bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐C‐217A‐04: Patient‐Specific Dosimetry for CT Examinations in the Pediatric Population
Authors: Carver D , Kost S , Clark J , Price R , Pickens D , Stabin M
Published: June 2012

Purpose: Radiation‐dose estimates from CT scans are commonly reported as CTDI values (mGy), which are derived from standard measurements made with one of two standard (16 or 32 cm diameter) acrylic phantoms for a given technique (kVp, mAs, collimation, and pitch). Values are assigned uniformly across pediatric and adult patients without regard to specific patient size and weight. The goal of this research is to create a database of whole body and organ doses for clinical CT scans in pediatric subjects to establish more patient‐specific dose estimates. Another goal of this project is to investigate how marrow dose and risk from CT imaging varies with age. Methods: We developed a Monte Carlo radiation‐transport code to simulate different CT scans. Several pediatric subjects that received chest, abdomen, and pelvis scans were selected for segmentation into voxelized phantoms for importation into our code. A series of anthropomorphic NURBS (non‐ uniform rational b‐spline) phantoms were developed to realistically represent median, as well as larger and smaller normal weight and obese pediatric individuals of various ages. With the development of a large number of these phantoms, dose estimates for individual pediatric subjects can be assigned from the most similar phantom in the database. Results: Our models provide individual organ doses from different CT exams, thus effective doses may be more accurate over those from CTDI calculations in two reference models, and future changes in organ‐weighting factors can be taken into account. Comparison of organ and marrow doses for standard NURBS models and real patients of similar stature segmented manually show very good agreement. Conclusion: Patient‐specific dosimetry may be achieved through the use of patient‐matched NURBS models for pediatric CT scans. The quality of dose data to be assigned to pediatric patients receiving CT examinations may be significantly improved using the information obtained in this study. Partially supported by NIH NCI 1 R01 CA155400‐01A1
SU‐C‐217A‐06: A Collaborative Approach to Dose Optimization in Fluoroscopy Guided Lumbar Spine Injection Procedures
Authors: Brown K , Kalapos P , Nguyen D , Thamburaj K , Rahman T
Published: June 2012

Purpose: To observe and evaluate technical acquisition and operating procedures used for lumbar spine injection procedures under fluoroscopy guidance performed by multiple neuroradiologists for potential patient dose reduction opportunities. Methods: Baseline skin dose measurements were acquired on patients undergoing lumbar spine injection procedures on a biplane fluoroscopy unit. Optically stimulated luminescent dosimeters were placed on the patient's abdomen corresponding to the anterior‐posterior plane beam entrance location and on the patient's right side corresponding to the lateral plane beam entrance location. Technical acquisition factors, treated levels, and patient demographics were recorded. In addition, observations were made of operating procedures such as the use of collimation and magnification, patient and equipment positioning, beam angulations, and exposure techniques used by individual neuroradiologists. Results: Baseline data and observations were reviewed with neuroradiologists. Opportunities to reduce dose were discussed and a series of acquisition and practice changes accepted. Changes were implemented and skin dose measurements repeated. Results showed a reduction in skin dose of 64% and 79% respectively for anterior‐posterior and lateral planes from baseline data. No adverse outcomes to procedure time, fluoroscopy time, or image quality were observed. Conclusions: Practices among physicians can vary substantially. Collaboration and standardization of acquisition and operating procedures can Result in substantial dose reduction for patients without compromising image quality or clinical productivity.
SU‐C‐218‐03: Can Cardiac Output Be Measured from a Pulmonary CT Circulation Time Series?
Authors: Yee S , Scalzetti E , Ogden K
Published: June 2012

Purpose: In order to determine the optimal prescan delay for CT pulmonary angiography (CTPA), pulmonary circulation time images can be acquired at the anatomical level of main pulmonary artery prior to the main CTPA. The purpose of this abstract is to demonstrate cardiac output can also be calculated from the preparatory CT series. Methods: The single slice pulmonary circulation time images were acquired on a GE CT scanner once per second in cine mode during infusion (5 cc/sec) of contrast (a blend of 25 cc Omnipaque and 50 cc saline), followed by a 30 cc saline bolus. The single slice CT series, covering superior vena cava, pulmonary artery, ascending aorta (AA) and descending aorta (DA) as in Fig A, were imported into the in‐house software to obtain time series at both AA and DA, as well as the essential geometrical info needed for determining the volume of aortic arch. The time series at DA, which is the downstream measurement of AA, was assumed equivalent to the mathematically convoluted time series of AA with a certain delay function. Considering the fast nature of flow in the aorta, an exponential delay function with the delay time constant, i.e. (l/d)*exp(−t/d), was assumed (ref 1 for exponential dispersion in fast flow). The delay time constant, which is the average time span between the cross sections of AA and DA, was determined by the least square error fitting while comparing the measured DA time series to the varying degree of convoluted time series of AA. The volume of the aortic arch and delay time constant were then used to calculate the cardiac output. Results and Conclusion: The cardiac output values for two subjects were 4.97 and 3.63 L/min, which are in good agreement with the reference range of 1.9 to 11.6 L/min(ref 2).
SU‐C‐218‐05: A CFD‐Based Approach to Validating Flow in a Prototype Dynamic Perfusion Phantom for Dynamic Contrast Fnhanced (DCE) Imaging
Authors: Thomas A , Hollister S , Balter J
Published: June 2012

