Virtual Clinical Trials in Medical Imaging System Evaluation and Optimisation

Barufaldi, Bruno; Maidment, Andrew D. A.; Dustler, Magnus; Axelsson, Rebecca; Tomic, Hanna; Zackrisson, Sophia; Tingberg, Anders; Bakić, Predrag R.

doi:10.1093/rpd/ncab080

Cited by 29 publications

(28 citation statements)

References 37 publications

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“…We have previously shown that voxel-replacement for calcifications results in realistic images. 5,7,9,14 This arises because the attenuation of calcifications is markedly higher than any soft tissue. As a result, the calcifications will always show positive contrast again breast tissue, either adipose, glandular, or carcinoma.…”

Section: Discussionmentioning

confidence: 99%

“…We have previously shown that voxel‐replacement for calcifications results in realistic images 5,7,9,14 . This arises because the attenuation of calcifications is markedly higher than any soft tissue.…”

Section: Discussionmentioning

confidence: 99%

“…Virtual clinical trials (VCTs) have been widely used as a rapid and cost-effective alternative for evaluating and optimizing imaging technologies. [1][2][3][4][5] VCTs allow for the simulation of images with voxel-wise ground-truth, which is not available in clinical practice.The images and ground truth can be used to evaluate the performance of imaging systems, modalities, and techniques. 1,6,7 The ground truth yields information regarding the strengths and weaknesses of imaging systems,providing valuable knowledge that can be used for myriad purposes including to support the regulatory approval of novel imaging systems.…”

Section: Introductionmentioning

confidence: 99%

“…To predict the diagnostic performance of this reader study using VCTs, virtual readers should be trained using sets of images with non-calcified lesions within the same threshold of detectability. 5,8,14 In previous studies, we attempted to replicate a clinical trial of a pre-market approval system using an in silico trial. 5,14 We conducted an extensive VCT using simulated DM and DBT images of voxelized breast phantoms with various lesions.…”

Section: Introductionmentioning

confidence: 99%

“…In previous studies, we attempted to replicate a clinical trial of a pre‐market approval system using an in silico trial 5,14 . We conducted an extensive VCT using simulated DM and DBT images of voxelized breast phantoms with various lesions.…”

Section: Introductionmentioning

confidence: 99%

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Computer simulations of case difficulty in digital breast tomosynthesis using virtual clinical trials

et al. 2022

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Purpose Virtual clinical trials (VCTs) require computer simulations of representative patients and images to evaluate and compare changes in performance of imaging technologies. The simulated images are usually interpreted by model observers whose performance depends upon the selection of imaging cases used in training evaluation models. This work proposes an efficient method to simulate and calibrate soft tissue lesions, which matches the detectability threshold of virtual and human readings. Methods Anthropomorphic breast phantoms were used to evaluate the simulation of four mass models (I–IV) that vary in shape and composition of soft tissue. Ellipsoidal (I) and spiculated (II–IV) masses were simulated using composite voxels with partial volumes. Digital breast tomosynthesis projections and reconstructions of a clinical system were simulated. Channelized Hotelling observers (CHOs) were evaluated using reconstructed slices of masses that varied in shape, composition, and density of surrounded tissue. The detectability threshold of each mass model was evaluated using receiver operating characteristic (ROC) curves calculated with the CHO's scores. Results The area under the curve (AUC) of each calibrated mass model were within the 95% confidence interval (mean AUC [95% CI]) reported in a previous reader study (0.93 [0.89, 0.97]). The mean AUC [95% CI] obtained were 0.94 [0.93, 0.96], 0.92 [0.90, 0.93], 0.92 [0.90, 0.94], 0.93 [0.92, 0.95] for models I to IV, respectively. The mean AUC results varied substantially as a function of shape, composition, and density of surrounded tissue. Conclusions For successful VCTs, lesions composed of soft tissue should be calibrated to simulate imaging cases that match the case difficulty predicted by human readers. Lesion composition, shape, and size are parameters that should be carefully selected to calibrate VCTs.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Computer simulations of case difficulty in digital breast tomosynthesis using virtual clinical trials

et al. 2022

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Development of scalable lymphatic system in the 4D XCAT phantom: Application to quantitative evaluation of lymphoma PET segmentations

