Publications by authors named "Hilde Kjernlie Andersen"

10 Publications

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Quantitative benchmarking of iodine imaging for two CT spectral imaging technologies: a phantom study.

Eur Radiol Exp 2021 Jun 23;5(1):24. Epub 2021 Jun 23.

Department of Life Sciences and Health, Oslo Metropolitan University, Box 4, St. Olavs plass, 0130, Oslo, Norway.

Background: The aim of this study was to quantitatively benchmark iodine imaging across specific virtual monoenergetic energy levels, iodine maps and virtual non-contrast images with different phantom sizes and iodine concentrations, using a rapid switching dual-energy CT (DECT) and a dual source DECT, in order to investigate accuracy and potential differences between the technologies.

Methods: Solutions of iodine contrast (10, 20, 30, 50, and 100 mg/mL), sterile water and saline were scanned in a phantom on a rapid switching single-source and dual-source DECT scanners from two different vendors. The phantom was equipped with polyurethane rings simulating three body sizes. The datasets were reconstructed in virtual monoenergetic energy levels (70, 80, 90, 100, 110, 120, 130, and 140 keV), virtual non-contrast images and iodine maps. HU and iodine concentrations were measured by placing ROIs in the iodine solutions.

Results: The iodine concentrations were reproduced with a high degree of accuracy for the single-source DECT (1.8-9.0%), showing a slight dependence on phantom size. The dual source DECT technique showed deviant values (error -33.8 to 12.0%) for high concentrations. In relation to the virtual non-contrast measurements, the images from both vendors were affected by the iodine concentration and phantom size (-127.8 to 539.1 HU). Phantom size did not affect the calculated monoenergetic attenuation values, but the attenuation values varied between the scanners.

Conclusions: Quantitative measurements of post-processed images are dependent on the concentration of iodine, the phantom size and different technologies. However, our study indicates that the iodine maps are reliable for quantification of iodine.
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June 2021

Image Quality Measured From Ultra-Low Dose Chest Computed Tomography Examination Protocols Using 6 Different Iterative Reconstructions From 4 Vendors, a Phantom Study.

J Comput Assist Tomogr 2020 Jan/Feb;44(1):95-101

From the Departments of Diagnostic Physics.

Purpose: This study aimed to evaluate image quality of ultra-low dose chest computed tomography using 6 iterative reconstruction (IR) algorithms.

Method: A lung phantom was scanned on 4 computed tomography scanners using fixed tube voltages and the lowest mAs available on each scanner, resulting in dose levels of 0.1 to 0.2 mGy (80 kVp) and 0.3 to 1 mGy (140 kVp) volume CT dose index (CTDIvol). Images were reconstructed with IR available on the scanners. Image noise, signal-to-noise ratios, contrast-to-noise ratios, uniformity, and noise power spectrum (NPS) were assessed for evaluation of image quality.

Results: Image quality parameters increased with increasing dose for all algorithms. At constant dose levels, model-based techniques improved the contrast-to-noise ratio of lesions more than the statistical algorithms. All algorithms tested at 0.1 mGy showed lower NPS peak frequencies compared with 0.39 mGy. In contrast to the statistical techniques, model-based algorithms showed lower NPS peak frequencies at the lowest doses, indicating a coarser and blotchier noise texture.

Conclusion: This study shows the importance of evaluating IR when introduced clinically.
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January 2020

Ultra-low dose chest computed tomography: Effect of iterative reconstruction levels on image quality.

Eur J Radiol 2019 May 18;114:62-68. Epub 2019 Feb 18.

Department of Diagnostic Physics, Oslo University Hospital, Oslo, Norway; The Department of Physics, University of Oslo, Oslo, Norway.

Purpose: To optimize image quality and radiation dose of chest CT with respect to various iterative reconstruction levels, detector collimations and body sizes.

Method: A Kyoto Kagaku Lungman with and without extensions was scanned using fixed ultra-low doses of 0.25, 0.49 and 0.74 mGy CTDI, and collimations of 40 and 80 mm. Images were reconstructed with the lung kernel, filtered back projection (FBP) and different ASIR-V levels (10-100%). Contrast-to-noise ratios (CNR) were calculated for 12 mm simulated lesions of different densities in the lung. Image noise, signal-to-noise ratios (SNR), variations in Hounsfield units (HU), noise power spectrum (NPS) and noise texture deviations (NTD) were evaluated for all reconstructions. NTD was calculated as percentage of pixels outside 3 standard deviations to evaluate IR-specific artefacts.

