bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐I‐81: Surface Dose of Angular Current‐Modulated CT Exams
Authors: Judy P , Nawfel R , Leidecker C , Silverman S
Published: July 2008

Purpose: An analytic procedure was developed and validated to determine why the TLD measured lateral skin dose of angular tube‐current‐modulated CT‐urography exams was 7% less than the anterior skin dose even though the tube current in the lateral projection was greater by about a factor of 2 than anterior tube current and the lateral skin was 6 cm closer to the x‐ray focal spot (the closest distance to tube focal spot path). Method and Materials: Exponential attenuation, exponential absorption, and inverse square law were used to estimate the anterior and lateral dose to a miscentered cylindrical test object. The source filter was described by the diameter of a cylindrical object, i.e., the filter would attenuate such that detected intensity is constant when such an object of that size is centered in the data collection field of view. Surface exposure measurements used 16‐cm, 20‐cm, and 32‐cm acyclic test objects. Results: For constant tube current the surface exposure was a decreasing function distance between the center of tube rotation and object surface. Surface doses had a weak dependence on phantom size when the skin surface was greater than 5 cm from center of tube rotation. A 100 cm filter fit surface phantom surface exposures. The analysis predicted that the lateral skin dose would be a factor of 2 lower than the anterior dose. Conclusion: The patient skin dose can be determined by the product CTDI measured in air at CT scanner center of tube rotation and a factor that is determined by the distance the skin surface is from the center of tube rotation. The comparisons with direct skin dose measurements were a useful QA procedure. Conflict of Interest: Christianne Leidicker is an employee of Siemens.
SU‐GG‐I‐84: Operation Logic of Coventional FluoroscopyAutomatic Brightness Control
Authors: Lin P
Published: July 2008

Purpose: New generation of fluoroscopic imaging systems are equipped with spectral shaping filters complimented with sophisticated automatic brightness (and image quality) control logic called fluoroscopy curve or trajectory. Such fluoroscopy curves were implemented first on cardiovascular systems, and are now available on conventional fluoroscopy equipment. This study is to investigate the control logic operations under the fluoroscopy and spot filming/acquisition modes of a conventional fluoroscopy system typically installed for Upper‐Lower GI Examination Suites, Interventional Endoscopy Laboratory, Gastrointestinal Laboratory and Pain Clinics. Method and Materials: A brand new GE Precision 500D fluoroscopy system was chosen for the investigation which was installed in the middle of February 2008. Two radiation detectors were employed to monitor the patient and image intensifier air kerma dose and dose rate as functions of increasing PMMA plastic phantom thickness. The measurement protocol utilized by the AAPM TG 125 was followed as much as possible with some exceptions due to the mechanical constraints. The image quality was evaluated with the NEMA‐SCAI phantom at 4″, 8″, and 12″ total phantom thicknesses. Results: The data analysis and the graphs obtained from this study showed extensive use of copper filters (up to 0.3 mmCu) similar to the cardiovascular imaging systems (up to 0.9 mmCu). However, it is with fewer steps of copper filters and less power input to the x‐ray tube, reflecting the differences of clinical applications, and complexity of examinations. As expected, it also showed somewhat narrower dynamic range the imaging system is able to cover with reasonable “penetration” as opposed to that of cardiovascular imaging systems. Conclusion: It is shown that compared against previous generations of fluoroscopy systems, the new conventional fluoroscopy systems equipped with spectral shaping filters provide reduced patient dose while maintaining reasonable (better than just acceptable) image quality. In‐depth discussion will be provided at the presentation.
SU‐GG‐I‐85: Tumor Shape Analysis Using Poisson's Equation
Authors: Sintay B , Bourland J
Published: July 2008

