bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐01: Quantification of Vascular Networks with the Aid of OCT in Order to Evaluate Re‐Endothelialization after Peripheral Angioplasty
Authors: Kagadis GC , Tsantis S , Bourantas G , Katsanos K , Karnabatidis D , Mihailidis D , Nikiforidis G
Published: November 2011

Purpose: In vivo dynamic visualization, recognition and quantification of vascular networks represent a very interesting methodological requirement of peripheral angioplasty. Optical coherence tomography (OCT) is a catheter‐based imaging method that employs near‐infrared light to produce high‐resolution intravascular images. The purpose of the present study is the inner‐outer lumen contours extraction as well as strut detection, so as to evaluate the re‐endothelialization degree in stented arteries derived from OCT images. Methods: Inner and outer lumen contours represent the regions of interest on OCT cross‐sectional images, from which data clinicians can determine degree of restenosis. In order to recognize and segment these contours a specifically designed algorithm was implemented. The algorithm was based on unsupervised segmentation, utilizing the Markov Random Field model (MRF) and Continuous Wavelet Transform (CWT) analysis. In order to segment struts the scale‐space responses derived from wavelet local maxima of Laplacian‐of‐Gaussian (LOG) across consecutive scales have been employed into a Probabilistic Neural Networks (PNN) based classification scheme. Results: A full OCT (270 frames) study was utilized in the study, deriving a case study of 61 consecutive frames including struts. All input scale‐space responses were divided in two main categories: Class I (284 cases) corresponding to struts and Class II (3236 cases) to various responses from other structures existing within the image. 15 features were automatically calculated from each scale‐space response signals on both classes. The employed PNN classifier exhibited high discrimination accuracy between strut and other responses achieving an area under curve (AUC) value of 0.96. Conclusions: We have developed a promising new tool for inner, outer lumen contours as well as strut position detection in OCT data. Its main characteristics are robustness, fast and automatic execution that could be easily adapted to a user friendly interface.
SU‐E‐I‐10: Skin Dose in Routine CT Brain Perfusion Studies Using Siemens 64 Slice, Definition Dual Source, and Flash CT Scanners
Authors: Emerson S , Liang Y , Aurand D , Schultz C
Published: November 2011

Purpose: To determine and compare the entrance skin doses from the routine CT brain perfusion protocols on various Siemens CT scanners. Methods: Four Siemens CT scanners were surveyed using their brain perfusion protocol (see supporting document): two Sensation 64‐slice scanners (EC‐CT‐2 and IP‐CT‐2), one Definition Dual Source (64‐slice), and one Definition Flash (128‐slice). The skin dose was measured using a RANDO® anthropomorphic phantom and Landauer optically stimulated luminescent (OSL) nanoDot dosimeters. We performed the scan three times on each scanner with the OSL nanoDots on the surface of the head at the 0, 90, 180, and 270 degree positions. We then averaged the skin doses from the three scans at each of the four positions to calculate an average skin dose for each CT scanner and an average skin dose per scan, independent of position. Results: The mean skin doses obtained were 341.7 mGy ± 44.5 for the Definition Dual Source, 326.7 mGy ± 37.3 for EC‐CT‐2 (64 slice), 326.6 mGy ± 55.6 for IP‐CT‐2 (64 slice), and 435.6 mGy ± 29.7 mGy for the Flash CT. The skin doses of the two 64‐slice scanners and the Definition dual source CT were similar, as expected, since they employed the same beam width. The skin dose of the Flash CT was 32.8% higher, which as expected, since its beam width is ∼33% larger (38.4 mm for the Flash vs. 28.8 mm for the others). Conclusions: Based on the phantom study, the skin doses for routine CT brain perfusion protocols on the mentioned scanners are 325–435 mGy, which is far below the dose threshold for possible radiation induced skin damage (2000 mGy)
SU‐E‐I‐12: Clinical Verification of Low Dose Pediatric Abdominal CT Technique Chart
Authors: Dong F , Reid J , Davros W , Primak A
Published: November 2011

Purpose: For pediatric CT, optimizing scan technique with reduced dose is critical. A previous phantom study demonstrated that abdominal circumference (AC) can be used effectively in selection of the scan technique. The goal of this study is to clinically verify and fine‐tune the technique by using a noise “insertion” software. Methods: 24 pediatric patients covering wide range of ACs were scanned on a 64‐slice CT using the technique chart initially generated from a phantom study. These scans were then reconstructed off‐line using a software which “injects” noise into CT projection data to mimic different degree of dose reduction without rescanning the patient. The accuracy of this software was verified on a water phantom. The original images and those mimicking dose‐reduced scans were evaluated by a pediatric radiologist based on the vasculature details in liver, and conspicuity of low contrast lesions. Optimized technique chart for adequate diagnostic image quality and lowest possible dose was generated for the AC from 40cm to 120cm. Results: The fine‐tuned technique chart followed well with the phantom study. For AC from 40 to 50cm, 80kVp with 60 to 100mAs provided adequate diagnostic image quality; for AC from 51 to 70cm, using 100kVp and 40 to 80mAs; for AC from 71 to 100cm, 120kVp with 60 to110mAs provided balanced dose and image quality; for AC over 100cm, 140kVp may be used, with >= 70mAs. The difference of the CT noise generated by the software vs. from an actual water phantom scan was within +/− 5% Conclusions: AC‐based pediatric abdominal CT technique chart was verified and fine‐tuned on this clinical trial with help of the noise insertion software. Using AC‐based chart can avoid ambiguity in selection of optimized scan parameters and it is relatively easy to implement in clinical.
SU‐E‐I‐16: CBCT with Flexible Imaging Trajectories to Improve Image Quality and Longitudinal Coverage — Concept, Simulation and Digital Phantom Study
Authors: Yang D , Goddu S , Li H , Klein E , Thorstad W , Parikh P
Published: November 2011

