bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐87: Pilot Testing of Software for Automated Remote Quality Control of Digital Mammography Equipment for Use in the Ontario Breast Screening Program
Authors: Bloomquist A , Jacobs J , Yaffe M
Published: November 2011

Purpose: We have evaluated the feasibility of using a software package to monitor the results of quality control (QC) testing on digital mammography units in the Ontario Breast Screening Program. The intent is to make the quality control process more efficient for the technologist and physicist, and improve the consistency of test performance and results interpretation. Methods: A DICOM service class provider, “GLADYS” (originally developed at University Hospitals Leuven) was installed at pilot screening sites. All images acquired on the sitesˈ mammography systems are automatically sent to GLADYS over the PACS networks. GLADYS recognizes QC images by predetermined patient names and performs an automated analysis, measuring various parameters and generating summary thumbnail images. Clinical images are de‐identified and the technique factors and dose are extracted for tracking. The QC and dose reports are sent by email to the central monitoring site. At the central site QC image measures are plotted and thumbnail images displayed for artefact evaluation. The patient header information is stored such that dose reports can be generated. Results: GLADYS has been installed at two remote screening sites, and locally for a total of six machines. QC and dose data have been collected for the past 5.5 months. 285 QC images have been analyzed. Artefacts and changes in automatic exposure control or detector behaviour are easily perceived. Dosimetry information from 18282 patient images has been collected, with an average mean glandular dose of 1.3 mGy. Conclusions: The automated analysis works well, and reduces the technologistˈs QC workload. The addition of features to allow for automated immediate feedback to the remote sites of test results to ensure rapid response to detected problems is under development. Incorporation of centralized automatic quality control has the potential to improve the consistency and reliability of the tests and results, while streamlining QC procedures.
SU‐E‐I‐88: Improvement of Mammography Quality after the Enforcement of Quality Assurance in Taiwan
Authors: Hwang Y , Chen C , Tsai H , Chen C , Chui C , Wan Y , Liu H
Published: November 2011

Purpose: The Standards for Medical Exposure Quality Assurance in mammography units were enacted on July 1, 2008 in Taiwan. For evaluating the trends in mammography quality before and after the regulation started in Taiwan, annual national mammography surveys were conducted from 2008 to 2010. Methods: On‐site measurements were conducted on 215 mammography units in 2008, 205 units in 2009 and 209 units in 2010, which comprised more than 95% of the total units in Taiwan. Phantom image quality, average glandular dose (AGD) and half value layer (HVL) were performed on all systems in all three years. Automatic exposure control (AEC) reproducibility, radiation output, compression conditions, viewbox luminance and processing conditions, exposure index confirmations and monitor conditions were performed on screening units only in 2008 and on all units in 2009 and 2010. Results: Mean phantom scores were improved from 2008 to 2010 (11.09 vs. 11.55, p<0.05 for screen/film units and 12.37 vs. 12.62 for digital systems). Mean AGDs were 1.47 and 1.39 in 2008 and were 1.39 and 1.37 in 2010 for screen‐film and digital systems respectively. Mean AGD decreased for both systems during the period. For screen/film systems, variations of sensitometric curves were greatly reduced in 2009 and 2010 as comparing to 2008. For the year in 2009 and 2010, 100% pass rates were reached in compression thickness reproducibility and AGD measurements. Pass rates were increased after the regulation took effect in almost all aspects. Lower pass rates have been continued in some tests that were not yet enforced in the regulation, such as viewbox luminance and AEC thickness tracking in screen/film systems. Conclusions: Survey data of mammography systems demonstrated quality improvements during the first two years after the quality assurance in mammography was enforced in Taiwan. The positive outcomes were attributed to facilitiesˈ compliance with the regulation.
SU‐E‐I‐89: A Standard Reference Material for Lung CT
Authors: Chen‐Mayer H , Levine Z , Zimmerman B , Mason D
Published: November 2011

Purpose: To investigate the feasibility of developing a “standard reference material” for tissue density variations obtained in CT scans. Methods: The Hounsfield unit (HU) is used universally in CT scanners to describe the radiodensity of tissues. The deceptively simple definition of the HU, the linear attenuation coefficient of a material relative to that of water, is made complicated by interactions of materials with the polychromatic beam, and by measurement geometry and detector response. The variations over time and across scanners can be addressed with a “reference standard” that is scanner‐independent. We began the development of one set of such standards by characterizing them in a NIST traceable standard beam quality, whose spectrum has been measured with a Ge detector; the spectrum compared well with IPEM report 78 for the given filtrations. Transmission through polyurethane foams of 4 different densities (nominally from 0.065 g/cm3 to 0.3 g/cm3) were measured in the M80 (80 kVp) beam using a CMOS x‐ray camera, recording the value of ln(I0/I) = mu*x, where x is the thickness of the foam in the range of 1.9 cm to 10 cm. A mu_eff is defined by (ln2)/h where h is the half value layer that can be experimentally measured. Results: For each density, the transmission was performed at 6 different thicknesses with an average statistical uncertainty of about 4%. With 4 densities, mu_eff can be determined to < 1 %. A calculation has been performed by folding in the measured spectrum with mu(E) based on XCOM output for polyurethane. The experimentally determined slope of mu_eff vs density is found to be 2.2% lower than the expected value, possibly due to a scattering contribution. Conclusion: Characterizing a material in a beam of known quality enables a direct assessment of the linear attenuation coefficient, which can serve as a scanner‐independent reference.
SU‐E‐I‐91: Use of the ACR CT Accreditation Phantom for Routine Quality Assurance of CBCT Imaging Systems in a Radiotherapy Environment
Authors: Hobson M , Parker W , Soisson E
Published: November 2011

