plan for both fractions in PDR image guided brachytherapy in cervix cancer.

Radiother Oncol 2013 Apr 17;107(1):32-8. Epub 2013 Jan 17.

Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.

Purpose: This study explores the feasibility of limiting dose optimisation to the first brachytherapy fraction (BT1) and applying the same plan for the second fraction (BT2).

Material And Methods: Seventy one consecutive patients were analysed. Pulsed dose rate (PDR) BT was initiated after about 4 weeks of external beam radiotherapy (EBRT). Thirty eight patients had only intracavitary applicator (IC), and 33 had combined IC with interstitial needles (IC/IS). The optimised BT1 plan was copied to BT2 images with no further optimisation (single plan scenario) and dose volume histogram (DVH) parameters were compared with those of full dose optimisation for every fraction (optimised plan scenario).

Results: 31/38 IC patients had similar applicator geometry in both fractions and mean DVH parameters were comparable between full optimisation and single plan. The mean HR CTV D90 in total EQD2 with optimisation was 94.5 Gy and with single plan scenario was 94.4 Gy (p=0.89). Organs at risk (OARs) planning aims were fulfilled with the single plan, although 5/31 patients would receive 3-10 Gy extra to the D(2cm(3)). The mean doses in total EQD2 for the D(2cm(3)) of the bladder, rectum, sigmoid and bowel were respectively 68.5, 61.0, 64.9 and 60.6 Gy for the optimised plan, and for the single plan scenario were 69.0, 61.3, 65.1 and 60.8 Gy respectively. The difference was statistically not significant. The standard deviation (SD) of the difference between the single plan and the optimised plan was 3.2 Gy for HR CTV and 2.9, 1.4, 1.2, 1.6 Gy for the bladder, rectum, sigmoid and bowel D(2cm(3)), respectively. Only 4/33 IC/IS patients had the same applicator geometry and single plan was therefore not feasible for the majority of these patients.

Conclusion: For IC BT in small volume tumours (primarily stage IB-IIB) with mean HR CTV volume at BT1=24±12 cm(3), comparable mean DVH parameters resulted when applying a single plan, but with considerable variations in individual patients. Yet since in our population the applied target doses are high and the OARs doses are lower than the dose volume constraints these variations may not have considerable clinical consequences. Individual optimisation for each BT fraction is recommended when interstitial needles are used.
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http://dx.doi.org/10.1016/j.radonc.2012.11.006DOI Listing
April 2013

Recommendations from Gynaecological (GYN) GEC-ESTRO Working Group (IV): Basic principles and parameters for MR imaging within the frame of image based adaptive cervix cancer brachytherapy.

Radiother Oncol 2012 Apr 30;103(1):113-22. Epub 2012 Jan 30.

Metropolitan Hospital, Athens, Greece.

The GYN GEC-ESTRO working group issued three parts of recommendations and highlighted the pivotal role of MRI for the successful implementation of 3D image-based cervical cancer brachytherapy (BT). The main advantage of MRI as an imaging modality is its superior soft tissue depiction quality. To exploit the full potential of MRI for the better ability of the radiation oncologist to make the appropriate choice for the BT application technique and to accurately define the target volumes and the organs at risk, certain MR imaging criteria have to be fulfilled. Technical requirements, patient preparation, as well as image acquisition protocols have to be tailored to the needs of 3D image-based BT. The present recommendation is focused on the general principles of MR imaging for 3D image-based BT. Methods and parameters have been developed and progressively validated from clinical experience from different institutions (IGR, Universities of Vienna, Leuven, Aarhus and Ljubljana) and successfully applied during expert meetings, contouring workshops, as well as within clinical and interobserver studies. It is useful to perform pelvic MRI scanning prior to radiotherapy ("Pre-RT-MRI examination") and at the time of BT ("BT MRI examination") with one MR imager. Both low and high-field imagers, as well as both open and close magnet configurations conform to the requirements of 3D image-based cervical cancer BT. Multiplanar (transversal, sagittal, coronal and oblique image orientation) T2-weighted images obtained with pelvic surface coils are considered as the golden standard for visualisation of the tumour and the critical organs. The use of complementary MRI sequences (e.g. contrast-enhanced T1-weighted or 3D isotropic MRI sequences) is optional. Patient preparation has to be adapted to the needs of BT intervention and MR imaging. It is recommended to visualise and interpret the MR images on dedicated DICOM-viewer workstations, which should also assist the contouring procedure. Choice of imaging parameters and BT equipment is made after taking into account aspects of interaction between imaging and applicator reconstruction, as well as those between imaging, geometry and dose calculation. In a prospective clinical context, to implement 3D image-based cervical cancer brachytherapy and to take advantage of its full potential, it is essential to successfully meet the MR imaging criteria described in the present recommendations of the GYN GEC-ESTRO working group.
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http://dx.doi.org/10.1016/j.radonc.2011.12.024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3336085PMC
April 2012

Dilation of the ascending aorta in Turner syndrome - a prospective cardiovascular magnetic resonance study.