Purpose: Cone beam CT (CBCT) image quality and volumetric coverage are very important for patient treatments. LINAC ‐mounted CBCT (Varian Trilogy) has limited 17 cm longitudinal coverage, not enough for many clinical sites including head‐neck. CBCT also suffers from poor image quality especially in the most superior and inferior slices. These problems hold back the usage of CBCT in many quantitative studies, including tumor response evaluation and daily dose computation. In this study, we evaluated a new idea of flexible X‐ray source trajectory CBCT to overcome these limitations. Methods: The core concept is to combine gantry rotation with simultaneous couch motion during CBCT acquisition. Longitudinal coverage can therefore be extended without interruption. Image quality can be enhanced by improving the image reconstruction algorithms which supports the flexible imaging‐trajectory utilizing all the projection data. To test these new ideas, we implemented CBCT simulation software tools to compute the projection images of digital phantoms according to any flexible source trajectories. We improved the FDK algorithm to reconstruct images from the simulation projection data. Results: We studied a few different source trajectory models including double circle and helical. The initial results were encouraging. The longitudinal coverage was extended. Image quality has been improved even with simple FDK reconstruction algorithm, comparing to multiple individual scans with a couch shift in‐between. Conclusions: We are still at the beginning of the project. It is quite clear that the new CBCT method has great potential. We are developing better reconstruction algorithms to fully take advantages of the new methods for image quality improvement. We are optimizing the source trajectory designs, mathematically and with simulation, to improve image quality, dose exposure and scan time. Anthropomorphic phantom studies with Varian TrueBeam, which could support this proposed CBCT method, are also planned.

This projection is partially supported by a Varian MRA grant with Washington University in Saint Louis.
SU‐E‐I‐19: Development of a High‐Resolution Breast CT System: Preliminary Study
Authors: Tomoyuki O , Atushii T , Ken O , Masatosi T , Hiroshi F
Published: November 2011

Purpose: To overcome the limitations of mammography, X‐ray breast computed tomography (breast CT) was developed. The prototype machines for this technique have been installed in some research institutes and are currently under clinical evaluation. Breast CT is expected to be an effective diagnosis tool because it can generate 3‐dimensional images of a breast. However, the spatial resolution of the existing system is not sufficient to identify microcalcifications within the breast. The purpose of this study was to develop a prototype of high‐resolution breast CT system. Methods: Our prototype system consists of a microfocus X‐ray tube (focus size: 5 um) and a flat panel detector (FPD, indirect conversion type, pixel pitch: 50 um, matrix size: 2366 × 2368) with C‐arm frame, bed, and computer for control. The spatial resolution of the images can be modified by altering the geometric magnification (minimum spatial resolution: 20 um). Images are reconstructed using cone‐beam X‐ray projections and the FDK algorithm. Results: The proposed system was evaluated by using the breast phantom with a mass lesion and microcalcifications. The breast was scanned using a continuous X‐ray source at a tube voltage of 100 kV, tube current of 0.1 mA, and spatial resolution of 80 um. The 3‐dimensional structure of the mass region and microcalcifications were clearly identified on the obtained images. Conclusions: We developed a prototype of high‐resolution breast CT system that employs a micro‐focus X‐ray tube and an FPD. Experimental results showed that our CT system offers exceptional spatial resolution. Thus, our breast CT system may be useful in the diagnosis of mass lesion and microcalcification.
SU‐E‐I‐26: A Monte Carlo Based Study on X‐Ray Characteristics of Two Commercial Multi‐Detector CT Simulators
Authors: Kim S , Song H , Movsas B , Chetty I
Published: November 2011

Purpose: As multi‐detector computed tomography (MDCT) scan is routinely performed for treatment planning in radiation oncology, understanding the characteristics of MDCT x‐ray beam is essential to optimize scan protocols as well as to estimate patient dose. The purpose of this study was to characterize the x‐ray beams of two commercial MDCT simulators with Monte Carlo (MC) simulations. Methods: X‐ray tube systems of two wide bore MDCT scanners (GE LightSpeed RT, LS and Philips Brilliance Big Bore, BB) were modeled in the BEAMnrc/EGSnrc systems. All the tube components were modeled: tungsten target, inherent filter, bowtie filter, and beam collimators. Three benchmark processes were performed to validate the MC models. (1) X‐ray spectra comparison between MC and manufacturersˈ data, (2) Half‐value layers (HVLs) between MC and measurements using aluminum sheets and multi‐functional radiation detectors, (3) Lateral and axial beam profiles between MC and radiochromic film measurements To understand the scatter effect of the MDCT beams, scatter‐to‐primary energy fluence ratios (SPRs) were derived and the total SPR for each CT system was calculated with CTDI head and body phantoms.. Results: MC generated x‐ray spectra agreed well with the manufacturer‐specified data over the entire energy range. Effective photon beam energies for 120kVp beam were found to be (MC, vendor‐specified): (60.8, 60.2keV) for LS scatter, and (65.4, 64.9keV) for BB scanner. MC‐computed HVLs were found to be within 1% of the ion chamber measurements on average. The lateral and axial profiles between film and MC showed overall good agreement within 10% on average. The total SPR ranged from 3.5 to 4.9% for head phantom and from 7.1 to 11.1% for body phantom. Conclusion: Complete characterizations of two MDCT scanners have been performed using the BEAMnrc/EGSnrc MC system. This information can be utilized to optimize scan protocols as well as patient‐specific dosimetry for the MDCT systems.
SU‐E‐I‐28: Pitch and Noise in Abdominal Multi‐Detector CT
Authors: Pike P , Yester M , Barnes G
Published: November 2011