Purpose: A dynamic phantom for quality assurance of dynamic contrast enhanced (DCE) imaging has been designed to achieve perfusion (in terms of flow rates) comparable to capillary exchange that occurs in human tissue. The validation of this physical phantom is critical to establishing its usefulness as a quality assurance tool. This study seeks to evaluate the use of computational fluid dynamics (CFD) to validate perfusion properties within the prototyped dynamic DCE phantom. Methods: The phantom was evaluated in two parts, the vascular network, followed by the porous media compartments. CFD simulation software (Fluent) approximates fluid motion assuming the polymer phantom to be a solid, rigid object, receiving constant laminar flow. The fluid simulated in this model was a blood analog with a non‐Newtonian fluid viscosity fitted to the Carreau model. The velocity across the system was visualized and the flow rates across the porous compartments were estimated. Results: The flow across the perfusion phantom was qualitatively and quantitatively evaluated. The flow rates for highly permeable compartments demonstrating high rates of perfusion were quantified to estimate the differential perfusion and flow rate. Less permeable compartments showed decreased velocity profiles and flow rates across the scaffold, in some cases resulting in low flow or backflow, which was also observed for less porous compartments under experimental conditions. The compilations of simulations offer a range of flow rates representative of normal and diseased tissue (in the liver). Conclusions: CFD is an effective tool for validation of design of a DCE phantom. The results of CFD analysis have been applied to both demonstrate the potential for the phantom to simulate a wide range of realistic perfusions characteristics, as well as to establish limits in the phantom design that would otherwise Result in non‐physiological flow and perfusion values. Sponsored by NIHP01CA59827 and F31 EB012436‐02. Sponsored by NIHP01CA59827 and F31 EB012436‐02.
SU‐D‐BRB‐02: Investigations of Secondary Ion Distributions in Carbon Ion Therapy Using the Timepix Detector
Authors: Gwosch K , Hartmann B , Jakubek J , Granja C , Soukup P , Jaekel O , Martisikova M
Published: June 2012

Purpose: Due to the high conformity of carbon ion therapy, unpredictable changes in the patient's geometry or deviations from the planned beam properties can result in changes of the dose distribution. PET has been used successfully to monitor the actual dose distribution in the patient. However, it suffers from biological washout processes and low detection efficiency. The purpose of this contribution is to investigate the potential of beam monitoring by detection of prompt secondary ions emerging from a homogeneous phantom, simulating a patient's head. Methods: Measurements were performed at the Heidelberg Ion‐Beam Therapy Center (Germany) using a carbon ion pencil beam irradiated on a cylindrical PMMA phantom (16cm diameter). For registration of the secondary ions, the Timepix detector was used. This pixelated silicon detector allows position‐resolved measurements of individual ions (256×256 pixels, 55μm pitch). To track the secondary ions we used several parallel detectors (3D voxel detector). Results: For monitoring of the beam in the phantom, we analyzed the directional distribution of the registered ions. This distribution shows a clear dependence on the initial beam energy, width and position. Detectable were range differences of 1.7mm, as well as vertical and horizontal shifts of the beam position by 1mm. To estimate the clinical potential of this method, we measured the yield of secondary ions emerging from the phantom for a beam energy of 226MeV/u. The differential distribution of secondary ions as a function of the angle from the beam axis for angles between 0 and 90° will be presented. In this setup the total yield in the forward hemisphere was found to be in the order of 10−1 secondary ions per primary carbon ion. Conclusions: The presented measurements show that tracking of secondary ions provides a promising method for non‐invasive monitoring of ion beam parameters for clinical relevant carbon ion fluences. Research with the pixel detectors was carried out in frame of the Medipix Collaboration.
SU‐D‐BRB‐06: Comprehensive Population‐Averaged Arterial Input Function (AIF) for DCE‐MRI of Head and Neck Cancer
Authors: Onxley J , Yoo D , Muradyan N , MacFall J , Brizel D , Craciunescu O
Published: June 2012

Purpose: To generate a composite population‐averaged(PA)‐AIF for quantitative analysis of DCE‐MRI data in head and neck (H&N) patients that is based on the right (RT) and left (LT) carotids, two pre‐treatment scans, and one post‐treatment scan. Methods: Twenty patients were imaged while undergoing concurrent chemoradiation (CRT) for H&N malignancies. The imaging protocol (1) included two baseline scans one week apart (Base1, Base2), and one scan 1 week post‐CRT (Post). For each patient and time point, regions of interest (ROIs) in both the RT and LT carotids were drawn on coronal images. The plasma concentration curves of all ROIs were averaged and fit to a bi‐exponential decay function to obtain the final PA‐ AIF (AvgAll). The ROIs were also divided by time point to obtain AvgBasel, AvgBase2, and AvgPost AIFs. The vascular transfer constant for both primary and nodes, Ktrans, was calculated (iCAD, Inc.) using the 4 AIFs, as well as the generic Weinmann's AIF. The median Ktrans values resulting from the AvgAll AIF were compared using Bland‐Altman plots with the ones obtained from each individual time point. The Wilcoxon signed‐rank test was used to compare the proposed AvgAll AIF and the generic AIF. Results: The plasma parameters for the AvgAll AIF were a1,2=27.1135/17.6486 kg/liter, m 1,2=11.7525/0.2054 min−1. The differences in Ktrans values using these coefficients vs. Weinmann's were statistically significant (p<0.0001). The median Ktrans values from the AvgBasel,AvgBase2, and AvgPost AIFs were, in most cases, not significantly different from the AvgAll values, indicating that the latter is appropriate foruse at all time points. Conclusions: A population‐averaged AIF for H&N was generated that accounts for differences in RT vs. LT carotids, day‐today AIF fluctuations, and treatment‐induced AIF changes. It is not necessary to measure a post‐treatment AIF to evaluate treatment‐induced Ktrans changes.l. Craciunescu et al., MedPhys, 37, 6, 2683, 2010
SU‐D‐213CD‐05: Identifying Prostate Brachytherapy Seeds at MRI: A Study in Phantom
Authors: Fatemi‐Ardekani A , Borg J
Published: June 2012