Purpose: Image guided radiation therapy using cone‐beam computed tomography (CBCT) is becoming routine practice in modern radiation therapy. The purpose of this work was to develop an imaging QA program for CT and CBCT units in our department based on the ACR CT accreditation phantom (model 464, Gammex‐RMI). It has four testing modules permitting one to test CT number accuracy, slice width, low contrast resolution, image uniformity, in plane distance accuracy, and high contrast resolution reproducibly with suggested window/levels for image analysis. Methods: Baseline values were obtained from images acquired on a Phillips Brilliance Big Bore CT simulator and CBCT images acquired on three Varian OBIs. DICOM images were exported and analyzed with software (Automated CT Software, Gammex‐RMI) or manually (OsiriX). Baseline values will be used to ensure that image quality stays consistent quarterly. Results: Initial CT simulator images showed that image quality was within ACR guidelines for all tested scanning protocols. Due to image noise and reconstruction artifacts, manual analysis should be used for future analysis of CBCT images. Image analysis from two OBIs showed that the HU calibration had drifted or was not properly calibrated, while the third OBI showed reasonable agreement with accepted values. All three OBIs were unable to distinguish the low contrast resolution plugs, had the same high contrast resolution, were within 0.7 mm of the accepted in plane resolution, and were within 0.5 mm of the nominal slice width. Conclusions: Preliminary analysis shows that the ACR phantom could be modified to be more useful in evaluating the low contrast resolution of CBCT systems. Suggestions will be made as to how ACR guidelines for image analysis could be modified to better suit CBCT systems, such as for image uniformity. It is expected to eventually incorporate all departmental CT imaging systems in into this imaging QA program.
SU‐E‐I‐93: Comparison of the AEC Thickness Tracking Using the Signal‐ Difference‐To‐Noise Ratio in 113 Flat‐Panel Digital Mammography Units
Authors: Hwang Y , Chen C , Tsai H , Chen C , Chui C , Wan Y , Liu H
Published: November 2011

Purpose: Signal‐difference‐to‐noise ratio (SDNR) can be served as an indicator representing the sensitivity of an x‐ray system. This study aimed to evaluate the automatic exposure control (AEC) performance using the SDNR based on the national survey data in Taiwan. Methods: Measurements were made on all the 113 flat‐panel digital mammography units in Taiwan during our 2010 national survey. They included GE Senographe 2000D (38), DS (15) and Essential (3), Hologic Selenia with Mo (20) and W (24) targets, Siemens Mammomat NovationDR(8) and Inspiration (4), and IMS Giotto Image3D (1). A disk was placed on top of the 2, 4 and 6‐cm thick acrylic blocks to simulate the contrast. Clinical AEC modes were selected to acquire images and SDNR were then measured as the mean pixel value differences between the disk and the background divided by the noise using the equation defined in ACRIN DMIST recommendations. Results: AEC systems of different manufacturers/models, or even different units with the same models resulted in different target/filter combinations and techniques when performing the thickness tracking. For example, 6‐cm thickness led to 40% Mo/Mo and 60% Mo/Rh in Hologic Selenia systems with Mo target and 4‐cm thickness led to 26% for Mo/Mo and 74% for Mo/Rh in GE 2000D systems. Decreasing SDNRs were observed when thickness increased in all the eight digital models. When normalized the mean SDNR of each model to their 4‐cm‐thickness data, large deviations between 2 cm and 6 cm were observed in the GE systems (94.7%, 87.1% and 63.0% for DS, Essential and 2000D, respectively). Deviations of the other five models ranged from 36.9% to 59.6%. Conclusions: Evaluating AEC performance using SDNR showed the decreasing trend with increasing thickness in all the eight digital models. Considering the average glandular dose together, Figure of Merit will be further investigated in the future.
SU‐E‐I‐99: Extending the Micro‐Angiographic Fluoroscope (MAF) Exposure Dynamic Range Using Variable Electronic Gain
Authors: Singh V , Jain A , Panse A , Bednarek D , Rudin S
Published: November 2011