Purpose: To quantify the effect of pitch on noise in abdominal multi‐detector CT. Methods: The standard acrylic abdominal CTDI phantom was modified so that it could be supported on the gantry shroud and remain stationary during a helical multi‐detector CT image acquisition. The table top height was positioned 1 cm below the phantom so that the table could move during helical image acquisition without touching the phantom. The phantom was scanned with the x‐ray tube voltage, x‐ray tube anode current, reconstructed slice thickness, multi‐detector selection and reconstruction kernel typically employed in a standard abdominal protocol for the different pitches available. On a given unit only the pitch was varied. The pixel standard deviation (noise) for four small (100 mm2) centrally located regions of interest were measured and averaged. Sixteen slice and 64 slice multi‐detector CT scanners were studied. On both scanners the standard filtered backprojection image reconstruction (FBP) algorithm was utilized. Results: On both the 16 slice and 64 slice scanners the noise varied to a reasonable approximation with the square root of the pitch for pitches ranging from ∼0.5 to ∼1.0. On the 16 slice scanner the noise increased only slightly when the pitch was changed from 1.375 to 1.75 Conclusions: In the cases of the CT scanners studied our results support the widely accepted fact that noise in an abdominal (noncardiac) mode multi‐detector helical CT image varies with pitch (and to the first order with the square root of the pitch) for pitches up to one when the FBP algorithm is employed. Our results do not support this fact when the pitch is increased above 1.0 and in particular as the pitch is increased to 1.75.
SU‐E‐I‐32: Experimental Evaluation of a Reconstruction Algorithm for Metal Artifact Reduction
Authors: Magnelli A , Xia P
Published: November 2011

Purpose: To evaluate a metal artifact reduction algorithm (MAR) developed by Philips Medical Systems Inc. for accurately reconstructing the density of a material obscured by metallic streaking artifacts due to a prosthetic hip implant. Methods: Two inserts with known densities of 1.84 and 1.15g/cm3 were placed in a water tank at distances of 0 and 20cm from a titanium hip prosthesis. CT images were acquired with the inserts at both positions, and each set of images was reconstructed twice: once with and once without MAR. The physical densities of the inserts in these CT images were determined by a clinical treatment planning system (Pinnacle 8.0) and were recorded and compared to the known values. Results: With MAR reconstruction, for inserts proximal to the titanium prosthesis, the measured physics densities were closer to the known values. The 1.84 g/cm3 insert had a mean density of 1.444 g/cm3 without MAR and 1.546g/cm3 with MAR, an improvement of 5.5%. The standard deviation of the measured density also decreased from 0.298 to 0.213. The 1.15 g/cm3 insert had a mean density of 0.744g/cm3 without MAR and 0.890g/cm3 with MAR, an improvement of 12.7%. Standard deviation decreased from 0.33 to 0.178. for inserts distal to the prosthesis, the measured densities were minimally changed by the MAR reconstruction, as the artifact did not affect the inserts. For the 1.84g/cm3 insert: 1.801 without MAR, 1.816 with MAR. for the 1.15 g/cm3 insert: 1.138 without MAR, 1.138 with MAR. Conclusions: Our experiments show that the MAR algorithm improves accuracy of reconstructed densities proximal to hip prosthesis, although up to 22% error in the physical densities may still be present depending on the specific materials. For tissues distal to the prosthesis, the MAR reconstruction algorithm does not adversely affect the reconstructed physical densities by the treatment planning system.
SU‐E‐I‐33: Low‐Dose CBCT by Iterative Image Reconstruction Using Non‐Local Edge‐Preserving Prior
Authors: Wang J , Ouyang L , Lu W , Solberg T
Published: November 2011

Purpose: Statistical iterative image reconstruction (SIR) algorithms are effective for reconstructing high‐quality low‐dose cone beam computed tomography (CBCT). The performance of SIR strongly depends on the prior/penalty term. In this work, we develop and evaluate an edge‐preserving penalty term in SIR that incorporates high‐order neighbors. Methods: CBCT projection data of a CatPhan 600 phantom was acquired on a Varian Acuity simulator (Varian Medical Systems, Palo Alto, CA) using two protocols: 80mA/12ms/projeciton for high dose and 10mA/10ms/projection for low dose. Low‐dose CBCT images were reconstructed by minimizing an objective function based on the penalized weighted least‐squares (PWLS) criterion. Conventionally, the penalty term is used to enforce the smoothness constraint within a local neighborhood (e.g. up to third‐order neighbors). In this work, we propose a non‐local anisotropic quadratic penalty term that incorporates higher‐order neighbors. The relative contribution from different neighbors is controlled by the absolute difference between the selected neighbors. For neighbors associated with larger differences, equivalence between them will be discouraged. Contrast‐to‐noise ratio (CNR) at different regions of interest (ROIs) is calculated to quantitatively evaluate the proposed high‐order neighborhood penalty. Results: Noise is substantially reduced in low‐dose CBCT reconstructed using the iterative PWLS algorithm, while the edges are well‐preserved. The CNRs in selected ROIs in PWLS‐reconstructed images are higher than that of the corresponding FDK reconstructed high‐dose images. Using the higher‐order neighbor penalty, the average CNR of the selected ROIs is 24% higher than the image reconstructed by PWLS using the penalty with the conventional local neighbor. Conclusions: A higher‐order neighborhood methodology is proposed for the penalty term in PWLS iterative image reconstruction for enhancement of low‐dose CBCT image quality. PWLS coupled with higher‐order neighbor penalty outperforms the PWLS with conventional local neighbor penalty.