Purpose: Conventionally, post‐implant CT scans are used for identification of prostate brachytherapy implant seed locations. The dosimetric quality of the seed implant in our institution is evaluated based on CT/MRI fusion and contouring of prostate and rectal wall on MRI. Post‐implant evaluation of prostate brachytherapy using MRI alone is generally not feasible due to the uncertainty associated with seed localization despite its excellent anatomical delineation. The fusion of CT and MRI has some variability and may be time consuming. The goal of our current work was to use SWI phase images for identification of prostate brachytherapy seeds. Using MRI alone to identify seeds will eliminate the need for CT scan of the patient post‐implant and eliminate the variability of the CT/MRI fusion. Methods: A prostate gel phantom containing five inactive brachy seeds (Advantage I‐125™, Biocompatibles, Oxford, CT) each has longitudinal cross section area of 3.6 mm2. It was assessed using CT, and MRI. Imaging was done using a GE Signa 3T HD MRI system (GE Heathcare, Millwaukee, WI). Imaging parameters for SWI were: 512×384 (zero filled to 512×512), FOV=10 cm, ASSET factor=2, TE/TR=20/42 ms, FA=15°, RBW= 80 Hz/pixel, spatial resolution=0.3 × 0.3 × 2.0 mm. Results: Brachytherapy seed, as confirmed on CT images, were easily identified in the phantoms on the filtered SWI phase images. The mean area for the 5 seeds, as measured on CT and SWI filtered phase images, was 3.5±0.5 mm2 and 3.8±0.6 mm2, respectively. There appeared to be linear relationship in seed area as determined by SWI filtered phase compared to CT (R2=0.8). Conclusions: With the improved resolution, SNR and proper filtering on high field MRI systems, SWI phase images can be used to identify prostate brachytherapy seeds on conventional MRI without using CT.
SU‐D‐218‐01: Support Vector Machine Tissue Classification of Multiparametric MRI Tumor Data
Authors: Heredia G , Koay G , Turski P , Meyerand M
Published: June 2012

Purpose: To test the accuracy of Support Vector Machines in the classification of Glioblastoma Multiforme tumor voxels usingmultiparametric MRI data. Methods: Various MRI scans were collected from patients with recurrent GBM. Each scan session collected post‐contrastT1(+C T1), T2, diffusion, perfusion, and multi‐echo hypoxia images. Thediffusion‐weighted images were converted to Apparent Diffusion Coefficient (ADC) maps. The perfusion images were corrected for leakage and represented as corrected rCBV maps. All of these scans were co‐registered to each other, giving an input matrix to our support vector machine consisting of roughly 13,000 voxels, each with 5 feature values (+C T1, T2, ADC, rCBVcorrected, delta T2*). The SVM was then trained usingradiologist confirmed labels for ‘cyst’, ‘tumor’, and ‘normal tissue’. These labels were obtained using longitudinal data as well as clinical scans, and tested on new data to determine the accuracy of classifying tumor and cyst voxels. Results: The tumor model resulted in a specificity of 0.9841 and a sensitivity of 0.7498. The cyst model resulted in a specificity of 0.9825 anda sensitivity of 0.9414. Both models showed improvement with increasing features. Conclusions: These results show that the SVM is capable of classifying tumor and cyst voxels in a single case study. Aside from optimizing the current tumor model, future work will focus on the potential for the SVM to help in early detection of recurrence. In order to achieve this,we will need to test SVMs across patients. If we truly aim for early detection, then we need to prove that the algorithm can be trained on a pool of subjects with recurrent disease, and then test that model on a new patient before recurrence is obvious.
SU‐E‐I‐04: Implementation of a Fast Monte Carlo Scatter Correction for Cone‐ Beam Computed Tomography
Authors: Watson P , Mainegra‐Hing E , Soisson E , Naqa I El , Seuntjens J
Published: June 2012

Purpose: To improve image quality in cone‐beam computed tomography (CBCT) scans by implementation of a fast and accurate MC‐based scatter correction algorithm. Methods: A Solid WaterTM phantom was imaged on a Varian OBI CBCT scanner using the standard‐dose head protocol (100 kVp, 151 mAs, partial‐angle). A fast Monte Carlo simulation developed in the EGSnrc framework was used to transport photons through the uncorrected CBCT scan. From the simulation output, the contribution from both primary and scattered photons for each projection image was estimated. Using these estimates, a subtractive scatter correction was performed on the CBCT projection data. This correction procedure was repeated iteratively, using the previous scatter corrected scan as input to the Monte Carlo simulation. Results: Implementation of the scatter correction algorithm on real CBCT data was shown to help mitigate scatter‐induced artifacts, such as cupping and streaking. The scatter corrected images were also shown to have improved accuracy in reconstructed attenuation coefficient values. In a region of interest centered on the Solid Water phantom, the number of voxels agreeing to within 10% of the theoretical attenuation coefficient increased from 46% to 97% after two iterations of the scatter correction. Conclusions: These results suggest that the proposed scatter correction algorithm is successful in improving image quality in real CBCT images. The accuracy of the attenuation coefficients extracted from the corrected CBCT scan renders the data suitable for on‐the‐fly dose recalculations, as well as vastly improved image registration.
SU‐E‐I‐11: A Novel High Resolution CT Imager for a Breast SPECT‐CT System
Authors: Zentai G , Richmond M , Partain L , Shah J , Tornai M
Published: June 2012

