bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐16: Automated Liver Segmentation Method for CBCT Dataset by Probabilistic Atlas Construction
Authors: Li D , Li H , Yin Y , Chen J
Published: June 2012

Purpose: The aiming is getting accurate liver contour structures automatically for following adaptive radiation therapy in daily CBCT images which is very low‐contrast comparing the planning CT. Methods: Probabilistic atlas is constructed by 50 intravenous contrast planning CT images by iterative affine registration process. The incoming CBCT images are registered with the atlas using deformable registration algorithm which is based on edge preserving scale space, and the liver contour structures are generated automatically by using the deformation map. Incorporating the intensity distribution of candidate liver region into the segmentation processing, we can further remove the irrelative tissue from the original liver region. Our algorithm is capable of segmenting the liver from low‐contrast cone beam CT images. In our probabilistic atlas construction process, firstly one training data is arbitrarily chosen as reference image while the rest of training datasets are registered to this reference using the affine transformation. For improving the efficiency of our method, iterative construction method is employed. The resulting atlas which is gained before is used as the reference image for the following atlas construction. This process can be iterated by many loops. However, we used two iterations for efficiency. This iterative atlas construction process can avoid bias toward the specific patient. Results: The experiments are tested on 10 newly incoming patient data. The volumetric overlap is on an average 87%–94% comparing with manually segmented tumors by oncologists. After evaluation by clinical oncologists, they concluded that the segmentation results are close to the manual results and the liver contours on CBCT which is produced by the deformation field automatically can be used for following adaptive radiation therapy. Conclusions: We can conclude that the proposed segmentation method is very effective with low contrast CBCT for adaptive radiation therapy in daily using.
SU‐E‐I‐21: Effect of Different Fluorescent Lights with Various Colors of a Reading Room on Chromaticity of LCD
Authors: Yano Y , Akamine H , Awamoto S , Nakamura Y , Morishita J
Published: June 2012

Purpose: To examine variation of chromaticity of LCD in different types of fluorescent lights in a reading room. Methods: A color LCD (RX320, antiglare type, 450 cd/m2, three‐megapixel, Eizo Nanao), and a monochrome LCD (G31‐S, anti glare type, 450 cd/m2, three‐megapixel, Eizo Nanao) were used in this study. The chromaticity in grayscale images with eighteen luminance levels were measured under five types of fluorescent lights with different color spectrums (Daylight: 6,700 K, Natural white: 5,000 K, White: 4,200 K, Warm white: 3,500 K, Light bulb: 3,000 K) by using a colorimeter (CS‐200: KONICA MINOLTA). The chromaticity of LCDs was measured at various ambient lighting conditions (a dark room, 36, and 300 lux) and different types of fluorescent lights. Results: The chromaticity of LCDs measured under ambient lights was changed from that measured in a dark room. The chromaticity of LCDs varied with different types of fluorescent lights. As illuminance of the room increased, variations in chromaticity at relatively lower luminance levels increased. The direction of changes in chromaticity shifted to the color for each fluorescent light. Conclusions: Fluorescent lights having different color spectra affect the chromaticity of LCDs.
SU‐E‐I‐22: Metal Artifact Correction Using KV and Selective MV Imaging
Authors: Keil A , Zhu L , Star‐Lack J , Fahrig R
Published: June 2012

Purpose: To improve the image quality of radiotherapy planning CTs for patients with metal implants or fillings by completing the missing kV projection data with selectively acquired MV data that does not suffer from photon starvation. Using both imaging systems that are available on current radiotherapy devices, streaking artifacts are avoided and the soft tissue contrast is restored, even in areas where the kV photons do not contribute any information. This enables a better delineation of structures of interest in planning CT images for patients with metal objects. Methods: An algorithm for combining kV and MV projection data from the two on‐board imagers of a radiotherapy device is presented in this work. It only requires selective MV imaging with the high energy X‐rays being collimated onto the metal implants, ensuring that the patient dose does not increase significantly. The algorithm can cope with non‐identical geometries of the two imagers and is based on stitching together kV and MV sinograms by estimating a ratio between them. A numerical head phantom with two dental fillings and two soft tissue patterns was used to quantitatively evaluate the proposed hybrid reconstruction algorithm. A structural similarity index (SSIM) with respect to the ground truth data was computed for two ROIs. Realistic, polychromatic spectra were used for both imagers with 120 keV(p) and 6 MeV(p). The patient dose was limited to about 6 cGy for both acquisitions combined. Results: The reconstruction results yield visually as well as objectively better results (SSIM=74.8%) than a simple sinogram interpolation of the kV data (SSIM=69.7%) or a reconstruction from the original data (SSIM=17.9%). Conclusions: We have successfully implemented a new reconstruction method for hybrid kV‐MV cone beam CT reconstruction that enables a better planning of radiotherapy treatments for patients with metal implants without compromising their safety. This work was funded by NIH grant 1R01CA138426‐01A1.
SU‐E‐I‐23: Effective Estimation of Focal Spot Isocenter for Sinograms Obtained with Flying Focal Spot Scans for Filtered Back Projection
Authors: Yu Y , Whiting B , Politte D , Williamson J
Published: June 2012

