bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐EE‐A4‐05: An Alternative Spatial Encoding Method for Magnetic Nanoparticle Imaging
Authors: Weaver J , Rauwerdink A
Published: July 2008

Purpose: Magnetic particle imaging, MPI, was introduced in 2005 and promises to be sufficiently sensitive to allow molecular imaging. We introduce and explore numerically an alternative method of encoding position in magnetic nanoparticle imaging. The original MPI method localized the nanoparticle signal at the 3rd harmonic frequency using a strong magnetic field to saturate the nanoparticles outside of the field free point (FFP). We present an alternative method of encoding the signal position in which the signal at the second harmonic is recorded so signal is produced along a magnetic field gradient. Method and Materials: The signal from 20nm magnetic nanoparticles was simulated with a Langevin model using iron oxide properties. Response matrices were calculated for a linear gradient across the sample and the condition number of the matrices was used as the metric for stability of the reconstruction. Results: The conditioning of the second harmonic is significantly better conditioned than that for the third harmonic. The condition number of the response matrix used to reconstruct the spatial distribution of the signal is nearly one for ideal cases. The size of the field gradient increases for increasing number of encoded pixels but need not be as large as that required to saturate the nanoparticles outside a single voxel. For a single size nanoparticle, the response function approximates a smoothed Haar wavelet function at the smallest scale and the best conditioning occurs when the scaling of the response functions approximates the scaling of a dyadic wavelet basis. Conclusion: A linear gradient can be used to encode nanoparticle position using the second or third harmonics. The signal at the second harmonic is significantly larger than at the third harmonic frequency and the conditioning is significantly better; the combination should allow an increase in sensitivity by a factor of from 2 to 8.
SU‐GG‐I‐08: Impact of Phase Shift Between Respiratory Surrogate and Internal Target On Retrospectively Reconstructed, 4D CT Images
Authors: Wang B , Hinkle J , Joshi S , Geneser S , Szegedi M , Varchena V , Salter B
Published: July 2008

Purpose: We quantified the impact of various phase shifts between an external surrogate motion and internal target motion on the 4D modeling of target motion using a 4D dynamic phantom. Method and Materials: The CIRS Dynamic Thorax phantom Model 008 (CIRS, Norfolk, VA) is capable of separating the target and surrogate motions via two independent motors. Phase shift impact on 4D images was studied for two types of breathing signals: a standard sinusoidal signal and a real patient breathing signal. The phantom was imaged on a LightSpeed RT CT 16 slice scanner (GE Health Care, Waukesha, WI) at 0.5s per revolution, 2.5 × 0.6 × 0.6 mm voxel size at 120 kV. The real‐time position management (RPM) system (Varian Oncology Systems, Palo Alto, CA) was used to measure the respiratory signal and GE AW 4D software v4.4 was used to generate 10 reconstructed CT phases. The 10 CT phases were then auto‐segmented by ITK‐SNAP program and evaluated for both target volume and shape. Result: The internal target volume (ITV) varied by 1% for the standard sinusoidal signal at different phase shifts, but varied by 10% for the real patient signal, with the change being larger for greater phase shifts. Because the internal target is a 3 cm diameter sphere, we used a “sphericity” metric to evaluate the degree of target shape distortion. For the case of 45° phase shift, the target shape remained essentially spherical (5% variation) throughout the 10 phases for the sinusoidal signal, but the shape changed significantly (28% variation) from phase to phase for the real patient signal. Conclusion: Our results suggest that phase shift variations between surrogate and target present a greater challenge to the 4D binning process in the case of irregular real patient breathing signal than for a standard sinusoidal signal.
SU‐GG‐I‐16: A Segmentation Technique to Estimate Breast Density From Cone Beam Breast CT Images
Authors: Han T , Chen L , Lai C , Liu X , Shen Y , Wang T , Shaw C
Published: July 2008

Purpose: To describe and demonstrate the use of an improved segmentation technique to estimate breast density from cone beam breast CT (BCT) images. Method and Materials: To compute the breast density, the dense tissue must be separated from the adipose tissue in the BCT images. To accomplish this task, the BCT images were first processed with a previously reported post‐reconstruction method to correct for the beam hardening and scatter induced cupping artifacts. With this method, the adipose signals were extracted from the coronal view CT image and used to form a 3‐D background map which was then subtracted from the original images for correction. The corrected data were edge enhanced and smoothed to reduce the noise levels in the images. The results were processed by threshold segmentation to separate the dense tissue from the adipose tissue and form a 3‐D dense tissue map which was then used to compute the dense tissue volume and the breast density. Results: For demonstration, the proposed technique was applied to cone beam CT images of mastectomy breast specimens to estimate the breast density. The cupping artifacts were successively corrected for and the dense tissue was successfully separated from the adipose tissue with the segmented dense tissue structures matching well with those visualized in the images. Conclusion: We have successfully implemented a method to use cone beam breast CT images to estimate the breast density. The technique was successfully demonstrated with cone beam CT images of mastectomy breast specimens. This technique lends itself to more accurate and consistent measurement of breast density which may be used an indicator for breast cancer risk.

