bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐14: Image Quality and Patient Dose Dependence on CT Scan Parameters for ATCM (CareDose4D)
Authors: Winslow J , Kappadath S
Published: November 2011

Purpose: To develop pediatric CT protocols by characterizing effects of CT parameters on pediatric CT dose using automatic tube‐current modulation (ATCM). Methods: Sections of varying AP thicknesses (∼80, 117, 149, 214mm) from the adult, 10‐year‐old, 5‐year‐old, and 1‐year‐old ATOM phantoms (CIRS, Norfolk, VA) were placed contiguously. They were scanned on a 16‐channel CT (Emotion 16, Siemens) using ATCM (CareDose4D) to characterize the relationships between image quality and patient‐dose under different scan conditions: scan‐kVp, adult/pediatric patient selection, and patient size. Effective‐mAs/slice was extracted from the DICOM header of each CT image to calculate the DLP/slice. Noise was estimated as the standard deviation in ROIs. Two figures of merit (FOM) were defined: FOM1 as (noisê2/DLP)̂^−1; FOM2 as the (CNR̂2/DLP). Each FOM was calculated for each image of each series acquired. Results: for scan acquired as pediatric patients, the effective‐mAs/slice was lower than the reference‐mAs value for patient AP thicknesses below 120 mm but greater above AP thicknesses of 149mm. These differences increased with patient thickness and at lower kVp. For scans acquired as adult patients, the effective‐mAs/slice was always lower than the reference‐mAs. Under ATCM, the percent difference between the FOM1 for 110 and 80kVp relative to 130kVp ranged from [7,−12]% and [13,−58]% for pediatric, and [3, −16]% and [5,−92]% for adult patients. Under ATCM, the percent difference between the FOM2 for 110 (80)kVp and 130kVp for increasing thickness ranged from 54 to 36 (130 to 78)% for pediatric‐entered patients, and 51 to 32 (125 to 43)% for adult entered patients. Conclusion: CT dose with ATCM decreased for adult‐patient and increased for pediatric‐patient selection. The AP thickness at which ATCM will use effective‐mAs/slice > reference‐mAs value for pediatric‐patients selection is 120–149mm. Adult ‐ patient selection maintains effective‐mAs/slice < reference‐mAs value.
SU‐E‐I‐15: CBCT Using a Robotic‐Arm Based Small Animal Irradiation System
Authors: Sharma S , Chao M , Yan Y , Corry P , Moros E
Published: November 2011

Purpose: To assess quality of cone beam computed tomography (CBCT) images obtained by an image‐guided, robotic‐arm based small animal conformal radiation therapy device (SACRTD). Method and Materials: The SACRTD is equipped with a 40–225 kV X‐ray tube mounted on a custom made gantry, a 1024×1024 pixels flat panel detector (200 μm resolution), a programmable six degrees of freedom robot for CBCT imaging and conformal delivery of radiation doses. A series of 2D radiographic projection images were recorded in cone beam mode by placing and rotating microCT phantoms on the “palm” of the robotic arm. Reconstructed images were studied for image quality (spatial resolution, image uniformity, CT number linearity, voxel noise and artifacts. Results: The Shelley microCT QA phantom was used to assess image quality. Distances between the 5 beads in the geometric calibration plate were measured to within 0.3%. CT‐numbers measured using the CT‐number plate were linear with iodine density (R2>=0.995). Qualitative evaluation of reconstructed axial CT slices using the resolution plate resolved 200 μm clearly. Quantitative spatial resolution was assessed using the slanted edge plate and found to be 3.16 lp/mm. Uniformity of the system was measured with the QRM microCT water phantom; the noise measured was 34 HU (average standard deviation of measured signal intensity). Finally, CBCT images of the QRM multidisk phantom had minimal artifacts or distortions. Conclusions: Results showed that the SACRTD is capable of producing CBCT images of high quality and sufficiently small spatial resolution for precise and conformal small animal dose delivery. With its combined dose delivery and imaging capabilities, the SACRTD is powerful tool for small animal research.
SU‐E‐I‐17: Evaluation of Cone Beam Breast CT (CBCT) System: Detection of Randomly Distributed Micro‐Calcification and the Effect of Beam Hardening Filter
Authors: Ge S , Lai C , Yi Y , Shen Y , Liu X , Zhong Y , You Z , Wang T , Shaw C
Published: November 2011

Purpose: Detectability of micro‐calcification is very important for breast imaging. The purpose of this study is to evaluate the breast CBCT system through its detectability of randomly distributed micro‐calcifications under different mean glandular dose (MGD) and with or without different thickness copper filters. Methods: Calcium carbonate grains of various sizes (Three size groups: 224–250μm, 250–280μm, 280–300μm) were used to simulate calcifications. A breast shaped plastic container filled with paraffin was used to simulate a fatty breast; the top half of the phantom was cylindrical with 12.5cm diameter and the total height of the phantom is 14.5cm. The phantom was imaged with a CBCT system in our lab. The system consists of a conventional tungsten target x‐ray tube (G‐1592) and an a‐Si:H/CsI flat panel detector (Paxscan 4030CB). The source to image detector and source to iso‐center distances were 152 and 100 cm, respectively, resulting in a magnification factor of 1.52 at the iso‐center. All the scans were conducted at 80 kVp. The experiment was conducted under MGD equal to 2.5, 4, 6, 8 mGy. With each MGD setting, the scan was conducted without filter, with 0.002″ copper filter or with 0.004″ copper filter. Feldkamp algorithm with a ramp filter was used for image reconstruction of all scans. Results: Our CBCT system is capable of imaging calcifications as small as 224–250μm with 6mGy MGD or 250–280μm with 4mGy MGD if set 50% visibility as threshold. To all three size groups, filtering improves visibility of micro‐calcification when the dose is between invisible and high visible settings. Conclusions: Filtering improves detectability of micro‐calcification for low dose image.