Purpose: To evaluate the intrinsic characteristics of a new high resolution, large area, small bezel, digital imager developed for a dedicated SPECT‐CT system for fully‐3D mammotomographic imaging applications. Methods: A new flat panel digital imager was developed having 127μm pixels (identical to those in the Paxscan 2520) with an active 40×30cm area and 3200×2304 total pixels, which is well suited for pendant breast imaging close to the chest wall. The readout and driver ASIC TAB bonding pads were arranged on only two sides of the imager plate, to eliminate dead edge spacing. A special housing was developed to accommodate this imaging plate providing very narrow 8mm edges (bezels) on two orthogonal sides The TFT array imager was coated with 600μm thick micro‐columnar CsI, which provides >90% absorption in the breast CT (60–80kVp) x‐ray energy range. It provides better than 70% absorption for RQA5 (70kVp 21mm Al filter) x‐ ray radiation. The readout ASICs are connected to 14 bit A/D converters, and special readout ASICs with gain switching feature, which provide an additional 4bit virtual (2–3 effective) dynamic range. Results: The MTF is ∼7.5% at the 3.9 lp/mm Nyquist frequency. The NPS curves continuously decrease with increasing spatial frequencies, characteristic of scintillator based imagers. The excellent DQE (0) measured at RQA5 is ∼75% in the 0.1–1mR dose range and ∼10% at the Nyquist frequency. The imager has excellent linearity over the full dynamic range, and high contrast images are readily acquired. Conclusions: The new 4030 flat panel imager is a high resolution, state of the art detector, ideal for breast imaging and other applications. This detector is included in the SPECT‐CT device in development.
SU‐E‐I‐12: Analysis of Image Noise in 3D Scatter Corrected Cone Beam CT Images as a Function of Object Size
Authors: Pachon J , Tornai M
Published: June 2012

Purpose: To characterize the spatial correlation of quantum noise of a cone beam CT (CBCT) system for breast imaging under scatter and non‐scatter corrected conditions as a function of object radius. Methods: Experiments were conducted using a conical phantom under scatter and non‐scatter corrected conditions. The cone phantom filled with 700ml of water was positioned near the isocenter of the quasi‐monochromatic CBCT imaging system. 360 projections were acquired and beam‐stop measured scatter correction was performed. Both scatter and non‐scatter corrected projections were reconstructed with an iterative ordered subsets convex (OSC) algorithm. NPS measurements were made at several cone radii (6–12cm) using 4 overlapping 50×50 pixel ROI's with a 50% overlap between adjacent ROIs. An ensemble average of NPS measurements was taken over 5 slices at each radius. Results: For both scatter and non‐scatter corrected data overall noise is higher with increasing object radius. Each 1‐D NPS area under the curve was found to be within the standard deviation of the respective ROI variance. The variance of scatter corrected images is higher at each radius. The 1‐D NPS indicates a decrease in peak value for both scatter and non‐scatter corrected images as radius increases. Scatter corrected NPS shows a slight shift in the peak towards higher spatial frequencies, and a larger spread of noise over all spatial frequencies as radius increases. Conclusions: This work demonstrates that scatter correction increases noise at each spatial frequency at various object radii. owever as radius increases, lower frequency noise decreases and concomitantly higher frequency noise increases. As a Result of this equalization of noise across spatial frequencies, the noise texture appears more uniform at larger radii under scatter corrected conditions. These results and methodology can be used to determine optimal detection of low contrast signals in phantoms of different radii and with clinical breast data.
SU‐E‐I‐24: Determining the Optimal B‐Values to Use in Diffusion Weighted Imaging for Differentiating Benign and Malignant Breast Lesions
Authors: Jacobs MA
Published: June 2012

Purpose: To investigate and determine the optimal b‐values for Diffusion Weighted Imaging(DWI) for Apparent Diffusion Coefficient(ADC) maps in differentiating normal, benign and malignant breast tissue. Methods: Twenty‐five patients underwent diffusion‐weighted magnetic resonance imaging (DWI‐MRI) and conventional breast MRI with suspicious breast fmdings(BIRADS >4). Breast lesions were defined by pathology. The DWI was acquired with different b‐values ranging from 0,500, 600,750 and 1000s/mm2. Apparent Diffusion Coefficient(ADC) maps of breast tissue were constructed using different b‐values, e.g., using either 2 b‐values(0– 1000) or combinations of 3 or more (0,500,1000 or 0,600,750,1000). Quantitative analyses of the ADC maps of glandular, fatty and lesion tissue were obtained. Ratios of lesion to glandular tissue(L/GT) and signal to noise(SNR) were assessed. Paired t‐tests were performed for statistical significance. Results: Eighteen patients had invasive ductal carcinoma and 7 had benign breast lesions. The mean ADC value for malignant lesions using all b values was 1.17±0.16×10‐3mm2/s with a lesion to glandular(L/GT) ratio=0.65. The benign lesions, ADC map value was 1.86±0.03×10‐3mm2/s with L/GT=0.98. There was a significant difference(P<0.05) between benign and malignant lesions ADC map value.The lowest SNR(12±6) was with single b‐values. There was a significant difference(P<0.05) in SNR with multiple b‐values(34±6) compared to single b‐values. The highest SNR was given by using two b values greater than 500. Finally, the background noise for all combinations was surprising stable and ranged between 60±20%. Conclusions: This is the first study to investigate the effect of changing different b values in DWI breast imaging. There were significant differences in the SNR between single and multiple b values. Our data show suggest that the recommended b‐values for DWI in breast are 0, and two that are 500 or greater. Therefore use of at least 3 b‐values in DWI/ADC mapping of breast lesions are needed for better characterization of benign and malignant breast tissue. P50CA88843, Avon Foundation for Women:01‐2008‐012, U01CA070095, andU01CA140204
SU‐E‐I‐25: Performance Evaluation of a Proposed CMOS‐Based X‐Ray Detector Using Linear Cascade Model Analysis
Authors: Jain A , Bednarek D , Rudin S
Published: June 2012