This work was supported in part by grants CA104759 and CA124585 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.
SU‐GG‐I‐27: Image Artifacts Caused by the Extra‐Focal Spot of An X‐Ray Tube in Cone‐Beam Computed Tomography
Authors: Cho S , Pearson E , Pelizzari C , Pan X
Published: July 2008

Purpose: We investigate the reconstruction artifacts induced by extra‐focal spot of x‐ray tube in cone‐beam computed tomography (CBCT). Method and Materials: The extra‐focal radiation problem of an x‐ray tube has been investigated for more than thirty years. However, these investigations have been mostly limited to fan‐beam computed tomography (FBCT) where only the quasi‐one‐dimensional source distribution matters. In contrast, CBCT is more vulnerable to the problem of extra‐focal field than FBCT because the quasi‐two‐dimensional distribution of source is significant. Extra‐focal radiation has been attributed to two physical processes: secondary electrons and field emission. Specifically, field emission of electrons from a cold cathode may create a well‐defined extra‐focal spot that can emit a substantial amount of x‐rays. We have observed a non‐negligible amount of x‐ray flux from an off‐focal spot in the x‐ray tube of an on‐board imager used for image‐guided radiation therapy, and have performed a numerical study to simulate the image artifacts induced by this strong extra‐focal spot. The 3‐D Shepp‐Logan phantom was used as an imaging object and circular cone‐beam projections were made with two focal source points separated by 8 mm along the rotation axis direction. The off center focal spot had an intensity of 10% that of the central spot. Results: We observed image artifacts such as overlaid structure of the object components in the coronal slice images and ghost objects in some transverse slice images. Conclusion: In addition to the well‐known image artifacts, due to spread extra‐focal field of an x‐ray tube, which include blurring of the images, well‐defined extra‐focal spots can introduce additional image artifacts such as overlaying structures and ghost objects.
SU‐GG‐I‐49: Iterative Reconstruction of Slow Rotation CT Data with Projection Object Masks to Decrease Motion Effects
Authors: Park H , Bowsher J , Colsher J , Stern E , Turkington T
Published: July 2008

Purpose: To investigate masking portions of projection data to decrease motion‐related artifacts using iterative image reconstruction techniques. Method and Materials: A phantom was constructed from a water‐filled plastic canister with two air‐filled spheres fixed inside to simulate gas pockets. Inferior‐superior motion was applied to the phantom to simulate breathing. A SPECT/CT scanner (InfiniaVC Hawkeye, GE Healthcare) with a 140 kVp, 2.5 mA tube, and slice thickness of 1 cm was used to acquire data. A single CT slice is acquired in 14 seconds. Projections identified to contain motion via data consistency conditions were combined with forward projected sinograms of the spheres to produce projection object masks (POMs). POMs were given various weights, smoothed using a Gaussian filter, and applied to the phantom sinogram and projection blank file. An OSTR iterative algorithm was used to reconstruct the POM sinogram. Contrast and uniformity data of the POM image were taken from different regions and compared to the filtered backprojected (FBP) image. Patient studies involving anatomical areas with little motion were also analyzed. Results: Projection data with no motion could be reconstructed with minimal artifacts when 6.7% of the projection angles were removed prior to reconstruction. For the moving phantom, motion artifacts were greatly reduced in the POM images compared to FBP images. Contrast and uniformity data showed significant improvement with the applied POM. Conclusion: CT images were successfully reconstructed with missing projection data, and motion can be detected in the projections. Initial work demonstrates that artifacts caused by moving gas pockets and a slow rotating CT such as this SPECT/CT scanner may be reduced through iterative image reconstruction with projections removed. Conflict of Interest: Research sponsored by GE Healthcare Corporation.
SU‐GG‐I‐53: The Impact of Scan Angles On the Visibility of Anatomy in On‐Board Digital Tomosynthesis (DTS) Images for Head and Neck Cancer Patients: A Single‐Observer Study
Authors: Ma J , Wu Q , Godfrey D , Yan H , Ren L , Yin F
Published: July 2008

Purpose: To assess the impact of scan angles on the visibility of anatomy in on‐board digital tomosynthesis (DTS) images as a means to optimize this technique. Method and Materials: Head and neck cancer patients undergoing intensity‐modulated radiotherapy (IMRT) were enrolled onto this study. For each session, the patient was positioned using laser marks. On‐board imaging data sets including CBCT scans as reference, and DTS with 20° and 40° scan angles in the coronal or sagittal directions, respectively, were obtained. Visibility of selected anatomic structures (1=much better, 2=slightly better, 3=comparable, 4=slightly worse, 5=much worse) were assessed by a single observer. Wilcoxon Signed Ranks Test was performed to analyze the statistical significance. Results: Image data sets were collected from 30 treatment fractions for 12 patients. Overall, in coronal direction, there was no statistically significant difference in visibility between the DTS scan angles of 20° and 40° for base of tongue and cervical vertebral body (p = 0.083, 0.157, respectively), except for thyroid cartilage (p =0.025). In sagittal direction, only the hyoid was found to have a statistically significant difference in visibility (p = 0.025), while no significant difference was found for the rest of anatomic structures (p = 0.317, 0.157, 0.317 for base of tongue, cervical vertebral body, and epiglottis, respectively). However, when assessments for multiple fractions were averaged, no statistically significant difference was found for all anatomic structures in either coronal or sagittal directions. Conclusion: This single‐observer study shows that visibility of anatomy is roughly equal for the scan angle of 40° than 20° in both coronal and sagittal direction. Due to the limitations of single‐observer study, more definitive conclusion could not be drawn. Further analysis with a multiple‐observer study of more patients is needed to confirm this preliminary result.
SU‐GG‐I‐64: Photoneutron Intensity Variation with Field Size Around Radiotherapy Linear
Authors: Al‐ghamdi H , Fazal‐ur‐Rehman  , Al‐Jarallah MI , Maalej N
Published: July 2008