This work was partially supported by American Cancer Society Institutional Research Grant (ACS‐IRG‐02‐196).
SU‐E‐I‐36: Cone‐Beam Artifact Reduction in Wide Collimation Pediatric Head Imaging
Authors: Dhanantwari AC , Patel R , Shechter G
Published: November 2011

Purpose: Cone‐beam artifacts can be a significant contributor in the degradation of brain image quality. The purpose of this study is to evaluate the frequency split cone‐beam reduction reconstruction algorithm as a means of improving IQ in brain imaging. The design of the frequency split filters and their effect on image quality and noise are evaluated. Also the potential of increasing the x‐ray beam collimation and reducing total scan time for head imaging is investigated. Method and Materials:Head scans from Philips iCT 256 slice and Brilliance 64 scanners, and simulations based on the Philips iCT 256 slice scanner were used in this study. The scans were reconstructed using conventional reconstruction techniques and frequency split reconstruction. The level of cone‐beam artifacts introduced when using larger beam collimations and the effectiveness of frequency split reconstruction for reducing cone‐beam artifacts were investigated. Also, the effect of the filters parameters in frequency split reconstruction on image quality and on noise texture were evaluated. The pediatric head IQ from the clinical data sets, and especially the delineation of the bone‐brain boundary and contrast detail in the posterior fossa, were evaluated. Results: Review of images reconstructed with frequency split reconstruction show significant reduction in the level of cone‐beam artifacts. Clinical images show significant improvements in uniformity and contrast in the posterior fossa. Improvement in image uniformity of up to1 5 HU has been realized by frequency split reconstruction. With proper design of frequency split filters, the change in image noise and NPS and can be minimized while achieving significant reduction of cone‐beam artifacts. Conclusions: Cone‐beam artifacts can be a significant contributor to image artifacts. The optimized frequency split reconstruction algorithm realizes significant IQ improvements in heads imaging. The frequency split cone‐beam reduction algorithm could also result in shorter scan times by allowing wider collimations during scan.

Authors are employed by Philips Healthcare
SU‐E‐I‐44: Investigation of the Contrast Ratio Required for Medical‐Grade Liquid‐Crystal Displays
Authors: Takarabe S , Akamine H , Yabuuchi H , Nakamura Y , Hashimoto N , Morishita J
Published: November 2011

Purpose: Liquid‐crystal displays (LCDs) with a higher contrast ratio (CR) have been recently developed. However, only a few studies have been reported regarding the CR of the LCDs required for displaying medical images. The purpose of this study was to investigate the CR of LCDs required for displaying medical images.Methods: A two‐megapixel monochrome LCD (GS220, maximum 1,000 cd/m2, recommended 500 cd/m2, Eizo Nanao, Japan) was used in this study. This LCD was calibrated to the grayscale standard display function (GSDF) with different maximum‐luminance settings such as 250, 500, and 700 cd/m2 for mammograms and 175, 500, and 700 cd/m2 for chest radiographs. The minimum luminance of the LCD was kept at 0.7 cd/m2 for each calibration. The CR was calculated from the maximum and minimum luminance of each luminance setting. Mammograms (40 images) and chest radiographs (10 images) were selected as research subjects. To examine the maximum luminance (Lmax) and the minimum luminance (Lmin) in each image, region of interests (ROIs) were set based on the histogram analysis. Then, luminance corresponding to ROIs was calculated by using the GSDF curve with different maximum luminance settings. Finally, luminance ratio (LRimg) in mammograms and chest radiographs were obtained from the Lmax and Lmin in each image.Results: The average LRimg of mammograms with the maximum‐luminance setting of 250, 500, and 700 cd/m2 was 209:1, 388:1, and 523:1, respectively. On the other hand, the average LRimg of chest radiographs with the maximum‐luminance settings of 175, 500, and 700 cd/m2 was 37:1, 70:1, and 86:1, respectively Conclusions: We found that the CR of the LCD required for displaying mammograms and chest radiographs ranged from 209:1 to 523:1 and 37:1 to 86:1, respectively. A significant difference in the CR of LCD required for displaying medical image was observed between mammograms and chest radiographs.
SU‐E‐I‐45: The Human Imaging Research Office (HIRO): Advancing the Role of Imaging in Clinical Research
Authors: Armato S , Gruszauskas N , MacMahon H , Torno M , Li F , Engelmann R , Starkey A , Pudela C , Marino J , Chang P , Giger M
Published: November 2011