This work was supported in part by grants CA104759, CA124585 and CA13852 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.
SU‐E‐I‐21: The Effects of MV Scatter on Image Quality of Cone Beam Scans Acquired Asynchronously during Rotational Delivery
Authors: Lovelock D , Munro P , Shapiro E , Star‐Lack J , Sun M , Ling C
Published: November 2011

Purpose: To effectively integrate image‐guidance into single dose (24 Gy) SBRT to bony targets, we propose to deliver the treatment in 6 consecutive VMAT arcs and simultaneously acquire a CBCT image during each arc. This would provide a means to check and correct for intra‐fractional target motion subsequent to the 1st arc. We investigate the effect of the MV scatter on CBCT image quality and report on the feasibility of simultaneous SBRT / CBCT for intra‐fractional imaging. Methods: The CatPhan and anthropomorphic Rando phantoms were irradiated with 360° arcs using a static 10×10 cm field, and kV CBCT projections were acquired simultaneously. To investigate the effect of MV scatter on CBCT image quality, we varied the phantom size, MV dose and dose rate, CBCT mAs, and the SSD of the kV detector. In addition, a CBCT reconstruction algorithm that reduced the detrimental effects of scattered MV radiation was studied. Results: : Scattered MV radiation added noise to reconstructed images, decreasing low contrast resolution while reducing Hounsfield Unit (HU) accuracies. Increasing the size of the phantom magnified these effects since the scatter‐to‐primary ratio is increased. In part, this could be compensated for by increasing the CBCT exposure (mAs), and by increasing the separation between the isocenter and the kV detector from 50 to 80 cm. The new CBCT scatter correction algorithm was shown to offer promise of increasing HU accuracies. With the combined methods to increase SNR, good quality CBCT images that clearly visualize bony targets were obtained, even when 750 MU was delivered in an arc treatment. Conclusions: For the proposed clinical application, kV‐CBCT scans are acquired concomitantly with MV radiation delivery. These images, if automatically registered to the planning CT scan, provide monitoring of possible intra‐fractional motion, and allow, if necessary, for corrections to be made.

Supported in part by Varian Medical Systems
SU‐E‐I‐22: Non‐Clinical Applications for Cobalt‐60 Cone Beam CT Imaging
Authors: Marsh M , Rawluk N , Nguyen H , Bevan G , Schreiner L
Published: November 2011

Purpose: To investigate possible applications of a Cobalt‐60 (Co 60) cone‐beam megavoltage computed tomography (CoCBCT) imaging system, developed for patient positioning on Co‐60 teletherapy machines, in non‐clinical fields such as archaeology and non‐destructive testing. Methods: CoCBCT scans were performed on a series of dense objects requiring nondestructive testing using a bench‐top imaging system consisting of a Theratron 780C Co 60 unit (Best Theratronics, Kanata, ON) and a Varian aS500 amorphous silicon portal imager (Varian, Palo Alto, CA). Images were obtained on a series of heavily concreted artifacts recovered from a 17th century shipwreck at LˈAnse aux Bouleaux in Québec. and on cylindrical test cylinders of hematite‐rich shielding concrete obtained during the construction of new linac bunkers in our cancer centre expansion. The CoCBCT images were generated using the FDK back‐projection algorithm from transmission portal images that were obtained by rotating the objects by 1.5° degree increments through a full rotation. Results: In the case of the shipwreck artifacts, CoCBCT allowed dense metal features such as lead shot to be identified within the concretion layers, and offered a clear view of the shape of voids and other features that would be difficult or impossible to see without damaging the objects. These images will guide subsequent manipulation of the objects during archaeological assessment. CoCBCT images of the concrete cylinders reveal details in the concrete structure, such as voids or aggregate segregation, that would affect the shielding performance of the concrete. Consistent, uniform distribution of the aggregate in most of the samples implied that the mix was stable and not likely to segregate in the shielding walls. Conclusions: Co 60 CBCT is also suitable for non‐destructive imaging of highly attenuating non‐clinical objects, including items with large metal features which would limit accurate imaging using kV CT or broad energy spectrum MV CT.

Funding from the Ontario government has been secured through the Ontario Consortium for Adaptive Interventions in Radiation Oncology (OCAIRO), which matches funding from an industrial partner, Best Theratronics (Kanata, ON).
SU‐E‐I‐24: Pediatric CT Effective Dose ‐ A Comparison Between the MOSFET Method and the DLP Method
Authors: Fredrickson M , Toncheva G , Frush D , Lowry C , Yoshizumi T
Published: November 2011