Purpose: CR‐39 NTDs were used to study the variation of fast and thermal neutron relative intensities around an 18 MeV linear accelerator x‐ray beam with the field size. Method and Materials: The linear accelerator (Varian 2300 CD) was used with maximum x‐ray energy : 18 MeV Fast neutron detection used Bare NTDs. Method and Materials: NTDs were covered with lithium tetra borate(Li2B4O7) converter. Results: Fast neutron relative intensity is symmetrical about the beam axis and exhibits almost an exponential‐like drop with distance from the isocenter of the accelerator for all the field sizes. Neutron intensities do not change significantly with beam size outside the primary beam. At the primary beam (isocenter), the relative fast neutron intensity is highest for 40×40 cm2 field size and decreases linearly with the decrease in the field size. Conclusion: The fast neutron relative intensity was found to be symmetrical about the beam axis and exhibits an exponential‐like drop with distance from the isocenter of the accelerator for all the field sizes. At the primary beam (isocenter), the relative fast neutron intensity is highest for 40×40 cm2 field size and decreases linearly with the decrease in the field size. Outside the primary beam, the fast neutron intensity does not change significantly with the field size. The thermal neutron intensity was found to be almost uniform for all the field sizes.
SU‐GG‐I‐65: The Effect of Measurement Location On In‐Air CTDI Values
Authors: Ogden K , Huda W
Published: July 2008

Purpose: To experimentally investigate the variation of CTDIair with radial distance from the scanner isocenter. Method and Materials: Radiation dose measurements were obtained on a Siemens Sensation 16 CT scanner operated with both the head and body beam filtration filters. Measurements were made of CTDIair (mGy/mAs) as a function of the radial distance r from the CT scanner isocenter. The radial profile CTDIair(r) was fit to a third order polynomial which permitted the average CTDI over any radius to be obtained analytically. Results: At r = 8 cm, values of CTDIair relative to the isocenter were 0.824 and 0.838 for the head and body filters, respectively; at r = 16 cm, the values of CTDIair relative to the isocenter were 0.521 and 0.546 for the head and body filters, respectively. Values of CTDIair averaged over an 8 cm radial distance were ∼0.91 × CTDIair(0), and averaged over a 16 cm radial distance were ∼ 0.74 × CTDIair(0). Conclusion: Quantification of variations of CTDIair(r) are of interest because: (a) this parameter quantifies the performance and effectiveness of beam shaping filters; (b) CTDIair data can be used to obtain Tissue Air Ratios that can estimate organ doses in CT.
SU‐GG‐I‐71: Acceptance and Routine Quality Control in Direct Radiography Systems: Initial Experiences with the Italian Association of Physicist in Medicine Protocol
Authors: Nitrosi A , Bertolini M , Borasi G , Botti A , Rivetti S
Published: July 2008

Medical x‐ray imaging systems must be designed to guarantee that maximum image quality is obtained for an acceptable radiation risk to the patient, and quality assurance (QA) procedures are used to ensure these standards are maintained. A quality control protocol for direct digital radiography (DDR) systems is described and discussed. A software to automatically process and analyze the required images for controls was developed, too. In this poster the initial results obtained on equipments of different DDR manufacturers were reported. In order to establish a generally acceptable baseline performance of the systems, fourteen different commercially available DDRs from four different manufactures were periodically tested and their results compared in the frame of the Digital Quality Assurance Task Group of the Italian Association of Physics in Medicine (AIFM). The protocol, designed to be performed in short time (all the tests were done in a clinical environment), seem to be able to highlight discrepancies from the standard operating performances.
SU‐GG‐I‐74: New IAEA Document On Acceptance Testing, Quality Assurance and Quality Control for PET and PET/CT Systems
Authors: El Fakhri G , Fulton R , Gray J , Marengo M , Zimmerman B , Dondi M , McLean I , Palm S
Published: July 2008

Purpose: The increased role played by PET and PET combined with computed tomography (PET/CT) in oncology as well as cardiology and neurology associated with increasing reimbursement of multiple PET indications has prompted the need for updated guidelines specific to PET and PET/CT in terms of acceptance testing as well as quality assurance and quality control. These new IAEA guidelines are intended to provide standard testing procedures for use by end users and manufacturers. Method and Materials: The document address more recent developments in PET technology, such as the addition of the CT component, the need to ensure proper registration of the PET and CT data, mobile PET/CT units, time‐of‐flight systems, and the significant natural radioactivity present in some detector materials. Results and Conclusion: The new IAEA document is a reference technical document that provides guidance about the specifications and prerequisites required for acceptance testing of PET and PET/CT scanners, including professionals to be involved, definition of applications, minimal required configurations and corresponding performances parameters as well as ancillary equipment. The document also provides guidelines for routine quality control of PET and PET/CT scanners and a framework for setting reference values, tolerances and action levels. Following these guidelines would ensure operation of the scanner under optimal conditions that yield the best performance in routine clinical tasks that involve lesion detection as well as quantification of radioactivity concentration.
SU‐GG‐I‐76: Estimating Image Quality and Radiation Dose Reduction with In‐Plane Bismuth Shielding for CT Examinations: Phantom Study
Authors: Liao YL , Tsai HY , Tyan YS , Cheng KY
Published: July 2008