Purpose: To extend the exposure dynamic range of the MAF using its variable gain so that objects with a wide range of differences in attenuation can be visualized. Methods: A phantom with low, medium, and high attenuating regions was constructed by placing two low‐contrast vascular stents and a dense steel screw as test objects on a three‐step‐wedge assembly of aluminum and copper plates. The phantom was imaged with a standard FPD which has a fixed dynamic range and with the high‐resolution MAF at two different gain settings of its light image intensifier with constant x‐ray technique parameters.Results: The stents and screw‐threads could not be visualized in all three step regions in the FPD image. For the MAF, although we could visualize the stents and screw in the low‐attenuating step at low MAF gain, we could not see well the part of the image in the high‐ attenuating region. By increasing the gain 14 times, however, we were easily able to visualize the objects in the high‐attenuating region although part of the image in the low‐attenuating region was then saturated. In the high‐ attenuating region, the signal‐to‐noise ratio and contrast‐to‐noise ratio for the screw increased from 3.5 to 4.1 and from 6.3 to 7.1, respectively, as the gain was increased. Normalized pixel values for line profiles in the image of a stent in the high‐attenuating region at low gain closely follows the same profile in the high‐gain image, however, with substantially more noise fluctuations due to increased contribution of instrumentation noise. Conclusions: Although not possible for the FPD, different gains can be used for the MAF to visualize an objectˈs details and improve the signal‐to‐noise ratio under conditions of large differences in background attenuation without changing the x‐ray technique parameters.
SU‐E‐I‐100: Establishment of Local Diagnostic Reference Levels for Typical Fluoroscopic Procedures
Authors: Tonkopi E , Gale M , Schofield S , VanLarkin J
Published: November 2011

Purpose: Diagnostic reference levels (DRLs) represent an efficient criterion for radiation protection of patients and for procedure optimization. The aim of our study was to establish local DRLs for typical fluoroscopic examinations in our institution. Methods: Three standard fluoroscopic procedures were considered in the survey: upper GI series, double contrast barium enema, and single contrast barium enema. The examinations were performed at four hospital sites in eight different rooms, including image‐ intensified systems and flat panel detector based rooms. The dose area product (DAP) was calculated from the recorded total fluoroscopy time, the FOV size, and the entrance exposure rate measured on the surface of the 20 cm water phantom. The survey included studies performed by seventeen radiologists on 280 average size patients. Local DRLs were determined as the third quartile (75th percentile) of the DAP distribution for each procedure. A one‐way ANOVA test was used to determine significance of the differences between the fluoroscopic systems and the radiologists. Results: Radiation dose to a patient in the rooms with flat panel detectors was up to 2.6 times lower than in the II‐based rooms. However, patient dose was affected not only by the performance of the system and total fluoroscopy time, but also by the chosen fluoroscopic mode. All differences between the rooms and the radiologists were significant at 95% confidence level. We had to accept the variations due to the fact that fluoroscopic examinations are patient and radiologist dependent. All local DRLs were below national values. Conclusions: We have established local diagnostic reference levels for standard fluoroscopic procedures in our institution. All values were lower than the national DRLs for those examinations. In order to implement ALARA in practice, it is important that all performing radiologists are familiar with the dose reduction options available on fluoroscopic systems existing in the institution.
SU‐E‐I‐101: A Toolkit for Automatic 2D/3D Medical Image Registration Using Graphic Processor Units
Authors: Yuan J
Published: November 2011

Purpose: To develop a toolkit for automatic 2D/3D medical image registration using graphic processing units (GPUs). Methods: We adopt the nonlinear least square object function for the registration. We use the L‐ BFGS algorithm to solve this optimization problem to find the rigid transform parameters so that the summation of squared differences of all pixels between the generated DRR image from rotating and translating the treatment 3D volume and the given portal image is minimum. The open source library libLBFGS is used for this purpose. A faster incremental version of the Siddon ray tracing algorithm was implemented for the DRR generation on both CPUs and GPUs with CUDA 1.2. It is based on ray tracing through the CT volume by integrating the Hounsfield values crossed by the CT voxel. The GPU runs on NVIDIA GeForce GTX 280M with 1 GB video memory. To validate the correctness of the algorithm, a clinical three‐field plan was employed as an example. The CT volume image and the RT plan were exported from a commercial treatment planning system and read by our application. Results: The accuracy of the GPU DRR calculations comparing with the CPU calculation is well acceptable. The preliminary results show that the speed up for 2D/3D registration using the GPU can be a factor of 14. Conclusions: We have developed a toolkit with a graphical user interface for rapid automatic 2D/3D medical image registration. The accelerated DRR computations in the iteration on the GPU significantly reduce the registration time.
SU‐E‐I‐103: Tissue Dependent Deformation Field Regularization through Collapsed Cone Convolution/Superposition
Authors: Zhou B , Yu C , Chen D , Hu X
Published: November 2011