Results: Compared to the FBP, image noise reduced (5-55%) with ASIR-V levels irrespective of dose or collimation. SNR correlated positively (r ≥ 0.925, p ≤ 0.001) with ASIR-V levels at all doses, collimations, and phantom sizes. ASIR-V enhanced the CNR of the lesion with the lowest contrast from 12.7-42.1 (0-100% ASIR-V) at 0.74 mGy with 40 mm collimation. As expected, higher SNR and CNR were measured in the smaller phantom than the bigger phantom. Uniform HU were observed between FBP and ASIR-V levels at all doses, collimations, and phantom sizes. NPS curves left-shifted towards lower frequencies at increasing levels of ASIR-V irrespective of collimation. A positive correlation (r ≥ 0.946, p ≥ 0.001) was observed between NTD and ASIR-V levels. NTD of the FBP was not significantly (p ≤ 0.087) different from NTD of ASIR-V ≤ 20%. The data from the NPS and NTD indicates a blotchier and coarser noise texture at higher levels of ASIR-V, especially at 100% ASIR-V.

Conclusion: In comparison with the FBP technique, ASIR-V enhanced quantitative image quality parameters at all ultra-low doses tested. Moreover, the use of ASIR-V showed consistency with body size and collimation. Hence, ASIR-V may be useful for improving image quality of chest CT at ultra-low doses.
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May 2019

Image quality with iterative reconstruction techniques in CT of the lungs-A phantom study.

Eur J Radiol Open 2018 8;5:35-40. Epub 2018 Mar 8.

Department of Diagnostic Physics, Oslo University Hospital, Oslo, Norway.

Background: Iterative reconstruction techniques for reducing radiation dose and improving image quality in CT have proved to work differently for different patient sizes, dose levels, and anatomical areas.

Purpose: This study aims to compare image quality in CT of the lungs between four high-end CT scanners using the recommended reconstruction techniques at different dose levels and patient sizes.

Material And Methods: A lung phantom and an image quality phantom were scanned with four high-end scanners at fixed dose levels. Images were reconstructed with and without iterative reconstruction. Contrast-to-noise ratio, modulation transfer function, and peak frequency of the noise power spectrum were measured.

Results: IMR1 Sharp+ and VEO improved contrast-to-noise ratio to a larger extent than the other iterative techniques, while maintaining spatial resolution. IMR1 Sharp+ also maintained noise texture.

Conclusions: IMR1 Sharp+ was the only reconstruction technique in this study which increased CNR to a large extent, while maintaining all other image quality parameters measured in this study.
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March 2018

Quantitative Measurements Versus Receiver Operating Characteristics and Visual Grading Regression in CT Images Reconstructed with Iterative Reconstruction: A Phantom Study.

Acad Radiol 2018 Apr 29;25(4):509-518. Epub 2017 Nov 29.

Department of Diagnostic Physics, Oslo University Hospital, P.O. Box, 0454 Oslo, Norway; Department of Physics, University of Oslo, P. O. Box 1048 Blindern, N-0316 Oslo, Norway.

Rationale And Objectives: This study aimed to evaluate the correlation of quantitative measurements with visual grading regression (VGR) and receiver operating characteristics (ROC) analysis in computed tomography (CT) images reconstructed with iterative reconstruction.

Materials And Methods: CT scans on a liver phantom were performed on CT scanners from GE, Philips, and Toshiba at three dose levels. Images were reconstructed with filtered back projection (FBP) and hybrid iterative techniques (ASiR, iDose, and AIDR 3D of different strengths). Images were visually assessed by five readers using a four- and five-grade ordinal scale for liver low contrast lesions and for 10 image quality criteria. The results were analyzed with ROC and VGR. Standard deviation, signal-to-noise ratios, and contrast-to-noise ratios were measured in the images.

