bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐I‐34: How Does Longitudinal Dose Profile Change with Tube Current Distribution in CT?
Authors: Li X , Yang K , Liu B 
Published: July 2016

Purpose:To investigate how longitudinal dose profile DL(z) in 30 cm‐diameter water cylinder change with tube current (mA) distribution and scan length.Methods:A constant and four variable mA distributions from two previous papers [Dixon et al., Med. Phys. 40, 111920 (14pp.) (2013); Zhang et al., Med. Phys. 41, 091911 (9pp.) (2014)] were adopted in three scan lengths of 10, 28.6, and 50 cm, and all mA distributions had the same average mA over scan ranges. Using the symmetry based dose calculation algorithms and the previously published CT dose equilibration data [Li et al., Med. Phys. 40, 031903 (10pp.) (2013); 41, 111910 (5pp.) (2014)], the authors calculated DL(z) on the phantom central and peripheral axes. Kolmogorov‐Smirnov (K‐S) test was used to compare the lineshapes of two arbitrary distributions.Results:In constant mA scans, DL(z) was “bell‐shaped”. In variable mA scans, DL(z) approximately followed the mA lineshape, and the K‐S distance generally changed with mA distribution. The distance decreased with scan length, and was larger on the central axis than on the peripheral axis. However, the opposite trends were found in the K‐S distance between the DL(z) distributions of constant and variable mA distributions.Conclusion:Radiation dose from TCM scan is best evaluated using the specific tube current distribution. A constant mA based evaluation may lead to inconsistent longitudinal dose profile with that of TCM scan. Their difference in lineshape is larger on the phantom peripheral axis than on the central axis and increases with scan length. This work confirms that radiation dose in CT depends on not only local mA but also the overall mA distribution and scan length. On the other hand, the concept of regional tube current may be useful when scan length is large, tube current peaks near scan range edge, or the target site is superficial.
SU‐F‐I‐36: In‐Utero Dose Measurements Within Postmortem Subjects for Estimating Fetal Doses in Pregnant Patients Examined with Pulmonary Embolism, Trauma, and Appendicitis CT
Authors: Lipnharski I , Quails N , Carranza C , Correa N , Bidari S , Bickelhaup M , Rill L , Arreola M 
Published: July 2016

Purpose:The imaging of pregnant patients is medically necessary in certain clinical situations. The purpose of this work was to directly measure uterine doses in a cadaver scanned with CT protocols commonly performed on pregnant patients in order to estimate fetal dose and assess potential risk.Method:One postmortem subject was scanned on a 320‐slice CT scanner with standard pulmonary embolism, trauma, and appendicitis protocols. All protocols were performed with the scan parameters and ranges currently used in clinical practice. Exams were performed both with and without iterative reconstruction to highlight the dose savings potential. Optically stimulated luminescent dosimeters (OSLDs) were inserted into the uterus in order to approximate fetal doses.Results:In the pulmonary embolism CT protocol, the uterus is outside of the primary beam, and the dose to the uterus was under 1 mGy. In the trauma and appendicitis protocols, the uterus is in the primary beam, the fetal dose estimates were 30.5 mGy for the trauma protocol, and 20.6 mGy for the appendicitis protocol. Iterative reconstruction reduced fetal doses by 30%, with uterine doses at 21.3 for the trauma and 14.3 mGy for the appendicitis protocol.Conclusion:Fetal doses were under 1 mGy when exposed to scatter radiation, and under 50 mGy when exposed to primary radiation with the trauma and appendicitis protocols. Consistent with the National Council on Radiation Protection & Measurements (NCRP) and the International Commission on Radiological Protection (ICRP), these doses exhibit a negligible risk to the fetus, with only a small increased risk of cancer. Still, CT scans are not recommended during pregnancy unless the benefits of the exam clearly outweigh the potential risk. Furthermore, when possible, pregnant patients should be examined on CT scanners equipped with iterative reconstruction in order to keep patient doses as low as reasonable achievable.
SU‐F‐I‐37: How Fat Distribution and Table Height Affect Estimates of Patient Size in CT Scanning: A Phantom Study
Authors: Silosky M , Marsh R 
Published: July 2016