Purpose: The role that tumor shape plays in disease treatment, progression, and outcome is not well understood. This work investigates the quantification of shape information required for the statistical analysis of tumors. Method and Materials: The statistical shape characterization method proposed by Haidar et al. 2006 that utilizes Poisson's equation is adapted for tumor shape parameterization. An extensive algorithm using finite differences and software toolset has been developed for efficient computation of the solution to Poisson's equation for three‐dimensional tumor volumes as well as general anatomic features. A characteristic plot that is unique to a given shape is generated. The statistical framework of this method utilizes a permutation test to establish significance between sets of characteristic plots. The method has been thoroughly tested for 2D and 3D test datasets that include simple geometric shapes as well as contoured volumes from images of the human brain. Results: This method is able to distinguish subtle differences in simple 2D and 3D phantoms as well as human brain anatomy. Such differences are difficult to quantify and often do not correlate to volume. Scale and translation insensitivity of the method are also proved. Imaging studies show that tumor geometries that are closely related have notably similar shape characteristics that correlate to p‐values less <0.5. Conclusion: Tumor shape can be statistically modeled by a metric based on a 3D solution to Poisson's equation to allow full analysis of morphology. This method yields a model by which tumors can be studied independent of translation or scale. Future work through a clinical trial aims to predict outcome based on shape‐related cues that are volume independent. Research supported in part by Varian Medical Systems.
SU‐GG‐I‐86: Validation of a One‐Click Spine Segmentation Approach for Online Planning of Palliative Radiation Treatment
Authors: Pekar V , Letourneau D , Jaffray D
Published: July 2008

Purpose: To develop an efficient automated method for spine segmentation in cone‐beam CT for online planning of spinal metastases radiotherapy. Method and Materials: A semi‐automated spine segmentation and labeling approach has been developed and validated. The user provides the position and label for an arbitrary vertebra center, and the algorithm automatically identifies the outlines and labels of all visible vertebrae in the field on view. The method is based on adapting 3‐D deformable vertebrae models, placed according to the relative positions derived from a spine atlas. Using the segmentation results, ellipsoid ROIs can be superposed automatically to the vertebrae using co‐registration of the segmented vertebrae with the vertebrae models in the atlas. Ellipsoid ROIs can be used for margin design and avoid excessive expansion due to vertebra processes. Results: The method has been validated on 29 CBCT spine datasets, representing all treatment areas: cervical, thoracic and lumbar. The total number of visible vertebrae was 234. For every dataset, segmentation was started from every visible vertebra. The deviations between the automatically detected position of the vertebra centers and their manual estimations were computed. For about 59% of all vertebrae, the median deviation was less than 5 mm, in approx. 33% of the cases was between 5 and 10 mm, and in approx. 8% of the cases was over 10 mm, which is an indication for a segmentation failure. The running time was a few seconds on a 3.4 GHz PC. Conclusion: Validation study of a one‐click semi‐automated approach to spine segmentation and labeling in cone‐beam CT has been performed. The method has the potential to significantly reduce the time required to identify clinically relevant areas in online planning. A fully automated version of the algorithm is currently under investigation. Conflict of interest: This research is supported in part by Philips Healthcare.
SU‐GG‐I‐87: Inconsistencies in Discrete Space and Continuous Space Lesion Boundary and Area Definitions
Authors: Sensakovic W , Armato S , Starkey A , Roberts R
Published: July 2008

Purpose: Measurement of the size of anatomic regions of interest is used to diagnose disease, track growth, and evaluate response to therapy. The discrete nature of medical images allows for both continuous and discrete definitions of region boundary. These definitions may, in turn, support several methods of area calculation that give substantially different values. This study investigated several boundary definitions and area calculation methods to quantify these differences. Method and Materials: Two sets of region boundaries were investigated, one defined in continuous space and one defined in discrete space. A total 1,764 manual lung nodule boundaries were obtained from the Lung Image Database Consortium (LIDC) database. Lung nodule area was calculated for each of these discrete‐space boundaries based on four area metrics: boundary‐excluded pixel counting, boundary‐included pixel counting, and two variants of Green's Theorem applied to vertices defined by the center of each boundary pixel. Adrenal gland area was calculated for 71 manual continuous‐space adrenal gland boundaries based of four area metrics: Green's Theorem applied to the original continuous boundary, boundary‐excluded pixel counting after direct conversion to discrete space, boundary‐included pixel counting after direct conversion to discrete space, and pixel counting after pixel‐center conversion to discrete space. Results: Based on the same set of adrenal gland boundaries, mean adrenal gland area ranged from 85.1 ± 35.4 pixels to 126.2 ± 42.8 pixels, depending on the method of area calculation. Based on the same set of lung nodule boundaries, mean lung nodule area ranged from 147.0 ± 212.1 pixels to 208.8 ± 251.7 pixels, depending on the method of calculation. Conclusion: Inconsistent application of region boundary definition and area calculation may substantially impact measurement accuracy. Substantial differences exist among the various area calculation methods supporting the necessity, in both the research and clinical settings, to consistently apply boundary definition and area calculation methods.
SU‐GG‐I‐93: A Fast and Simple Software‐Based Method for X‐Ray Scatter Reduction in Portable X‐Ray Systems
Authors: Sechopoulos I , Schmitz A , Eberhard J
Published: July 2008