Purpose: To validate the determination of parameters required to preprocess sinograms obtained by fan beam CT with flying focal spot (FFS) scans, such that a combined data set could be used with existing filtered back projection (FBP) reconstruction software based on single focal spot (SFS) geometry. Methods: The preprocessing step requires determination of the isocenter for each FFS in the target reconstruction geometry. A Philips Brilliance Big Bore CT was used to obtain FFS sinograms, which double samples the number of gantry positions relative to SFS sinograms, having the same number of detector measurements for each gantry position. Mass weighting of sinograms of a Teflon rod scan and curve fitting were used to determine isocenters for focal spots. FFS sinograms were reformatted before FBP such that each pair of adjacent gantry‐step measurements were combined by interleaving detector readings. The interleaved measurements were assigned to the average gantry angle. Image transition sharpness was compared for 33 images of the Teflon rod reconstructed with 1/8 focal spot deflection difference to test the isocenter Result. SFS and FFS Sinograms of a high‐ resolution bar pattern phantom were reconstructed by an in‐house reconstruction code package for resolution comparison. In‐house reconstructed images of the Teflon rod were compared with scanner images for verifying the effectiveness of this sinogram reformatting method. Results: Image profile was the sharpest when the Teflon rod sinogram was reconstructed with isocenter parameters found by the curve fitting experiment. It was comparable to the sharpness of scanner image profile when the in‐house image was reconstructed with resolution of 1.0mm FWHM. Conclusions: The good clinical resolution of images reconstructed with investigated FFS isocenters suggests that the experiment of estimating focal spot centers and reformatting sinograms is effective for utilizing reconstruction software that does not support FFS geometry. Supported by grant R01 CA149305 and a grant from Varian Medical Systems.
SU‐E‐I‐26: Estimation of Micro‐Angiographic Fluoroscope (MAF) Gain Settings for Digital Subtraction Angiography (DSA) Based on the Fluoroscopic Exposure
Authors: Ionita C , Loughran B , Nagesh S Setlur , Jain A , Bednarek D , Rudin S
Published: June 2012

Purpose: The MAF is a new high‐resolution detector which is being clinically evaluated in neuro‐vascular procedures. The detector contains a large‐dynamic‐range, high‐sensitivity light image intensifier with variable gain. Since the MAF is a research prototype only partially integrated with the clinical system, x‐ray technique parameters must be set manually. To improve workflow we developed an automatic method to estimate and set the proper LII voltage (MAF gain) for DSA acquisition based on the fluoroscopic parameters. Methods: The detector entrance exposure (XD) can be written as the x‐ray tube output exposure (Xo) times an object attenuation factor and an inverse‐square correction. If the object attenuation, scatter and distances are unchanged and the effect of x‐ray kVp changes are neglected, then the DSA XD can be expressed as the ratio of Xo(DSA)/Xo(Fluoroscopy) multiplied with XD(fluoroscopy). We measured Xo for fluoroscopy and DSA for mAs and kVp ranges appropriate to neuro‐ vascular interventions and fit the data with a 2D function. To estimate the XD(Fluoroscopy) we derived a curve of XD versus LII‐voltage for a mid‐ dynamic‐range average pixel gray‐level. Since the MAF system during clinical fluoroscopy automatically adjusts the LII voltage until the desired gray‐level value is achieved, by reading that voltage we can estimate the XD(Fluoroscopy). Using the 2D‐fit function, Xo(DSA) is automatically calculated for the kVp and mA values set and XD(DSA) can be estimated using the relation above. Using the inverse LII calibration curve, the proper LII‐voltage can be determined for the desired average gray‐level. Results: The algorithm was implemented and evaluated in thirty‐two in‐vivo DSA runs on rabbits. The proper LII voltage was selected in all cases with no failures. Conclusions: Using the fluoroscopic LII gain setting to determine the appropriate DSA setting can greatly improve the workflow in clinical evaluations of the MAF. NIH Grants R01‐EB008425, R01‐EB002873 and an equipment grant from Toshiba Medical Systems Corp
SU‐E‐I‐30: Impact of Physician Practice on Patient Radiation Dose during CT Guided Biopsy Procedures
Authors: Weir V , Zhang J , Bruner A
Published: June 2012

Purpose: The major concern with CT fluoroscopy is patient radiation dose, which is determined by applied technical parameters as well as practitioner/operator practice, e.g. habits and choice of dose saving features. This study is to investigate the effects of these intangible factors on patient doses. Methods: 381 patients underwent CT biopsy were retrospectively studied. Patient doses (dose length product, DLP) were analyzed and compared. Comparisons were made among physicians using only conventional intermittent shots, physicians using a low mA dose saving feature, and physicians using a combination of both. Linear regression analyses were performed to investigate any possible relationship between the variables and the patient dose. The Patient detriment index (PDI) was developed to set a threshold for the purpose of the Joint Commission sentinel dose events monitoring. An odds ratio was calculated to determine the odds of a group of patients receiving a dose above the median threshold when compared to another group. Results: The median DLP for all physicians was 1194 mGy‐cm. There is a significant difference (p<0.01) between the doses patients received (DLP=539.8 ±76 mGy‐cm) when physicians used dose saving feature vs. when the feature was not used (DLP=1269.7±659 mGy‐cm). In general, those physicians who used dose saving feature have a lower relative PDI (<1) compared to the PDIs (>1) without dose feature. This is not absolute since some physicians who did not use the dose saving feature have PDIs<l. An odds ratio estimate of 7.7 with a 95% confidence interval of 3.27 to 18.1 indicates that patient radiation dose strongly depends on the practitioner. Conclusions: Adjustments of practice habits, the use of CT dose saving features or both may be needed to improve patient care for CT fluoroscopy.
SU‐E‐I‐31: Evaluating Brain Imaging Material (BIM) as a Brain Tissue Surrogate for Use in Neuro‐Endovascular Imaged Guided Intervention (EIGI) Research
Authors: Loughran B , Ionita C , Bednarek D , Rudin S
Published: June 2012