Purpose: The effective doses (ED) were compared between the MOSFET method and the DLP method for a variety of clinical CT scans. Methods: Two CT scanners (Manufacturer A and B) were used in this study. Organ doses were measured with MOSFET detectors. Twenty MOSFET detectors were inserted in the 5‐year‐old anthropomorphic phantom (CIRS, Norfork, VA). The calibration factor for each MOSFET was determined using equivalent CT beam quality of respective manufacturer separately. The phantom was scanned using head, chest, abdomen‐pelvis and chest‐abdomen‐pelvis protocols at our institution. CTDIvol and DLP were recorded from the scanner console display. The MOSFET method employed the ICRP 103 weighting factors to calculate ED; the DLP method used the AAPM 96 (2008) anatomy‐age specific k‐factors. Pediatric protocols except head used CTDIvol data from 32 cm CTDI phantom. For this reason a factor of approximately 2 was applied to the CTDIvol and DLP in body protocols. In addition, CTDIvol measurements were performed with a Piranha CT Dose Profiler (RTI, Fairfield, NJ). Results: The calculated ED from manufacturer A scans underestimated the ED for the head, chest, chest‐abdomen‐pelvis and abdomen‐pelvis scans by 133.27%, 55.84%, 30.24% and 19.13%, respectively. The calculated ED from manufacturer B scans underestimated the ED for the head by 85.66% and overestimated the ED for the chest, chest‐abdomen‐pelvis and the abdomen‐pelvis scans by 102.81%, 114.52% and 96.19%, respectively. The percent difference between console and measured CTDIvol ranged from 11.04% to 24.88% Conclusions: ED calculations from the DLP method differed grossly from the MOSFET method. Console displayed CTDIvol showed good agreement with measured values. One possible explanation for ED disagreement between the two methods may lie in inaccuracies of k‐factors. These k‐factors were computed from old Monte Carlo codes based on mathematical phantoms. Additionally, manufacturer specific conversion factors may need to be proposed.

Funding for this research was provided by GE Healthcare and Siemens Healthcare.
SU‐E‐I‐25: Organ Dose Reduction by Lowering Tube Voltage from 120kVp to 80kVp for Fixed Tube Current Chest CT Scans
Authors: Khatonabadi M , Zhang D , Turner A , DeMarco J , Cody D , Stevens D , McNitt‐Gray M
Published: November 2011

Purpose: Reduced kVp scanning is being recommended for pediatric patients as well as when contrast studies are being performed. The purpose of this work is to quantitatively compare the organ doses resulting from scans at different kVP and determine the ratio of mAs at each kVp that results in equivalent organ dose. Methods: Using Monte Carlo simulations, two fixed tube current chest exams with 120kVp and 80kVp were simulated for 18 voxelized adult female patient models. Each patient had lung and glandular breast tissues contoured, so that doses to these tissues could be estimated. The resulting organ doses for two kVps were compared for a given mAs, which allowed a comparison to identify the ratio of mAs values needed to achieve the same organ dose for 120kVp and 80kVp. For a further comparison, these values were compared to CTDIw values obtained at both kVps in both 16cm and 32cm CTDI phantoms. Results: For lung dose, the ratio of dose from 120kVp to 80kVp was 3.96 (standard deviation of 0.17) for a given mAs across all 18 patient models; similarly, the glandular breast dose ratio was 4.15 (standard deviation of 0.12). For the CTDIw phantom values, the ratio of dose values from 120kVp to 80kVp were 3.37 and 3.78 for 16 cm and 32 cm phantoms, respectively. Conclusions: Monte Carlo simulation results indicate that lowering tube voltage from 120 to 80 results in almost 4 fold radiation dose reduction for a given mAs. Stated another way, the mAs at 80kVp could be increased by up to a factor of four compared to mAs used at 120kVp and still receive a similar organ dose in chest scans. This is an even higher ratio than predicted by CTDI phantom results. Future studies include pediatric models with contoured lungs and breast.
SU‐E‐I‐27: CTDI Verification with a Farmer Chamber
Authors: Emerson S , Liang Y , Aurand D , Schultz C
Published: November 2011

Purpose: The goal of our research is to determine the viability of a Farmer ion chamber in verifying the reported CTDIvol from CT scanners. Methods: We used a Siemens Somatom Sensation 16 slice scanner, three CTDI phantoms, a RadCal 100 mm pencil chamber (Model 10X6‐3CT), a RadCal Farmer ion chamber (Model 10X6‐0.6CT), and a RadCal Model 9015 control unit. Exposures were made with our routine adult chest protocol, for a 100 mm scan length of the phantom. Readings were made at the center and 12 oˈclock positions. Results: We found the doses measured by the Farmer chamber to be greatly dependent on the pitch. Scans with a pitch < 1 are generally result in a larger CTDIvol than what was reported by the scanner, while scans with a pitch > 1 are generally lower and give very inconsistent results. The dose rate is higher when p >1, but the tube may not pass directly over the detector when at the 12 oˈclock position. If the p > 1, an average of all the 3, 6, 9, and 12 clock positions should be made. Conclusions: The CTDI measurements with the Farmer chamber seem most accurate at a pitch less than 1 for longer scans. We plan expand the study of to other scanners with wider beams as well as more pitch values between 0.85 and 1.0.
SU‐E‐I‐30: Fast and Reliable Cone‐Beam CT Reconstruction Using Cloud Computing
Authors: Meng B , Pratx G , Xing L
Published: November 2011