Purpose: To develop a processing method to reduce the effects of x‐ray scatter in images acquired with portable x‐ray systems without an anti‐scatter grid. Method and Materials: Due to the varying geometry inherent in portable x‐ray systems, the use of anti‐scatter grids with a high ratio is challenging. For clinical applicability, the algorithm must be fast and preserve the image texture. First an adequate understanding of the x‐ray scatter signal present in different radiography applications was obtained using Monte Carlo (MC) simulations of several clinical applications. From the simulations it was confirmed that the x‐ray scatter fields consisted of a low‐frequency offset, with very different shapes and magnitudes depending on the image being acquired. The developed algorithm, a modified version of unsharp masking, involves masking the open field area and the thin sections of the body, replacing these areas with the mean signal from the edges of the body, applying a low pass filter, and then subtracting a weighted version of the latter from the original image. The masking is performed to avoid the inclusion of the very high signal areas from the low pass image, which would result in an overestimation of the signal to be removed. Results: The algorithm reduced the x‐ray scatter signal in simulated MC images by 50&–80%, depending on the image and the location analyzed. When applied to images of a thorax phantom obtained with a portable x‐ray system without a grid, the quality of the images were improved enough to be comparable to those obtained with a clinical fixed system with a grid. Conclusion: The use of the developed scatter reduction algorithm seems to compensate for the inability to use a high ratio grid in portable systems. Further testing will be performed. Conflict of Interest: Research sponsored by GE Global Research.
SU‐GG‐I‐97: Automated Extraction of White Matter Regions in Multiple Sclerosis Based On High Resolution Magnetic Resonance Imaging
Authors: Magome T , Arimura H , Kakeda S , Yamamoto D , Kawata Y , Ohki M , Toyofuku F , Higashida Y , Korogi Y
Published: July 2008

Purpose: The atrophy of white matter (WM) in multiple sclerosis (MS) could correlate with the progression of MS. Therefore, quantitative diagnosis of the atrophy in WM regions is crucial for diagnosing or follow‐up MS using magnetic resonance imaging (MRI), which should have high resolution. However, it is laborious for neuroradiologists to assess the area or volume of WM in MR images on a slice‐by‐slice basis. Our goal of this study was to develop an automated method for extraction of WM regions from high resolution MR images. Method and Materials: High resolution MR images (matrix size: 512×512, pixel size: 0.43mm) of eight patients with MS lesions and four control subjects were acquired from a 3.0T MRI scanner. First, a brain parenchymal (BP) region was extracted from a T1‐weighted image based on a statistical analysis of a gray‐level histogram. Second, initial WM regions were segmented on a T2‐weighted image by using an automated threshold technique for a gray‐level histogram in the BP region. Third, the “nominal” WM region including basal ganglia was determined by means of a level set function changing with a speed function, which decreases at around boundaries between gray matter and WM regions. Finally, WM regions were determined by subtracting basal ganglia from the nominal region, which was segmented based on approximation of neighboring WM regions by using a two‐dimensional second order equation. Results: For evaluation of our method, we calculated an overlap measure between the WM regions obtained by our method and neuroradiologists. As a result, the average overlap measure of WM regions was 73 ± 6.8 % for 12 cases. Conclusion: Our automated extraction method of the white matter seemed fairly reliable, and might be useful for monitoring progression of MS.
SU‐GG‐I‐100: A Mesh‐Based Anatomical Deformation Method for Creating Size‐Adjustable Whole‐Body Patient Models
Authors: Na Y , Zhang J , Xu X
Published: July 2008