Purpose: A brain tissue surrogate material was needed to fill the anatomical cavity of a skull to create a phantom for use in simulated Neuro‐EIGI procedures. To enable diagnostic and interventional procedure simulation, the BIM must fit into and be congruous with the interior surface of the skull, be reusable, and allow the implantation of vascular phantoms. The material must reasonably reproduce the automatic technique parameter selections observed during Neuro‐EIGI procedures. Methods: We formulated a putty‐ like material to be used as the BIM. Its x‐ray attenuation properties were evaluated by comparison of the fluoroscopic and radiographic technique parameters automatically selected for a BIM‐filled skull on a Toshiba Infinix angiographic C‐arm unit to those of a solid anthropomorphic head phantom at various projection angles. The same comparison was made between the skull phantom without BIM in the cavity and the anthropomorphic head phantom. The BIM linear attenuation coefficient was calculated and compared to that of PMMA, a common tissue analog plastic. Results: The BIM keeps its shape, is moldable and reusable, and is congruent to the skull's interior surfaces. It allows for insertion and interchange of various custom vascular phantoms at proper anatomic locations. Addition of the BIM to the skull cavity improves the matching of the automatically selected parameters to those of the anthropomorphic phantom by an average of 96.3% for mAs and by 4.2% for kVp in fluoroscopy mode and by 88.6% and 9.0%, respectively, in DSA mode. The BIM's experimental and theoretical linear attenuation coefficient for the RQA5 spectrum differed from PMMA's by about 30%. Conclusions: Despite the difference in attenuation coefficients between the PMMA and BIM, the BIM is a good surrogate material for Neuro‐EIGI research as shown by its properties of congruity, reusability, and device implantation, along with the demonstrated improvement of automatically selected technique parameters. Supported in part by: NIH Grants R01‐EB008425, R01‐EB002873, and an equipment grant from Toshiba Medical Systems Corp.
SU‐E‐I‐32: Sterile Radiation Reduction Gloves May Be Contraindicated in Fluoroscopically Guided Interventions
Authors: Pasciak A , Neveu M , Sriharan A , Balius A , Jones A
Published: June 2012

Purpose: Sterile radiation reduction gloves have been widely used in the past decade to provide modest decreases in operator hand dose when the hands are placed in the field of view (FOV). While multiple publications have quantified the potential dose reduction from the use of such gloves, possible effects on the patient have not yet been assessed. The aim of this study was to determine if radiation reduction gloves can Result in a significant increase in patient dose and increased risk of radiation induced skin injury when used in interventional radiology. Methods: The effect of radiation reduction gloves when used in the FOV was determined by measurement of patient entrance exposure rate (EER) for a variety of patient sizes and varying operating and magnification modes. EERs were measured with no glove in the FOV, with one glove and, to replicate the actions of many dose‐conscious radiologists, with double gloves in the FOV. Results: Compared to an ungloved hand, the use of a single radiation reduction glove near the center of the FOV results in a 2‐fold average increase in patient EER. The use of double radiation reduction gloves results in a 3‐fold average increase in EER. In both cases, this increase was only weakly dependent on the size of the patient and on the operating and magnification modes used. In fact, patient thicknesses ranging from 6–14 inches and operating modes ranging from low‐dose fluoroscopy to DSA produced less than a 20% deviation from the increases in EER quoted above. Conclusions: When used in the FOV, radiation reduction gloves can substantially increase patient EER. This increase in patient dose, when compared with the relatively small published reduction in extremity dose provided to the operator, may make their use contraindicated in cases where radiation induced skin injury is a possible risk.
SU‐E‐I‐35: Experience with Th Zero Gravity Suit
Authors: Pierno J , Hamilton C
Published: June 2012

Purpose: To compare the effectiveness of the Zero Gravity Suit (CFI Medical Solutions) in reducing the annual dose received by one physician in the Cardiac Catheterization Lab. Methods: A physician with a history of receiving high annual dose equivalents was purchased a Zero Gravity Suit. Film badges (Landauer) were worn at the collar and waist and monitored monthly. Previous dose history was acquired via the Landauer Exposure Report Archive. Annual values for Deep Dose Equivalent (DDE), Eye Dose Equivalent (LDE), and Shallow Dose Equivalent (SDE) were compared for the first full year of the Zero Gravity Suit (2011) to the previous four years (2007–2010). Readings for 2009 and 2007 were corrected for improper wear of the film badges. Results: The reduction in dose equivalent for DDE ranged from 70%–87%. The reduction in dose equivalent for LDE ranged from 16%–60%. The reduction in dose equivalent for SDE ranged from 16%–60%. Conclusions: : It was determined that the Zero Gravity Suit is effective at reducing the exposure of a physician with a history of high annual dose equivalents in our facilities Cardiac Catheterization Lab. While the suit did reduce the LDE and SDE it was more effective at reducing the DDE. During 2010 the suit was acquired midyear. The dose equivalent values would likely be similar to 2011 if the suit was introduced at the beginning of the year. In 2009 the physician was pregnant and attempting a reduced workload. The physician only uses the suit if a procedure is expected to take longer than fifteen minutes. The accuracy of the study is dependent upon the physician wearing the badges consistently and correctly and the physician using the Zero Gravity Suit consistently.
SU‐E‐I‐36: A Study to Compare Operator Dosimeter Exposure versus Fluoroscopic Time and Air Kerma in Fluoroscopically Guided Interventional Procedures
Authors: McKetty M
Published: June 2012