Purpose: To estimate the image quality and radiation dose reduction by using bismuth shielding materials during in‐plane CT scanning. Method and Materials: Bismuth shielding was used to block the low energy photons of radiation beam to reach an ACRCT accreditation phantom. The shielding materials were coated with foam to decrease the beam hardening artifact at the interface between bismuth and phantom surface. Images were acquired by Siemens Sensation 64 CT scanner with four kVps. The image quality affected by bismuth shielding, including CT number deviations, noise distribution, contrast, and artifacts, were estimated. The radiation dose reduction was measured by using high sensitive thermoluminescent dosimeters. Results: The water CT number and noise without shielding are −3.25±0.4 HU and 6.09±0.49 HU at 120 kVp. The CT number changes are 3.56, 8.56, 20.52, and 33.05HU near the shielding regions for 1T, 2T, 4T, and 6T bismuth (1T= 0.035 g/cm2), and 1.9, 2.8, 3.6, and 5.9 HU far from the shielding regions. The foam is needed to decrease the beam hardening artifact at the interface of the phantom. The radiation dose reduction is 14.4 %, 20.6 %, 33.9 %, and 50.5 % for 1, 2, 4, and 6T bismuth. The image contrast change after shielding is within 9 %. Conclusion: In‐plan bismuth shielding could block useless low energy radiation to reduce patients and protect radiosensitive organs. The radiation dose reduction is remarkable with in‐plan bismuth shielding. Covering the bismuth shielding on patients potentially changes the CT number accuracy, but has no impact on image contrast. The CT number variation is slightly apparent near the shielding region than the far regions. However, the variations are acceptable. The foam keeps the shielding away from the patient surface to diminish beam hardening artifact and to maintain the diagnostic acceptability.
SU‐GG‐I‐78: How Well Does the CT MAs Predict Patient Dose?
Authors: Frey G , Elojeimy S , Huda W
Published: July 2008

Purpose: CT clinical protocols often specify technique factors in terms of x‐ray tube voltage and tube current‐rotation time product (mAs). In this study, we investigated variations in CTDI100 per unit mAs value at a fixed x‐ray tube voltage (120 kV). Method and Materials: Data were obtained for CTDI100 in head and body phantoms for 47 scanners from the four major imaging equipment vendors from the ImPACT web site. Data were analyzed as follows: (a) all CTDI100 (mGy/mAs) data were plotted as a single histogram, and the 10th, 50th, and 90th percentile values determined; (b) CTDI100 for each vendor were averaged and compared with each other; and (c) CTDI100 for each vendor were plotted as a function of the introduction of the CT scanner model under consideration. Results: The median CTDI100 values were 0.18 mGy/mAs and 0.076 mGy/mAs for head and body phantoms respectively. The ratio of the 90th percentile value to the 10% value was 2.0 for body phantoms, and 1.8 for head phantoms. Average vendor CTDI100 ranged between 0.17 and 0.20 mGy/mAs for head phantoms, and 0.07 and 0.10 mGy/mAs for body phantoms. There were no evident trends in CTDI100 as a function of time for any one of the four vendors investigated. Conclusion: Conclusions. At the same kV/mAs, patient doses can differ by up to a factor of approximately two, and clinical protocols should therefore be based on patient dose (CTDI100) rather than the selected mAs value.
SU‐GG‐I‐89: Automatic Segmentation of Risk Structures
Authors: Schulz H , Vik T , Bystrov D , Leavens C , Kaus M , Jaffray D , Pekar V
Published: July 2008

Purpose: The clinical implementation of conformal radiotherapy IMRT has substantially increased the need for automated contouring tools. Implementation of image‐guided adaptive RT will further increase the need. The objective of this work is to develop and assess a fully automated method for delineating risk structures on the basis of statistical models and anatomical atlases. Method and Materials: Anatomical variability is modeled from a set of training images from multiple patients, where structures of interest were manually contoured by clinical experts, and salient anatomical landmarks were defined, e.g. the mastoid process. We use landmark correspondences and thin‐plate spline (TPS) approximation to map all training data into a common geometrical reference frame and generate a mean volumetric image and mean 3D surfaces; spatial variation and dependency of the landmarks is encoded in a statistical model and their local appearance is derived from the mean image. This model is then used to automatically find the positions of the landmarks in a new patient image. TPS is used to map the contours from the mean volume onto the new volume. Finally, the mapped contours are refined using a model‐based segmentation technique. Results: We evaluated our method for three anatomical regions: head‐neck, pelvis and thorax, on multiple clinical datasets accompanied with manually created contours. Quantitative results where collected for spatial accuracy, both for detection of the landmarks as well as for the final contours. For initialization the distance to ground‐truth was 8.9 ± 4.8 mm, contour distance was 3.5 ± 4.5 mm across all anatomies. Computation time was below 50 seconds in all cases. Conclusion: A fully automated segmentation method was developed and quantitatively evaluated for risk structures from CT images in the head‐neck, pelvis and thorax. Future work will increase consistency and efficiency for structures with poor image contrast.
SU‐GG‐I‐98: Hermitian Curve Interpolation for CT‐Data Re‐Sampling
Authors: Volken W , Frei D , Manser P , Mini R , Born EJ , Fix MK
Published: July 2008