Purpose: Whole‐body patient models are needed for the assessment of organ doses in various CT imaging and external‐beam radiation treatment procedures. The Boundary REPresentation (BPRE) type of geometry offers greater control over the anatomical shapes and tissue/organ surfaces could be flexibly deformed. Currently tedious and time‐consuming manual adjustment is necessary. This paper discusses an automatic modeling method recently developed to create two adjustable adult male and female mesh models with dynamically deformable organs. Method and Materials: The algorithm for the development of the deformable RPI Adult Male/Female phantoms was implemented by MATLAB® 7.4. The anatomical mesh models were based the Anatomium™ 3D models whose organ geometries were morphed to agree within 0.5% with the ICRP reference male and female organ volume/mass data. These mesh morphing algorithms were used to automatically pre‐modify the dataset to have unique mesh information in each of organ boundaries and deform the whole meshes based on the ICRP volume/mass reference without unwanted surface overlapping through the special mesh overlap avoiding process. After the deformations, the RPI Adult Male/Female mesh models were transformed to the solid geometries through the voxelization process with 3.2 mm and 3.0 mm, respectively. Results: These phantoms have been used by transforming the solid geometries into the voxel domain that is compatible with well‐validated Monte Carlo radiation transport simulations such as MCNP, EGSnrc and GEANT4codes. Through these mesh deformation algorithms, complicated bone (cavity, spongiosa, and cortical bones) and muscle structures have been described in the RPI Adult Male/Female mesh models. Conclusion: This study has demonstrated the feasibility to create deformable RPI Adult Male/Female phantoms. These phantoms will be applied to various applications of including person specific adjustments depended on age, weight, and height changes.
SU‐GG‐I‐105: A Process to Determine Optimal Oblique Contouring Planes
Authors: Abraham C , Low D , Liu L , Parikh P , Mutic S , Thorstad W , Khullar D , Apte A , Deasy J , Ju T
Published: July 2008

Purpose: To create a more efficient and accurate method for contouring and contour reviewing. This study is concerned with the determination of the minimum number and optimal orientation of oblique planes for contouring structures. Method and Materials: A process was developed to determine the minimum number and optimal orientation of oblique contours to accurately describe prostate volumes. The process began with the development of a library of segmented prostates. The library was generated from the contours of previously treated conformal therapy patients. Surfaces were created using these clinical contours. A custom‐developed tool was used to select oblique cut planes through the surfaces. The intersections of the planes with the surfaces were used as the contours that were used to regenerate the surface. A comparison of the original and reconstructed surfaces was used to determine the accuracy of the regenerated surface. The number and orientation of the cut planes were varied to determine the minimum number and optimal orientation of the planes. Results: Examination of the oblique segmentation method for prostate volumes demonstrated an accurate segmentation surface while reducing the number of contours for five test cases. In the best instance the use of oblique segmentation was able to reduce the number of contours by a factor of two (19 to 9). However, in the worst instance the oblique segmentation method was only able to reduce the number of contours by 1.5 (12 to 8). Conclusion: This was the first in a series of studies intended to develop and evaluate the use of optimized oblique planes for manual contouring and indicated that the number of oblique segmented slices may be less than the number required when using transverse planes. Future studies will investigate if the use of oblique planes improves the overall accuracy of manual segmentation.
SU‐GG‐I‐107: Positron Emission Tomography Phantom Studies for Radiation Therapy Target Delineation
Authors: Lawrence M , Bourland J
Published: July 2008