et al. 2022

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Background: Digital anthropomorphic phantoms, such as the 4D extended cardiac-torso (XCAT) phantom, are actively used to develop, optimize, and evaluate a variety of imaging applications, allowing for realistic patient modeling and knowledge of ground truth. The XCAT phantom defines the activity and attenuation for a simulated patient, which includes a complete set of organs, muscle, bone, and soft tissue, while also accounting for cardiac and respiratory motion. However, the XCAT phantom does not currently include the lymphatic system, critical for evaluating medical imaging tasks such as sentinel node detection, node density measurement, and radiation dosimetry. Purpose: In this study, we aimed to develop a scalable lymphatic system in the XCAT phantom, to facilitate improved research of the lymphatic system in medical imaging. Using this scalable lymphatic system, we modeled the lymph node conglomerate pathology that is characteristically observed in primary mediastinal B-cell lymphoma (PMBCL). As an extended application, we evaluated positron emission tomography (PET) image quantification of metabolic tumor volume (MTV) and total lesion glycolysis (TLG) of these simulated lymphomas, though the phantoms may be applied to other imaging modalities and study design paradigms (e.g., image quality, detection). Methods: A template model for the lymphatic system was developed based on anatomical data from the Visible Human Project of the National Library of Medicine. The segmented nodes and vessels were fit with non-uniform rational basis spline surfaces, and multichannel large deformation diffeomorphic metric mapping was used to propagate the template to different XCAT anatomies. To model conglomerates observed in PMBCL, lymph nodes were enlarged, converged within the mediastinum, and tracer concentration was increased. We used the phantoms as inputs to a PET simulation tool, which generated images using ordered subsets expectation maximization reconstruction with 2-8 mm Gaussian filters. Fixed thresholding (FT) and gradient segmentation were used to determine MTV and TLG. Percent bias (%Bias) and coefficient of variation (COV) were computed as measures of accuracy and precision, respectively, for each MTV and TLG measurement. Results: Using the methodology described above, we introduced a scalable lymphatic system in the XCAT phantom, which allows for the radioactivity and attenuation ground truth to be generated in 116 ± 2.5 s using a 2.3 GHz processor. Within the Rhinoceros interface, lymph node anatomy and function were modified to create a cohort of 10 phantoms with lymph node conglomerates. Using the lymphoma phantoms to evaluate PET quantification of MTV, mean

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Line‐based iterative geometric calibration method for a tomosynthesis system

Choi,

Vent,

Acciavatti

et al. 2024

Medical Physics

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BackgroundA next generation tomosynthesis (NGT) system, capable of two‐dimensional source motion, detector motion in the perpendicular direction, and magnification tomosynthesis, was constructed to investigate different acquisition geometries. Existing position‐based geometric calibration methods proved ineffective when applied to the NGT geometries.PurposeA line‐based iterative calibration method is developed to perform accurate geometric calibration for the NGT system.MethodsThe proposed method calculates the system geometry through virtual line segments created by pairs of fiducials within a calibration phantom, by minimizing the error between the line equations computed from the true and estimated fiducial projection pairs. It further attempts to correct the 3D fiducial locations based on the initial geometric calibration. The method's performance was assessed via simulation and experimental setups with four distinct NGT geometries: X, T, XZ, and TZ. The X geometry resembles a conventional DBT acquisition along the chest wall. The T geometry forms a “T”‐shaped source path in mediolateral (ML) and posteroanterior (PA) directions. A descending detector motion is added to both X and T geometries to form the XZ and TZ geometries, respectively. Simulation studies were conducted to assess the robustness of the method to geometric perturbations and inaccuracies in fiducial locations. Experimental studies were performed to assess the impact of phantom magnification and the performance of the proposed method for various geometries, compared to the traditional position‐based method. Star patterns were evaluated for both qualitative and quantitative analyses; the Fourier spectral distortions (FSDs) graphs and the contrast transfer function (CTF) were extracted. The limit of spatial resolution (LSR) was measured at 5% modulation of the CTF.ResultsThe proposed method presented is highly robust to geometric perturbation and fiducial inaccuracies. After the line‐based iterative method, the mean distance between the true and estimated fiducial projections was [X, T, XZ, TZ]: [0.01, 0.01, 0.02, 0.01] mm. The impact of phantom magnification was observed; a contact‐mode acquisition of a calibration phantom successfully provided an accurate geometry for 1.85× magnification images of a star pattern, with the X geometry. The FSD graphs for the contact‐mode T geometry acquisition presented evidence of super‐resolution, with the LSR of [0°‐quadrant: 8.57, 90°‐quadrant: 8.47] lp/mm. Finally, a contact‐mode XZ geometry acquisition and a 1.50× magnification TZ geometry acquisition were reconstructed with three calibration methods—position‐based, line‐based, and iterative line‐based. As more advanced methods are applied, the CTF becomes more isotropic, the FSD graphs demonstrate less spectral leakage as super‐resolution is achieved, and the degree of blurring artifacts reduces significantly.ConclusionsThis study introduces a robust calibration method tailored to the unique requirements of advanced tomosynthesis systems. By employing virtual line segments and iterative techniques, we ensure accurate geometric calibration while mitigating the limitations posed by the complex acquisition geometries of the NGT system. Our method's ability to handle various NGT configurations and its tolerance to fiducial misalignment make it a superior choice compared to traditional calibration techniques.

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Virtual Clinical Trials in Medical Imaging System Evaluation and Optimisation

Cited by 29 publications

References 37 publications

Computer simulations of case difficulty in digital breast tomosynthesis using virtual clinical trials

Computer simulations of case difficulty in digital breast tomosynthesis using virtual clinical trials

Development of scalable lymphatic system in the 4D XCAT phantom: Application to quantitative evaluation of lymphoma PET segmentations

Line‐based iterative geometric calibration method for a tomosynthesis system

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