Purpose: To conceptually prove the cloud‐computing application on large‐scale medical physics problems and to develop a fast, reliable and distributed Cone‐Beam (CB) computed tomography (CT) reconstruction technique using MapReduce, a cloud‐computing framework. Methods: We propose a CBCT reconstruction algorithm based on Hadoop, an open source MapReduce model. Two functions are used to complete the process: a Map function that reconstructs partial results from each projection and a Reduce function that aggregates those partial results to form the whole volume. The map function and the reduce function are automatically parallelized on a large cluster of machines. In addition, the proposed algorithm accelerates the reconstruction in two ways: (1) Typedbytes format speeds up data transferring; (2) Efficient partial results grouping scheme optimizes communication effort. The proposed CBCT algorithm was executed on a commercial computer cloud.Results: 2.3× speedup of reconstruction time is achieved using 18 computing machines (nodes) compared with that on a single‐threaded node. Mean square error between the results using cloud and a single machine is within 0.04%. The linearity between the time and the number of nodes implies higher efficiency is expected with more computing nodes deployed. Hadoop cloud computing is also proved to be fault tolerant; the reconstruction completes successfully with identical results even half of the nodes were terminated manually during the process. Conclusions: Cloud computing provides researchers in medical physics with an efficient and reliable means of solving large‐scale problems. A fast, reliable and scalable CBCT reconstruction algorithm is developed with the MapReduce framework.
SU‐E‐I‐34: CT Metal Artifact Reduction in Clinical Perspective: Novel Methods Tailored to Specific Implants
Authors: Verburg J , Seco J
Published: November 2011

Purpose: To develop novel methods for CT artifact reduction in patients with metallic implants, specifically tailored to implant materials commonly used in clinical practice. To retrospectively evaluate the performance of these methods using clinical scan data. Methods: Two artifact reduction methods were developed. A physics‐based method was designed that corrects for first‐order beam hardening effects, without requiring specific knowledge about the implant or X‐ray spectrum. A limited data reconstruction method was developed for implants which fully attenuate X‐rays, with smoothness regularization in image space. Both methods were retrospectively applied to projection data obtained from a GE LightSpeed RT 16 scanner of patients with different metallic implants. Results: Artifacts in patients scans of the both spinal and head & neck regions were significantly reduced. It was shown that beam hardening is the primary cause of artifacts due to titanium orthopedic hardware. Best results were therefore obtained using physics‐based correction, because information in all projection measurements is preserved. High‐density implants such as platinum fully attenuated the CT X‐rays. In this case, artifacts were reduced using the limited data reconstruction method. Smoothness regularization ensured clinically sensible solutions. Conclusions: The physical origin of CT metal artifacts depends on the material of the implant. For effective artifact reduction, methods should be tailored to specific implants in order to maximize the use of information in the CT projections. Using appropriate methods for either low‐ or high‐density metallic implants, clinical scans are significantly improved.
SU‐E‐I‐35: A GPU Optimized DRR Algorithm
Authors: Folkerts M , Jia X , Choi D , Gu X , Majumdar A , Jiang S
Published: November 2011

Purpose: To develop and evaluate a new DRR algorithm on GPU and compare itˈs accuracy and efficiency to two other commonly used DRR algorithms. Methods: We developed a new fixed grid algorithm optimized for GPU. This new algorithm first rotates and re‐samples CT data layer by layer and then traces rays through voxel slabs perpendicular to the projection axis. We also implemented the fixed stride algorithm and Siddonˈs incremental algorithm on GPU. We compared the accuracy of each algorithm to a ground truth that was generated by sampling 1024 evenly spaced ray paths per pixel using Siddonˈs incremental algorithm. We then computed the relative error for 36 equally spaced projections in a full rotation about the SI axis for 5 different voxel resolutions (ranging from 512 to 32 cubed). We compared the efficiency of each algorithm by simulating 360 projections, one per degree, of a clinically sized phantom (512×512×128) in a full rotation about the SI axis. Both tests simulated common CBCT geometry with a 40.0×30.0 cm, 1024×768 pixel detector. XCAT phantoms were used in all tests. Results: We found that all three DRR algorithms attain small error as a function of decreasing voxel size ranging from 10% at 16.0 mm/voxel to less than 0.2% at 1.0 mm/voxel. We also found the average projection time for the fixed grid algorithm is 21.8 ms/projection, 40% faster than Siddonˈs incremental algorithm which had an average projection time of 36.5 ms. The fixed stride algorithm is 18% faster than Siddonˈs incremental algorithm with an average projection time of 28.7 ms. Conclusion: By specifically designing a DRR algorithm for GPU, we were able to improve the computation efficiency without losing accuracy. This work will be useful for computational tasks requiring frequent rendering of DRR projections.
SU‐E‐I‐37: Coherent Scatter Computed Tomography (CSCT) in Kidney Stones Imaging‐Composition Analysis
Authors: Dihel C , Cunningham I
Published: November 2011

Purpose: To compare the ability of coherent scatter computed tomography (CSCT) to determine the composition of kidney stones, including the core components which are thought to be most important for recurrence prevention, with conventional infra‐red spectroscopy (IRS) in the management of urinary stone disease. Methods: CSCT is a tomographic imaging method being developed in our laboratory that is based on x‐ray diffraction measurements of intact specimens. In this study, intact kidney stones and large fragments obtained from minimal invasive surgery in 118 patients were collected and scanned using CSCT to determine the distribution of minerals, and in particular minerals at the stone core, before undergoing the conventional (destructive) IRS analysis. Results: Overall, the CSCT‐IRS agreement rate for the primary (most abundant) component was 85%. CSCT produces “maps” of each component including the core. In 42%, CSCT found a core mineral not reported by IRS. Overall, CSCT has detected minerals missed by IRS in 46% of all cases. In particular, struvite, which indicates a urinary bacterial involvement, was found in the stone core significantly more often (22%) than previously believed based on IRS.: Conclusions: The high agreement rate with IRS gives overall confidence in both CSCT and IRS. The ability of CSCT to identify the composition of the core where stone formation first starts, suggests an improved method for kidney stone composition analysis. The elevated presence of struvite in the stone core may indicate a more prominent role of specific bacteria in urolithiasis than generally accepted at present.
SU‐E‐I‐39: Metal Artifacts Reduction Using Sinogram Pre‐Processing and Post‐ Processing in Computed Tomography (CT)
Authors: Meng B , Wang J , Xing L
Published: November 2011