Purpose: The total effective dose equivalent limit for occupationally radiation exposed persons has remained at 50 millisieverts per year since the 1960s. There is ongoing discussion whether this limit should be lowered. Whether or not it is lowered, all facilities have to adhere to the principle of ALARA (as low as reasonably achievable). In a hospital environment, the workers who typically have exposures which Result in ALARA investigations having to be performed include interventional radiologists, cardiologists, and mobile C‐arm operators. At our institution there are a limited number of interventional radiologists with one person being responsible for performing the majority of the procedures and sometimes exceeding the ALARA investigational levels. Methods: A limited study was performed to compare the number, type of studies, cumulative air kerma, and fluoroscopic time versus the exposure measured by the personnel dosimeters worn by the radiologists. This was also related to the type of angiographic equipment in use. Results: The length of fluoroscopic time and cumulative air kerma and cumulative DAP appeared to be related to the higher exposures received by the operator. The number of procedures performed did not correlate with the personnel dosimeter exposure; rather it was the type and complexity of a study and the length of fluoroscopic time that was related. Conclusion: The number of ALARA investigations required has decreased gradually. This could be attributed to several factors. These include increased use of available safety items. With an increase in the number of interventionalists the work load is distributed more equitably. The purchase of new angiographic equipment has resulted in better image quality and more shielding options for the operators. The operators are periodically reminded to keep fluoroscopic time to a minimum and use appropriate settings on the equipment. The equipment is calibrated to provide adequate image quality at mid‐dose settings.
SU‐E‐I‐39: Intensive Monitoring of System Performance and Protocols on CT Systems
Authors: Weaver J , McNulty N , Tsapakos M
Published: June 2012

Purpose: The regulatory response to the recent CT overdoses is still in the process of being implemented. The more action taken before the regulations take effect reduces the exposure of the institution to medical and legal problems. Therefore, eighteen months ago we implemented an intensive QC program to ensure CT safety. The first component was to monitor the dose and SNR produced by a single CT examination weekly to identify changes. The second was to monitor changes in the protocols. Methods: We measured the CTDI and SNR for the routine head examination. We developed a script to identify and log changes in any of the 234 protocols. Results: Surprisingly, there were many changes to the protocols: on one unit 388 protocols were changed on 26 dates over the 18 month period. The reasons included: protocol optimization, scanner service, software reloads, mistakes, mistakenly loading the protocols from another section's scanner. The standard deviation of the CTDI was 2% to 3%. The dominant source of variation was probably positioning. The standard deviation of the SNR was 4% to 9%. The entire procedure requires 30min to 50min to test five CT scanners each week. Conclusions: The standard deviations of the CTDI values and of the SNR values are sufficiently small to allow anomalies to be identified using these relatively simple methods. Frequent protocol checking is an important component to any QC program.
SU‐E‐I‐40: Effective Dose Normalized to Dose Length Product for Pediatric and Adult Reference Phantoms in Computed Tomography Examinations
Authors: Lamart S , Kim K , Bolch W , Lee C
Published: June 2012

Purpose: To develop a set of conversion factors from dose length product (DLP) to effective dose (E) for pediatric and adult reference individuals undergoing computed tomography (CT) examinations. Methods: This study used 12 hybrid computational phantoms representing reference pediatric and adult individuals in compliance with the International Commission on Radiological Protection (ICRP) reference data. The phantoms were combined with a model of the Siemens Sensation 16 scanner, to compute organ doses from CT examinations using a radiation transport code, MCNPX2.7. Effective doses based on ICRP 60 and 103 tissue weighting factors were calculated. The DLP was derived from the scan length and Computed Tomography Dose Index (CTDI)vol. The resulting DLP‐to‐E conversion factors were analyzed. Results: The results consist in a set of DLP‐to‐E conversion factors for head, chest, abdomen, abdomen‐pelvis, and chest‐abdomen‐pelvis CT examinations for newborn, 1‐, 5‐, 10‐, 15‐year‐old and adult reference phantoms, for 80, 100 and 120 kVp and for ICRP 60 and 103 tissue weighting factors. The DLP‐to‐E factors decrease with smaller tube potential, with the greatest decrease for the head examinations for which values at 80 kVp are 20% smaller than at 120 kVp on average. The ICRP 103 weighting factors, compared to ICRP 60, Result in variations of DLP‐to‐E from 0.8 to 1.2‐fold with a systematic increase for the chest, 1.14‐ fold on average, due to the increased breast weighting factor. The DLP‐to‐E factors for the body examinations are relatively similar to each other but 5 to 12‐fold higher than for the head exam. The factors decrease with age until 15 years and then slightly increase for adult except for head. Conclusions: An updated set of DLP‐to‐E conversion factors were established based on more realistic human phantoms and provide an improved accuracy to obtain effective dose from DLP for patients undergoing CT examinations.
SU‐E‐I‐42: Measurement of X‐Ray Beam Width and Geometric Efficiency in MDCT Using Radiochromic Films
Authors: Liillau T , Liebmann M , von Boetticher H , Poppe B
Published: June 2012