Purpose Previous Tissue‐dependent deformation field filters incur a relatively high computation cost. We present a collapsed‐cone based adaptive filtering method to reduce the computational overhead. Our proposed method is able to reduce the computational complexity of the superposition process from O(q3N3) to O(MN3) time, where q is the chosen neighborhood size, N is the volume dimension and M is the number of kernel axes. Method and Materials Our proposed filter performs diffusion along chosen kernel axes instead of within a size‐limited cubic neighborhood. During the ray tracing process along the kernel axis, the contribution of a given voxel to its neighbors is exponentially attenuated to simulate the physical characteristics of tissues. During the attenuation, local biomedical information can be naturally incorporated by scaling the ray tracing length according to the underlying tissue stiffness. This scaling makes a voxel within soft tissues more “malleable” with respect to its neighborsˈ movements. Results: We integrated different regularization methods into the same deformable registration approach (Demons algorithm). The kernel size of the Gaussian filter was set to be 5; the number of kernel directions for the CC filter were 4 in 2D and 16 in 3D. The experiments shows that our results produces are no‐worse result with a faster speed than these from other techniques. By investigating the finer details, the proposed method shows better capability of tracking changes. Conclusion Wpresented a collapsed‐cone (CC) based technique for the regularization of the deformation fields in image registration, which provides realistic deformation field and is useful for studying and modeling organs in motion. Since the CC filter can cover the entire 3D volume of interest, a better maintenance of the overall object shapes can be achieved. The incorporation of tissue information allows the CC filter to adjust its behavior to match the tissue biomedical characteristics.
SU‐E‐I‐107: Compositing Daily Images for Coverage and Enhancement
Authors: Gering D
Published: November 2011

Purpose: Images acquired daily during IGRT typically do not cover the entire treatment area, and they have lower image quality than the planning image. Conventionally, a small daily image is merged with the full‐size planning image in order to form a complete picture of the patient in treatment position. In such a merged image, a given voxel contains new data if it was covered by the daily scan, and otherwise old data from the planning image. The aim of this work is to form a composite image from all available fractions so that the aggregate covers the entire target and exhibits higher image quality. Instead of using just the newest data at each voxel, all available data is blended together. Methods: Every image is segmented automatically into 5 tissue types and 42 anatomic structures. Warp fields that map daily images to the planning image are computed from 4‐parameter rigid registration, 10‐parameter Marionette deformation, and free‐form deformation. The Marionette model allows small images to impact areas outside their scan because bone movements and weight loss are global. Each daily image is warped to every other daily image, and combined via weighted averaging. Weights are assigned to fractions based on age, deformation similarity, and STAPLE probabilities for mandible and spinal cord. Weights are assigned to voxels based on tissue discrepancy to secure data integrity and avoid blurring features. Results: The method was validated on head/neck datasets from 20 patients with a total of 466 daily images. The daily images are helical megavoltage CT. The SNR in muscle was measured to increase by an average of 55%, while CNR between muscle and fat increased by 50%. Conclusions: Image quality was measured to improve in all cases, and small daily images were shown to be useful components of a broader mosaic.

Supported by TomoTherapy
SU‐E‐I‐108: Deformable Registration Using Edge Preserving Scale Space for Adaptive Image Guided Radiation Therapy
Authors: Chen J , Li D
Published: November 2011

Purpose: A new multi‐scale deformable registration method is proposed by combining edge preserving scale space with the multi‐level free form deformation (FFD) grids for CBCT based on adaptive image guided radiation therapy (AIGRT) system. Methods: The edge preserving scale space which is able to select edges and contours of the image according to their geometric size is derived from the total variation model with the L1 norm (TV‐L1). At each scale, despite of the noise and contrast resolution differences between the planning CT and CBCT, the selected edges and contours are sufficiently strong to drive the deformation using the FFD grid, and the edge preserving property ensures more meaningful spatial information for mutual information based registration. At last the deformation fields are gained by a coarse to fine manner. Furthermore, considering clinical application we design an optimal estimation of the TV‐ L1 parameters by minimizing the defined offset function for automated registration.Results: The deformation differences gained by EFFD are always smaller than the NFFD, which indicate that EFFD is more accurate than the NFFD for three level of deformation. H&N case is the easiest one to recover the deformation, which is indicated by the smallest deformation difference. The rectum and prostate cases are in the same level when recovering the deformation, and the breast and chest are also in the same level to recover the deformation. The lung case is the most difficult type to recover the deformation. Conclusions: We can conclude that EFFD is more robust than NFFD method with more stable lower DDs for six kinds of cancer registration and three levels of deformation.We prove the significance of our proposed registration method both quantitatively and qualitatively with ground‐truth known.
SU‐E‐I‐111: Freesurfer MRI Data Analysis of Brain Cortical Thickness Variations in Individuals
Authors: Dennis M , Wall J , Xie H , Cotton A , Mooney R , Kane J , Wang X
Published: November 2011

Purpose: Group studies have demonstrated thinning of the brain cortex over decades as we age, but thickness is generally considered constant over shorter periods of time. This study evaluates the constancy and measurable variations in cortical thickness over time periods of minutes, weeks, months and years in individuals.Methods: Eight healthy adults (2 female, 6 male, 24–60 yrs) received back‐to‐back scans on 8 to 12 occasions. Each data acquisition consisted of 160 high resolution IR‐SPGR MRI images yielding a 1×1×1mm resolution. Freesurfer software (http://surfer.nmr.mgh.harvard.edu) was used to analyze this data, producing tens of thousands of thickness measurements and providing automatic segmentation of the cortical regions. Differences in back‐to‐back scans were used as an estimate of measurement error. Each scan was considered a valid measure, and all combinations of scans were compared and evaluated as time periods of weeks, months and years. Confidence intervals at the 95% level were established based on the estimated error. Results: Within each individual there were regions demonstrating 95% of the measured differences to be within the confidence interval, demonstrating anatomical stability and consistency in measurements. Other areas in each individual, however, showed significantly increased variation with greater than 15% of the measured differences outside of the confidence interval. These variations were specific to individuals, with different profiles of areas and intervals of stability and of variance Conclusions: This work expands on prior group analysis to the longitudinal measurement of cortical changes within normal individuals without intervention. Understanding the dynamics of cortical thickness measures is critical if such measurements are to be used as biomarkers of physiologically significant cortical changes. Cortical areas reconsolidate in individually specific and reversible ways during week, month, and longer periods of life.
SU‐E‐I‐114: Simulations of Scintillation Events in a High‐Resolution Liquid Xenon Micro‐PET System
Authors: Clements C , Bryman D , Glister J , Kurchaninov L , Miceli A , Retiere F , Sossi V , Zhu H
Published: November 2011