Purpose: The clinical imaging infrastructure has been designed for the consistent execution of standard‐of‐care imaging examinations. Many imaging protocols for clinical research, however, have unique requirements that may burden the established infrastructure. Our purpose was to develop a solution to the many imaging demands and challenges presented by clinical research.Methods: We have created the Human Imaging Research Office (HIRO) at our institution. The HIRO is responsible for coordinating the acquisition, collection, analysis, and maintenance of images and related data associated with clinical research studies involving human subjects. The purpose of the HIRO is to coordinate, harmonize, and streamline the imaging aspects of clinical research, so that these non‐standard examinations can be performed as required by the study protocol. In effect, the HIRO is becoming the institutional resource for a broad spectrum of research imaging needs. The activities and services of the HIRO include site validation and image quality verification, development of standardized research‐specific requisition and reporting forms, scheduling, implementation of research billing codes, study‐specific image‐based measurements, collection of customized image databases, and distribution of anonymized images to researchers and study sponsors.Results: The HIRO has helped facilitate the acquisition of images for clinical research for 117 active, pending, or recently closed clinical research studies. These clinical research studies are being conducted by 60 unique principal investigators across 14 different sections and departments within the Medical Center. The HIRO has filled over 650 requests for de‐identified images, accounting for over 42.3 million images Conclusions: Imaging for clinical research often has requirements that differ substantially from those of clinical imaging. The complex infrastructure for standard‐of‐care imaging typically is stressed by the unique technical and administrative needs of a research protocol. The HIRO is able to respond effectively to the dynamic imaging needs of clinical research.

SGA, HM, and MLG receive royalties and licensing fees through the University of Chicago related to computer‐aided diagnosis. HM is a consultant for Riverain Medical.
SU‐E‐I‐46: Methods to Determine Peak Skin Dose and Organ Doses for Computed Tomography Examinations
Authors: de las Heras H , Minniti R , Wilson S , Benevides L , Skopec M , Chakrabarti K
Published: November 2011

Purpose: This work describes methodologies for determining peak skin dose (PSD) and organ doses in computer tomography (CT) examinations. These methods are demonstrated for the routine adult head protocol. This work allows directly relating the widely used CT dose index parameter, CTDIvol, to actual PSD and organ dose values.Methods: Values of the CT dose index, CTDIvol, available in all commercially available CT units tested in this work, were derived independently from ionization chamber measurements. Simultaneously, either, PSDs (first method) or organ doses (second method) were measured as well. In the first method, PSDs were measured using radiochromic film placed on the outer surface of the phantom. Optical densities were measured with a transmission densitometer. In the second method doses to the brain, eye lens and face skin were measured using an anthropomorphic head phantom configured with optical stimulated luminescence (OSL) dosimeters. The ionization chamber, films and OSLs used in these measurements were calibrated at NIST in x‐ray beams that spectrally approximated those typically produced by CT scanners in clinical use.Results: The suggested PSD method is reliable, cheap and fast. PSD values of up to 160 mGy were observed in a single scan in some CT scanners. Variations in the PSD values up to a factor of 2 are observed for a fixed value of CTDIvol, which supports characterizing independently each scanner using the proposed methods. Results show a quite homogenous distribution of organ doses inside the head. Conclusions: Clinical facilities may apply these methods to relate the values of CTDIvol shown on their CT units to actual PSDs and organ doses delivered. Furthermore, this provides a direct method for obtaining PSD and organ dose, as opposed to the more common practice approach of estimating effective dose derived from CT machine parameter values (CTDIvol and scan length).

The first author was funded by an ORISE grant at FDA. He is working for Quart GmbH since March 1, 2011. We are very thankful to Chad Mitchell for his initial encouragement on this project, to Dave Spelic for his advice on the manuscript, and to the group of CT technicians at NIH and NNMC.
SU‐E‐I‐49: Estimating Effective Doses to Patients Undergoing CT Pulmonary Arteriography
Authors: Ogden K , Scalzetti E , Gabbour M , Neuffer M , Roskopf M
Published: November 2011

Purpose: To estimate the effective dose (E), corrected for patient size, delivered to patients undergoing CT Pulmonary Arteriography (CTPA). Method and Materials: IRB exemption was obtained to review CT scans for 650 consecutive patients undergoing CTPA in 2005, who were followed for additional CTPA through 2009. Information was collected to calculate the dose‐length product (DLP), as CT dose reports were available only for more recent studies. Patient dimensions were used to estimate patient mass. E was estimated using E/DLP conversion factors for 70kg patients. Patient mass was used to estimate the energy imparted relative to a 70 kg patient. Relative energy imparted and patient mass were used to calculate effective dose correction factors. Cumulative E for individual patients was also calculated. Results: The average number of scans per patient was 1.33, with 14 patients receiving >3 scans. Single‐scan DLP values averaged 316. ± 44.2 mGy‐cm. Using an E/DLP conversion factor of 17.5 μSv/mGy‐cm yields an uncorrected average effective dose of 5.4 ± 0.75 mSv with a range of 0.65 to 7.9 mSv. Correction factors ranged from 0.48 for the heaviest patient to 1.42 for the lightest patient, with a mean of 0.92. After correction, the mean effective dose was 5.1 ± 1.1 mSv, with a range of 0.92 to 8.7 mSv. Cumulative effective doses averaged 7.0 ± 6.9 mSv, with a range of 0.92 to 111.9 mSv. The highest cumulative dose was for a patient who received 14 CTPA exams. Conclusions: Effective dose calculations in CT are generally performed without correction for patient mass. This may result in errors of about a factor of two. CTPA effective doses are similar to other thoracic CT exams; however it is not uncommon for individuals to have repeat exams. Cumulative effectve doses can exceed 100 mSv, potentially increasing the risk of cancer induction.
SU‐E‐I‐50: The UF Family of Hybrid Phantoms of the Developing Human Fetus for Computational Radiation Dosimetry
Authors: Maynard M , Geyer J , Aris J , Shifrin R , Bolch W
Published: November 2011