Purpose: The purpose of this work was to measure the x‐ray beam width and geometric efficiency (GE) of a multi detector computed tomography scanner (MDCT) for different beam collimations using radiochromic films. In MDCT, the primary beam width extends the nominal beam collimation to irradiate the active detector elements uniformly (called ‘over‐beaming’) which contributes to increased radiation dose to the patient compared to single detector CT. Therefore, the precise determination of the primary beam width and GE is of value for any CT dose calculation using Monte Carlo or analytical methods. Methods: Single axial dose profiles free in air were measured for 6 different beam collimations nT for a Siemens SOMATOM Sensation 64 Scanner with Gafchromic XR‐QA2 films. The films were calibrated relative to the measured charge of a PTW semiflex ionization chamber (type: 31010) for a single rotation in the CT scanner at the largest available beam collimation of 28.8 mm. The beam energy for all measurements in this work was set to 120 kVp. For every measured dose profile and beam collimation the GEin‐air and the full‐width‐at‐half‐ maximum value (FWHM) as a value for the x‐ray beam width was determined. Over‐beaming factors FWHM / nT were calculated accordingly. Results: For MDCT beam collimations from 7.2 (12×0.6 mm) to 28.8 (24×1.2 mm) the geometric efficiency was between 58 and 85 %. The over‐ beaming factor ranged from 1.43 to 1.11. For beam collimations of 1×5 mm and 1×10 mm the GE was 77 % and 84 % respectively. The over‐beaming factors were close to 1, as expected. Conclusions: This work has shown that radiochromic films can be used for accurate x‐ray beam width and geometric efficiency measurements due to their high spatial resolution. The measured free‐in‐air geometric efficiency and the over‐beaming factor depend strongly on beam collimation.
SU‐E‐I‐44: The UF/NCI Family of Hybrid Computational Phantoms Representing the Current US Population of Male and Female Children and Adolescents Applications to CT Organ Dosimetry
Authors: Geyer A , O'Reilly S , Lee C , Long D , Bolch W
Published: June 2012

Purpose: To assist in the rapid reporting of patient organ doses, researchers at the University of Florida and the National Cancer Institute have developed a family of computational hybrid phantoms, constructed from NURBS and polygon mesh surfaces, that fully represent the ICRP 89 50th percentile reference newborn, 1‐year‐old, 5‐year‐old, 10‐year‐old, 15‐year‐ old male and female, and adult male and female. Coupled with Monte Carlo simulations, these phantoms can be used to estimate patient organ doses. Substantial increases seen in childhood obesity in the United States have prompted us to undergo a major revision to the UF/NCI phantom library. Methods: A decision was made to construct the new library in a gridded fashion by height/weight without further reference to age‐dependent weight/height percentiles. At each height/weight combination, secondary circumferential parameters are also defined and used for phantom construction. All morphometric data for the new library are taken from the CDC NHANES survey data over the time period 1999 to 2006, the most recent reported survey period. A subset of the phantom library was then used in a CT organ dose sensitivity study to examine the degree to which full Monte Carlo simulations would be required to track organ doses for patients that are severely underweight to obese in body size. Results: Using primary and secondary parameters, a grid containing 85 pediatric male height/weight bins and a grid containing 73 pediatric female height' weight bins were constructed. These grids will provide the blueprints for later constructing a comprehensive library of patient' dependent phantoms containing 158 pediatric phantoms. Conclusions: In the future, the UF/NCI phantom library will be used to construct pre‐computed dose libraries for individuals undergoing CT examinations. Ultimately, these libraries can be deployed in the clinic for electronic recording of patient organ dosimetry following diagnostic imaging procedures.
SU‐E‐I‐47: Comparison of Risks for Two Medical Imaging Procedures
Authors: Choudhury K Roy , Tian R , Li X , Samei E
Published: June 2012

Purpose: Radiologists may need to decide which type of image procedure is most appropriate for a particular patient. One factor relevant in making this decision is the relative risk of secondary cancers due to each relevant procedure. Differences in the risk posed by each method are not just due to the total radiation dose imparted by each procedure, but also the distribution of absorbed dose across various organs in the imaging procedure. Two imaging procedures with the same total radiation dose may pose different risks of differential sensitivity to radiation across organs. Methods: New methods of radiation dosimetry enable us to estimate the dose distribution across organs in individual patients. We propose a measure of the relative risk of two medical imaging procedures derived from the hazard function of cancer incidence. The relative risk measure is shown to approximately equal to a weighted sum of the dose difference in each organ. The weights are proportional to organ specific incidence rates. The measure is also sensitive to factors such as the patient's age at exposure to radiation, the attained age and gender, as well as the incidence characteristics of the population to which the patient belongs. We propose to quantify the effects of these factors using information from publically available SEER database for US based patients as well as the LSS study of atomic bomb survivors. The method is illustrated by application to a study comparing chest and abdominal CT scans for a group of pediatric patients. Results: Fig. 1 shows higher absolute relative risk for those exposed at younger ages, with chest scans being riskier for females while abdominal scans were riskier for males. At higher ages, the relative risk is approximately equal. Conclusions: Relative risks can quantify risks comparisons between imaging procedures.
SU‐E‐I‐49: Influence of Scanner Output Measurement Technique on KERMA Ratios in CT
Authors: Ogden K , Roskopf M , Scalzetti E
Published: June 2012