Results: All data were compared to FBP. The results of the quantitative measurements were improved for all algorithms. ROC analysis showed improved lesion detection with ASiR and AIDR and decreased lesion detection with iDose. VGR found improved noise properties for all algorithms, increased sharpness with iDose and AIDR, and decreased artifacts from the spine with AIDR, whereas iDose increased the artifacts from the spine. The contrast in the spine decreased with ASiR and iDose.

Conclusions: Improved quantitative measurements in images reconstructed with iterative reconstruction compared to FBP are not equivalent to improved diagnostic image accuracy.
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April 2018

[Radiation-induced cataracts].

Tidsskr Nor Laegeforen 2016 Nov 22;136(21):1809-1812. Epub 2016 Nov 22.

Intervensjonssenteret Oslo universitetssykehus, Rikshospitalet og Fysisk institutt Universitetet i Oslo.

The dose limit for the lens of the eye for occupationally exposed workers that is stipulated in the Norwegian Regulation on radiation protection is based on outdated threshold doses for radiation-induced cataracts. Recent studies have shown that injuries may occur at significantly lower radiation doses than previously assumed. The results from the new studies will impact upon future legislation and recommendations regarding radiation hygiene for personnel in x-ray laboratories and operating theatres who may be exposed to significant radiation doses in the course of their work.
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November 2016

Can use of adaptive statistical iterative reconstruction reduce radiation dose in unenhanced head CT? An analysis of qualitative and quantitative image quality.

Acta Radiol Open 2016 Aug 17;5(8):2058460116645831. Epub 2016 Aug 17.

The Intervention Centre, Oslo University Hospital, Postbox 4950, Nydalen, 0424 Oslo, Norway; Institute of Physics, University of Oslo, 0027 Oslo, Norway.

Background: Iterative reconstruction can reduce image noise and thereby facilitate dose reduction.

Purpose: To evaluate qualitative and quantitative image quality for full dose and dose reduced head computed tomography (CT) protocols reconstructed using filtered back projection (FBP) and adaptive statistical iterative reconstruction (ASIR).

Material And Methods: Fourteen patients undergoing follow-up head CT were included. All patients underwent full dose (FD) exam and subsequent 15% dose reduced (DR) exam, reconstructed using FBP and 30% ASIR. Qualitative image quality was assessed using visual grading characteristics. Quantitative image quality was assessed using ROI measurements in cerebrospinal fluid (CSF), white matter, peripheral and central gray matter. Additionally, quantitative image quality was measured in Catphan and vendor's water phantom.

Results: There was no significant difference in qualitative image quality between FD FBP and DR ASIR. Comparing same scan FBP versus ASIR, a noise reduction of 28.6% in CSF and between -3.7 and 3.5% in brain parenchyma was observed. Comparing FD FBP versus DR ASIR, a noise reduction of 25.7% in CSF, and -7.5 and 6.3% in brain parenchyma was observed. Image contrast increased in ASIR reconstructions. Contrast-to-noise ratio was improved in DR ASIR compared to FD FBP. In phantoms, noise reduction was in the range of 3 to 28% with image content.

Conclusion: There was no significant difference in qualitative image quality between full dose FBP and dose reduced ASIR. CNR improved in DR ASIR compared to FD FBP mostly due to increased contrast, not reduced noise. Therefore, we recommend using caution if reducing dose and applying ASIR to maintain image quality.
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August 2016

Image texture and radiation dose properties in CT.

J Appl Clin Med Phys 2016 05 8;17(3):408-418. Epub 2016 May 8.

Gjøvik University College.

The aim of this study was to compare image noise properties of GE Discovery HD 750 and Toshiba Aquilion ONE. The uniformity section of a Catphan 600 image quality assurance phantom was scanned with both scanners, at different dose levels and with extension rings simulating patients of different sizes. 36 datasets were obtained and analyzed in terms of noise power spectrum. All the results prove that introduction of extension rings significantly altered the image quality with respect to noise properties. Without extension rings, the Toshiba scanner had lower total visible noise than GE (with GE as reference: FC18 had 82% and FC08 had 80% for 10 mGy, FC18 had 77% and FC08 74% for 15 mGy, FC18 had 80% and FC08 77% for 20 mGy). The total visible noise (TVN) for 20 and 15 mGy were similar for the phantom with the smallest additional extension ring, while Toshiba had higher TVN than GE for the 10 mGy dose level (120% FC18, 110% FC08). For the second and third ring, the GE images had lower TVN than Toshiba images for all dose levels (Toshiba TVN is greater than 155% for all cases). The results indi-cate that GE potentially has less image noise than Toshiba for larger patients. The Toshiba FC18 kernel had higher TVN than the Toshiba FC08 kernel with additional beam hardening correction for all dose levels and phantom sizes (120%, 107%, and 106% for FC18 compared to 110%, 98%, and 97%, for FC08, for 10, 15 and 20 mGy doses, respectively).
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May 2016

