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Tomosynthesis Imaging

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Medical Physics 2015年第11期42卷 6770-6771页

作者： John M. Sabol

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Iterative image-Domain Decomposition for Dual-Energy CT

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MEDICAL PHYSICS 2014年第6期41卷 475-476页

作者： Niu, T. Dong, X. Petrongolo, M. Zhu, L. Georgia Inst Technol Atlanta GA 30332 USA

Purpose: Dual energy CT (DECT) imaging plays an important role in advanced imaging applications due to its capability of material decomposition. Direct decomposition via matrix inversion suffers from significant degradation of image signal-to-noise ratios, which reduces clinical values of DECT. Existing denoising algorithms achieve suboptimal performance since they suppress image noise either before or after the decomposition and do not fully explore the noise statistical properties of the decomposition process. In this work, the authors propose an iterative image-domain decomposition method for noise suppression in DECT, using the full variance-covariance matrix of the decomposed images. Methods: The proposed algorithm is formulated in the form of least-square estimation with smoothness regularization. Based on the design principles of a best linear unbiased estimator, the authors include the inverse of the estimated variance-covariance matrix of the decomposed images as the penalty weight in the least-square term. The regularization term enforces the image smoothness by calculating the square sum of neighboring pixel value differences. To retain the boundary sharpness of the decomposed images, the authors detect the edges in the CT images before decomposition. These edge pixels have small weights in the calculation of the regularization term. Distinct from the existing denoising algorithms applied on the images before or after decomposition, the method has an iterative process for noise suppression, with decomposition performed in each iteration. The authors implement the proposed algorithm using a standard conjugate gradient algorithm. The method performance is evaluated using an evaluation phantom (Catphan©600) and an anthropomorphic head phantom. The results are compared with those generated using direct matrix inversion with no noise suppression, a denoising method applied on the decomposed images, and an existing algorithm with similar formulation as the prop

关键词： Computed tomography Matrix theory Noise Numerical linear algebra general statistical methods Spatial resolution computerised tomography conjugate gradient methods covariance matrices edge detection image denoising image resolution iterative methods least squares approximations matrix inversion medical image processing phantoms dual-energy CT image-domain decomposition noise suppression best linear unbiased estimation edge predetection Computerised tomographs Biological material, e.g. blood, urine Haemocytometers Digital computing or data processing equipment or methods, specially adapted for specific applications image data processing or generation, in general image enhancement or restoration, e.g. from bit-mapped to bit-mapped creating a similar image Medical imaging Medical image noise Computed tomography Medical image reconstruction Medical image spatial resolution Medical X-ray imaging Spatial resolution Matrix inversion Medical image smoothing Density measurement

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Highly cited papers in Medical Physics

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MEDICAL PHYSICS 2014年第8期41卷 43-44页

作者： Eaton, David J. Mt Vernon Hosp Natl Radiotherapy Trials QA Grp London HA6 2RN England

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Transrectal ultrasound based prostate volume determination: Is the frustum algorithm more accurate than planimetry?

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MEDICAL PHYSICS 2013年第3期40卷 031705页

作者： Liu, Derek Usmani, Nawaid Sloboda, Ron S. Cross Canc Inst Dept Med Phys Edmonton AB T6G 1Z2 Canada Univ Alberta Dept Oncol Edmonton AB T6G 2R3 Canada Cross Canc Inst Dept Radiat Oncol Edmonton AB T6G 1Z2 Canada

Purpose: To compare reconstructed volumes calculated via planimetry and frustum algorithms in the context of stepped transrectal ultrasound (US) imaging, and to estimate the reconstruction error for prostate volumes. Methods: Prostate contours for 40 permanent implant patients were delineated on magnetic resonance (MR) and transrectal US images by a radiation oncologist. Simulated images of ellipsoid and truncated cone geometrical objects were constructed to determine volume calculation accuracy. Simulation results were used to deduce the algorithm-associated error made when calculating transrectal US prostate volumes. Results: For imaging without deliberate slice positioning, planimetry reconstruction was mostly accurate while the frustum algorithm underestimated the volume. The discrepancy was mostly due to the end slice reconstruction. For slice positioning that reflected US image acquisition, planimetry overestimated by half the superior slice volume on average while frustum underestimated by half the inferior slice volume. The estimated algorithm errors for prostate contours were 4% and -3%, respectively. Conclusions: The planimetry and frustum algorithms offer different interpretations for reconstruction and yield systematic differences in calculated volumes. Both algorithms introduce bias into transrectal US prostate volume determinations that may have clinical implications, planimetry overestimating and frustum underestimating the volume. (C) 2013 American Association of Physicists in Medicine. [http://***/10.1118/1.4789920]