Purpose: KERMA ratios (RK) are defined as the ratio of KERMA measured at a specific phantom location (K) to in‐air isocenter CT scanner output (KCT). In this work we investigate the impact of measurement methodology on KCT values. Methods: OSL dosimeter chips were used to measure KCT for a GE VCT scanner (GE Medical Systems, Waukesha WI), using the 40 mm nominal beam width. Methods included a single point measurement at the center of the beam (1 tube rotation), and extended z‐axis measurements using multiple adjacent OSL's (7.5 cm extent), with single tube rotation, multiple contiguous axial scans, and helical scans (pitch of 1.375). Measurements were made in air and on the scan table at 80 and 120 kV. Results: Averaged single point measurements were consistent, with a mean coefficient of variation of 2.5%. For extended measurements with a single tube rotation, the mean value was equivalent to the single point measurements. For multiple contiguous axial scans, the in‐air KCT values were higher than the single rotation mean value and single point measurements by 13% and 10.3% at 120 and 80 kV, respectively, and for the on‐table measurements the values were 14.9% and 8.1% higher at 120 and 80 kV, respectively. The increase is due to beam overlap caused by z‐ axis over‐beaming. Extended measurements using helical scanning were equivalent to the multiple rotation axial measurements when corrected for the helical pitch. For all methodologies, the in‐air values exceeded the on‐ table measurements by an average of 23% and 19.4% at 80 and 120 kV, respectively. Conclusions: Scanner KCT values must be measured to allow organ dose estimation using published RK values. It is imperative that the KCT measurement methodology is the same as for the published values, or large errors may be introduced into the resulting organ dose estimates.
SU‐E‐I‐50: The ACR CT Dose Index Registry: Implementation Challenges and Preliminary Data
Authors: Kanal K , Zamora D , Price C , Robinson J , Shuman W
Published: June 2012

Purpose: To successfully register our institution into the American College of Ragiology (ACR) CT Dose Index Registry (DIR), to discuss the technical and implementation challenges of doing so, and to review preliminary results. Methods: TRIAD is the American College of Radiology Imaging Network's (ACRIN) image acquisition and management software, with the purpose of receiving and then transmitting DICOM structured dose report files from institutional CT scanners around the country. TRIAD was installed onto a virtual machine server at our institution so that anonymized and encrypted DICOM structured dose report files from our 6 CT scanners could be sent to the TRIAD Application Server at ACR. Doing so required collaboration between ACR and IT, PACS personnel and the physicist on site. Implementation involved several challenges, such as software installation and data transmission consistency problems. Since numerous institutions are involved, the ACR required an exam mapping process via the Radlex playbook to unify the protocol classification. These challenges have been overcome and data is being successfully transmitted to and analyzed by the ACR. Results: The first report comparing dose data (CTDI and DLP by examination and by scan) between our site and others around the region and country was made available recently. For each exam, the report includes boxplots and histogram data for a variety of standard protocols. For example, for a CT head exam, our median CTDIvol and DLP were 44 mGy and 736 mGy‐cm compared with 64 mGy and 844 mGy‐cm respectively, for all other facilities registered in the DIR. Conclusions: The ACR CT DIR registry is a useful tool for dose data mining and will eventually establish national benchmarks for CT dose indices. Our experience will allow others to anticipate these challenges and have potential solutions available for when they do arise.
SU‐E‐I‐52: Noise Level and Contrast Dependent Behavior of MTF in Iterative Reconstruction CT Imaging
Authors: Jin H , Kim J
Published: June 2012

Purpose: Iterative reconstruction (IR) technique is growingly used in clinical CT imaging due to its ability to provide improved image quality at lower patient doses. However, the nonlinear frequency response of IR technique, which may affect quantitative analysis, is rarely explored. This study evaluates noise level and contrast dependent behavior of MTF in IR CT imaging with a multi‐contrast slit phantom scanned at different dose levels. Methods: A multi‐contrast slit phantom was created consisting of acrylic panel and aluminum foils of different thickness. Images were acquired on multi‐detector CT (Discovery CT750 HD: GE) at two dose levels (10mAs and 200mAs), and were reconstructed using FBP and two IR technique (ASIR50 and VEO). Line spread functions were extracted across slits of two different thickness (80um and 144um) on images scanned at two dose levels, and were Fourier transformed to evaluate the MTFs of IR and FBP reconstruction techniques, producing a total of 12 MTF curves. Results: MTF of 200mAs scan showed clearly higher responses up to 28% than that of 100mAs scan in VEO, marginally higher values up to 5% in ASIR50, and were in good agreement in FBP. At same dose level, the MTFs with higher contrast slit (144um) showed marginally higher response than that of lower contrast slit (80um) in VEO and ASIR50. Conclusions: Our study revealed that MTF of IR technique degrades depending on noise level at low dose scan. Therefore, we recommend that its characteristic should be considered in quantitative analysis such as lesion size measurement.
SU‐E‐I‐58: Objective Models of Breast Shape Undergoing Mammography and Tomosynthesis Using Principal Component Analysis
Authors: Feng SSJ , Sechopoulos I
Published: June 2012