Improved Liver Lesion Conspicuity With Iterative Reconstruction in Computed Tomography Imaging.

Curr Probl Diagn Radiol 2016 Sep-Oct;45(5):291-6. Epub 2015 Dec 15.

The Intervention Centre, Rikshospitalet, Oslo, Norway; Institute of Physics, University of Oslo, Oslo, Norway.

Studies on iterative reconstruction techniques on computed tomographic (CT) scanners show reduced noise and changed image texture. The purpose of this study was to address the possibility of dose reduction and improved conspicuity of lesions in a liver phantom for different iterative reconstruction algorithms. An anthropomorphic upper abdomen phantom, specially designed for receiver operating characteristic analysis was scanned with 2 different CT models from the same vendor, GE CT750 HD and GE Lightspeed VCT. Images were obtained at 3 dose levels, 5, 10, and 15mGy, and reconstructed with filtered back projection (FBP), and 2 different iterative reconstruction algorithms; adaptive statistical iterative reconstruction and Veo. Overall, 5 interpreters evaluated the images and receiver operating characteristic analysis was performed. Standard deviation and the contrast to noise ratio were measured. Veo image reconstruction resulted in larger area under curves compared with those adaptive statistical iterative reconstruction and FBP image reconstruction for given dose levels. For the CT750 HD, iterative reconstruction at the 10mGy dose level resulted in larger or similar area under curves compared with FBP at the 15mGy dose level (0.88-0.95 vs 0.90). This was not shown for the Lightspeed VCT (0.83-0.85 vs 0.92). The results in this study indicate that the possibility for radiation dose reduction using iterative reconstruction techniques depends on both reconstruction technique and the CT scanner model used.
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April 2017

Choosing the best reconstruction technique in abdominal computed tomography: a systematic approach.

J Comput Assist Tomogr 2014 Nov-Dec;38(6):853-8

From *The Intervention Centre, Oslo University Hospital; †Department of Physics, University in Oslo; ‡Department of Radiology and Nuclear Medicine, Oslo University Hospital, Rikshospitalet; and §Department of Medicine, University in Oslo, Oslo, Norway.

Objective: There is uncertainty regarding the effect of iterative reconstruction (IR) techniques and other reconstruction algorithms on image quality. The aim of this study was to optimize image quality in relation to radiation dose in computed tomography (CT) liver examinations by comparing images reconstructed with different abdominal filters with and without IR.

Methods: An anthropomorphic phantom was scanned on a Toshiba Aquilion ONE CT scanner. Images at 2 different dose levels were reconstructed with 12 different body reconstruction filters, all with both filtered back-projection and Adaptive Iterative Dose Reduction 3 dimensional. Receiver operating characteristic curves were constructed. The 2 reconstruction combinations with the highest scores from the phantom study were evaluated in a second comparison of clinical images. Six liver examinations were reconstructed with both filters and evaluated using visual grading analysis.

Results: Two combinations of reconstruction filters and IR were the only 2 options among the 8 best images at both dose levels (area under the curve, 0.96 and 0.94 for 15 mGy as well as 0.86 and 0.84 for 10 mGy). In the patient study, one of these filters in combination with IR scored slightly higher than the other in combination with IR (mean score, 2.60 and 2.57, respectively; P = 0.56). Iterative reconstruction did not significantly increase lesion detectability for any of the filters.

Conclusions: This study indicates that the preferred choice for reconstruction of CT liver examinations performed with the Toshiba Aquilion ONE should be the FC18 filter with IR, although the IR technique did not significantly improve lesion detectability and did not compensate for the dose reduction in this study.
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January 2015