Purpose: To create and employ a PET threshold model to contour NSCLC nodules and compare the results to a standard threshold method. Method and Materials: 8 FDG PET/CT scans were obtained of a cylindrical phantom containing 6 spheres of various volumes (16cc – 0.5cc) at various signal to background ratios (18 – 1.67). The peak activity of each spherical target and background activity was obtained (μCi/cc). The threshold that matched the PET target volume to the known volume was recorded for all scans, and threshold models were created for various target volumes and signal to background ratios. These models were then retrospectively applied to 3 NSCLC tumors treated with SBRT. Three tumor volumes were contoured using CT, our PET threshold model, and a constant 42% threshold. The conformity of all PET volumes to the CT volume was calculated. Results: The CT volumes for the NSCLC tumors were 7.2cc, 2.4cc, and 3.0cc. The threshold model produced PET thresholds of 37%, 34%, and 34% for the 3 NSCLC tumors. The resulting tumor volumes were 3.1cc, 2.8cc, and 2.4cc. Using the 42% threshold produced tumor volumes of 2.5cc, 2.1cc, and 1.8cc. The threshold model PET volumes spatially matched the CT volumes better than the PET volumes based upon the 42% threshold. Conclusion: A threshold model that varies with signal to background ratio and volume has been created. This study reveals the ability of the PET threshold model to improve NSCLC PET tumor contouring. PET volumes based upon the threshold model more closely match the CT volume than PET volumes based upon a constant threshold. In the future complex non‐spherical phantoms will provide further threshold models for PET target delineation, and this work is in progress with preliminary results.
SU‐GG‐I‐109: Using EGSnrc Within GATE to Improve the Efficiency Of positron Emission Tomography Simulations
Authors: Kawrakow I , Mitev K , Gerganov G , Madzhunkov J , Kirov A
Published: July 2008

Purpose: GATE, a Geant4 based application for use in emission tomography, is a powerful package that permits realistic Monte Carlo simulations of both, the scanner geometry and the digitization chain. The main problem when using GATE in practice is its slow simulation speed. The purpose of this investigation is to improve the efficiency of PET related simulations. Method and Materials: An EGSnrc based radiation transport tool, referred to as egs_pet, is developed. egs_pet can be used together with GATE in two modes: In mode 1, egs_pet performs the simulation of radiation transport in the phantom and passes exiting particles to GATE for further transport through the scanner geometry and for digitization. In mode 2, egs_pet performs the entire simulation and writes energy depositions in the detectors to a file. GATE is modified to be able to read this file when performing the digitization. Results: The correct operation of egs_pet within GATE is validated using benchmark calculations of a source within a water phantom and a detailed model of the GE Advance PET scanner. In mode 1, the number of singles and coincidences are found to agree with GATE within the statistical uncertainties (0.2% for singles). Differences of about 0.5% are observed in mode 2, which can be attributed to differences between Geant4 and EGSnrc when modeling binding effects for photon interactions in BGO. For a 4 mm voxel phantom, the simulation efficiency is increased by a factor of 4 in mode 1, and by a factor of 130 or 44 with digitization excluded or included in mode 2. Conclusion: A new Monte Carlo tool for PET simulations based on EGSnrc is developed and incorporated into GATE. Significant gains in simulation efficiency are achieved. Results from egs_pet simulations agree with GATE at the 1% level.
SU‐GG‐I‐110: Study of the Use of Protons and Carbon Ions for Patient Imaging
Authors: Seco J , Safai S , Paganetti H
Published: July 2008