关键词： Ultrasonographic imaging Magnetic resonance imaging Cancer image quality Reconstruction biological organs biomedical MRI biomedical ultrasonics cancer data acquisition image reconstruction medical image processing tumours ultrasonic imaging Involving electronic [emr] or nuclear [nmr] magnetic resonance, e.g. magnetic resonance imaging Diagnosis using ultrasonic, sonic or infrasonic waves data acquisition and logging Digital computing or data processing equipment or methods, specially adapted for specific applications image data processing or generation, in general Ultrasonography Medical imaging Computed tomography Interpolation Medical magnetic resonance imaging Medical image reconstruction Magnetic resonance image reconstruction Brachytherapy Medical treatment planning

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Four-dimensional Monte Carlo simulations demonstrating how the extent of intensity-modulation impacts motion effects in proton therapy lung treatments

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MEDICAL PHYSICS 2013年第12期40卷 121713页

作者： Dowdell, Stephen Grassberger, Clemens Paganetti, Harald Massachusetts Gen Hosp Dept Radiat Oncol Boston MA 02114 USA Harvard Univ Sch Med Boston MA 02114 USA Paul Scherrer Inst Ctr Proton Therapy CH-5232 Villigen Switzerland

Purpose: To compare motion effects in intensity modulated proton therapy (IMPT) lung treatments with different levels of intensity modulation. Methods: Spot scanning IMPT treatment plans were generated for ten lung cancer patients for 2.5Gy(RBE) and 12Gy(RBE) fractions and two distinct energy-dependent spot sizes (sigma similar to 8-17 mm and similar to 2-4 mm). IMPT plans were generated with the target homogeneity of each individual field restricted to <20% (IMPT20%). These plans were compared to full IMPT (IMPTfull), which had no restriction on the single field homogeneity. 4D Monte Carlo simulations were performed upon the patient 4DCT geometry, including deformable image registration and incorporating the detailed timing structure of the proton delivery system. Motion effects were quantified via comparison of the results of the 4D simulations (4D-IMPT20%, 4D-IMPTfull) with those of a 3D Monte Carlo simulation (3D-IMPT20%, 3D-IMPTfull) upon the planning CT using the equivalent uniform dose (EUD), V-95 and D-1-D-99. The effects in normal lung were quantified using mean lung dose (MLD) and V-90%. Results: For 2.5Gy(RBE), the mean EUD for the large spot size is 99.9% +/- 2.8% for 4D-IMPT20% compared to 100.1% +/- 2.9% for 4D-IMPTfull. The corresponding values are 88.6% +/- 8.7% (4D-IMPT20%) and 91.0% +/- 9.3% (4D-IMPTfull) for the smaller spot size. The EUD value is higher in 69.7% of the considered deliveries for 4D-IMPTfull. The V-95 is also higher in 74.7% of the plans for 4D-IMPTfull, implying that IMPTfull plans experience less underdose compared to IMPT20%. However, the target dose homogeneity is improved in the majority (67.8%) of plans for 4D-IMPT20%. The higher EUD and V-95 suggests that the degraded homogeneity in IMPTfull is actually due to the introduction of hot spots in the target volume, perhaps resulting from the sharper in-target dose gradients. The greatest variations between the IMPT20% and IMPTfull deliveries are observed for patients with the la

关键词： Therapeutic applications, including brachytherapy Monte Carlo simulations Dosimetry/exposure assessment Computed tomography Registration Cancer cancer computerised tomography dosimetry image motion analysis image registration lung medical image processing Monte Carlo methods radiation therapy Computerised tomographs Radiation therapy Biological material, e.g. blood, urine Haemocytometers Digital computing or data processing equipment or methods, specially adapted for specific applications image data processing or generation, in general Analysis of motion Scintigraphy Lungs Protons Cancer Dosimetry Monte Carlo methods Proton therapy Medical treatment planning Radiation treatment Drug delivery Computed tomography

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Technical Note: Skin thickness measurements using high-resolution flat-panel cone-beam dedicated breast CT

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MEDICAL PHYSICS 2013年第3期40卷 031913页