Purpose: To develop a novel metal artifacts reduction (MAR) technique through sinogram pre‐processing and post‐processing techniques. Methods: The proposed MAR method consists of two steps. In the pre‐processing step, we reconstruct a binary image delineating the locations and shapes of metal objects through a non‐linear amplification of the sinogram. The boundaries of metallic objects are obtained by using a penalized weighted least‐squares (PWLS) algorithm with adequate intensity gradient‐controlled. The obtained metal only image with the associate intensity is the metal image model. Forward‐projection of the metal image model gives us the metal projection pattern. The sinogram post‐processing step includes matching of the metal projection pattern in the projection space, smart subtraction of the metal projection pattern from the original projections and a final smoothing step. The post‐processed projections are used to reconstruct the metal artifacts free image through FDK algorithm. A series of experimental studies of a head phantom with different numbers and shapes of metals are performed to evaluate the proposed approach. Results: The study shows that the proposed method is capable of remarkably reducing metal artifacts, and improving soft‐tissue visibility. Even with multiple metal objects inserted, each one of them is identified after the preprocessing step. The accuracy of the metal artifacts free images are within 3 pixels Conclusions: The proposed method demonstrates to be effective to achieve metal artifacts free images. The combination of sinogram preprocessing and post‐processing provides a viable way of reducing metal artifacts in CT imaging.
SU‐E‐I‐41: The DCE Tool: A Freeware Analysis Tool for DCE CT and MR Studies
Authors: Yeung I , Haider M , Gonzalez N , Kim S , Coolens C , Yeung T , Driscoll B , Jaffray D
Published: November 2011

Purpose: To develop a freeware tool for analysis of dynamic contrast enhanced (DCE) CT and MR studies.Methods: The DCE Tool was developed as FREEWARE to work as a plugin for the the ClearCanvas 2.0SP1 framework. It combined the NET Platform and the MATLAB MCR to provide robust DCE analysis. The software was designed to support CT and MR studies with display capability of DCE data. The analysis included simple metrics on time‐intensity curves as well as on compartmental modeling analysis. Easy export of results to spreadsheet file was also a design requirement.Results: The DCE Tool has been developed to process DCE CT and MR studies. DICOM images from CT and MR studies can be loaded to the software and a 4D time browser is available to view the images. Region of interest tool is available which produces time intensity curves, for which the DCE Tool provides analysis on area under curve, initial slope and peak etc. It also provides analysis using the 1‐compartment model, 2‐compartment model, the ATH (adiabatic tissue homogeneity) model for CT, as well as the Toftˈs model for MR study. Pixel‐by‐pixel analysis is available and functional maps can be generated. Numerical and graphic results can readily be exported to EXCEL files. The tool has been used by a number of researchers for phantom and pre‐clinical studies. The DCE Tool is available for free download at www.thedcetool.com Conclusions: The DCE Tool has been developed for DCE CT and MR studies. It provides analysis based on density intensity curves as well as tracer kinetic modeling. The DCE Tool is potentially an invaluable research tool for CT and MR perfusion studies.

The project is partly funded by Ontario Institute of Cancer Research
SU‐E‐I‐43: Verification of the Usefulness of Evaluation Method for Angular Performance with the ANG Test Pattern
Authors: Ikushima Y , Akamine H , Nakamura Y , Hashimoto N , Morishita J
Published: November 2011

Purpose: A simple method with the ANG test pattern to evaluate the angular performance of medical‐grade liquid‐crystal display (LCD) monitors was proposed by the International Electrotechnical Commission (IEC) in December 2009 (IEC 62563‐1). The purpose of this study was to investigate correlation between the results obtained by using the ANG test pattern and the angular performance measured by a luminance meter. We also examined the effect of ambient‐light conditions on the results evaluated by using the ANG test pattern. Methods: Three LCDs, a medical‐grade monochrome LCD (Radiforce GS220, 500 cd/m2, Eizo Nanao), a medical‐grade color LCD (Radiforce RX211, 300 cd/m2, Eizo Nanao), and a general‐purpose LCD (SyncMaster940B, 180 cd/m2, Samsung) were used in this study. The ANG test pattern was observed by eight observers under three ambient‐light conditions (0, 35, and 327 lux). Two different scoring methods were used. One is the method proposed by the IEC 62563‐1, and the other is the method modified for comparison of results measured by a luminance meter. The luminance performance was measured as a function of viewing angle, and evaluated as the relative contrast ratio. Finally, the results in terms of the modified scores were compared to the luminance performance in various viewing angles. Results: Variations of the modified scores and the relative contrast ratio as a function of viewing angle indicated a similar tendency for medical‐grade LCDs. On the other hand, the two results did not correspond well for the general‐purpose LCD. The difference between the results obtained at 0 and 327 lux was 0.11 at a maximum for all LCDs used in this study. Conclusions: The evaluation method with the ANG test pattern is considered to be useful for evaluation of the angular performance for medical‐grade LCDs taking ambient‐light conditions into consideration.
SU‐E‐I‐52: Use of Radiochromic Film for the Estimation of CTDI100 and In‐ Phantom Dose Profiling
Authors: Wunderle K , Dong F , Davros W
Published: November 2011