Purpose: A high‐resolution micro‐PET system based on liquid xenon (LXe) is under development. The system employs LXe time projection ionization detectors (TPC) and large‐area avalanche photodiodes (LAAPDs) light sensors. The energy and positions of interactions with the liquid xenon are measured by combining signals received from ionization charge in the TPC with scintillation light from the LAAPD arrays. The energy from scintillation light is used to select events in the 1st‐stage of a 2‐stage event selection. In this work we investigated methods of determining interaction locations from the LAAPD data by employing neural network (NN) computation algorithms. The position resolutions achievable by these methods under various degrees of reflectivity of the surfaces within the detector are presented. Methods: Simulations were performed using GEANT4 code. A simulated isotropic point source of 10220 optical photons (representing scintillation light from 511 keV gamma photons) was located at various points within the sector. The scintillation signal on the LAAPDs was calculated for all points within the sector on a 2×2×2 mm three dimensional grid for various levels of reflectivity. A random distribution of interactions within the sector was then evaluated with the NN algorithm. Results: The simulation studies indicate that under conditions of no optical reflectivity within the sector, interaction locations can be successfully reconstructed in 3 dimensions with approximately 8 mm FWHM 3‐D spatial resolution. When reflective surfaces are added to the inner walls of the sector, the position resolution is improved to 3.5 mm FWHM 3‐D spatial resolution, depending on the amounts and locations of the reflective surfaces. Conclusions: Scintillation position measurements of up to 3.5 mm FWHM 3‐D spatial resolution are achievable with various levels of surface reflectivity for the PET scanner employing LXeTPC detectors. Further analysis and techniques for improving signal to noise ratio in LAAPDs could improve the resolution.
SU‐E‐I‐119: Short‐TE 2D Proton Echo Planar Spectroscopic Imaging in Adolescents with Attention‐Deficit Hyperactivity Disorder
Authors: Zhang J , OˈˈNeill J , Thomas S , Hudkins M , Yee V , Ly R , Kurth F , Doss A , Loo S , Posse S , Alger J , Levitt J
Published: November 2011

Purpose: This study provides evidence of basal ganglia neurometabolite concentration alteration in adolescents with attention‐deficit hyperactivity disorder (ADHD) using a high‐speed magnetic resonance spectroscopic imaging pulse sequence with spatial‐spectral encoding. Methods: Spectroscopy data were acquired on a Siemens Trio 3T scanner with 12‐ channel phased‐array head coil, automatic shimming and outer volume suppression. Raw spectral data were reconstructed with an in‐house processing pipeline written in IDL. Spectra data were analyzed with a prior knowledge based fitting software LC Model. To ensure that differences in tissue concentration did not account for metabolite differences between subject groups, the gray, white and CSF compositions of each imaging voxel was determined by registering FSL segmented whole brain tissue masks with spectroscopic voxels via an in‐house processing program in IDL. FreeSurfer software was used for automatic brain segmentation at the basal ganglia region. Statistical analysis of neurometabolites was carried out in R. Results: Compounds that can be identified using PEPSI acquisition include N‐acetylaspartate (NAA), creatine/phosphocreatine (Cr+PCr), glycerophosphorylcholine/phosphorylcholine (GPC+PC), glutamate/ glutamine (Glx) and myo‐inositol (Ins). Compared with healthy controls, adolescents with ADHD had a significantly lower mean choline level in the left putamen (P = 0.016) and higher mean NAA level in the right putamen (P = 0.032). There were no significant differences in any other metabolite measured at the putamen and thalamus. Conclusions: In our efforts to investigate the pathobiochemical processes of ADHD by using fast short TE PEPSI acquisition method, we have found possible evidence of metabolite level differences between ADHD subjects and healthy controls in left putamen choline and right putamen NAA.
SU‐E‐I‐120: Automated Analysis of MRI Radio Frequency Coil Performance
Authors: Greene T , Stafford R , Reeve D
Published: November 2011