Purpose: An evaluation of protons and carbon‐ions for generating radiographic images is performed. The contrast, signal‐to‐noise ratio, energy and spatial spread of protons and carbon ions passing through various tissues defined in ICRU were evaluated for different incident energies. Method and Materials: The Monte Carlo package GEANT4 was used to simulate the transport of protons/carbon‐ions through different ICRU soft tissues such as: , lung, adipose tissue, soft‐tissue, muscle, cartilage and cortical bone. Proton energies were 150–300 MeV and carbon ion energies were 360–500 AMeV. In order to study how the energy and the spatial spread of the beam varies for different thicknesses of ICRU tissues. The incident proton and carbon ions were pencil beam like with spot size of 1 micron‐meter and with direction of motion perpendicular to the surface of the phantom. The spatial spread of exit particles is obtained from the standard deviation of the position of the exit particles relative to the center of the incident beam. Results: The spatial‐spread of 200–300MeV protons and 360–500 AMeV carbon‐ions passing through 20cm of soft‐tissue, representing a typical body thickness, was respectively 2mm and 0.05mm. Carbon‐ions allow significantly better spatial resolution than proton beams. The mean exit energy for protons and carbon‐ions was respectively 87–223MeV and 113–320 AMeV. The energy spread of the protons and carbon‐ions was respectively 5.1–8.0MeV and 1.28–0.91 AMeV. The contrast of 10mm of bone‐to‐soft tissue is 7.20%–2.1% and 59%–53% respectively for protons and carbon‐ions. Conclusions The spatial‐resolution attainable with protons and carbon‐ions passing through 20cm is respectively 2mm and 0.050mm. The significantly heavier carbon ions suffer less multiple Coulomb scatter within the patient than the protons and therefore can allow sharper images. Contrast of bone‐to‐tissue is higher in carbon‐ions than in protons. The high contrast makes this tool attractive for online treatment‐position‐verification.
SU‐GG‐I‐114: Detector Characterization of a New Flat‐Panel Imager: Prospects for Image Quality Improvement in Fluoroscopy and Cone‐Beam CT
Authors: Mail N , Moseley D , Siewerdsen J , Jaffray D
Published: July 2008

Purpose: To characterize the imaging performance of a new flat‐panel‐imager (FPI) with respect to metrics such as detector gain, linearity, lag, modulation transfer function (MTF), noise‐power spectrum (NPS), and detective quantum efficiency (DQE) and to evaluate its potential application in fluoroscopy and cone‐beam CT for radiation therapy guidance. Method and Materials: The detector examined was a Trixell (Pixium 4343RF) indirect‐ FPI with a 2881×2880 array of 0.143×0.143 mm2 pixels, 43×43 cm2 FOV and a 0.06 mm thick CsI:Tl x‐ray converter. The FPI was operated at a frame rate 3 fps. Gain, linearity and NPS were calculated using gain‐corrected flood images. MTF was measured using an edge‐spread function method. DQE was calculated from the measured MTF and NPS. Image lag was characterized as a function of incident exposure. NPS, MTF, DQE and lag were compared with a FPI design (Perkin Elmer RID1640) currently employed in image‐guided radiotherapy. Results: The dark current stabilizes after 30 minutes. The detector has high gain and linearity with R2∼1. The 50% MTF was achieved at 1.51 and 0.91 lp/mm at 120 kVp for Trixel and Perkin Elmer (PE) FPI, respectively. The spatial resolution was limited by the focal spot size. The NPS(f) is found lower than the PE at 120 kVp for the same pixel saturation. The DQE is calculated 55 and 34% at 1.25 lp/mm for Trixel and PE, respectively. The first frame lag is 7 times lower than Perkin Elmer for the same pixel saturation at 120 kVp. Radiographic images of a head phantom show high contrast and spatial resolution. Conclusion: Imaging performance metrics (in particular, the high linearity, low lag, and high DQE(f)) suggest a significant improvement for the Trixell FPI and strongly support potential application of this detector for fluoroscopy and cone‐beam CT.

Research sponsored by Elekta.
SU‐GG‐I‐115: Characterization of Clinical CBCT and MVCT Systems Based On Fundamental MTF, NPS and DQE Measurements Using a Conventional CatPhan Phantom
Authors: Gopal A , Samant S
Published: July 2008