Purpose:Localizer projection radiographs acquired prior to CT scans are used to estimate patient size, affecting the function of Automatic Tube Current Modulation (ATCM) and hence CTDIvol and SSDE. Due to geometric effects, the projected patient size varies with scanner table height and with the orientation of the localizer (AP versus PA). This study sought to determine if patient size estimates made from localizer scans is affected by variations in fat distribution, specifically when the widest part of the patient is not at the geometric center of the patient.Methods:Lipid gel bolus material was wrapped around an anthropomorphic phantom to simulate two different body mass distributions. The first represented a patient with fairly rigid fat and had a generally oval shape. The second was bell‐shaped, representing corpulent patients more susceptible to gravity's lustful tug. Each phantom configuration was imaged using an AP localizer and then a PA localizer. This was repeated at various scanner table heights. The width of the phantom was measured from the localizer and diagnostic images using in‐house software.Results:1) The projected phantom width varied up to 39% as table height changed.2) At some table heights, the width of the phantom, designed to represent larger patients, exceeded the localizer field of view, resulting in an underestimation of the phantom width.3) The oval‐shaped phantom approached a normalized phantom width of 1 at a table height several centimeters lower (AP localizer) or higher (PA localizer) than did the bell‐shaped phantom.Conclusion:Accurate estimation of patient size from localizer scans is dependent on patient positioning with respect to scanner isocenter and is limited in large patients. Further, patient size is more accurately measured on projection images if the widest part of the patient, rather than the geometric center of the patient, is positioned at scanner isocenter.
SU‐F‐I‐38: Patient Organ Specific Dose Assessment in Coronary CT Angiograph Using Voxellaized Volume Dose Index in Monte Carlo Simulation
Authors: Fallal Mohammadi Gh. , Riyahi Alam N. , Graily Gh. , Paydar R. 
Published: July 2016

Purpose:Clinical use of multi detector computed tomography(MDCT) in diagnosis of diseases due to high speed in data acquisition and high spatial resolution is significantly increased. Regarding to the high radiation dose in CT and necessity of patient specific radiation risk assessment, the adoption of new method in the calculation of organ dose is completely required and necessary. In this study by introducing a conversion factor, patient organ dose in thorax region based on CT image data using MC system was calculated.Methods:The geometry of x‐ray tube, inherent filter, bow tie filter and collimator were designed using EGSnrc/BEAMnrc MC‐system component modules according to GE‐Light‐speed 64‐slices CT‐scanner geometry. CT‐scan image of patient thorax as a specific phantom was voxellised with 6.25mm3 in voxel and 64×64×20 matrix size. Dose to thorax organ include esophagus, lung, heart, breast, ribs, muscle, spine, spinal cord with imaging technical condition of prospectively‐gated‐coronary CT‐Angiography(PGT) as a step and shoot method, were calculated. Irradiation of patient specific phantom was performed using a dedicated MC‐code as DOSXYZnrc with PGT‐irradiation model. The ratio of organ dose value calculated in MC‐method to the volume CT dose index(CTDIvol) reported by CT‐scanner machine according to PGT radiation technique has been introduced as conversion factor.Results:In PGT method, CTDIvol was 10.6mGy and Organ Dose/CTDIvol conversion factor for esophagus, lung, heart, breast, ribs, muscle, spine and spinal cord were obtained as; 0.96, 1.46, 1.2, 3.28. 6.68. 1.35, 3.41 and 0.93 respectively.Conclusion:The results showed while, underestimation of patient dose was found in dose calculation based on CTDIvol, also dose to breast is higher than the other studies. Therefore, the method in this study can be used to provide the actual patient organ dose in CT imaging based on CTDIvol in order to calculation of real effective dose(ED) based on organ dose.This work has been supported by the research chancellor of tehran university of medical sciences(tums), school of medicine, Tehran, Iran
SU‐F‐I‐39: In Search of Infinity: Finding the Limiting Dose for An Infinite CT Scan On a Cylinder of Finite Length
Authors: Bakalyar D 
Published: July 2016