Purpose: Development of an interpolation algorithm for re‐sampling spatially distributed CT‐data with the following features: global and local integral conservation, avoidance of negative interpolation values for positively defined datasets and the ability to control re‐sampling artifacts. Method and Materials: The interpolation can be separated into two steps: first, the discrete CT‐data has to be continuously distributed by an analytic function considering the boundary conditions. Generally, this function is determined by piecewise interpolation. Instead of using linear or high order polynomial interpolations, which do not fulfill all the above mentioned features, a special form of Hermitian curve interpolation is used to solve the interpolation problem with respect to the required boundary conditions. A single parameter is determined, by which the behavior of the interpolation function is controlled. Second, the interpolated data have to be re‐distributed with respect to the requested grid. Results: The new algorithm was compared with commonly used interpolation functions based on linear and second order polynomial. It is demonstrated that these interpolation functions may over‐ or underestimate the source data by about 10%–20% while the parameter of the new algorithm can be adjusted in order to significantly reduce these interpolation errors. Finally, the performance and accuracy of the algorithm was tested by re‐gridding a series of X‐ray CT‐images. Conclusion: Inaccurate sampling values may occur due to the lack of integral conservation. Re‐sampling algorithms using high order polynomial interpolation functions may result in significant artifacts of the re‐sampled data. Such artifacts can be avoided by using the new algorithm based on Hermitian curve interpolation. Conflict of Interest: This work was supported in part by Varian Medical Systems.
SU‐GG‐I‐103: Patients Registration Accuracy in Prostate Cancer with OBI Guidance Including and Excluding Gold Fiducials
Authors: Mardirossian G , Zheng Y , Fitian I
Published: July 2008

Purpose: To test, validate and compare registration accuracy in prostate cancer following KV and CBCT image guidance with and without the utilization of implanted Gold fiducial makers. Method and Materials: Four Gold fiducial were implanted in each of 10 prostate cancer patients enrolled in IMRT daily treatment delivery on a Trilogy system with OBI. By ignoring the fiducial seeds, the image registration with CBCT was first performed by four professional individuals using transitional and rotational alignment of the anatomical definition of the prostate as observed from both planning CT and daily CBCT. Contours were also utilized in performing the registration and occasional KV images were also acquired. The shifting coordinates were recorded. Occasionaly, KV imaging was also performed and recorded the shift for later comparison with CBCT. Fiducial registration was then performed to provide the actual treatment shifts. Accordingly, a total of 265 image registrations were performed and 510 translational offset shifts were recorded presenting anatomical and fiducial positioning. Results: KV and CBCT shifts were correlated in the lateral and longitudinal directions (0.9 and 0.8), but not in the vertical (0.4) with an average overall variation (SD) 2.8 mm. Correlation analysis of the seed relative locations revealed limited inaccuracy in seed registration with CBCT. The overall SD in the lateral, Longitudinal and vertical axis are 0.7, 0.8 and 1.5 mm respectively. Adequate registration would require a margin of 2 mm for lateral and longitudinal and 3.5 mm for the vertical (98% confidence). The anatomical registration requires larger prostate margin; Mean (range) as 3.2 (2.5–4.5) mm, 6.2 (5.2–7.9) mm and 5.5 (4.5–6.1) mm for lateral, longitudinal and vertical directions respectively (98% confidence). Conclusion: Daily CBCT fiducial registrations are more consistent as compared to KV\CBCT Fusion. CBCT interpretation is anatomically challenging and requires larger margin compare to fiducial fusion for dose coverage.
SU‐GG‐I‐104: A Data Structure for B‐Spline Registration
Authors: Sharp G , Wu Z , Kandasamy N
Published: July 2008

Purpose: To design a better data structure for B‐spline registration. Method and Materials: We have designed a grid alignment technique and a data structure that greatly improves the computation speed of B‐spline registration. The basic idea is to align the B‐spline grid with the voxel grid, so that the volume is partitioned into tiles of equal size. The use of equal sized tiles is important for this approach, because it allows the coefficient multipliers used for B‐spline interpolation to be precomputed. A data structure consisting of four tables is used to provide fast access to precomputed index and multiplier values used for interpolation and gradient computations. Voxel indices are decomposed into tile and offset values which are accumulated in a single loop for each voxel. Results: We have implemented the aligned B‐spline registration method, and compared its performance against ITK B‐splines and demons registration. Aligned B‐splines with a mean‐squared error cost function was found to be roughly equivalent in speed to the demons algorithm, and considerably faster than ITK B‐splines. Running times were found to depend only on the image size, and not on the B‐spline control point spacing. Conclusion: When possible, an aligned grid should be used for B‐spline registration.
SU‐GG‐I‐106: Evaluation of Free‐Form B‐Spline Deformable Registrations for Noisy CBCT/SimCT Images
Authors: Kim J , Chetty I
Published: July 2008