Purpose: To develop an objective model of the shape of the compressed breast undergoing mammographic or tomosynthesis acquisition. Methods: Automated thresholding and edge detection was performed on 984 anonymized digital mammograms (492 craniocaudal (CC) view mammograms and 492 medial lateral oblique (MLO) view mammograms), to extract the edge of each breast. Principal Component Analysis (PCA) was performed on these edge vectors to identify a limited set of parameters and eigenvectors that. These parameters and eigenvectors comprise a model that can be used to describe the breast shapes present in acquired mammograms and to generate realistic models of breasts undergoing acquisition. Sample breast shapes were then generated from this model and evaluated. The mammograms in the database were previously acquired for a separate study and authorized for use in further research. Results: The PCA successfully identified two principal components and their corresponding eigenvectors, forming the basis for the breast shape model. The simulated breast shapes generated from the model are reasonable approximations of clinically acquired mammograms. Conclusions: Using PCA, we have obtained models of the compressed breast undergoing mammographic or tomosynthesis acquisition based on objective analysis of a large image database. Up to now, the breast in the CC view has been approximated as a semi‐circular tube, while there has been no objectively‐obtained model for the MLO view breast shape. Such models can be used for various breast imaging research applications, such as x‐ray scatter estimation and correction, dosimetry estimates, and computer‐aided detection and diagnosis.
SU‐E‐I‐59: Investigation of the Usefulness of a Standard Deviation and Mammary Gland Density as Indexes for Mammogram Classification
Authors: Takarabe S , Yabuuchi H , Morishita J
Published: June 2012

Purpose: To investigate the usefulness of the standard deviation of pixel values in a whole mammary glands region and the percentage of a high‐ density mammary glands region to a whole mammary glands region as features for classification of mammograms into four categories based on the ACR BI‐RADS breast composition. Methods: We used 36 digital mediolateral oblique view mammograms (18 patients) approved by our IRB. These images were classified into the four categories of breast compositions by an experienced breast radiologist and the results of the classification were regarded as a gold standard. First, a whole mammary region in a breast was divided into two regions such as a high‐density mammary glands region and a low/iso‐density mammary glands region by using a threshold value that was obtained from the pixel values corresponding to a pectoral muscle region. Then the percentage of a high‐density mammary glands region to a whole mammary glands region was calculated. In addition, as a new method, the standard deviation of pixel values in a whole mammary glands region was calculated as an index based on the intermingling of mammary glands and fats. Finally, all mammograms were classified by using the combination of the percentage of a high‐density mammary glands region and the standard deviation of each image. Results: The agreement rates of the classification between our proposed method and gold standard was 86% (31/36). This result signified that our method has the potential to classify mammograms. Conclusions: The combination of the standard deviation of pixel values in a whole mammary glands region and the percentage of a high‐density mammary glands region to a whole mammary glands region was available as features to classify mammograms based on the ACR BI‐ RADS breast composition.
SU‐E‐I‐62: Investigation of Dominant Factors Affecting Fatigue in Image Reading of Radiologists
Authors: Ikushima Y , Yabuuchi H , Honda H , Morishita J
Published: June 2012

Purpose: To investigate dominant factors affecting fatigue in image reading of radiologists. Methods: Two kinds of fatigue were assessed in this study. One was fatigue in the central nervous system evaluated by the critical fusion frequency (CFF). The other was eye fatigue evaluated by a score determined from a questionnaire based on the oculomotor strain subscale from the Simulator Sickness Questionnaire (SSQ). When fatigue increases, the CFF and the SSQ score indicate low and high values, respectively. The fatigue of seventeen radiologists was assessed before and after their daily image reading. The reading times and the numbers of images were different among the assessments, and ranged about 1.5 – 5.0 hours and 1,000 – 12,000 images, respectively. The assessments of fatigue were repeated four times for each radiologist on different days. Finally, the measurements of the two kinds of fatigue were analyzed in terms of years of experience, age, sleeping time the previous night, ambient light conditions, reading time, and the numbers of interpreted images, series, and cases. Results: The CFF and SSQ score after image reading were significantly lower and higher than those measured before image reading, respectively. Younger and less experienced radiologists indicated a higher level of fatigue than older and more experienced radiologists in both the CFF and the SSQ score. When radiologists interpreted clinical images for longer hours, the SSQ score tended to be higher. On the other hand, there was little incremental difference in the CFF among different lengths of reading time. No obvious differences were observed in the other items. Conclusions: Less experience with reading images, a younger age, and a longer reading time could be dominant factors affecting fatigue in image reading.
SU‐E‐I‐65: Magnetic Resonance Spectroscopy of the Prostate: A Phantom Study of Metabolite Concentrations
Authors: Hossain M , Richardson T , Buyyounouski M K , Schirmer T , Noeske R , Chen L , Ma C
Published: June 2012