Purpose: Historically, the development of computational phantoms for radiation dosimetry have primarily been directed at capturing and representing adult and pediatric anatomy, with less emphasis devoted to models of the human fetus. As concern grows over possible radiation‐ induced cancers from medical and non‐medical exposures of the pregnant female, the need to better quantify fetal radiation doses, particularly at the organ‐level, also increases. To address this need a series of hybrid computational phantoms was constructed for fetal ages 8, 10, 15, 20, 25, 30, 35 and 38 weeks post‐conception. Methods: Two specimen‐specific fetal hybrid computational phantoms were constructed using high‐quality magnetic resonance imaging (MRI) and computed tomography (CT) image sets obtained for two well‐preserved fetal specimens aged 11.5 and 21 weeks post‐conception. Individual soft tissue organs, bone sites, and outer body contours were segmented from the images using 3D‐DOCTORTM and imported into the 3D modeling software package RhinocerosTM for further modeling and conversion of soft tissue organs, certain bone sites and outer body contours to deformable non‐uniform rational B‐spline (NURBS) surfaces. The two specimen‐specific phantoms, along with a modified version of the 38 week UF hybrid newborn phantom, comprised a set of base phantoms from which a series of hybrid computational phantoms was derived for fetal ages 8, 10, 15, 20, 25, 30, 35 and 38 weeks post‐ conception. Results: A set of fetal computational phantoms accounting for the following age‐dependent parameters: (1) variations in skeletal size and proportion, (2) bone‐dependent variations in relative levels of bone growth, (3) variations in individual organ masses and total fetal masses and (4) statistical percentile variations in skeletal size, individual organ masses, and total fetal masses. Conclusions: The resulting series of fetal hybrid computational phantoms is capable of organ‐level and bone‐level internal and external radiation dosimetry for human fetuses of various ages and weight percentiles.
SU‐E‐I‐55: Application Specific Mathematical Optimization of Lead‐Free Apron Composition
Authors: Pasciak A , Jones A
Published: November 2011

Purpose: In the past decade, manufactures have introduced lead‐equivalent (lead‐free) radiation shielding garments which have become quite popular in interventional radiology (IR) due to their reduced weight when compared with traditional lead aprons. The material composition of lead‐equivalent aprons varies significantly from manufacturer to manufacturer, and while some manufacturers use an undisclosed blend of materials, others publish their aprons composition. However, there does not yet exist any published scientific report describing the optimal lead‐equivalent garment composition and under what conditions such a garment is most effective. Methods: To reflect modern practice, our analysis is based on the assumption that IR staff will never be in the primary beam, and their radiation protection garment should therefore be optimized to attenuate scattered x‐ray spectra. Using a Monte Carlo radiation transport code, the scattered spectrum at different points in an interventional suite was determined for a modern angiographic system as a function of patient size, C‐arm configuration and the position of the physician within the room. A sequential quadratic programming optimization routine was used to determine the optimal combination of metals to produce the lightest apron which attenuates the scattered x‐ray spectrum as effectively as a traditional 0.5 mm thick lead apron. Results: Our analysis indicates that for the scattered x‐ray spectra most apparent to IR personnel, lead is not the most efficient shielding material by weight. Using numerical optimization and a specific analysis of typical IR suite scatter spectrum, we are able to recommend a shielding garment construction which is equally effective to a standard lead garment but with a 44% reduction in weight. Conclusions: A clear algorithm is presented for determining the best composition to satisfy a variety of endpoints which can be used both in apron manufacturing and in verification that the claims of a lead‐free garment manufacturer are valid.
SU‐E‐I‐56: Computational Internal Dosimetry Methods as Applied to the UF Series of Hybrid Phantoms
Authors: Wayson M , Lee C , Sgouros G , Bolch W
Published: November 2011

Purpose: To compute specific absorbed fractions for monoenergetic photons and electrons for all UF hybrid ICRP‐reference phantoms. Ultimately, radionuclide S values will be calculated for all radionuclides of interest in nuclear medicine. Methods: Voxelized versions of the UF newborn hybrid computational phantoms were used in conjunction with the radiation transport code MCNPX v2.6 to determine the absorbed fraction of energy per unit mass (SAF) for a variety of source‐target organ combinations for 21 photon and electron energies. A method known as a fluence‐to‐dose response function was used, for the first time in a model of the newborn child, to determine the absorbed dose to active marrow and total shallow marrow, the radiosensitive tissues of the skeleton. A novel method for minimizing the poor statistics associated with electron transport was also introduced. First, a simulation was completed which only tracked primary electrons, giving the dose contribution solely attributed to collisional energy losses. Next, a simulation was completed which recorded the initial energy of any photons produced by the primary electrons. Monoenergetic photon SAFs, determined previously, were then weighted according to each monoenergetic electron bremsstrahlung energy spectrum so as to procure low uncertainty photon dose from the primary electrons. Results: The novel method for electron dosimetry was benchmarked and found to be an accurate and effective way of reducing the uncertainty associated with electron cross‐dose. S values were generated for Tc‐99m and compared to estimates provided by OLINDA/EXM 1.0. Noticeable differences were seen for both self‐dose and cross‐dose scenarios. Conclusion: The work performed represents a state‐of‐the‐art internal dosimetry model, and once dosimetry has been performed on the entire UF series of phantoms, the results will be incorporated into an online accessible software package which can be of use in imaging and dose optimization for pediatric nuclear medicine patients.
SU‐E‐I‐59: CT DOSE REDUCTION WITHOUT SACRIFICING IMAGE QUALITY: A Collaborative Intradepartmental Effort
Authors: Patel P , Campbell M , Kirshenbaum K
Published: November 2011