Purpose: A key component of an effective MRI quality control program is radio frequency (RF) coil testing. Coil testing includes the assessment of SNR, uniformity, and ghosting. Performing RF coil analysis can be very time consuming due to the quantity of coils being assessed and the large number of ROIˈs that need to be drawn to obtain the coil performance data. Analysis of acquired data is extremely repetitious, follows a strict set of rules, and therefore, may be amenable to automation. Methods: Software was written using MATLAB (R2009b, The MathWorks, Inc.), a technical computing language. A graphical user interface provided an easy to use structure for the end user to analyze annual coil test images. The algorithm locates the image closest to the isocenter and will automatically place the 8 ROIˈs needed to perform the annual coil assessment as directed by the ACR MR Accreditation Program. Results are displayed in the GUI and exportable to text or a preformatted Excel Spreadsheet for inclusion in an annual physics report. Results: The program has been benchmarked against three physicists and demonstrates an increase in precision of 3% for SNR, 1% for uniformity, and 5% for ghosting. Furthermore, the program eliminates the variance of subsequent measurements of an identical image. Whereas, the measurements of a single physicist varied by 5% for SNR, 1% for uniformity, and 14% for ghosting. Additionally, the average time to process a coil was decreased from 4 minutes manually to less than 8 seconds. Conclusions: The preliminary results demonstrate that automation has the potential to eliminate some of the inherent variability of test results due to manual measurement. Higher precision may facilitate increased sensitivity of the tests for assessment of subtle changes in system performance that may indicate a change in system performance or impending equipment failure.
SU‐E‐I‐122: Polymer Gel and Magnetic Resonance Relaxometry Based 3D Dose Monitoring
Authors: Hira R , Sinha U , Sinha S , Pawlicki T
Published: November 2011

Purpose: Recent advances in Radiation Therapy allow accurate shaping of the dose volume so that normal tissue and critical regions can be spared. However, it is important to monitor the 3D dose distribution of these complex treatment plans to verify the delivered dose distribution. Our aim was to optimize Magnetic Resonance imaging to map the 3D dose distribution of a novel radiation therapy system, TrueBeam sn1018(Varian) using a polymer gel. Methods: The polymer gel (BANG KIT, MGS Research) was prepared under normoxic conditions and stored in glass vials. A calibration was performed in the dose range of 3–18 Gy with irradiation using the True Beam. Several imaging sequences (Fast Spin Echo, Multi (8) Spin Echo, Single Spin Echo) were evaluated for spin‐spin relaxometry (T2) at 1.5 T (GE Medical Systems) with focus on accuracy, high spatial resolution, SNR while minimizing acquisition time. Treatment plan based irradiations (simulating different volumes and shapes) were performed at a dose rate of 600 MU/min for verification of the dose maps. Results: The calibration curve (1/T2 vs Dose) was linear in the range of irradiation. The three imaging sequences were consistent in 1/T2 values in the low dose range with the FSE sequence showing some saturation at high dose values. The treatment plan dose mapping is currently underway and will be aligned with the treatment plan simulation to evaluate the degree of match between the plan and actual irradiation.Conclusion: The polymer gel and MR monitoring can enable generation of 3D dose maps with high accuracy and spatial resolution to verify treatment plans of small volumes and steep dose gradients.
SU‐E‐I‐125: Uniform Sampling of Projections during Pulsed Electron Paramagnetic Resonance Imaging Data Acquisition
Authors: Redler G , Epel B , Seifi P , Bryant J , Halpern H
Published: November 2011

Purpose: To devise a generalized, object‐independent method for uniform acquisition of projections from 3D pulsed electron paramagnetic resonance imaging (EPRI) experiments so that intermediate images approximating the final image may be reconstructed from an incomplete set of projections.Methods: Projection directions for 3D pulsed EPRI experiments can be represented as points on a hemisphere. A new technique is developed to divide the hemisphere into sectors of equal area and sample the projection points such that the standard deviation of the number of these points per sector is minimized. These sectors are defined by number of divisions in azimuthal and polar angles. Images of a cylindrical phantom were obtained using the current polar‐azimuthal raster scheme as well as this new uniform sampling scheme with different hemisphere divisions for comparison of rapidity of convergence to the final image. The mean square difference between intermediate images and the final image was the metric compared.Results: The uniform‐sampling method produces intermediate images that converge to the true final image more rapidly. An image reconstructed from half projection data is 44.6% closer to the final image than an image reconstructed from half projection data using the polar‐ azimuthal raster method. Conclusions: A novel method is developed to uniformly sample projection data for 3D pulsed EPRI that is independent of the object and produces intermediate images converging to the fully sampled image more rapidly than those from a polar‐azimuthal raster sampling scheme. This method can be implemented to allow the user to view the image being created while acquiring projections so that problems with the scan become evident earlier without the need to wait for the entire scan to finish. This new scheme also gives better temporal resolution with the addition of minor artifacts by under sampling projections and requiring less imaging time.