Purpose:The ICRU/TG200 phantom is a cylinder of polyethylene, 30 cm in diameter and 60 cm long. The dose h(L) in the central plane of the phantom resulting from a scan of length L increases asymptotically with increasing L to a limiting value Deq. However, even after scanning the entire length of this phantom, it is clear that the resultant dose h(60 cm) is still somewhat below the limiting value. The known behavior of h(L) provides a means for estimating the true limit.Methods:h(L) approaches its limiting but unknown value Deq exponentially. By estimating Deq as Deq* and plotting Deq* − h(L) as a function of L on a semi‐log scale, a straight line will result only if Deq* = Deq. If not, there will be significant curvature at the end of the plotted data. Adjusting Deq* by trial‐and‐error or by an iterative scheme will, if done correctly, accurately determine Deq.Results:The log of Deq* − h(L) was plotted as a function of L using Microsoft Excel. The coefficient of determination (R‐squared) was displayed and Deq* was adjusted until R‐squared equaled 1. Alternatively, iteration using the Solver tool in Excel can automatically find the best estimate of Deq. The resultant values for Deq was were an increase of around 1.5% above h(60 cm) for the center and 0.8% at the periphery.Conclusion:The experiments show that a 60 cm phantom is long enough for the central dose to be within a couple of percentage points of what would be achieved with an infinite phantom. Though this small underestimation of Deq is of little consequence for dose estimates, an accurate determination of Deq allows for a better parameterization of continuous functions representing h(L).
SU‐F‐I‐40: Impact of Scan Length On Patient Dose in Abdomen/pelvis CT Diagnosis
Authors: Park I , Song J , Kim K 
Published: July 2016

Purpose:To analysis the impact of scan length on patient doses in abdomen/pelvis CT diagnosis of each hospital.Methods:Scan length of 7 hospitals from abdomen/pelvis CT diagnosis was surveyed in Korea. Surveyed scan lengths were additional distance above diaphragm and distance below pubic symphysis except for standard scan range between diaphragm and pubic symphysis. Patient dose was estimated for adult male and female according to scan length of each hospital. CT‐Expo was used to estimate the patient dose under identical equipment settings (120 kVp, 100 mAs, 10 mm collimation width, etc.) except scan length. Effective dose was calculated by using tissue weighting factor of ICRP 103 recommendation. Increase rate of effective dose was calculated comparing with effective dose of standard scan rangeResults:Scan lengths of abdomen/pelvis CT diagnosis of each hospital were different. Also effective dose was increased with increasing the scan length. Generally increasing the distance above diaphragm caused increase of effective dose of male and female, but increasing the distance below pubic symphysis caused increase of effective dose of male.Conclusion:We estimated the patient dose according to scan length of each hospital in abdomen/pelvis CT diagnosis. Effective dose was increased by increasing the scan length because dose of organs with high tissue weighting factor such as lung, breast, testis were increased. Scan length is important factor on patient dose in CT diagnosis. If radiologic technologist interested in patient dose, decreasing the unnecessary scan length will decrease the risk of patients from radiation.This research was supported by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number: HI13C0004).
SU‐F‐I‐42: Evaluation of Multiple Atlas Segmentation Methods for the Abdomen
Authors: Pirozzi S , Nelson A 
Published: July 2016