J Cardiovasc Magn Reson 2011 Apr 28;13:24. Epub 2011 Apr 28.

Department of Endocrinology, Aarhus Hospital NBG, Aarhus University Hospital, Aarhus, Denmark.

Background: The risk of aortic dissection is 100-fold increased in Turner syndrome (TS). Unfortunately, risk stratification is inadequate due to a lack of insight into the natural course of the syndrome-associated aortopathy. Therefore, this study aimed to prospectively assess aortic dimensions in TS.

Methods: Eighty adult TS patients were examined twice with a mean follow-up of 2.4 ± 0.4 years, and 67 healthy age and gender-matched controls were examined once. Aortic dimensions were measured at nine predefined positions using 3D, non-contrast and free-breathing cardiovascular magnetic resonance. Transthoracic echocardiography and 24-hour ambulatory blood pressure were also performed.

Results: At baseline, aortic diameters (body surface area indexed) were larger at all positions in TS. Aortic dilation was more prevalent at all positions excluding the distal transverse aortic arch. Aortic diameter increased in the aortic sinus, at the sinotubular junction and in the mid-ascending aorta with growth rates of 0.1 - 0.4 mm/year. Aortic diameters at all other positions were unchanged. The bicuspid aortic valve conferred higher aortic sinus growth rates (p < 0.05). No other predictors of aortic growth were identified.

Conclusion: A general aortopathy is present in TS with enlargement of the ascending aorta, which is accelerated in the presence of a bicuspid aortic valve.
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http://dx.doi.org/10.1186/1532-429X-13-24DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3118376PMC
April 2011

Thoracic aortopathy in Turner syndrome and the influence of bicuspid aortic valves and blood pressure: a CMR study.

J Cardiovasc Magn Reson 2010 Mar 11;12:12. Epub 2010 Mar 11.

Medical Department M (Endocrinology and Diabetes) and Medical Research Laboratories, Aarhus Sygehus NBG, Aarhus University Hospital, DK-8000 Aarhus C, Denmark.

Background: To investigate aortic dimensions in women with Turner syndrome (TS) in relation to aortic valve morphology, blood pressure, karyotype, and clinical characteristics.

Methods And Results: A cross sectional study of 102 women with TS (mean age 37.7; 18-62 years) examined by cardiovascular magnetic resonance (CMR- successful in 95), echocardiography, and 24-hour ambulatory blood pressure. Aortic diameters were measured by CMR at 8 positions along the thoracic aorta. Twenty-four healthy females were recruited as controls. In TS, aortic dilatation was present at one or more positions in 22 (23%). Aortic diameter in women with TS and bicuspid aortic valve was significantly larger than in TS with tricuspid valves in both the ascending (32.4 +/- 6.7 vs. 26.0 +/- 4.4 mm; p < 0.001) and descending (21.4 +/- 3.5 vs. 18.8 +/- 2.4 mm; p < 0.001) aorta. Aortic diameter correlated to age (R = 0.2 - 0.5; p < 0.01), blood pressure (R = 0.4; p < 0.05), a history of coarctation (R = 0.3; p = 0.01) and bicuspid aortic valve (R = 0.2-0.5; p < 0.05). Body surface area only correlated with descending aortic diameter (R = 0.23; p = 0.024).

Conclusions: Aortic dilatation was present in 23% of adult TS women, where aortic valve morphology, age and blood pressure were major determinants of the aortic diameter.
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http://dx.doi.org/10.1186/1532-429X-12-12DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2847561PMC
March 2010

Caval blood flow during supine exercise in normal and Fontan patients.

Ann Thorac Surg 2008 Feb;85(2):599-603

Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Skejby, Aarhus, Denmark.

Background: Extracardiac total cavo-pulmonary connection (TCPC) bypasses the right atrium and has in theory better hemodynamics than intraatrial TCPC repair. Both are thought to have inferior hemodynamics compared with a normal circulation. Direct comparison of flow rates at rest and during exercise with magnetic resonance imaging technique have not been performed.

