Medical Physics
Công bố khoa học tiêu biểu
* Dữ liệu chỉ mang tính chất tham khảo
There has been considerable research effort into obtaining quantitative measures of perfusion using dynamic contrast‐enhanced MRI. Absolute quantification of the arterial input function (AIF) and/or venous output function (VOF) in major blood vessels improves perfusion estimates, however reliable techniques for doing so are lacking. Using changes in phase (Δφ) in blood vessels is thought to be the best way to quantify the AIF or VOF. However, it is not yet clear how best to deal with the susceptibility physics when the blood vessels have a complex geometry. We propose a methodology for obtaining absolute quantification of the AIF or VOF using a Fourier‐based calculation of field inhomogeneities, in order to convert Δφ to absolute contrast agent concentration, regardless of the blood vessel geometry. This methodology was tested in an aqueous phantom system. The experimentally measured Δφ was divided by the expected Δφ on a pixel by pixel basis. Ideally, this ratio should be one. Considering all pixels in the phantom tubing, the measured Δφ divided by expected Δφ had a mean value of 1.02 and standard deviation of 0.172. The Fourier‐based calculation can therefore successfully predict Δφ and thus can be used to account for the effect of the vessel geometry and orientation in the conversion of MR phase to contrast agent concentration. The methodology is thus promising for making absolute measurements of the AIF or VOF.
Sự nén hình ảnh hiệu quả trong khi vẫn giữ lại chất lượng hình ảnh có khả năng tạo ra bước đột phá lớn cho việc chẩn đoán và điều trị lâm sàng từ xa, vì điều kiện kết nối Internet kém thường là rào cản chính trong các dịch vụ này. Bài báo này trình bày một khuôn khổ nén hình ảnh theo từng cơ quan cho các can thiệp từ xa dựa trên phương pháp học sâu và bộ lọc khuếch tán dị hướng.
Phương pháp đề xuất, học sâu và khuếch tán dị hướng (DLAD), sử dụng kiến trúc mạng nơ-ron tích chập để trích xuất bản đồ xác suất cho cơ quan mục tiêu; bản đồ xác suất này hướng dẫn bộ lọc khuếch tán dị hướng mà làm mịn hình ảnh, ngoại trừ vị trí của cơ quan mục tiêu. Sau đó, một phương pháp nén, chẳng hạn như BZ2 và HEVC-không mất mát về mặt hình ảnh, được áp dụng để nén hình ảnh. Chúng tôi áp dụng phương pháp đề xuất trên các hình ảnh CT ba chiều (3D) thu được cho quy trình phá hủy tế bào bằng sóng radio (RFA) đối với các tổn thương gan. Chúng tôi đánh giá định lượng phương pháp đề xuất trên 151 hình ảnh CT sử dụng tỷ lệ tín hiệu đỉnh trên tỷ lệ nhiễu (PSNR), độ tương đồng cấu trúc (SSIM), và tỷ lệ nén (CR). Cuối cùng, chúng tôi so sánh các đánh giá của hai bác sĩ chẩn đoán hình ảnh về việc phát hiện tổn thương gan và chú thích tâm tổn thương gan bằng cách sử dụng 33 bộ hình ảnh gốc và hình ảnh đã nén.
Kết quả cho thấy phương pháp có thể cải thiện một cách đáng kể PSNR của hầu hết các phương pháp nén nổi tiếng. DLAD kết hợp với HEVC-không mất mát về mặt hình ảnh đạt được PSNR trung bình cao nhất là 6.45, cao hơn 36% so với HEVC gốc và vượt trội hơn các phương pháp nén hình ảnh y tế không mất mát tiên tiến khác. Giá trị trung bình của PSNR và SSIM lần lượt là 70 dB và 0.95. Ngoài ra, hiệu ứng nén không ảnh hưởng một cách có ý nghĩa thống kê đến các đánh giá của các bác sĩ chẩn đoán hình ảnh về phát hiện tổn thương gan và chú thích trung tâm tổn thương.
Vì vậy, chúng tôi kết luận rằng phương pháp này có tiềm năng cao để được áp dụng trong các ứng dụng can thiệp từ xa.