作者： Shi, Linxi Vedantham, Srinivasan Karellas, Andrew O'Connell, Avice M. Univ Massachusetts Sch Med Dept Radiol Worcester MA 01655 USA Univ Rochester Med Ctr Dept Radiol Rochester NY 14642 USA

Purpose: To determine the mean and range of location-averaged breast skin thickness using high-resolution dedicated breast CT for use in Monte Carlo-based estimation of normalized glandular dose coefficients. Methods: This study retrospectively analyzed image data from a clinical study investigating dedicated breast CT. An algorithm similar to that described by Huang et al. ["The effect of skin thickness determined using breast CT on mammographic dosimetry," Med. Phys. 35(4), 1199-1206 (2008)] was used to determine the skin thickness in 137 dedicated breast CT volumes from 136 women. The location-averaged mean breast skin thickness for each breast was estimated and the study population mean and range were determined. Pathology results were available for 132 women, and were used to investigate if the distribution of location-averaged mean breast skin thickness varied with pathology. The effect of surface fitting to account for breast curvature was also studied. Results: The study mean (+/- interbreast SD) for breast skin thickness was 1.44 +/- 0.25 mm (range: 0.87-2.34 mm), which was in excellent agreement with Huang et al. Based on pathology, pair-wise statistical analysis (Mann-Whitney test) indicated that at the 0.05 significance level, there were no significant difference in the location-averaged mean breast skin thickness distributions between the groups: benign vs malignant (p = 0.223), benign vs hyperplasia (p = 0.651), hyperplasia vs malignant (p = 0.229), and malignant vs nonmalignant (p = 0.172). Conclusions: Considering this study used a different clinical prototype system, and the study participants were from a different geographical location, the observed agreement between the two studies suggests that the choice of 1.45 nun thick skin layer comprising the epidermis and the dermis for breast dosimetry is appropriate. While some benign and malignant conditions could cause skin thickening, in this study cohort the location-averaged mean breast skin thickne

关键词： Computed tomography Mammography Cancer Applications Spatial resolution Segmentation cancer computerised tomography data analysis dosimetry estimation theory image resolution image segmentation mammography medical image processing Monte Carlo methods skin statistical analysis thickness measurement tumours Computerised tomographs Digital computing or data processing equipment or methods, specially adapted for specific applications image data processing or generation, in general Skin Computed tomography Pathology Medical imaging Dosimetry Mammography Cancer Statistical analysis Cone beam computed tomography data analysis

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Resolution modeling enhances PET imaging

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MEDICAL PHYSICS 2013年第12期40卷

作者： Alessio, Adam M. Rahmim, Arman Orton, Colin G. Univ Washington Dept Radiol Seattle WA 98195 USA Johns Hopkins Univ Sch Med Dept Radiol & Radiol Sci Baltimore MD 21287 USA Wayne State Univ Detroit MI USA

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Progressive Cone Beam CT Dose Control in image-Guided Radiation Therapy

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MEDICAL PHYSICS 2013年第6期40卷 060701页

作者： Yan, H. Zhen, X. Cervino, L. Jiang, S. Jia, X. Univ Calif San Diego Ctr Adv Radiotherapy Technol San Diego CA 92103 USA Southern Med Univ Guangzhou Guangdong Peoples R China

OBJECTIVE:Cone beam CT (CBCT) in image-guided radiotherapy (IGRT) offers a tremendous advantage for treatment guidance. The associated imaging dose is a clinical concern. One unique feature of CBCT-based IGRT is that the same patient is repeatedly scanned during a treatment course, and the contents of CBCT images at different fractions are similar. The authors propose a progressive dose control (PDC) scheme to utilize this temporal correlation for imaging dose reduction.;METHODS:A dynamic CBCT scan protocol, as opposed to the static one in the current clinical practice, is proposed to gradually reduce the imaging dose in each treatment fraction. The CBCT image from each fraction is processed by a prior-image based nonlocal means (PINLM) module to enhance its quality. The increasing amount of prior information from previous CBCT images prevents degradation of image quality due to the reduced imaging dose. Two proof-of-principle experiments have been conducted using measured phantom data and Monte Carlo simulated patient data with deformation.;RESULTS:In the measured phantom case, utilizing a prior image acquired at 0.4 mAs, PINLM is able to improve the image quality of a CBCT acquired at 0.2 mAs by reducing the noise level from 34.95 to 12.45 HU. In the synthetic patient case, acceptable image quality is maintained at four consecutive fractions with gradually decreasing exposure levels of 0.4, 0.1, 0.07, and 0.05 mAs. When compared with the standard low-dose protocol of 0.4 mAs for each fraction, an overall imaging dose reduction of more than 60% is achieved.;CONCLUSIONS:PINLM-PDC is able to reduce CBCT imaging dose in IGRT utilizing the temporal correlations among the sequence of CBCT images while maintaining the quality.