Methods: The study comprised 20 children. Six children (median age, 9.3 years; interquartile range, 2.2) had undergone extracardiac TCPC. Eight children (median age, 8.9 years; interquartile range, 5.0) had an intraatrial TCPC, and 6 children (median age, 10.3 years; interquartile range, 2.6) were healthy control subjects. Blood flows in the aorta, inferior vena cava, and superior vena cava were measured at rest and during two levels of submaximal supine bicycle exercise (0.5 W/kg and 1.0 W/kg) using a magnetic resonance imaging scanner mounted with a bicycle.

Results: Heart rate, respiratory rate, inspiratory fraction, and blood flow rates in the aorta and inferior vena cava increased equally in all three groups. If patients were grouped together, flow rates were significantly lower, and the inspiratory flow fraction in the inferior vena cava was significantly higher, than in control subjects. Retrograde flows were observed in all three groups at rest but tapered off with exercise.

Conclusions: At submaximal levels of lower limb exercise, patients with extracardiac as well as intraatrial TCPC showed a similar increase in respiration, heart rate, and aortic and caval flow rates as healthy control subjects. This is in accordance with the observation that many patients with TCPC perform well during daily life activities.
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http://dx.doi.org/10.1016/j.athoracsur.2007.08.062DOI Listing
February 2008

Determination of peak velocity in stenotic areas: echocardiography versus k-t SENSE accelerated MR Fourier velocity encoding.

Radiology 2008 Jan 19;246(1):249-57. Epub 2007 Oct 19.

Institute for Biomedical Engineering, University and Swiss Federal Institute of Technology Zurich, Wolfgang-Pauli-Str 10, CH-8093 Zurich, Switzerland.

The study was approved by the local ethical committees, and informed consent from each participant was obtained. The purpose of the study was to compare accelerated magnetic resonance (MR) Fourier velocity encoding (FVE), MR phase-contrast velocity mapping, and echocardiography with respect to peak velocity determination in vascular or valvular stenoses. FVE data collection was accelerated by using the k-space and time sensitivity encoding, or k-t SENSE, technique. Peak velocities were evaluated in five healthy volunteers (one woman, four men; mean age, 28 years; range, 23-34 years), three patients with stenotic aortic valves (two women, one man; mean age, 67 years; range, 39-82 years), two patients with pulmonary valvular stenosis (a 14-year-old girl and a 36-year-old man), and two patients with aortic stenosis (two women aged 18 and 27 years). In volunteers, peak velocity determined by the different methods agreed well. In patients, similar peak velocities were obtained by using accelerated MR FVE and echocardiography, while phase-contrast MR imaging results tended to underestimate these values.
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http://dx.doi.org/10.1148/radiol.2453061366DOI Listing
January 2008

Strut chordal-sparing mitral valve replacement preserves long-term left ventricular shape and function in pigs.

J Thorac Cardiovasc Surg 2005 Dec;130(6):1675-82

Department of Cardiothoracic and Vascular Surgery T, Aarhus University Hospital, Skejby Sygehus, Brendstrupgaardsvej, Denmark.

Objective: Mitral valve replacement with preservation of the entire subvalvular apparatus entails superior postoperative left ventricular function compared with other techniques. However, this option is often not possible because of valve pathology. We hypothesized that preservation of only 4 mitral valve secondary ("strut") chordae would be functionally and geometrically equivalent to total valve preservation in the long-term setting. In a porcine mitral valve replacement model we investigated the long-term effects of 3 surgical techniques on left ventricular function and geometry: (1) total preservation of the native valve, (2) strut chordal preservation, and (3) total excision of the subvalvular apparatus.

Methods: Forty 60-kg pigs were randomized to 1 of the 3 techniques. Global and regional left ventricular function and dimensions were assessed with cardiovascular magnetic resonance and conductance catheter 90 days after mitral valve replacement. Groups were compared by multivariate analysis of variance.

Results: There was no overall difference between groups 1 and 2. Group 3 animals had (1) greater base-apex diastolic and systolic lengths, and smaller short-axis diameters, and (2) lower sphericity indices, and greater base-apex and short-axis fractional shortening than groups 1 and 2. Regional analysis showed slimming and elongation to occur primarily in the basal left ventricular segments. Left ventricular contractility and hemodynamic parameters did not differ between groups.