The purpose of this study was to quantify gender diversity in leadership positions within the field of medical physics, as well as within award categories and other recognitions by the American Association of Physicists in Medicine. The April 2019 PDF version of the AAPM membership directory was searched for all users self‐reporting as holding a leadership position at their place of employment, those elected to leadership positions within the AAPM, those serving as chair of an AAPM council, and those listed as having received an award or other such recognition from AAPM (beginning in 1972 with the William D. Coolidge Award). Historical data for these categories were obtained from archived membership directories on the AAPM website. The AAPM website was also used to identify members who have served on the Medical Physics Editorial Board. The Commission on Accreditation of Medical Physics Education Programs (CAMPEP) website was used to identify the current directors of graduate and residency programs (as of July 2019). Because gender was not a reported field in any of these categories, gender was assigned by reviewing names and photographs. Percentage representation in these respects was compared to the overall percentage of women in the AAPM in 2019 (23.3%) and reported the number of women working as medical physicists globally (29.8%). Within the AAPM, the percentage of women reporting clinical leadership roles is 12.0% within the US, 13.6% in Canada, and 18.0% in all other countries combined. Women comprise only 7.5% of CAMPEP graduate program directors and 21.5% of residency program directors. The percentage of female presidents in AAPM is 8.1%. A woman has never served as Editor‐in‐Chief of Medical Physics, and the average for the past 10 yr for female board membership is 13.6%. With the exception of the John R. Cameron Young Investigators Symposium Award, the percentage of all female AAPM awardees is less than the percentage of women AAPM members. The lowest percentage of female representation within AAPM is among council chairs with only one woman having held a chair position out of 42 positions (2.4%) from 1970 to July 2019. Similar to the traditional discipline of physics, medical physics displays a clear gender disparity with regard to leadership positions, both within educational training programs and the AAPM. Further investigation into the demographics of the field and psychosocial factors affecting medical physicists may help to elucidate the origin of these disparities and inform strategies to address them.
Ablation zone segmentation in contrast‐enhanced computed tomography (CECT) images enables the quantitative assessment of treatment success in the ablation of liver lesions. However, fully automatic liver ablation zone segmentation in CT images still remains challenging, such as low accuracy and time‐consuming manual refinement of the incorrect regions.
Therefore, in this study, we developed a semi‐automatic technique to address the remaining drawbacks and improve the accuracy of the liver ablation zone segmentation in the CT images.
Our approach uses a combination of a CNN‐based automatic segmentation method and an interactive CNN‐based segmentation method. First, automatic segmentation is applied for coarse ablation zone segmentation in the whole CT image. Human experts then visually validate the segmentation results. If there are errors in the coarse segmentation, local corrections can be performed on each slice via an interactive CNN‐based segmentation method. The models were trained and the proposed method was evaluated using two internal datasets of post‐interventional CECT images ( = 22, = 145; 62 patients in total) and then further tested using an external benchmark dataset ( = 12; 10 patients).
To evaluate the accuracy of the proposed approach, we used Dice similarity coefficient (
The proposed semi‐automatic CNN‐based segmentation method can be used to effectively segment the ablation zones, increasing the value of CECT for an assessment of treatment success. For reproducibility, the trained models, source code, and demonstration tool are publicly available at
The use of magnetic resonance imaging (MRI) in radiation oncology is expanding rapidly, and more clinics are integrating MRI into their radiation therapy workflows. However, radiation therapy presents a new set of challenges and places additional constraints on MRI compared to diagnostic radiology that, if not properly addressed, can undermine the advantages MRI offers for radiation treatment planning (RTP). The authors introduce here strategies to manage several challenges of using MRI for virtual simulation in external beam RTP.
A total of 810 clinical MRI simulation exams were performed using a dedicated MRI scanner for external beam RTP of brain, breast, cervix, head and neck, liver, pancreas, prostate, and sarcoma cancers. Patients were imaged in treatment position using MRI‐optimal immobilization devices. Radiofrequency (RF) coil configurations and scan protocols were optimized based on RTP constraints. Off‐resonance and gradient nonlinearity‐induced geometric distortions were minimized or corrected prior to using images for RTP. A multidisciplinary MRI simulation guide, along with window width and level presets, was created to standardize use of MR images during RTP. A quality assurance program was implemented to maintain accuracy and repeatability of MRI simulation exams.