Purpose: Recent headlines have put radiation dose and its potential deleterious effects in the limelight, and have caused some anxiety amongst patients and radiation safety personnel. Thus, it is even more important to minimize the stochastic effects associated with radiation. We demonstrate how an integrated departmental approach to reducing CT dose without sacrificing image quality can be achieved. Methods: A cohort of subspecialized radiologists, radiology residents, a radiation safety officer, a medical physicist, and radiology technologists was assembled. Using, but also significantly modifying, the ACR (American College of Radiology) CT Chest dose reduction Practice Quality Improvement (PQI) project as a template, multiple factors were manipulated to evaluate their effect on dose reduction. Initially, a retrospective review of patient dose data from head, chest and body CT examinations was performed. Next, selected changes were made to select body parts. For example, the kVp of a chest CT was reduced from 120 to 100, and image quality before and after the alteration was assessed and compared. Similarly, abdominal CT slice thickness was increased from 1.25mm to 2.5mm. Results: After the two interventions of decreasing the kVp and increasing the slice thickness, dose reduction of 23% and 20% was achieved, respectively. Conclusions: : A multidisciplinary approach to CT dose reduction with dedicated involvement from the entire Radiology department can result in significant dose reduction to patients. Using easily modifiable parameters, an intuitive flow chart was developed to help facilitate data tracking. While data has only been evaluated on some of the variables to date, we look forward to seeing the impact of other interventions as the study continues. Additionally, we believe this process can be replicated at other institutions with similar success, to ultimately reduce dose dramatically without significantly impacting image quality.
SU‐E‐I‐61: Application of the ALARA Principle in Digital Radiography Systems
Authors: Brindhaban A , Abdulwahab F , Essa F , Tariq N
Published: November 2011

Purpose: To investigate the effect of using higher x‐ray tube voltage (kVp), than those recommended by manufacturers, on patient dose and image quality during digital radiography (DR) examination of the Lumber Spine. Methods: Reference images of an RSD (Radiology Support Devices, Long Beach, CA, USA) anthropomorphic lumber spine phantom were obtained using 3 different DR systems using exposure factors, kVp and tube‐current time product (mAs), recommended by the manufacturer of each system. Test images were obtained, on each system, using kVp values which were 15% and 30% higher than those recommended by the respective manufacturers, while reducing the mAs to 50% and 25% respectively of the reference exposure. The images were evaluated subjectively by 3 experienced Radiologist using the image quality criteria recommended by the Commission of the European Communities (CEC) for LS examination, on a 5‐point scale. For each image, the entrance surface exposure, including backscatter, to the phantom was measured using the Victoreen Model 8000 NERO TM mAx system and the entrance surface dose and effective dose were calculated. Any statistically significant differences between the average scores for the images were tested using Kruskal‐Wallis test at p=0.05. Results: The average score from the 3 Radiologists were above the clinically acceptable levels for all of the images. Within each system, the average scores for the images obtained with different exposure factors did not show any statistically significant differences. The entrance surface doses to the phantom and the calculated effective doses decreased by approximately 30% for a kVp increase of 15% and approximately by 50% for kVp increase of 30% in all 3 systems. Conclusions: Dose reduction up to 50% can be achieved without affecting the diagnostic quality of all images in the 3 systems by using kVp and mAs values other than those recommended by the DR systemˈs manufacturer.
SU‐E‐I‐63: Multi‐Channel Film Dosimetry with Non‐Uniformity Correction
Authors: Micke A , Lewis D , Yu X
Published: November 2011

Purpose: A new method to evaluate radiochromic film dosimetry data scanned in multiple color channels is presented. The multi‐channel method allows for the separation and removal of the non‐dose‐dependent portions of a film image and performs superior to the traditional single channel method. Methods: Exposed radiochromic films were scanned in RGB format on a flatbed color scanner and measured to build calibration. Images were converted to dose maps using both single color channel and multi‐channel method. The multi‐channel method allows for the separation of the scanned signal into one dose‐dependent part and another dose‐independent part and enables the correction of a variety of disturbances including non‐ uniformities of the film as well as scanner related artifacts. The fundamental mathematics of the two methods is described and the dose maps calculated with both methods are compared and analyzed. Results: The multi‐channel dosimetry method was shown to remove effectively non‐dose dependent abnormalities from radiochromic dosimetry film images and improve the integrity of the dose information and also reduces random noise in the dose images and mitigates scannerrelated artifacts such as lateral position dependence. In providing an ability to calculate dose maps from data in all the color channels the multi‐channel method provides the ability to examine the agreement between the color channels. The method permit compensation for nonuniformities in the film, increases the signal to noise level, mitigates scanners effect of the calculated dose map and extends the evaluable dose range to 10 cGy – 100. Conclusions: Multi‐channel dosimetry is shown to have significant advantages over single channel method in ensuring the best data integrity and dosimetric accuracy.