Purpose: To establish a methodology for the use of radiochromic film in the estimation of CTDI100 and provide an in‐phantom spatial description of the radiation dose profile. Methods: Standard CTDI 32cm body and 16cm head phantoms were used with a modified Acrylic pin to allow for the insertion of radiochromic. Two CT scanners were evaluated at various beam collimations in both center and 12 oˈclock pin locations. For comparison purpose, CTDI 100 measurements were obtained using a 100mm pencil ionization chamber. A 48‐bit optical scanner was used to scan the radiochromic film. Software code was written to analyze the film images. A set of calibration films was acquired on a fluoroscope with similar beam quality (kVp and HVL) as the CT scanner. Results: For reproducibility three films from each of 21 different collimation and pin location combinations were analyzed. Three films were excluded because of prominent moiré patterns observed likely caused by moisture on the film or scanner platform. Three images that were included slightly exceeded the calibration range of the film. The percent differences between the CTDI 100 values obtained with the 100mm pencil chamber and the film ranged from 0– 17.2% with an average difference of 8.6%. The relative standard deviation of the CTDI100 film values ranged between 0.3–3.6% with an average of 1.9%. Though not novel, visual indication of the z axis in phantom beam profile provided very clear evidence that at large collimations radiation dose extends well beyond a 100mm region. Conclusions: Radiochromic film has the potential to estimate CTDI 100 with reasonable accuracy; future calibration methods may bring better accuracy. This method provides additional value by yielding a visual indication of the CT dose profile and potential for easily incorporating dose beyond 100mm.
SU‐E‐I‐60: Correspondance Between HVLs Measured by Direct Reporting Instruments and Traditional Methods
Authors: Omphroy K , Prasad G , Rao U
Published: November 2011

Purpose: To examine the correspondence between half value layers (HVLs) measured by traditional methods to those obtained by an instrument that reports HVLs with a single open beam. Methods: The HVL was obtained from generating a transmission curve at 60, 80, and 100 kVp in the radiographic range and typically used kVp and target/filter combinations in the mammography range. These HVLs were compared to the ones obtained by instruments which provide direct value with a single open beam. Unfors and Neromax instruments were used to obtain HVL by direct single measurement. A three phase table top radiographic unit was used. Measurements were performed in good geometry using Al 115 H filters supplied Gammex Corporation. This filter is 99.9% pure aluminum. Results: By and large there is good agreement between the HVL obtained by the two methods for regulatory compliance applications. However, there are minor differences when one is interested in a precise value for scientific applications. Conclusions: One can use these direct HVL reporting instruments for routine regulatory compliance measurements.
SU‐E‐I‐62: Dose Reduction to Anterior Surface with Organ‐Based Tube Current Modulation: Evaluation of Performance in a Phantom Study
Authors: Duan X , Wang J , Christner J , Leng S , Grant K , McCollough C
Published: November 2011

Purpose: To evaluate in a phantom study image quality and dose reduction to the anterior surface with organ‐based tube current modulation in head and thoracic CT. Methods: Organ‐based tube current modulation is designed to reduce dose to superficial radiosensitive organs such as the lens of the eye, thyroid and breast by decreasing the tube current when the tube passes closest to these organs. Dose and image quality were evaluated in phantoms for clinical head and thorax exam protocols with and without organ‐based tube current modulation. Surface dose reduction as a function of position was measured using a 32‐cm CT Dose Index (CTDI) phantom, an anthropomorphic adult phantom and ion chambers. Surface dose reduction as a function of patient size was investigated using three semi‐ anthropomorphic phantoms with posteroanterior dimensions of 14, 25 and 31 cm. Image noise (the standard deviation of CT numbers in regions of interest) was evaluated for the anthropomorphic and the semi‐ anthropomorphic phantoms. Results: For equivalent scanner output (Volume CTDI), dose to the midline of the anterior surface was reduced by 27–50%, depending on anatomic region (head or thorax) and phantom size; dose to the posterior surface was correspondingly increased. Image noise was not significantly different between scans with and without organ‐based tube current modulation (p=0.35). Conclusions: Organ‐based tube current modulation can reduce dose to the anterior surface of patients, without increasing image noise, by commensurately increasing dose to the posterior surface. This can reduce dose to anterior radiosensitive organs for head and thoracic CT scans.
SU‐E‐I‐64: Weekly Exposure Contributions from Radioactive Patients in A Busy Comprehensive Imaging Center
Authors: Siman W , Kappadath SC , Rong J
Published: November 2011

Purpose: To investigate radiation exposure from radioactive patients to the surrounding workers in a busy comprehensive imaging center. Methods: Follow‐up of oncology patients often include nuclear medicine and diagnostic CT examinations. Many patients present themselves for CT imaging after they have been administered radioactivity. An Ion‐chamber survey meter (Victoreen 45 1p) was used to monitor the dynamic radiation environment in a CT facility. The survey meter was placed at a centrally located nurse station that was surrounded by 6 patient‐preparation rooms (at 2.5m away) and 5 CT scanners. The radiation environment was monitored for 5 days and correlated with the clinical schedule to estimate the radiation from radioactive patients. Typically 190 patients/day are scanned at this CT facility; ∼6% of which are radioactive (10 99mTcMDP and 1 18F‐FDG) patients). The typical doses for such procedures in our facility are 20mCi and 10mCi respectively. The air‐kerma rate was modeled based on Gamma Factor and ICRP‐53 biokinetic models for Tc‐99m‐labelled phosphates and 18F‐FDG. Results: In the absence of radioactive patients, the average radiation level was measured to be 0.05μSv/hr and independent of the CT duty‐cycle; thus validating the CT shielding design. The radiation level increased in the afternoon due to the presence of radioactive patients. The typical cummulative dose/day in the area was 1.3μSv, which is 3.25 times the background dose (0.4μSv). Our model predicts that 11 99mTcMDP patients or 418F‐FDG patients would contribute up to 5μSv/week (25% of the weekly limit) Conclusions: The presence of radioactive patients in the diagnostic CT facility may contribute non‐negligible radiation exposure to the employees in the surrounding the CT suite. If the exposure of a non‐ radiation worker can potentially exceed 25% of the annual effective dose limit, then the site operator should ensure that the annual exposure of the maximally exposed individual does not exceed 1 mSv.
SU‐E‐I‐66: Estimating Organ and Effective Doses for Digital Tomosynthesis Imaging Using PCXMC Software
Authors: King J , Ma H , Elbakri I
Published: November 2011