Purpose: In image guided radiation therapy (IGRT), the performance of image guidance modalities like kilovoltage cone‐beam computed tomography (CBCT) and megavoltage computed tomography (MVCT) systems is qualitatively verified with a vendor‐provided CatPhan phantom. For a more meaningful QA tool, a methodology to use CatPhan phantoms for fundamental measurements of modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) for CBCT and MVCT systems is presented. Method and Materials: We have extended the method of using bar‐pattern line‐pairs for MTF measurement (that we recently validated for megavoltage imaging) to CBCT and MVCT imagers by using line‐pair inserts within the CatPhan for axial plane MTF measurement. The MTF was also obtained by evaluating a point response from a tungsten carbide bead insert to validate our method. Axial slices representing homogenous water‐equivalent regions of the CatPhan were used to measure NPS that along with the MTF was used to compute DQE. The photon fluence contribution to each slice of the CatPhan was estimated from ion‐chamber dose measurements in a water phantom for identical image settings and Monte Carlo simulation based fluence — dose factors. Phantom set‐up was typically completed within a minute and all analyses were conducted by an automated software program within seconds. Results: Good agreement was observed between MTF curves obtained from the bar‐pattern and point response methods. Our CatPhan based QA methodology was applied to a Varian Trilogy CBCT system as well as a Hi‐ Art Tomotherapy unit. Conclusion: CatPhan based MTF, NPS and DQE measurements for CBCT and MVCT QA present several advantages including simplicity, speed and the use of widely acclaimed radiographic metrics. They can be easily extended to quantify several factors that affect image quality (beam settings, filtering, sampling, reconstruction, field size, etc).
SU‐GG‐I‐116: Modulation Transfer Function Above Nyquist Frequency: A Robust Algorithm for the Edge Image Method
Authors: Manciu M
Published: July 2008

Purpose: We present a simple and robust numerical algorithm for the MTF calculation from an edge image, accurate up to frequencies (much) higher than the Nyquist frequency, even in the presence of noise. Method and Materials: The oversampling of the edge image is obtained, as usual, by positioning the edge at a small angle with respect to the detector grid. The angle does not have to be adjusted manually; its value is very accurately calculated using a numeric algorithm, which does not involve recording the Edge Spread Function (ESF) on a sub‐sampling grid, and the Fourier coefficients are subsequently calculated numerically. The quality of the MTF calculation is investigated on a simulated ESF, in the presence of the noise due to the quantum nature of the radiation. Results: The numerical algorithm proposed is able to recover the angle between the edge and the detector grid with a relative error of the order of 10−5, even for noise‐affected data. The center of the Line Spread Function is also detected with an accuracy of the order of 10−3 pixels. For low levels of noise, the MTF was accurately calculated up to about 10 Nyquist frequencies; for high noise levels, an algorithm that avoids the numerical differentiation, by employing integration by parts, has been suggested. The latter algorithm was shown to provide a good estimation of the MTF up to frequencies much higher than Nyquist frequency. Conclusion: The MTF can be accurately calculated from an edge image, when the edge is slanted with respect to the detector grid. The choice of the best algorithm for calculating the MTF depends on the level of noise; even for relatively large levels of noise the MTF can be accurately calculated up to and above the Nyquist frequency.
SU‐GG‐I‐123: When Things Go Kaboom! Handling the Safety of An MRI Facility During a Nearby Building Implosion
Authors: Sobol WT
Published: July 2008

Purpose: To develop methods of assessing the risk associated with implosive demolition of a large building, located in the immediate vicinity of a large MR imaging facility. To devise appropriate protocols for monitoring the impact of building collapse on the status of MR Imaging equipment. Method and Materials: Blasting and demolition industry follows regulations, designed to prevent damage by shock waves to building structures located near the blasting sites. On the other hand, manufacturers of MRI equipment specify limits of mechanical vibration levels allowed at magnet locations. The major problem is, these two approaches focus on very different goals (preserving a building structure vs. ensuring proper quality of MR images). Thus, each party uses different definitions, nomenclature, testing methodology, and compliance guidelines. As a result, statements made by one party (the demolition monitoring experts) are incompatible with concerns raised by the other party (the MRI equipment manufacturers). Information about the blast monitoring technology was reviewed and adopted to the task of assessing the risk of damage to the MRI equipment caused by shockwaves resulting from building collapse. Blast vibration monitoring seismographs have been evaluated to assess sensitivity and precision limits of acquired data. Methods of translating engineering system of units, used by blasting industry, into units used by MRI equipment vendors, have been developed. Results: Two major possible types of damage to MRI equipment have been identified: magnet quenches and structural damage to the RF shielding. Since no prior data regarding recommended limits of blast vibration levels at MRI magnet location were found, a conservative limit of 500 μg was adopted in risk analysis. Conclusion: As a result of careful planning, the building demolition was successful with no demonstrable effect on MRI equipment. The largest recorded vibration level at the MRI site was about 30 μg at 30 Hz.
SU‐GG‐I‐128: Biophysical Studies of Tendon to Elucidate Magic Angle MRI
Authors: Lanctot A , Rahal A , Cameron I , Fullerton G
Published: July 2008