All authors are employees of International Specialty Products, Manufacturer of Gafchromic Films
SU‐E‐I‐65: Estimation of Secondary Cancer Risk Induced by Diagnostic Imaging Radiations during Proton Therapy
Authors: Jeong H , Shin D , Lee S , Yoo S , Min B
Published: November 2011

Purpose: To quantify the secondary cancer risk (SCR) induced by daily‐anatomical imaging during proton therapy. Methods: First, we measured the characteristic radiation properties of a diagnostic imaging system used in proton therapy in our institute, digital imaging positioning system (DIPS, IBA, Belgium). Subsequently, we incorporated the measured beam data into a commercial radiation treatment planning system, Eclipse (Varian Medical System, USA) to efficiently calculate the distribution of dosage due to image‐guided procedure. The secondary cancer risk additionally induced by the diagnostic‐imaging radiation was estimated based on organ‐equivalent dose concept. For the analysis, we select a 43‐years‐old female patient case, in which the patient underwent proton treatment at the treatment site of lumbar spine with prescribed dose of 4600 cGy and 23 fraction size. Results: It was calculated that the diagnostic‐imaging radiation for daily‐patient imaging produced relatively small dose of ∼4.7 cGy in average in the patient body, which corresponded about 0.1 % to the prescribed dose of 4600 cGy. However, this small dose substantially raise the radiation‐induced SCR upto ∼8 % in the ordinary patient treatment regimen and can further increase the SCR depending on irradiation conditions, particularly the imaging‐field size with respect to targeted‐tumor volume. Conclusions: The present findings strongly suggest that not only the therapeutic radiation but also imaging radiation must be carefully managed in image‐guided proton therapy.
SU‐E‐I‐75: Feasibility of An IT‐Based Dose Management in Diagnostic Radiology
Authors: Fiebich M , Schmidt A , Ningo A , Voigt J , Krombach G
Published: November 2011

Purpose: Good performance in diagnostic radiology is not only defined by image quality but also by patient exposure. However, there is no established method for the automatic calculation of the effective dose received by patients, during diagnostic radiological examinations. Our objective is to develop a method for the automated evaluation of radiation exposure to patients, and to examine the plausibility of its implementation for dose‐management. Methods: Patient data including exposure information collected over three month, were extracted from a radiological information system, anonymized and saved in a database. A program was written to automatically calculate the effective dose, received by each patient from examinations with radiography systems. The parameters exam type, voltage (kVp), tube current‐time product (mAs) and dose‐area‐product (Gy*cm2), if available, were used for effective dose calculation for a standard patient. The calculated values were saved in a database. A comparison was done between the calculated effective dose of the patients, and the diagnostic reference levels for diagnostic X‐ray examinations dependent on age, period of time, and examination type. The examination type with the relative highest dose was optimized for patient exposure. Results: On average, the dose applied to patients during diagnostic X‐ray and computed tomography examinations significantly lower than the diagnostic reference level values. In the CT of the lumbar spine the exposure was only 20 % lower than the diagnostic reference level and therefore selected for further optimization. Change of FoV, kVp, pitch and mAs was performed to further reduce patient exposure without significantly reducing the image quality. Conclusions: A method was developed, for the automatic calculation of the individual effective dose received by patients. This process can be implemented for dose management including optimization of patient exposure.
SU‐E‐I‐77: Reduction of Fetal Dose in Computed Tomography Using Anterior Shields
Authors: Button T , Fernandez T , Gillet A , Dunkin J , Zhang Y , Bonvento M , Adam C
Published: November 2011

Purpose: The potential application of “in beam” anterior shields were examined from fetal dose reduction and image quality perspectives.Methods: Dose reduction afforded by commercially available bismuth impregnated synthetic rubber fabricated as 12.5 and 25 cm wide anterior shields was measured. Thermoluminescent dosimeters (TLDs) irradiated in a Rando phantom were used to estimate fetal dose. Average fetal position at 0 and 18 weeks post conception were determined based on ultrasound data of fetal position by gestational age. The latter stage of pregnancy (18 weeks) was simulated by adding tissue equivalent bolus material over the anterior surface of the phantom. To assess the impact of anterior shielding on image quality, an RMI 461A body phantom with low contrast resolution phantom insert was employed. The minimum size of low contrast resolution target visualize was recorded with no shielding, 12.5 cm wide shielding and 25 cm wide shielding.Results: At 120kVp, the 12.5 cm wide bismuth impregnated synthetic rubber shield was shown to reduce fetal dose 14% and 17% at 0 and 18 weeks post conception while the 25 cm shield reduced fetal dose 22% and 38% at 0 weeks and 18 weeks post conception. These shields produce only minor artifacts and do not adversely impact low contrast resolution. It should be noted that the use of these shields in automatic tube current modulation mode may not reduce fetal dose. Conclusions: These shields may prove to be useful for clinical fetal dose reduction early in pregnancy. It should be noted that similar results may also be achieved by tube current modulation to reduce the anterior dose contribution.