Purpose: The need for high‐resolution, dynamic x‐ray imaging capability for neurovascular applications has put an ever increasing demand on x‐ray detector technology. Present state‐of‐the‐art detectors such as flat panels have limited resolution and noise performance. A linear cascade model analysis was used to estimate the theoretical performance for a proposed CMOS‐based detector. Methods: The proposed CMOS‐based detector was assumed to have a 300‐micron thick HL type CsI phosphor, 35‐micron pixels, a variable gain light image intensifier (LU), and 400 electron readout noise. The proposed detector has a CMOS sensor coupled to an LII which views the output of the CsI phosphor. For the analysis the whole imaging chain was divided into individual stages characterized by one of the basic processes (stochastic/deterministic blurring, binomial selection, quantum gain, additive noise). Standard linear cascade modeling was used for the propagation of signal and noise through the stages and an RQA5 spectrum was assumed. The gain, blurring or transmission of different stages was either measured or taken from manufacturer's specifications. The theoretically calculated MTF and DQE for the proposed detector were compared with a high‐resolution, high‐sensitive Micro‐Angio Fluoroscope (MAF), predecessor of the proposed detector. Results: Signal and noise for each of the 19 stages in the complete imaging chain were calculated and showed improved performance. For example, at 5 cycles/mm the MTF and DQE were 0.08 and 0.28, respectively, for the CMOS detector compared to 0.05 and 0.07 for the MAF detector. Conclusions: The proposed detector will have improved MTF and DQE and slimmer physical dimension due to the elimination of the large fiber‐optic taper used in the MAF. Once operational, the proposed CMOS detector will serve as a further improvement over standard flat panel detectors compared to the MAF which is already receiving a very positive reception by neuro‐vascular interventionalists. (Support:NIH‐Grant R01EB002873) NIH Grants R01‐ EB008425, R01‐EB002873 and an equipment grant from Toshiba Medical Systems Corp.
SU‐E‐I‐29: Dose Rate and Image Quality Comparison Between Philips Veradius and GE OEC 9900 Elite Fluoroscopic C‐Arms
Authors: Springer A , Solem E , Kobistek R
Published: June 2012

Purpose: The radiation dose rate and image quality were compared on GE OEC 9900 Elite Vas 8 and Philips Veradius fluoroscopic C‐arms. Methods: Plastic (PMMA) phantoms were used to simulate various thicknesses of soft tissues encountered during fluoroscopically‐guided interventional procedures while aluminum and copper phantoms were used to simulate extremities of different sizes. An image quality test tool and an ionization chamber were included in the setup of each phantom. The phantoms were imaged in several fluoroscopy modes and at different dose levels. The entrance surface air KERMA rate (ESAKR) was measured for each phantom in each fluoroscopy mode. Simultaneously, the image quality was assessed by counting the number of low‐contrast objects visible in the image quality test tool. For a given phantom type and thickness, the ESAKR was plotted versus the number of visible low‐contrast objects to compare the dose rate required for a given level of image quality. Additionally, the mean ESAKR per number of objects was calculated and p‐values were used to test for statistically significant differences between the C‐arms. Results: For comparable image quality with a given phantom type and thickness the ESAKR with the OEC was typically much higher than with the Veradius. One‐tailed, unpaired t‐tests confirm that the mean ESAKR per number of visible low‐contrast objects was lower for the Veradius than for the OEC with all thicknesses of PMMA (p < 0.05). The differences for the aluminum and copper phantoms were much smaller and were not statistically significant (p‐values ranged from 0.2 to 0.47). Conclusion: In general, the Veradius C‐arm provided better low‐contrast image quality during fluoroscopy, with lower ESAKR than the OEC 9900 Elite Vas 8. The differences were statistically significant only with PMMA phantoms. Funding support provided by Philips Healthcare (Bothell, WA).
SU‐E‐I‐38: Optimizing CT Slice Width Measurements
Authors: Marteinsdóttir M , Olafsdottir H , Fredriksson J , Andresson A , Healy A , Kristbjornsson A , Kristinsson S , Levy J , Goodenough D
Published: June 2012