Conclusions: Strut chordal preservation was equivalent to total valve preservation during mitral valve replacement, whereas total chordal resection caused significant left ventricular slimming with compensatory increases in fractional shortening. Therefore, to preserve left ventricular geometry, special attention must be paid to maintain the valvular-ventricular continuity through the strut chordae during mitral valve replacement. This concept may have important therapeutic implications for chordal-sparing mitral valve replacement.
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http://dx.doi.org/10.1016/j.jtcvs.2005.07.042DOI Listing
December 2005

Spiral coronary angiography using a blood pool agent.

J Magn Reson Imaging 2005 Aug;22(2):213-8

MR Center, Institute of Clinical Medicine, Skejby Sygehus, Aarhus University Hospital, Brendstrupgaardsvej 100, DK-8200 Aarhus N., Denmark.

Purpose: To experimentally investigate the optimum dose of an iron-oxide-based blood pool agent for spiral coronary MR angiography (MRA), and the difference between single and multiple spiral excitations in each cardiac cycle.

Materials And Methods: Images using single and triple spiral excitations in each cardiac cycle were obtained in late diastole of the left main coronary artery in eight pigs following an inversion prepulse. Measurements were obtained before and after injection of increasing doses of an iron oxide blood pool agent (Clariscan) corresponding to concentrations of 0.8, 2.2, and 3.9 mg Fe/kg BW. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured.

Results: For 0.8 mg Fe/kg BW relative to precontrast values, a significant increase was observed for both one (SNR: 2.3, CNR: 3.8) and three (SNR: 1.4, CNR: 2.2) excitations (P < 0.01). When the dose was increased from 0.8 mg Fe/kg BW to 2.2 mg Fe/kg BW, only the SNR (P < 0.01) increased further. Significantly higher CNR (1.6-1.8) and SNR (1.4-1.6) values were seen for one excitation relative to three excitations at all concentrations (P < 0.05).

Conclusion: At low concentrations, an iron oxide blood pool agent can increase SNR and CNR significantly with both single excitation and triple excitations using an inversion-prepared spiral acquisition scheme. At higher concentrations, T2* effects reduce image quality.
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http://dx.doi.org/10.1002/jmri.20371DOI Listing
August 2005

Accelerated dynamic Fourier velocity encoding by exploiting velocity-spatio-temporal correlations.

MAGMA 2004 Nov 9;17(2):86-94. Epub 2004 Nov 9.

Institute for Biomedical Engineering, Swiss Federal Institute of Technology (ETH), University of Zurich, Zurich, Switzerland.

Objective: To describe how the information content in a Fourier velocity encoding (FVE) scan can be transformed into a very sparse representation and to develop a method that exploits the compactness of the data to significantly accelerate the acquisition.

Materials And Methods: For validation, fully sampled FVE datasets were acquired in phantom and in vivo experiments. Fivefold and eightfold acceleration was simulated by using only one fifth or one eighth of the data for reconstruction in the proposed method based on the k-t BLAST framework. Reconstructed images were compared quantitatively to those from the fully sampled data.

Results: Velocity spectra in the accelerated datasets were comparable to the spectra from fully sampled datasets. The detected peak velocities remained accurate even at eightfold acceleration, and the overall shape of the spectra was well preserved. Slight temporal smoothing was seen in the accelerated datasets.

Conclusion: A novel technique for accelerating time-resolved FVE scan is presented. It is possible to accelerate FVE to acquisition speeds comparable to a standard time-resolved phase-contrast scan.
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http://dx.doi.org/10.1007/s10334-004-0062-8DOI Listing
November 2004

On the influence of training data quality in k-t BLAST reconstruction.

Magn Reson Med 2004 Nov;52(5):1175-83

MR-Centre, Skejby Hospital, Aarhus University Hospital, Denmark.

This work investigated how the quality of prior information (i.e., data acquired during the training stage) influences k-t BLAST reconstruction. The impact of several factors, such as the amount of training data, the presence of spatial misregistration in the training data, and the effects of filtering, was investigated with simulations and in vivo data. It is shown that k-t BLAST outperforms sliding window reconstruction, even with very limited training data. By increasing the amount of training data, reconstruction error continues to decrease, albeit by a diminishing amount. However, an increased amount of training data also increases susceptibility to misregistration of the training data. Filtering of the training data with the goal of reducing truncation artifacts had only minor impact on reconstruction errors. Considering the balance among obtaining the most benefit from the training data, minimizing susceptibility to misregistration, and keeping data acquisition to a minimum, it is concluded that in cardiac imaging the training datasets should be limited to 10-20 profiles in k-space for a typical field of view. The training data may be acquired in a separate breathhold without much penalty, if care is taken to minimize misregistration, such as with a navigator.
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http://dx.doi.org/10.1002/mrm.20256DOI Listing
November 2004

Arterial MR imaging phase-contrast flow measurement: improvements with varying velocity sensitivity during cardiac cycle.