关键词： Dose-volume analysis Dosimetry/exposure assessment Monte Carlo methods image enhancement Computed tomography Treatment planning computerised tomography dosimetry image enhancement medical control systems medical image processing Monte Carlo methods phantoms radiation therapy cone beam CT imaging dose nonlocal GPU Computerised tomographs Radiation therapy Digital computing or data processing equipment or methods, specially adapted for specific applications image data processing or generation, in general image enhancement or restoration, e.g. from bit-mapped to bit-mapped creating a similar image Medical imaging Cone beam computed tomography Medical image quality image guided radiation therapy Dosimetry Medical image noise Computed tomography Medical image reconstruction Radiation treatment Anatomy

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Real-time catheter tracking for high-dose-rate prostate brachytherapy using an electromagnetic 3D-guidance device: A preliminary performance study

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MEDICAL PHYSICS 2013年第2期40卷 021716页

作者： Zhou, Jun Sebastian, Evelyn Mangona, Victor Yan, Di William Beaumont Hosp Dept Radiat Oncol Royal Oak MI 48073 USA

Purpose: In order to increase the accuracy and speed of catheter reconstruction in a high-dose-rate (HDR) prostate implant procedure, an automatic tracking system has been developed using an electromagnetic (EM) device (trakSTAR, Ascension Technology, VT). The performance of the system, including the accuracy and noise level with various tracking parameters and conditions, were investigated. Methods: A direct current (dc) EM transmitter (midrange model) and a sensor with diameter of 1.3 mm (Model 130) were used in the trakSTAR system for tracking catheter position during HDR prostate brachytherapy. Localization accuracy was assessed under both static and dynamic analyses conditions. For the static analysis, a calibration phantom was used to investigate error dependency on operating room (OR) table height (bottom vs midposition vs top), sensor position (distal tip of catheter vs connector end of catheter), direction [left-right (LR) vs anterior-posterior (AP) vs superior-inferior (SI)], sampling frequency (40 vs 80 vs 120 Hz), and interference from OR equipment (present vs absent). The mean and standard deviation of the localization offset in each direction and the corresponding error vectors were calculated. For dynamic analysis, the paths of five straight catheters were tracked to study the effects of directions, sampling frequency, and interference of EM field. Statistical analysis was conducted to compare the results in different configurations. Results: When interference was present in the static analysis, the error vectors were significantly higher at the top table position (3.3 +/- 1.3 vs 1.8 +/- 0.9 mm at bottom and 1.7 +/- 1.0 mm at middle, p < 0.001), at catheter end position (3.1 +/- 1.1 vs 1.4 +/- 0.7 mm at the tip position, p < 0.001), and at 40 Hz sampling frequency (2.6 +/- 1.1 vs 2.4 +/- 1.5 mm at 80 Hz and 1.8 +/- 1.1 at 160 Hz, p < 0.001). So did the mean offset errors in the LR direction (-1.7 +/- 1.4 vs 0.4 +/- 0.5 mm in AP and 0.8 +/- 0.8 mm in S

关键词： Reconstruction Dosimetry Probability theory, stochastic processes, and statistics Therapeutic applications, including brachytherapy Biophysical mechanisms of interaction bioelectric potentials biomagnetism brachytherapy cancer catheters dosimetry electromagnetic fields image reconstruction medical image processing phantoms statistical analysis Catheters Hollow probes Radiation therapy Digital computing or data processing equipment or methods, specially adapted for specific applications image data processing or generation, in general Ultrasonography Position sensitive detectors Tracking devices Brachytherapy Ferromagnetic materials Medical imaging Error analysis Direct current power transmission Calibration Dosimetry

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Response to "Comment on 'It is not appropriate to "deform" dose along with deformable image registration in adaptive radiotherapy'" [Med. Phys. 39, 6531-6533 (2012)]

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MEDICAL PHYSICS 2013年第1期40卷 017102页

作者： Schultheiss, T. E. Tome, W. A. City Hope Canc Ctr Duarte CA 91010 USA Montefiore Med Ctr Albert Einstein Coll Med Radiat Oncol Inst Oncophys Bronx NY 10461 USA

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