Purpose: For almost four decades bead and wire ramps have been used in the evaluation of slice width as part of QA testing for CT scanners. While each of these approaches have been recognized and accepted as reliable, in this paper we investigate the differences, advantages and limitations of these tools. Moreover, we study the effect of varying the field of view (FOV) and focal spot size. Methods: The Catphan® 700 phantom includes two pairs of bead ramps (coarse and fine) and a pair of wire ramps in the same module providing an ideal setting for comparing bead ramps and wire ramps. The phantom was scanned using three devices from two different manufacturers. The data set consisted of 428 slices of 0.5,1,2,4,8 and 10 mm thickness. For the study of FOV and focal spot, 512 slices from the Catphan® 600 were acquired. All images were analyzed using Image Owl Catphan® QA software. Results: For 0.5mm slices, bead ramps gave more accurate and precise (lower variance) estimation of the thickness than wire ramps. For 2–4 mm slices, the two approaches performed on equal terms while for the thickest slices (8 and 10mm), the wires gave more precise results. For thin slices, a small FOV (100mm) gave better results and lower spread than a large FOV (240mm). Finally, a small focal spot gave significantly better results than a large one using wire ramps for 0.5 and 1mm slices. Conclusions: For measuring thin slices, the use of bead ramps, with adequately small FOV and a small focal spot should be advised. For measuring thick slices, wire ramps will give less variability although bead ramps give equally accurate results on average. Funding provided by The Phantom Laboratory, Incorporated and Image Owl, Incorporated
SU‐E‐I‐41: Characterization of a Linear Fiber‐Optic Coupled Dosimeter
Authors: Hoerner M , Hintenlang D
Published: June 2012

Purpose: This study investigated the dosimetry performance of a linear fiber‐optic coupled dosimeter with a sensitive element varying from 3 to 15 cm in length. The dosimeter is comprised of a tissue equivalent plastic scintillating fiber coupled to a photomultiplier tube (PMT). The sensitive element has a length representative of the dimensions of common adult internal organs and measures the absorbed dose along the entire sensitive length. The measurement of absorbed dose in one dimensional space provides a more meaningful measure of the average organ dose compared to current dosimeters which evaluate the dose at a small volume, or point inside the organ. Method and Materials: A fiber‐optic coupled dosimetry system was modified by increasing the linear dimension of the sensitive element to sizes ranging from 3 to 15 cm. A FOC element providing a variable output as a function of exposed dosimeter length, beam energy, depth, and beam intensity, was characterized for various exposure parameters relating to Computed Tomography. A clinical x‐ray tube, with half‐value layer of 5.60 mm Al at 120 kVp, was used to evaluate the dosimeter response to beam energy, intensity, beam quality, and exposed length. Results: The system consistently demonstrated linearity with tube output and length of the sensitive element and offering excellent sensitivity and reproducibility. The dosimeter also demonstrated a linear response of detected counts to length of scintillation material in the x‐ray field over the range of interest. The sensitivity with respect to energy and depth showed a positive linear dependence. An 8% variation in sensitivity across a 12 cm depth was observed within a soft tissue‐equivalent medium. Conclusion: The system allows for rapid and accurate average organ dose measurements relevant to x‐ray sources within the diagnostic energy range. The response to previously discussed parameters was independent of the sensitive element length.
SU‐E‐I‐45: Measurement of CT Dose to An HDPE Phantom Using Calorimetry: A Feasibility Study
Authors: Chen‐Mayer H , Tosh R , Bateman F , Zimmerman B
Published: June 2012

Purpose: Radiation dose in CT is traditionally evaluated using an ionization chamber calibrated in terms of air kerma in a phantom of specific dimensions. The radiation absorbed dose, J/kg, can also be realized directly by measuring the temperature rise in the medium. We investigate using this primary method to determine the CT dose at a point (a few mm), using the recently proposed (APMM TG220) high density polyethylene (HDPE) phantom as a medium. Methods: The calorimeter detection scheme is adapted from the second generation NIST water calorimeter using sensitive thermistors in a Wheatstone bridge powered by a lock‐in amplifier. The temperature sensitivity is about 3 microK. The expected temperature rise in PE is about 0.6 mK per Gy. The thermistor sensors were placed inside a 26 cm dia. × 10 cm HDPE phantom. Two preliminary tests were made: at a linear accelerator with a 6 MV photon beam, and at a 16‐slice CT scanner with a 120 kV beam, each with the thermal sensor and with a calibrated ionization chamber. Results: The 6 MV photon beam with 10 on/off cycles at 60 s each yielded the (uncorrected) run‐to‐run average dose of 3.06 Gy per cycle (sdm 0.3%), about 8% higher than the Result from the ionization chamber (calibrated in terms of absorbed to water). The CT measurements were also made in the middle section of the TG200 30 cm phantom. Twenty consecutive axial scans at 250 mA, which delivers a nominal accumulated dose (CTDIvol) of 705 mGy in 50 s at three axial and three radial locations were measured. The accumulated dose measured by the ionization chamber at the center of the smaller phantom was 347 mGy. Conclusions: The calorimeter data show qualitative tracking of the chamber measurements. Detailed thermal and electrical analysis of the system are planned to obtain quantitative results.
SU‐E‐I‐46: Quantitative Effects of Clinical Practice on the Efficiency of CT Tube Current Modulation for Radiation Dose Reduction
Authors: Zhang J , Cornett J
Published: June 2012