Purpose:Atlas segmentation has the potential to provide time savings for contour generation in various treatment sites. Previously we evaluated the optimal number of atlas matches for head and neck, lung, liver, and prostate cancer. Our goal in the current work is to find the optimal number of atlas matches and method for combining atlas contours for an abdominal CT atlas.Methods:An abdominal CT atlas containing 37 subjects was utilized for atlas segmentation and was evaluated using a leave‐one‐out methodology. Each atlas subject contained manually defined contours of the aorta, left and right kidneys, large bowel, liver, spinal cord, stomach, and vertebral body. The one, three, four, five, and seven best matches from the atlas were automatically found for each subject and were deformed to the test subject. The contours were combined for each multi‐atlas method using Majority Vote (MV) and STAPLE. The average Dice Similarity Index was calculated for each method compared to manual contours.Results:Majority vote with five (MV‐5) and seven matches (MV‐7) had the highest dice for 6 out of the 8 structures including the aorta (0.75), left kidney (0.80), right kidney (0.83 and 0.84), liver (0.91), spinal cord (0.78), and vertebral body (0.71 and 0.72). For the large bowel, STAPLE‐5 and MV‐4 had the highest dice score (0.38 and 0.37), while MV4 provided the highest dice (0.65) for the stomach. The best method was statistically significant over the next best method for the aorta, left and right kidneys, liver, large bowel, and stomach with p‐values ranging from 0.0002 – 0.05.Conclusion:Atlas‐based segmentation using MV‐5 and MV‐7 provided the most accurate contours for the majority of structures, with only STAPLE‐5 and MV‐4 being more accurate for the large bowel and MV‐4 being more accurate for the stomach.Aaron Nelson is a part owner and employee of MIM Software Inc. Sara Pirozzi is an employee of MIM Software Inc.
SU‐F‐I‐43: A Software‐Based Statistical Method to Compute Low Contrast Detectability in Computed Tomography Images
Authors: Chacko M , Aldoohan S 
Published: July 2016

Purpose:The low contrast detectability (LCD) of a CT scanner is its ability to detect and display faint lesions. The current approach to quantify LCD is achieved using vendor‐specific methods and phantoms, typically by subjectively observing the smallest size object at a contrast level above phantom background. However, this approach does not yield clinically applicable values for LCD. The current study proposes a statistical LCD metric using software tools to not only to assess scanner performance, but also to quantify the key factors affecting LCD. This approach was developed using uniform QC phantoms, and its applicability was then extended under simulated clinical conditions.Methods:MATLAB software was developed to compute LCD using a uniform image of a QC phantom. For a given virtual object size, the software randomly samples the image within a selected area, and uses statistical analysis based on Student's t‐distribution to compute the LCD as the minimal Hounsfield Unit's that can be distinguished from the background at the 95% confidence level. Its validity was assessed by comparison with the behavior of a known QC phantom under various scan protocols and a tissue‐mimicking phantom. The contributions of beam quality and scattered radiation upon the computed LCD were quantified by using various external beam‐hardening filters and phantom lengths.Results:As expected, the LCD was inversely related to object size under all scan conditions. The type of image reconstruction kernel filter and tissue/organ type strongly influenced the background noise characteristics and therefore, the computed LCD for the associated image.Conclusion:The proposed metric and its associated software tools are vendor‐independent and can be used to analyze any LCD scanner performance. Furthermore, the method employed can be used in conjunction with the relationships established in this study between LCD and tissue type to extend these concepts to patients’ clinical CT images.
SU‐F‐I‐44: Using the Air Signal to Characterize Image Noise in CT
Authors: Szczykutowicz T , Malkus A 
Published: July 2016

Purpose:With increasing emphasis on CT image quality and low dose, quality activities analyzing noise levels in images will need to be increasingly automated. This work describes a new automated method for characterizing noise in CT. To obviate the need to segment out anatomical structure, this work introduces the use of noise statistics of air to understand the noise in the scanned object.Methods:Scans of a uniform water phantom were acquired at four dose levels. Using a modified version of the global noise index, the image noise was calculated in both the air surrounding the phantom and in the phantom itself. The method involved subtracting adjacent image slices, breaking up the image into 7 mm square regions of interest (ROI), thresholding the ROIs by CT number to only include ROIs of air or water, and then taking the mean of the air or water ROIs’ standard deviation values. We refer to this metric as the meanGNI.Results:Not only does the meanGNI within the phantom decrease as dose increases, but also the meanGNI in the air exhibits the same behavior.Conclusion:The meanGNI in air is a useful proxy for meanGNI or GNI in the scanned object. Our air based method does not involve any edge detection or advanced signal processing. Therefore, no tuning of segmentation parameters is needed to be applicable to different types of anatomy (e.g. brain vs. lung).Research and equipment support provided by GE Healthcare.
SU‐F‐I‐53: Coded Aperture Coherent Scatter Spectral Imaging of the Breast: A Monte Carlo Evaluation of Absorbed Dose
Authors: Morris R , Lakshmanan M , Fong G , Kapadia A , Greenberg J 
Published: July 2016