Purpose: In order to accurately model a tomosynthesis image acquisition for estimating organ and effective doses with PCXMC, we must consider each discrete projection angle of the x‐ray tube separately, compute the dose in each case, and sum the results. This can be a time‐consuming task that requires a considerable amount of data entry. We have developed two techniques that we can use to improve the user‐friendliness and time‐efficiency of obtaining dose estimates for a tomosynthesis sweep. Methods: We developed a MATLAB program to automatically generate the definition files for each x‐ray tube position and compared the resulting definition files and dose calculations to those that we created manually for two test cases. We also calculated the doses by simplifying the imaging geometry to neglect the motion of the x‐ray tube during the tomosynthesis sweep. We applied the sum of the incident air kerma for the entire sweep to a single, central projection, and evaluated the impact of this simplification on the speed and accuracy of the dose calculations. Results: Our program produced the same definition files and doses as our manual calculation in both cases, and using the program resulted in a dramatic reduction in the amount of time required to complete the calculations. When neglecting the motion of the x‐ray tube, the doses to some organs were over‐ or underestimated but the effective doses still agreed with the values calculated using the more accurately modeled geometry. Conclusions: Our MATLAB program allows us to accurately model the imaging geometry of a tomosynthesis exam in PCXMC in a time‐efficient manner. For both test cases, a reasonable estimate of the effective dose can be achieved very quickly by neglecting the motion of the x‐ray tube, but this also sacrifices the accuracy of individual organ dose calculations.

This research was supported by funding from GE Healthcare.
SU‐E‐I‐69: Development of An Automatic System for the Readout of Etch‐Track Neutron Dosimeters
Authors: Entz K , Mäder U , Barbier J , Million M , Fiebich M
Published: November 2011

Purpose: To simplify and accelerate the readout of etch‐track neutron dosimeters made of poly‐allyl diglycol carbonate (PADC) by automating the process of counting ion tracks caused by neutrons in the detector material. Methods: A LabVIEW application and an ImageJ macro were developed for the analysis of images of the detector surface which were taken by a camera mounted onto a microscope. The LabVIEW application is used to control the microscope, to start the ImageJ macro and to adjust different parameters such as the format of the image to be analyzed. The ImageJ macro is used for the analysis of the images. After a background correction an edge filter is used in order to enhance the tracks. Afterwards an appropriate threshold is determined. All tracks with a certain minimum size were counted with ImageJˈs Analyze Particles function. False positives due to surface defaults or other artefacts such as dust or scratches on the detectors were eliminated according to their circularity, solidity and distribution in the image. All results are saved in a log file. A warning is displayed if surface defaults are detected. Results: The developed ImageJ macro is able to analyze most images correctly. The number of tracks (± 1) was determined correctly in 98 % of the images. Artefacts due to dust or scratches are not counted as tracks. Surface defaults are sometimes not detected which results in a higher number of tracks. In most of those cases the number of tracks and therefore the corresponding dose is still under the reporting limit. Conclusions: The LabVIEW application and the ImageJ macro developed in this work simplify the readout of PADC etch‐track neutron dosimeters. The number of correctly analyzed images is in the same range or even higher as that from a trained operator who counts the tracks manually.
SU‐E‐I‐70: Characterisation of the Parameters Defining a Kilovoltage Source for Accurate Dose Computation
Authors: Poirier Y , Tambasco M , Kouznetsov A
Published: November 2011

Purpose: To perform a sensitivity analysis of the parameters that define beam quality for a kilovoltage (kV) x‐ray sourceMethods: Using a previously developed hybrid approach to calculate radiation dose deposited by x‐ray beams of energies <150 kVp, we computed dose inside a simulated heterogeneous phantom for varying beam spectra to evaluate the sensitivity of calculated dose to half‐value layer (HVL). The approach involves computing the primary photon component deterministically and scattered component stochastically, accounting for the real micro cross sections of the materials involved. We characterized the spectrum of the Varian® On‐Board Imaging® units at our institution by HVL measurements made using of a Farmer‐type Capintec ion chamber (0.06cc) in air. We compared doses computed with our characterized source spectrum with measurements inside water‐equivalent Gammex® Solid Water® phantom. Measurements were done using a 10×10 cm2 field at 100 cm SSD at every centimeter for depths 1 to 12 cm. Results: We found that measuring kV and HVL gives us sufficient beam quality information for accurate [>0.5%] x‐ray dose calculations. We also showed that HVL varies by less than 0.1 mm Al for field sizes over 5×5 cm2, allowing us to use one HVL irrespective of field size. Agreement between calculations and experimental measurements was better than 2% for a transverse profile and the central axis depth dose. This implies that our approach to characterizing the beam quality of a kV source is suitable for ensuring accurate results Conclusions: We have determined the parameters we need to characterize the source in order to obtain good agreement between theoretical calculations and experimental measurements. This is a crucial step in developing an independent tool to calculate patient dose from kV beams such as cone‐beam CT and brings us closer to our goal of calculating patient‐specific dose from imaging procedures.
SU‐E‐I‐71: Effective Dose and Thyroid Dose in Interventional Neuroradiology
Authors: Magill D
Published: November 2011