Acknowledgement of support: R01 CA98575; P41 EB002034
SU‐E‐I‐126: Feasibility of Myelin Water Fraction Quantification Using Multi‐ Component Gradient Echo Sampling of Spin Echoes
Authors: Gagnon Y , Gelman N , Théberge J
Published: November 2011

Purpose: Multi‐component T2 is a magnetic resonance imaging technique which allows the quantification of the myelin water fraction (MWF) non invasively in the brain. The MWF is the proportion of the shorter T2 signal arising from water trapped within layers of the myelin sheath and has been shown to be closely related to aberrant white matter microstructure, such as in multiple sclerosis lesions. The purpose of this study was to evaluate the theoretical ability of a new method to calculate the MWF in a two‐ component model using simulated data and realistic temporal signal to noise (SNR) profiles. Methods: The signal is sampled at equal intervals using gradient echoes placed symmetrically about multiple spin echoes while they rephase and subsequently dephase. Considering a two component model with a bi‐exponential signal decay, a ratio of the signal before and after the spin echo can be obtained which depends on the MWF and a short and long T2 component. Using Matlab, data was generated based on the acquisition of three spin echoes at echo times of 16, 50 and 150ms respectively flanked by 8, 18 and 40 pairs of gradient echoes spaced 1 ms apart. Realistic temporal SNR profiles were generated for the case of zero static dephasing and for a worst scenario case scenario based on realistic expectations at 3T. Results: Simulation results indicated a slight overestimation of the MWF, but distributions and standard deviations were well behaved at worsening SNR levels. Conclusions: The ability of this acquisition scheme and simple model to evaluate the contribution of a short T2 component was demonstrated. Future work will focus on the practical implementation of this technique in‐vivo which would enable the assessment of white matter microstructure by providing MWF data in a clinically relevant scan time of approximately 10 to 20 minutes.
SU‐E‐I‐137: Incorporation of Regional Homogeneity in Seed‐Based Resting‐State Functional MRI Analysis Improves Default‐Mode Network Detection in Patients with ICA Stenosis
Authors: Yan F.X. , Lee T.H. , Wong H.F. , Liu H.L.
Published: November 2011

Purpose: Functional connectivity (FC) within the default mode network (DMN) as detected by resting‐state (RS) functional MRI (fMRI) has generated significant interests in neuroscience and clinical studies. We proposed a method for improving the sensitivity of the conventional seed‐ based correlation analysis (SCAC) by incorporating the regional homogeneity information (SCAReHo). The study aimed to analyze DMN connectivity in patients with stenosis of the internal carotid artery (ICA), before and after stenting, and compare the results of SCAC and SCAReHo. Materials and Methods: Nine patients with unilateral ICA stenosis (1 Female; age: 66±7.84y) were scanned twice (before and six months after stenting) at a 3T MRI scanner. A T2*‐weighted single‐shot gradient‐echo EPI sequence was applied for the RS‐fMRI with TR/TE/FA=2000ms/50ms/90° and 150 phases. For SCAC analysis, the correlation coefficients between the reference time course (obtained from the posterior cingulate cortex (PCC) seed region at (0,−51,30) and radius=4mm) and the time course of each voxel were computed across the whole‐brain. For SCAReHo analysis, first Kendall coefficient of concordance (KCC) maps were computed for each subject and then the reference time curve were obtained from the common voxels of a PCC mask and the KCC mask (KCC>0.5). Results: With the SCAC analysis, only few or no voxels in the seed and the DMN regions were detected in most patients. The SCAReHo method significantly improved the detection in all patients. Heterogeneous and bipolar distributions of correlation coefficients were found in the conventional PCC region, which may explain the failure of the SCAC analysis in this patient group. Improvement of FC was found after the treatment with the SCAReHo analysis. Conclusion: The SCAReHo analysis improved the detection of FC in DMN using the RS‐ fMRI. This method may be particular helpful for subject groups with functional anatomy that likely differs from the normal population.
SU‐E‐I‐139: Transition from CT to MR Imaging of Titanium Applicators for 3D Image‐Based High Dose Rate Cervix Cancer Brachytherapy
Authors: Esthappan J , Ramirez J Garcia , Hu Y , Grigsby P
Published: November 2011

Purpose: To verify against CT the effect of different MR imaging sequences and acquisition parameters on the determination of treatment dwell positions in a titanium tandem applicator for 3D‐image‐based high dose rate cervix brachytherapy. Methods: A titanium tandem and ovoid applicator, fixed rigidly within a plastic phantom containing copper sulfate solution, was imaged on a multi‐slice CT scanner to obtain a reference image dataset and subsequently on a 1.5T MR scanner to obtain nine test image datasets acquired using different MR sequences (T2‐weighted, T1‐weighted, and proton‐density‐weighted with turbo‐spin‐echo technique), slice thicknesses (0.5 cm and 0.25 cm in the parasagittal plane), and fold‐over directions. All images were imported into a brachytherapy treatment planning system, fused, and planned for delivery of an HDR treatment with a 0.5 cm Ir‐192 source using our standard treatment protocols. The treatment programming, i.e., number and arrangement of dwells, as well as the 3D coordinates of dwells activated along the tandem on the reference CT were compared against those on the registered MR datasets in terms of differences in right‐ left (RL), foot‐head (FH), and anterior‐posterior (AP) directions. Results: Distortions along the tandem on MR were non‐uniform. Despite this, mean differences in RL, FH, and AP coordinates of activated dwells were approximately 0.1 cm or less, 0.2 cm, and 0.1 cm, respectively. The number and arrangement of dwells activated along the tandem on the MR datasets were identical to those on CT. Conclusions: The slice thicknesses, sequences, and fold‐over directions used in this study had clinically insignificant effects on treatment dwells defined on MR images versus those on CT. It is recommended that other centers do a similar evaluation before making the transition from CT to MR to better understand how identification of the tandem and determination of HDR treatment dwell positions compares between MR and CT.
SU‐E‐I‐142: A Review of Digital Mammography Detector Failure Modes Encountered in Clinical Practice
Authors: Schueler B , Walz‐Flannigan A
Published: November 2011