The combination of a large bore scanner, high field strength, and circumferentially wrapped, flexible phased array RF receive coils permitted acquisition of thin slice images with high contrast‐to‐noise ratio (CNR) and image intensity uniformity, while simultaneously accommodating patient setup and immobilization devices. Postprocessing corrections and alternative acquisition methods were required to reduce or correct off‐resonance and gradient nonlinearity induced geometric distortions.
The methodology described herein contains practical strategies the authors have implemented through lessons learned performing clinical MRI simulation exams. In their experience, these strategies provide robust, high fidelity, high contrast MR images suitable for external beam RTP.
In patients with chronic obstructive pulmonary disease (COPD), diaphragm function may deteriorate due to reduced muscle fiber length. Quantitative analysis of the morphology of the diaphragm is therefore important. In the authors current study, they propose a diaphragm segmentation method for COPD patients that uses volumetric chest computed tomography (CT) data, and they provide a quantitative analysis of the diaphragmatic dimensions.
Volumetric CT data were obtained from 30 COPD patients and 10 normal control patients using a 16‐row multidetector CT scanner (Siemens Sensation 16) with 0.75‐mm collimation. Diaphragm segmentation using 3D ray projections on the lower surface of the lungs was performed to identify the draft diaphragmatic lung surface, which was modeled using quadratic 3D surface fitting and robust regression in order to minimize the effects of segmentation error and parameterize diaphragm morphology. This result was visually evaluated by an expert thoracic radiologist. To take into consideration the shape features of the diaphragm, several quantification parameters—including the shape index on the apex (SIA) (which was computed using gradient set to 0), principal curvatures on the apex on the fitted diaphragm surface (CA), the height between the apex and the base plane (H), the diaphragm lengths along the
The overall accuracy of the combined segmentation method was 97.22% ± 4.44% while the visual accuracy of the models for the segmented diaphragms was 95.28% ± 2.52% (mean ± SD). The quantitative parameters, including SIA, CA, H, XL, YL, ZL, FZL, C, and SA were 0.85 ± 0.05 (mm−1), 0.01 ± 0.00 (mm−1), 17.93 ± 10.78 (mm), 129.80 ± 11.66 (mm), 163.19 ± 13.45 (mm), 71.27 ± 17.52 (mm), 61.59 ± 16.98 (mm), 0.01 ± 0.00 (mm−1), and 34 380.75 ± 6680.06 (mm2), respectively. Several parameters were correlated with the PFT parameters.
The authors propose an automatic method for quantitatively evaluating the morphological parameters of the diaphragm on volumetric chest CT in COPD patients. By measuring not only the conventional length and surface area but also the shape features of the diaphragm using quadratic 3D surface modeling, the proposed method is especially useful for quantifying diaphragm characteristics. Their method may be useful for assessing morphological diaphragmatic changes in COPD patients.
Ultrasound has been the greatest imaging modality worldwide for many years by equipment purchase value and by number of machines and examinations. It is becoming increasingly the front end imaging modality; serving often as an extension of the physician's fingers. We believe that at the other extreme, high‐end systems will continue to compete with all other imaging modalities in imaging departments to be the method of choice for various applications, particularly where safety and cost are paramount. Therapeutic ultrasound, in addition to the physiotherapy practiced for many decades, is just coming into its own as a major tool in the long progression to less invasive interventional treatment. The physics of medical ultrasound has evolved over many fronts throughout its history. For this reason, a topical review, rather than a primarily chronological one is presented. A brief review of medical ultrasound imaging and therapy is presented, with an emphasis on the contributions of medical physicists, the American Association of Physicists in Medicine (AAPM) and its publications, particularly its journal
Further progress in the development of polymer gel dosimetry using MRI is reported, together with examples of its application to verify treatment plans for stereotactic radiosurgery and high dose rate brachytherapy. The dose distribution image produced in the tissue‐equivalent gel by radiation‐induced polymerization, and encoded in the spatial distribution of the NMR transverse relaxation rates (
This study presents the first theoretical analysis of the absolute dose‐rate distribution about the Model 200
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