Purpose: Accurately registering noisy cone‐beam CT (CBCT) images to simulation CT (SimCT) is a challenging task. The goal of this study is to evaluate B‐spline based free‐form deformable registrations with noisy CBCT images. Method and Materials: CBCT images were retrospectively selected with large rectum gases and/or significant motion artifacts around bones. Then, they were registered to corresponding SimCT images using Elastix, a software package implemented in conjunction with ITK (Insight Segmentation and Registration Toolkit). Each registration consisted of three sequential stages; translation, affine, and B‐spline. Each stage had three resolutions to avoid local minima and to reduce the overall registration time. The B‐spline grid spacing in the finest resolution was (8, 8, 2) voxel in the (x, y, z) directions respectively. Mutual information (MI) was chosen as similarity metric with random sampling per iteration. The sampling size was 10% of the image size. Registrations were evaluated using an interactive blending software. Results: External skin boundaries were found to match well, but internal organ registration included notable errors, especially near areas containing large amount of rectum gas. Errors were also observed around the top and bottom slices of the input CBCT images, where the bones were shown to “stretch” in the superior/inferior direction. Conclusion: Based on the preliminary results, the metric MI with free‐form deformation alone is inadequate for noisy CBCT/SimCT registrations. Our future study includes using rigidity constraints on bones and customary constraints on deformable organs.
SU‐GG‐I‐113: A Phantom for Functional CT/CBCT Breast Cancer Imaging
Authors: Clarkson R , Yeung I
Published: July 2008

Purpose: Cone Beam CT (CBCT) breast scans are an emerging technology with the potential for a significant impact on breast imaging. Our purpose was to develop a phantom allowing us to test a method of achieving a Dynamic Contrast Enhanced (DCE) CBCT scan. This required a phantom that allows an injection of contrast that can change over time. Method and Materials: The breast phantom(s), of which 2 were developed, were adapted from the shape and size of the CIRS (Norfolk, VA) breast phantom model 051. Our two phantoms were manufactured using a Stratasys rapid prototyping machine, model Vantage (Stratasys, Eden Prairie, MN). We inserted one lesion (phase I) or two lesions (phase II) with water/contrast able to flow through the lesions, and in phase II, water/contrast was also able to flow through the main cavity as background. The phantoms were quantified using the in‐house GE Lightspeed CT machine, using a Manostat E‐series (phase I)/ecoline VC‐MC/CA8‐6 (phase II) peristaltic pump for water flow, and the Harvard Apparatus PHD 22/2000 programmable syringe pump for injection of contrast. Results: We scanned for four different types of uptake curves (impulse injection, plateau, increasing and decreasing), with 4–5 injections per trial, over 4 days/curve type, in order to completely quantify each phantom. This was done so as to have a reliable gold standard of curves for comparison with future CBCT curves. The impulse uptake curve can also be de‐convoluted with its injection curve, in order to obtain a characteristic function for each lesion. Each of the other types of uptake curves can then be successfully predicted through convolution of this characteristic function with the respective injection curve. Conclusion: Both phantoms have been successfully, fully quantified as to their characteristics with contrast injection, and are usable as phantoms to test our method for DCE‐CBCT scanning.
SU‐GG‐I‐121: Facing a Horrifying Reality: An Anatomy of MR Magnet Explosion
Authors: Sobol WT
Published: July 2008

Purpose: To investigate several recent sentinel events that led to catastrophic MR magnet failures, including magnet explosions. Method and Materials: An analysis of root cause for a catastrophic magnet failure has been performed, using available manufacturer's documentation. Practical on‐site conditions have been verified by conducting several walk‐through inspections. Further information was gathered during on‐site visits to two MR magnet factories in the US. Results: During past few years, there has been anecdotal evidence of increased frequency of incidental magnet quenches at customer installations throughout the US. Most of them were “white” (i.e. non‐destructive) quenches that occurred during magnet handling at installation or routine servicing (e.g. ramping up). These types of events have been known for a long time and are not subject of this presentation. However, spontaneous quenches have been recorded as well, especially for high field (3T) units. In most cases, the root cause of these events could not be immediately determined. This is a cause for concern, since a few of these events (author has documented knowledge of three that occurred in the Southeast US within the last year) represented a catastrophic magnet failure that can be described in simple words as magnet explosion. The root cause analysis, performed using available data, could not unequivocally determine the reason for the explosions. However, a failure of the magnet's cryogenic venting system has been identified as a strong, plausible candidate for the explanation of observed events. Conclusion: MR magnet explosions, long considered a myth, have become a reality. Since the most likely failure scenario is linked to failures of the magnet's cryoventing system, the medical physics professionals supporting MRI installations are urged to become familiar with the operational characteristics of magnet cryosystems, learn about proper site planning design, and develop methods of competent monitoring of cryoventing systems performance.
SU‐GG‐I‐124: A Universal Analysis On Temporal Uncertainty of FMRI Methods with Different Biophysical Mechanisms
Authors: Liu H , Hong Y , Wai Yau‐Yau
Published: July 2008