Purpose:Coherent scatter based imaging has shown improved contrast and molecular specificity over conventional digital mammography however the biological risks have not been quantified due to a lack of accurate information on absorbed dose. This study intends to characterize the dose distribution and average glandular dose from coded aperture coherent scatter spectral imaging of the breast. The dose deposited in the breast from this new diagnostic imaging modality has not yet been quantitatively evaluated. Here, various digitized anthropomorphic phantoms are tested in a Monte Carlo simulation to evaluate the absorbed dose distribution and average glandular dose using clinically feasible scan protocols.Methods:Geant4 Monte Carlo radiation transport simulation software is used to replicate the coded aperture coherent scatter spectral imaging system. Energy sensitive, photon counting detectors are used to characterize the x‐ray beam spectra for various imaging protocols. This input spectra is cross‐validated with the results from XSPECT, a commercially available application that yields x‐ray tube specific spectra for the operating parameters employed. XSPECT is also used to determine the appropriate number of photons emitted per mAs of tube current at a given kVp tube potential. With the implementation of the XCAT digital anthropomorphic breast phantom library, a variety of breast sizes with differing anatomical structure are evaluated. Simulations were performed with and without compression of the breast for dose comparison.Results:Through the Monte Carlo evaluation of a diverse population of breast types imaged under real‐world scan conditions, a clinically relevant average glandular dose for this new imaging modality is extrapolated.Conclusion:With access to the physical coherent scatter imaging system used in the simulation, the results of this Monte Carlo study may be used to directly influence the future development of the modality to keep breast dose to a minimum while still maintaining clinically viable image quality.
SU‐F‐I‐63: Relaxation Times of Lipid Resonances in NAFLD Animal Model Using Enhanced Curve Fitting
Authors: Song K‐H , Yoo C‐H , Lim S‐I , Choe B‐Y 
Published: July 2016

Purpose:The objective of this study is to evaluate the relaxation time of methylene resonance in comparison with other lipid resonances.Methods:The examinations were performed on a 3.0T MRI scanner using a four‐channel animal coil. Eight more Sprague‐Dawley rats in the same baseline weight range were housed with ad libitum access to water and a high‐fat (HF) diet (60% fat, 20% protein, and 20% carbohydrate). In order to avoid large blood vessels, a voxel (0.8×0.8×0.8 cm3) was placed in a homogeneous area of the liver parenchyma during free breathing. Lipid relaxations in NC and HF diet rats were estimated at a fixed repetition time (TR) of 6000 msec, and multi echo time (TEs) of 40–220 msec. All spectra for data measurement were processed using the Advanced Method for Accurate, Robust, and Efficient Spectral (AMARES) fitting algorithm of the Java‐based Magnetic Resonance User Interface (jMRUI) package.Results:The mean T2 relaxation time of the methylene resonance in normal‐chow diet was 37.1 msec (M0, 2.9±0.5), with a standard deviation of 4.3 msec. The mean T2 relaxation time of the methylene resonance was 31.4 msec (M0, 3.7±0.3), with a standard deviation of 1.8 msec. The T2 relaxation times of methylene protons were higher in normal‐chow diet rats than in HF rats (p<0.05), and the extrapolated M0 values were higher in HF rats than in NC rats (p<0.005). The excellent linear fit with R2>0.9971 and R2>0.9987 indicates T2 relaxation decay curves with mono‐exponential function.Conclusion:In in vivo, a sufficient spectral resolution and a sufficiently high signal‐to‐noise ratio (SNR) can be achieved, so that the data measured over short TE values can be extrapolated back to TE = 0 to produce better estimates of the relative weights of the spectral components. In the short term, treating the effective decay rate as exponential is an adequate approximation.