Radiology 2004 Jul;232(1):289-94

MR Center, Institute of Experimental Clinical Research, Aarhus University Hospital, Skejby Sygehus, Brendstrupgaardsvej, DK-8200 Aarhus N, Denmark.

To reduce noise in velocity images of magnetic resonance (MR) phase-contrast measurements, the authors implemented and evaluated a pulse sequence that enables automatic optimization of the velocity-encoding parameter V(enc) for individual heart phases in pulsatile flow on the basis of a rapid prescan. This sequence was prospectively evaluated by comparing velocity-to-noise ratios with those from a standard MR flow scan obtained in the carotid artery in eight volunteers. This sequence was shown to improve velocity-to-noise ratios by a factor of 2.0-6.0 in all but the systolic heart phase and was determined to be an effective technique for reducing noise in phase-contrast velocity measurements.
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http://dx.doi.org/10.1148/radiol.2321030783DOI Listing
July 2004

Wall shear rates differ between the normal carotid, femoral, and brachial arteries: an in vivo MRI study.

J Magn Reson Imaging 2004 Feb;19(2):188-93

MR-Center, Institute of Experimental Clinical Research, Aarhus University Hospital, Aarhus, Denmark.

Purpose: To investigate wall shear rates in vivo in the common carotid, brachial, and superficial femoral arteries using very high resolution magnetic resonance imaging (MRI) phase contrast measurements.

Materials And Methods: Mean, maximum, and minimum wall shear rate and an oscillatory shear index were measured for 20 volunteers, aged 23.3 +/- 1.9 years, in the three arteries, using phase contrast imaging with 0.0625 mm2 resolution and three-dimensional paraboloid fitting.

Results: The superficial femoral artery had the lowest mean (130.3 +/- 13.1 second(-1)), maximum (735.8 +/- 32.4 second(-1)), and minimum (-224.5 +/- 17.0 second(-1)) wall shear rate, as well as the highest oscillatory shear index (0.21 +/- 0.02). All values were significantly different (P < 0.05) from both the brachial artery and the common carotid artery values. The highest mean (333.3 +/- 13.6 second(-1)) and minimum (117.9 +/- 24.5 second(-1)) wall shear rates and the lowest oscillatory shear index (0 +/- 0) were found in the common carotid artery.

Conclusion: It is possible to measure wall shear rate in vivo in different arteries using MRI with very high resolution. The findings exhibit the in vivo environment of wall shear rates and suggest a nonuniform distribution of wall shear rates throughout the arterial system.
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http://dx.doi.org/10.1002/jmri.10441DOI Listing
February 2004

Intraventricular dispersion and temporal delay of early left ventricular filling after acute myocardial infarction. Assessment by magnetic resonance velocity mapping.

Magn Reson Imaging 2002 Apr;20(3):249-60

Department of Cardiothoracic and Vascular Surgery, Skejby Sygehus, Aarhus University Hospital, Aarhus, Denmark.

This article aims to describe early left ventricular diastolic inflow using magnetic resonance velocity mapping in patients with recent acute myocardial infarction and in normal volunteers. Magnetic resonance velocity mapping was performed in a long axis plane through the hearts of 46 patients with recent, first time acute myocardial infarction and 43 age-matched normal volunteers. The peak velocities at six levels of the early diastolic inflow stream were recorded. A velocity index was calculated as the peak velocity in each position relative to the peak velocity at the mitral leaflet tips. Also, the temporal delay of velocity propagation was computed. Velocity index 4 cm downstream of mitral leaflet tips was lower in the acute myocardial infarction group (0.42 (0.17)) (mean (SD)) compared to controls (0.59 (0.25)) (p < 0.001). Temporal delay in the same position was longer in the acute myocardial infarction group (62 (67) ms) than in controls (32 (39) ms) (p < 0.02). Blood flow patterns in patients after acute myocardial infarction were characterized by increased dispersion of velocities and increased temporal delay of velocity propagation, probably reflecting impaired active left ventricular relaxation. Intraventricular flow measurements constitute a promising new technique for non-invasive assessment of left ventricular diastolic function.
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http://dx.doi.org/10.1016/s0730-725x(02)00495-2DOI Listing
April 2002
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