Purpose: Functional MRI (fMRI) using BOLD contrast has been widely applied to localize brain activations. However, the venous origin of the BOLD signal can cause varied temporal uncertainties in different brain regions. Besides the vasculature variations, determination of the BOLD response timing is also affected by the contrast‐to‐noise ratio (CNR). In this study, we propose a universal analysis to differentiate the temporal uncertainty resulted from different biophysical mechanisms. The analysis was applied to compare CBV‐ and BOLD‐based experiments at different field strengths. Method and Materials: Eight normal volunteers participated in this study (3 at a 1.5T Vision and 5 subjects at a 3T Tim‐Trio scanner). A GE‐EPI was used for the BOLD experiment (TR/TE/FA = 1000ms/60ms/90° at 1.5T and 1000ms/35ms/64° at 3T). A non‐slice‐selective IR‐GE‐EPI sequence was used for the vascular space occupancy (VASO) experiment (TI/TR/TE/FA = 665 ms/2000ms/9.3ms/90° at 1.5T and 710ms/2000ms/12ms/90° at 3T). Each experiment contained 30 repeated trials of brief (1s) visual stimulation. CNR and response onset time were quantified for each activated voxels in the visual area. Results: The measured CNR increased with number of trials averaged. The plot of the standard deviation of onset time (ΔT) vs. CNR was able to differentiated VASO from BOLD results, showing less onset variations in the VASO measurements when comparing at the same CNR levels. The same two curves (BOLD and VASO) were able to describe results obtained at different field strengths, i.e. 1.5T and 3T results shared the same curves with 3T shifted to higher CNR regions. Conclusion: We proposed to analyze temporal uncertainty of HRs measured in fMRI at different CNRs which were manipulated by averaging different numbers of repeated trials. The results demonstrated that this analysis was universal to measurements at different field strengths and able to characterize distinguished biophysical mechanisms of different fMRI methods.
SU‐GG‐I‐133: Low Dose Dual Energy Breast Imaging with An Energy Resolving Photon Counting Detector
Authors: Ducote JL , Klopfer MJ , Molloi S
Published: July 2008

Purpose: To investigate the feasibility of low dose dual energy imaging with an energy resolving photon counting detector using a single exposure / single kVp technique for the measurement of breast density (the percentage of glandular breast tissue) in mammography. Method and Materials: An analytical simulation model was developed to determine the mean glandular dose required to quantify breast density with a novel energy resolving photon counting detector to within an accuracy of 1%. The detector was modeled as a 3 mm thick layer of CdZnTe. All detected photons above 15 keV were counted and separated into either a low or high energy bin as determined by a user defined threshold. Only stochastic x‐ray noise sources were considered. The breast was modeled as a semicircle 10 cm in radius with homogenous equal thicknesses of adipose and glandular tissues, corresponding to a density of 50%. Polyenergetic spectra from a tungsten target anode x‐ray tube were simulated from 20 – 150 kVp. Tube filtration was 1.0 mm Be and 0.5 mm Al. At each kVp, the threshold energy was varied to determine the optimal dual energy SNR in the breast density image. Results: For a 4.2 cm breast, the optimal beam energy determined from simulation was determined to be 95 kVp with a threshold separating low and high energy beam spectra at 30 keV. The predicted required minimal mean glandular dose for the dual energy image was low (< 1 μGy), and the corresponding incident photon fluence was approximately 10,000 photons per square millimeter. Conclusion: The results suggest that breast density, a quantity strongly associated with the risk of breast cancer, can be accurately measured at low dose, with an energy counting photon counting detector.
SU‐GG‐J‐40: Automated Detection of Gold Seeds in Prostate Electronic Portal Images
Authors: Liu X , DeMarco J , Lee S
Published: July 2008

Purpose: Implanted gold seed markers are currently used to localize the relative prostate position in prostate electronic portal images during radiation therapy. This study describes a new algorithm that automatically identifies the gold seed marker positions in the Anterior‐Posterior (AP) and Lateral (LAT) prostate electronic portal image pairs. Method and Materials: Four prostate patients were imaged on a Siemens Oncor linear accelerator using standard AP and LAT image projections. The automated detection algorithm includes two phases: The first phase is to preprocess the image by passing a selected bandpass filter, including “Intensity Autoscale” and “Contrast Saturation” functions to produce a better visual contrast of the three gold seeds; The second phase is to do automatic detection by utilizing “Prewitt” edge detection method to convert the image into black and white image, and then detecting each gold seed position in a pre knowledge based selected window for AP and LAT images. The automatic detection algorithm was written in Matlab, and the detection results were compared to the positions which we marked in EPID images by using ImageJ. Results: For all the collected images, the gold seed markers are clearly visualized on the preprocessed images. We tested 8 pairs (AP/LAT) of images using the automatic detection algorithm and compared the gold seed positions to the manually marked seed positions. The automatic detection algorithm is able to locate the seed to within ±4 pixels (which is within ±1.6mm) of the manual seed location. Conclusion: This method improves visualization of EPID images and also has good accuracy for localizing the position of gold seeds on AP and LAT projections. Future work will adapt the localization algorithm for routine clinical use for the automatic detection of gold seeds in prostate EPID images.
SU‐GG‐J‐47: Clinical Implementation of An Integrated System for Image‐Guided Radiation Therapy (IGRT) and Adaptive Radiation Therapy (ART)
Authors: Yoo S , Wu Q , Yin F
Published: July 2008