Purpose: Magnetic Resonance Spectroscopy (MRS) of the prostate is not used in radiotherapy departments on a regular basis due to a number of issues. The indication and severity of prostate cancer is related to the presence of choline in the prostate, in particular, the ratio of choline (plus creatine) to citrate. In‐vivo data supports this theory only marginally but lacks strong correlation with biopsy data. The situation is further complicated by the lack of precise spatial information in biopsy, variation of magnetic susceptibility, and spatial dependence of MRS data on the distance from the endo‐rectal coil. The latter also cause low signal‐to‐noise ratio (SNR). We intend to understand how the level of metabolite concentrations and spatial dependences determine what is observed in MRS. Methods: A spherical phantom is filled with water solutions containing various amounts of metabolites. It is placed on top of an endo‐rectal coil with the balloon filled with per fluorocarbon. MRS data is acquired on a GE 1.5 T MR scanner. The metabolite values, their ratios etc as reported in GE software, FuncTool are studied as functions of metabolite concentrations in the phantom. Results: Analysis of the phantom data indicates that the metabolite ratio reported in FuncTool is approximately linearly correlated to the metabolite concentrations used in the phantom to a certain point and then saturates whereas the largest metabolite value is well correlated with its concentration in the phantom. All metabolite values become weaker and SNR lower as we move away from the coil. Conclusions: This work indicates the potential of using metabolite values directly provided their spatial dependences on the distance of the voxels from the endo‐rectal coil can be accommodated.
SU‐E‐I‐67: Multi‐Shot RESOLVE Compared to Single‐Shot EPI Diffusion‐ Weighted MR Imaging Acquisition Scheme
Authors: Tullos H , Dale B , Bidwell G , Perkins E , Raucher D , Khan M , James J
Published: June 2012

Purpose: The purpose of this project was to configure the parameters for optimal comparison of image quality differences between the prototype imaging technique, read‐out‐segmented EPI multi‐shot (RESOLVE) and the clinically used single‐shot EPI (SS‐EPI) MRI sequence for Diffusion Weighted Imaging (DWI) in a saline phantom, followed by a normal rat brain. Methods: Saline phantom (4.2 × 4.2 cm2) and a rat brain were imaged on the 1.5T ESPREE (Siemens, Germany) MRI magnet using a wrist coil. Both the SS‐EPI and RESOLVE DWI were optimized with equal imaging parameters such as slice thickness/slice gap = 3.0/0 mm, field of view = 210 mm, phase resolution = 100%, and diffusion b values = 0, 600 s/mm2 while other parameters were given similar settings such as the base resolution, which had to be interpolated for the SS‐EPI to 96i to match the RESOLVE as it was unable to be set at 192. Image quality was compared in terms of signal intensity, distortion, % ghosting and Apparent Diffusion Co‐efficient (ADC) measurements from each sequence. Results: A marked enhancement of overall image quality with superior detail was observed in each of the scans from the RESOLVE sequence when compared to the SS‐EPI. Comparing the efficiency of both sequences in terms of image quality, RESOLVE demonstrated a better stable image with minimal distortion and ghosting. The phantom dimensions obtained from RESOLVE images matched the actual dimensions perfectly. RESOLVE images had signal intensities significantly higher than (2.4×) the SS‐EPI images (p=0.0008) and ∼0.6 % times less ghosting compared to SS‐EPI (p=0.82) which also exhibited distortion with reduced phantom dimensions (4.05 × 3.28 cm) from original. The ADC values computed were almost identical to be (p=0.32) from SS‐EPI (2.21mm2/sec) and RESOLVE (2.19mm2/sec). Conclusions: The RESOLVE sequence has significantly superior image quality compared to SS‐EPI at 1.5 T with reasonable scan times. DWI with RESLOVE acquisition scheme can be highly beneficial in obtaining distortion free images in routine clinical studies to characterize tumors and other pathological mechanisms with much greater detail than the current clinically used SS‐EPI.
SU‐E‐I‐68: The Effect of Partially Parallel Imaging on SNR Across Scanning Platforms
Authors: Goerner F , Stafford R , Duong T , Clarke G
Published: June 2012

Purpose: Different manufacturers implement partially parallel imaging (PPI) with different proprietary reconstruction methods and algorithms. Additionally, signal to noise ratio (SNR) associated with PPI is highly dependent on coil design and conformation, as quantified by the g‐factor. This potentially leads to differences in SNR across coils and scanners. This study seeks to characterize the impact of PPI on SNR across four MRI platforms. Methods: Turbo spin echo (TSE) scans of a spherical phantom filled with an aqueous solution were acquired in a head coil on a 3T Siemens Tim Trio, 3T Philips Achieva, 1.5T Toshiba Vantage and 3T GE Signa Excite HD. Scans at each available integer R‐value and reconstruction method were taken on each scanner. SNR was measured in each image using the difference method. SNR was normalized to a maximum value of 1.0 for each reconstruction method. Linear regressions and percent change in SNR relative to R‐value were determined for each reconstruction method. Coefficient of variation (CV) was used to determine the relationship between PPI implementations. Results: Slopes of the linear regressions ranged from ×0.24 to ×0.27. Percent SNR on average was 67.3%±3.7%, 43.3%±2.9% and 27.4%±6.9% of the associated non‐PPI scan at R=2, 3 and 4 respectively. The range of percent SNR relative to non‐PPI scans was 62.1%–71.7%, 39.8%–46.8% and 20.7%–34.5% at R=2, 3 and 4 respectively. The CV was 7.75% at R=2, 16.05% at R=3 and 21.79% at R=4. Conclusions: Slopes of the linear regressions ranged from −0.24 to −0.27. Percent SNR on average was 67.3%±3.7%, 43.3%±2.9% and 27.4%±6.9% of the associated non‐PPI scan at R=2, 3 and 4 respectively. The range of percent SNR relative to non‐PPI scans was 62.1%–71.7%, 39.8%–46.8% and 20.7%–34.5% at R=2, 3 and 4 respectively. The CV was 7.75% at R=2, 16.05% at R=3 and 21.79% at R=4.