Purpose: To investigate the effects of x‐ray tube voltage and projection angle on the effective dose and thyroid gland dose from Interventional Neuroradiology (INR) procedures performed in the head and neck as a function of the Kerma Area Product. Methods: X‐ray tube voltage, image size, and projection angle data were collected on 68 adult INR procedures conducted during a one‐month period. These procedures consisted of diagnostic, and treatments for aneurysm, AVM, and stroke. A commercial patient Dosimetry software package (PCXMC 2.0.1) was used to simulate typical radiation beam geometries established from the collected data at a series of projections in the Posteroanterior (PA) and Lateral (L) planes to estimate effective dose (E) and thyroid gland dose (DT). For a given projection and beam quality normalized E and DT were obtained by dividing by the Kerma Area Product (KAP) (ie. mSv, or mGy, per mGy‐cm̂2). Results: The typical x‐ray tube voltages ranged between 95 to 105 kV in the PA plane, and were more varied in the L plane with the two most common voltages at 72 and 102 kV. The PA plane showed greater variability in the image size than the L plane by a factor of 1.8, and ranged from 11 cm to 32 cm. Projections angles ranged up to 40 degrees from the centerline in both planes. Projection angle changes in the PA showed an increase in the DT/KAP by a factor of 2 when greater than 30 degrees. Conclusions: Patient radiation doses are reduced in the PA compared with the L projections, and lower when the majority of the imaging is centered in the head versus the neck region. E is ∼30% greater for imaging done in the neck than the head, and DT is 4 times greater in the L than the PA projection.
SU‐E‐I‐72: Evaluation of CTDIw under the New Scan Modes of GE HD 750 Scanner
Authors: Liang Q , DeWerd L
Published: November 2011

Purpose: To evaluate the weighted computed tomography dose index (CTDIw) under the high resolution mode of the state‐of‐the‐art GE Discovery HD750 scanner. The pencil ionization chamber measurements were cross‐validated with thermoluminescent dosimeters (TLDs).Methods: CT scans were performed on a GE Discovery CT 750 HD scanner under high resolution axial mode, using the scan parameters of 120 kVp, and 200 mA, 1 sec/rotation. Two beam collimations were used in this study: 40mm and 10mm. A Standard Imaging Exradin A101 CT ionization chamber (effective length 12.08 cm) was used to determine CTDIw. To calculate CTDIw using TLDs, the CT dose profiles at both central and peripheral positions in a CTDI head phantom were measured with arrays of TLD‐100 chips. With the measured dose profiles, integrations along the z‐direction within ± 50 mm were performed to calculate CTDI100 values. CTDIw with TLD was determined and compared with pencil chamber measurements.Results: In the studied scan modes, for 40 mm scan thickness, CTDIw was determined to be 34.37 mGy and 35.67 mGy (in terms of dose to air) from charge readings with pencil chamber and TLD‐measured CT dose profile, respectively. For 10 mm scan thickness, CTDIw was determined to be 41.97 mGy and 44.60 mGy with the pencil chamber and TLDs, respectively. Conclusions: The CTDIw determined by the TLD‐measured dose profile agreed well with pencil chamber measurements for both scan thicknesses studied. Future work will include measurements using additional scan thicknesses and under another new scan mode provided by the scanner: Gemstone Spectral Imaging (GSI) mode. Comparison with regular scan modes will be performed as well.
SU‐E‐I‐76: Investigation of Patient Dose in Mammography in Japan by 2010
Authors: Suzuki S , Otsuka T , Horita K , Inagaki K , Koga M , Yagami K
Published: November 2011

Purpose: In Japan, mammography units are shifting from screen‐film (S/F) mammography to digital (DR) mammography. However, no studies have investigated the actual radiation dose received by patients undergoing mammography using DR units. In order to assess the present situation, we conducted a survey of the actual radiation dose at 92 participating mammography facilities in 2010. Methods: The units used were F/S (5%), computed radiography (CR) (47%), and flat panel display (FPD) (48%).The incident air kerma was obtained from the irradiation conditions of each facility, and the average glandular dose (AGD) was calculated. Specifically, the AGD was calculated using a quality control phantom (model 156 phantom) and a polymethyl methacrylate (PMMA) phantom (10, 20, 30, 40, 50 and 60 mm thicknesses) equipped with automatic exposure control (AEC) systems. An ionization chamber dosimeter （Radcal Model 9015） with a parallel plate ionization chamber calibrated based on national standards was used. Aluminum plates (99.997 % purity) were used for half value layer assessment. Results: The AGD was not greater than 3 mGy in all cases and was taken to be the patient dose. Mean dose was 1.8 mGy, and coefficient of variation (CV) was not greater than 0.3. Approximately 75% of facilities used a dose of not greater than 2 mGy. The range of doses was approximately three‐fold. Mean AGD was the lowest for F/S and highest for CR. Conclusions: There are about 10,000 radiologic technologists for mammography in Japan, and radiographic imaging at most facilities is performed by these technologists. As a result, there is little variation among facilities, and a minimum radiation dose is used.