Purpose: Flat panel detector failure in digital mammography systems can result in significant added operating expense, clinical down‐time and added personnel time for trouble‐shooting and acceptance testing prior to clinical use. The purpose of this study is to review modes of full‐field digital mammography detector failure and detector lifetime encountered in a clinical setting.Methods: Mammography detector history was maintained over 6 years for 3 facilities. When detector failure occurred, the reason for detector rejection and duration of detector lifetime were determined.Results: Out of the 11 digital mammography units followed during the review period, a total of 15 detector failures occurred. All rejected detectors and failure modes were verified by the manufacturer. Detector failure modes included dead pixel clusters (10), excessive ghosting (3), gate failure (1), detector crystallization (1) and charge build‐up defect (1) (One detector exhibited 2 different failure modes). Detector lifetime ranged from a minimum of 1 month (gate failure) to a maximum of 36 months (detector still in clinical use). The mean detector lifetime was 15 months Conclusions: Data from multiple digital mammography units and facilities collected over 6 years show that relatively short detector lifetime is common. Compiled detector failure data is useful for comparing ownership expense expected for different digital mammography models and to assist in determination if service contract coverage of detector replacement is advisable.
SU‐E‐I‐143: Feasibility of Using Chemical Analysis to Validate Breast Density Measurement from Dual Energy Mammography
Authors: Klopfer M.J. , Ducote J.L. , Molloi S.Y.
Published: November 2011

Purpose: Currently, there is no accepted standard for measuring breast density. Dual energy mammography, which has demonstrated accurate measurement in phantoms, has been proposed as one possible method. The purpose of this study was to assess the possibility of using chemical analysis to validate measurements of breast density made with a dual energy mammography system.Methods: Fourteen ex‐vivo bovine tissue samples composed of varying amounts of pure lean tissue and pure adipose tissue in increments of 10%, as measured by their lean percentage, were imaged using dual energy mammography. This was followed by chemical analysis of the tissue samples based on desiccation, trituration, and fat extraction with petroleum ether. Breast density, as measured from dual energy mammography, and the glandular volume percentage, as derived from chemical analysis data, were compared to the known lean percentages. Breast density was also compared to the glandular volume percentage.Results: Breast density (BD) was related to the tissue sampleˈs volumetric lean fraction (VLF) by BD = 1.52*VLF + 10.0 (r2>0.99). Glandular volume percentage (GVP) was related to VLF by GVP = 0.74*VLF + 26.1 (r2>0.99). BD was related to GVP by BD= 2.06*GVP‐ 43.59 (r2>0.99) Conclusions: The results of this study show strong linear relationships between different parameters and indicate that chemical analysis should be a useful technique to help validate breast density measurements. The relationship between breast density and glandular volume percentage from a bovine tissue model could help to interpret the analysis of human breast tissue samples of unknown composition.
SU‐E‐I‐145: A Spectral Reconstruction Method for Digital Breast Tomosynthesis
Authors: Feng SSJ , Nagy J , Chung J , Mejia‐Bustamante V , Sechopoulos I
Published: November 2011

Purpose: To develop and test a novel reconstruction method that incorporates the varying attenuation properties of the full spectrum of x‐ray energies generated by the x‐ray tube and used to acquire the tomosynthesis projections. Methods: The spectral reconstruction (SR) method utilizes a polyenergetic x‐ray source model and reconstructs the breast volume where each voxel represents a glandular fraction. The glandularity of each voxel is approximated by a maximum likelihood (ML) estimate that takes into account the attenuation of x‐rays of all energies in the spectrum and the subsequent beam hardening that occurs as they travel through the volume. A gradient descent optimization algorithm is used to compute the ML estimates of the entire volume. The SR method was used to reconstruct images of a heterogeneous breast tomosynthesis phantom and patient images. These images were compared to reconstructions obtained from a standard monoenergetic maximum likelihood expectation maximization (MLEM) iterative reconstruction method. The contrast‐to‐noise ratio (CNR) of masses and the Full Width at Half Maximum (FWHM) of the signal profiles in two directions of microcalcifications were assessed. Results: The image quality of the SR phantom and patient images was higher than that demonstrated by the MLEM reconstructions. The swirl patterns of the heterogeneous tomosynthesis phantom are more clearly defined and beam hardening artifacts are greatly reduced. The images reconstructed with the SR method also demonstrated an increase in CNR of up to 81% of masses embedded in the breast tomosynthesis phantom. In the signal profile measured perpendicular to x‐ray tube movement, the FWHM of microcalcifications of the SR images differed by less than 5% from that of the MLEM images. Conclusions: SR method has the potential to greatly enhance the image quality of breast tomosynthesis images, reduce reconstruction artifacts, and provide quantitative reconstructions.