Purpose: CT tube current modulation (TCM) represents one of the most important and efficient methods for radiation dose reduction and has been well accepted. However, the possible influence of clinical practice is likely to be ignored although venders may provide clinical protocols and instructions. This study is designed to further investigate the quantitative effects of clinical operation, including radiograph direction and patient positioning, on the efficiency of TCM by measuring patient radiation dose and image quality. Methods: An anthromorphologic chest phantom was scanned in a Sensation 40 and a lightSpeed 16 CT scanner, respectively, using routine chest protocols with TCM. We first investigated the effects of radiograph direction. Anterior‐posterior (AP), lateral, and posterior‐anterior (PA) directions were chosen. CTDIvol and dose‐length‐product (DLP) were recorded for analyses. Our second experiment studied the influence of patient position. First the phantom was positioned at the iso‐center then scanned with AP direction. CTDIvols and DLPs were recorded as reference. Then the phantom was moved out of iso‐center, up or down 2 and 4 cm respectively then scanned. CTDIvols and DLPs were recorded for comparison. For each setting, image noise was measured. Results: CTDIvol increases approximately 20% for PA direction, compared to AP or lateral direction which generates similar CTDIvol and DLP with TCM. Image noise for the PA direction is less than those for the AP or lateral directions. CTDIvol increases approximately 9% for LightSpeed 16 and 13% for Sensation 40 when the phantom was moved up 4 cm, while CTDIvol decreases approximately 5% for LightSpeed 16 and 8% for Sensation 40 when the phantom was moved down 4 cm. Conclusions: Our quantitative study can direct clinical practice to improve the efficiency of CT tube current modulation and reduce patient radiation dose.
SU‐E‐I‐57: CT Dose Metrics: What Are We Tracking
Authors: Guild J , Arbique G , Blackburn T , Gallet J , Anderson J
Published: June 2012

Purpose: Recent guidance by The Joint Commission and CRCPD recommendations require establishing CT reference dose levels (RDLs) for clinical protocols and recording CT dose metrics in the patient's medical record. This presentation addresses which dose values in the CT report should be recorded for the purposes of monitoring patient dose and determining RDLs effectively. Methods: CT dose reports are commonly recorded in the PACS as screen captures, although structured reporting is becoming available on current CT scanners and PACS systems. The goal is to obtain data that correctly reflects the patient's dose, but the dose information captured is not standardized across vendors and can be difficult to compare. Multi‐phase studies, deviations from established protocols and dynamic scanning present problems when recording numbers to establish RDLs because of the lack of information on the anatomy scanned. The cumulative DLP and CTDIvol manually entered by radiologic technologists into the electronic medical record were compared with more detailed dose metrics compiled from PACS images. Results: Analysis of this data showed that simple cumulative metrics are a poor indicator of patient dose. Major problems are 1) the inclusion of dynamic scan doses associated with bolus tracking, which can skew protocol CTDIvol values by a factor of up to 20, and 2) add‐on scans of non‐overlapping anatomy which can inaccurately increase apparent patient dose. Conclusions: Recording CTDIvol to monitor patient doses is not straightforward, since details of the actual anatomy scanned are lacking without image‐based review. More granular dose reporting which identifies individual acquisitions is required; however, current RIS systems do not provide the flexibility necessary to capture all this information.
SU‐E‐I‐60: Validation of An Optically Stimulated Luminescent (OSL) Dosimeter for Use in Output Exposure Control Verification of Mammography Imaging Systems
Authors: Ranger R , Butler P , Yahnke C , Valentino D
Published: June 2012

Purpose: To develop and validate an Optically Stimulated Luminescent (OSL) dosimeter for exposure control verification of x‐ray projection mammography imaging systems. Methods: The active detection element of the dosimeter is a strip of OSL material 3.0 mm wide, 0.13 mm thick and 30.0 mm long with an overlying aluminum step wedge with thicknesses of 0, 0.2, 0.4 and 0.6 mm Al, encapsulated in a light‐tight plastic enclosure with outer dimensions of 10.0 mm wide, 5.4 mm thick, and 54.0 mm long. The dosimeter is used in conjunction with a breast phantom for the purpose of estimating the half‐value layer (HVL), entrance surface exposure (ESE), and average glandular dose (AGD) in conventional projection mammography. ESE and HVL were computed based on analysis of exposure profiles obtained from exposed strip dosimeters. The AGD was estimated by multiplying the ESE by the appropriate exposure to dose conversion factor for the thickness and % glandular tissue fraction represented by the phantom and target‐filter combination employed. The accuracy and reproducibility of the ESE, HVL and AGD estimates obtained using the dosimeter positioned on the surface of the ACR phantom at the chest wall edge, was evaluated using mammography systems utilizing different imaging receptor technology, i.e. screen‐film (SF), computed radiography (CR) and direct radiography (DR) and compared against results obtained using a calibrated ion chamber fitted with a mammography probe. Results: ESE, AGD and HVL results obtained using the OSL mammography QA dosimeter agreed with results obtained using an ion chamber to within 5–10%, depending on the target‐filter combination used. Repeat readings were highly consistent with a coefficient of variation = 5%. Conclusions: The OSL mammography QA dosimeter has been shown to effectively estimate ESE, HVL and AGD, demonstrating its usefulness for secondary monitoring of output exposure of mammography imaging systems.
SU‐E‐I‐69: Magnetic Resonance Metal Artifact Evaluation with Routine Clinical Cardiac Sequences
Authors: Joyner D , Rivard A , Craft D , Liu T , Callaway S , James J
Published: June 2012