Purpose: It is critical that image‐guided radiation therapy (IGRT) and adaptive radiation therapy (ART) are performed with clearly defined goals without abusing the technologies. This study illustrates the current integrated system that provides efficient implementation of IGRT and ART. Method and Materials: The process of IGRT starts with planning CT, where the target volumes and critical organs are delineated in the treatment planning system (TPS). A treatment plan is designed and proper QA is performed. For daily treatment, a patient is setup based on skin markers, followed by 2D imaging guidance with radiographs and DRR Positioning correction is achieved by automatically shifting the treatment couch. Couch positions before and after shift are recorded with the images in the integrated system. Based on the results of daily 2D imaging guidance over the first week, the patient‐specific IGRT protocol is determined between daily and bi‐weekly/weekly IGRT. The process of ART is performed to adapt patient specific variations using 3D CBCT imaging guidance. If a significant geometrical variation (e.g. deformation, rotation, tumor shrinkage/enlargement) is observed, a verification plan based on CBCT is generated in TPS. We evaluate the dosimetrical consequences of the geometrical variation that cannot be corrected on‐line by couch shift. Following the evaluation, a decision is made among choices of a new immobilization device, redesign of the PTV‐margin or OAR‐margin, re‐planning based on CBCT or new planning CT, and IGRT frequencies. Results: The integration of IGRT and ART is achieved by the ARIA (Varian Medical Systems, Inc), which has one server connected to CT/MR/PET units, TPS, record‐and‐verifying system, treatment consoles, and offline review for IGRT evaluation. IGRT takes 2–5 min and ART takes 1–2 days. Conclusion: Efficient and effective evaluation and decision‐making process for IGRT and ART are possible with the integrated system in a timely manner.
SU‐GG‐J‐49: Clinical Utility of a Portable Ultrasound Bladder Scanner in Prostate External‐Beam Radiation Therapy
Authors: Schinkel C , Kudchadker R , Choi S , Lee A
Published: July 2008

Purpose: External‐beam radiation prostate patients are treated with a full bladder to minimize the amount of bladder in the field, to maintain a reproducible daily setup during treatment and to push the bowel away from the target volume. This work investigates the feasibility of using a portable hand‐held ultrasound scanner, the BladderScan® (Verathon, Bothell, WA), to determine the degree of bladder fullness before each treatment. Method and Materials: First, the accuracy of the bladder scanner (BS) relative to volume estimates from axial and sagittal ultrasound images was examined. Daily ultrasound images were acquired immediately before treatment for each of five patients with a B‐mode Acquisition and Targeting (BAT) ultrasound system (Best Nomos, Cranberry Township, PA). Bladder volume was estimated from the images by taking orthogonal measurements and using the formula 0.72*x*y*z. The BS was also used to determine bladder volume before each treatment, and the results were compared with the corresponding BAT measurements. Second, the accuracy of the BS relative to computed tomography (CT) was investigated. For a number of patients, the BS was used to measure bladder volume shortly after the simulation CT scan was acquired. The BS measurements were then compared with the bladder contour volumes calculated by a treatment planning system. Results: A strong correlation was found (r = 0.87 for all five patients combined) between the daily bladder volume estimated from BAT images and the BladderScan measurements. Preliminary results for 38 patients indicate that there is also a correlation between CT and BS volumes (r = 0.59). Conclusion: The bladder scanner provides a reasonable estimate of daily bladder volume. It is more efficient than BAT for this purpose, and could potentially be used to determine daily bladder volume for post prostatectomy patients as well as those with implanted fiducials.
SU‐GG‐J‐50: Comparing IGRT Shifts with MVision and CT On Rails Systems Using Anthropomorphic Phantom
Authors: Mota H , Ferreira M , Wolfe M , Allison R , Sibata C
Published: July 2008

Purpose: To evaluate the IGRT repositioning shifts determined by MV Cone Beam CT and by CT on rails using an anthropomorphic phantom. Method and Materials: Two IGRT systems installed in the same Linac room were studied. The CT based IGRT has been used in our Siemens Primus since 2004. Recently, a MV conebeam CT (Siemens MVision) was implemented with the objective to reduce the therapist time to obtain the IGRT shifts. The shifts and the corresponding total time were evaluated using an anthropomorphic PIXY® phantom. CTs of the phantom were obtained for head‐and‐neck, pelvis and lung and treatment planning was generated in XIO‐CMS for each site. The set of images, structures and plans was sent to both IGRT stations. Bbs were placed on the phantom surface at the isocenter axis, as a reference for the daily CT images. For each plan the MVCBCT was obtained three times to determine its reproducibility for 5 and 8 MU protocols. The registration for MVCBCT was done automatically and verified with manual registration. The table was then flipped to the CT position and the images acquired. In this case the registration is done manually and the isocenter shift is obtained through the bbs position. The procedures ware repeated for all sites. The total time to obtain the shifts and the image quality were also registered. Results and Discussion: The reproducibility of the MVCBCT for different protocols was within 2 mm. The maximum difference for MVCBCT and CT was 4 mm. The MVCBCT has poor image for soft tissue, and the fusion registration is based on mutual information. The total time to obtain the shifts is about 3 min for the new system and 7 to 8 min for the CT based system. This study excludes any deviation due to patient rotation and internal changes.