Purpose: To examine schemes to grade the severity of metal susceptibility artifacts on image quality using cardiac MRI pulse sequences. Methods: A post‐thoracotomy patient was simulated with a stainless steel sternal wire (Syneture,MA; size=6, diameter=48mm), placed securely on an ACR MRI phantom. Phantom was scanned on a 1.5‐T Siemens using cardiac MRI sequences:1)TrueFISP, 2)Gradient‐Recalled‐Echo (GRE), 3)Turbo‐Spin‐ Echo (TSE), 4)Turbo‐Inversion‐Recovery‐Magnitude (TIRM), 5)Dark‐ blood‐IR‐FS (DBFS) with and without the wire (FOV=30×30cm, slice‐ thickness/slice‐gap=7.0/1.5mm, matrix size=192×192, slices=17). Image quality degradation was assessed in terms of signal loss and spatial deformation; signal loss by a) measuring the largest diameter of signal drop and b) number of slices with a signal drop and spatial deformation in VelocityAI (Atlanta,GA) by computing the rigid transformation indices between the phantom's internal grid with and without the metal. Results: Image quality was evaluated in terms of signal loss, spatial deformation and ring artifacts. Signal loss: TruFISP and GRE showed the largest signal drop diameter (13 and 16cm respectively). GRE sequence showed a signal drop in —12 slices where as signal drop occurred in only ∼4–5 slices with other sequences. Spatial deformation: GRE sequence showed the maximum with a ∼9mm grid deflection followed by TSE and DBFS (∼8mm). An average deflection of 5.4mm was observed on most of the sequences except T rueFISP and TIRM (Omm). Rigid body transformation showed a maximum x,y,z‐translation of −4.7, 0.3 and 1.69 mm and x,y,z‐angular rotation of 0.2, − 1.5 and 0.5° for GRE sequence followed by TSE and DBFS confirming the spatial distortion results. Concentric ring artifacts with signal loss were also observed on TrueFISP and DBFS images. Conclusions: Quantification of cardiac MR sequences to metal tolerance and the impact on image quality has shown that GRE and TrueFISP are the most metal‐susceptible and TIRM is the most metal‐tolerant sequence in terms of both signal loss and spatial deformation. This study helped in creating a separate cardiac metal protocol comprising of mainly metal‐tolerant sequences thus reducing scan time and patient discomfort.
SU‐E‐I‐73: Gray Matter Atrophy and White Matter Tract Abnormalities by Voxel Wise Correlation Analysis in Patients with Alzheimer's Disease
Authors: Juh R , Suh T , Kim S
Published: June 2012

Purpose: We evaluated the relationship between white matter (WM) tract disintegration and gray matter (GM) atrophy in patients with Alzheimer's disease (AD), mild cognitive impairment (MCI) and controls, using diffusion tensor imaging (DTI) and an optimized voxel‐based analysis. Methods: Two hundred thirty one individuals (61 controls, 116 MCI and 54 AD) were included. Voxel‐based WM tract statistics was used to obtain whole‐brain maps of WM bundles for FA. Voxel‐based morphometry (VBM) was conducted to detect regions of gray matter (GM) atrophy in the AD, MCI group relative to the control group. FA maps were processed to make voxel‐wise comparison of tract based analysis in whole brain between each the two groups. The relationship between locations of abnormalities in the WM and GM were examined. Results: Patients with AD showed significant GM atrophy in posterior cingulate gyrus (BA31, 32) to the precuneus, the middle temporal lobe (BA19), the superior frontal (BA9) to the anterior cingulate (BA 32), the medial frontal lobe (BA 11, BA25), the hippocampus, the parahippocampal gyrus (BA30/34) and the insula, and WM tract disintegrity of the uncinate fasciculus, posterior cingulate fasciculus and fornix compared with the control and MCI groups. These abnormalities in the AD group were caused by either structural changes in GM atrophy or neural dysfunction due to functional disconnections in the WM tract. Conclusions: The GM atrophy resulting from WM tract disintegration or GM atrophy itself may be the first step in the AD process, resulting in anatomically congruent correlations between WM disintegration and regional GM atrophy. Using tract based spatial statistics and voxel based analysis, both of which are useful in investigating GM and WM changes in individuals with neurodegenerative disorders.
SU‐E‐I‐80: Optimizing Scanning‐Beam Digital X‐Ray Tomosynthesis of the Lungs
Authors: Nelson G , Yoon S , Krishna G , Wilfley B , Fahrig R
Published: June 2012

Purpose: We propose to optimize the geometry of the Scanning‐Beam Digital Tomography system (SBDX) for application to lung tumor biopsies, thereby providing real‐time 3D tomographic reconstructions for target verification. The unique geometry of the system requires trade‐offs between patient dose, imaging field of view and tomosynthesis angle. Methods: We used PCXMC, a Monte Carlo simulation software package, to determine the dose to organs of interest as well as the Average body dose and Effective Dose (both ICRP 60 and 103) for source to detector distances (SDDs) between 90cm and 150cm. To facilitate modeling our system, a modified version of PCXMC was created. We also used matlab to evaluate the possible tomosynthetic angles that Result across the field of view for the same SDDs. Results: To maximize the tomosynthesis angle while leaving space for the patient, an SDD of between 90cm and 110cm is appropriate. At SDD 100cm, patient centered at 40 cm from the detector, operated in fluoro mode, the SBDX system delivers ∼0.38x the dose of a normal mobile fluoroscopy system operating at 30 fps. Because of the inverse geometry of the system, the dose to the patient goes up as the patient gets closer to the detector. Tomosynthetic angles up to 15 degrees over a 5‐cm field‐of‐view can be achieved for this geometry. The patient must be placed within 45cm of the detector in order to achieve the benefits from reduced SDD and increased tomosynthetic angle. Conclusions: The dose‐rate for our optimized geometry is acceptable, although higher dose rates for improved nodule visualization may be required. Additional dose optimization steps include modifying the scanning beam pattern to optimize for tomosynthetic image acquisition. Overall dose during the biopsy procedure will likely decrease since nodule targeting will be improved and the overall number of biopsies required will be reduced. This work has received funding from NIH grant R21 HL098683, as well as from the Lucas Foundation.