Purpose: The “Magic Angle Effect” observed in cartilage, tendon and other collagen rich tissues of the extracellular matrix have largely unused potential for evaluation of musculo‐skeletal disease processes. These studies seek to improve understanding of the molecular basis for magic angle phenomena based on collagen hydration. We hypothesize that improved understanding will provide a conceptual framework and extend the ability of musculo‐skeletal radiologists to design protocols using MRI orientational contrast for better accuracy and specificity. Method and Materials: These studies use Differential Scanning Calorimetry (DSC) to directly measure the enthalpy and entropy of water bound to rat tail collagen/tendon at different hydration levels. Water vapor sorption and recovery rehydration rates of rat tail collagen/tendon at 22 °C were also measured. Measured bound water fractions are compared to the theoretical values (h=0.263 g/g) predicted from the molecular structure of collagen. Bound water hydration measured with both methods agreed with the molecular prediction of water bound to the protein back bone. Statistical analyses performed using Graphpad Prism. Results: The water vapor sorption and DSC studies of collagen/tendon at 22 °C show that both equilibrium hydration and enthalpy are linear functions of relative humidity up to critical hydration of the protein backbone h = 0.26 g/g. The water bridge hydration hypothesis identifies three hydration water fractions in direct contact with the protein that differ in motional/orientational properties from bulk water. Comparison to T1 and T2 relaxation rate and orientational studies shows the relaxation rate of tendon is determined by fast exchange of water between these motional and orientational restricted water fractions. Conclusion: This work offers evidence for the important role of protein main chain hydration in determining MRI contrast due to dielectric binding of polar water molecules interacting with partial electric charges separated on the backbone by steric restrictions of the collagen molecule.
SU‐GG‐I‐132: A Scatter Removal Method for Digital Breast Tomosynthesis
Authors: Liu B
Published: July 2008

Purpose: To develop a scatter removal method for digital breast tomosynthesis based on physical measurements. Method and Materials: A Hologic prototype digital beast tomosynthesis system was used to generate projection images. A CIRS anthropomorphic breast phantom was first imaged at a low mAs with an array of beam stops between the x‐ray source and the breast. For each projection image, local minima, which were near the centers of the beam‐stop shadows, were located using a Matlab program. The pixel values at these local minima were then interpolated and a scatter image was generated. The breast phantom was then imaged again at a higher mAs without the beam‐stop array. The total mAs of two exposures was kept the same as the mAs recommended by Hologic for a breast with the same thickness. The scatter‐free projections were obtained by subtracting the scaled scatter images from the corresponding projections acquired in the second exposure. 3D breast was reconstructed from the scatter‐free projections. Results: For a 6 cm breast, the scatter‐to‐primary ratio could be as high as 0.4 even though there was an air gap between the breast and the detector. The scatter‐free projection images shown higher image contrast. Conclusion: Contrast‐to‐noise ratio may be increased and artifacts due to scatter may be reduced when 3D breast is reconstructed from scatter‐free projections. The overall effect of scatter subtraction on the image quality needs further investigation.
SU‐GG‐J‐44: Carbon Nanotube Field Emission Technology Enables Novel Imaging and Irradiation System Development for Cancer Research and Clinical Application
Authors: Chang S , Zhou O
Published: July 2008

Purpose: Carbon nanotube field emission is an emerging nanotechnology for novel x‐ray imaging and radiation delivery systems development for cancer research and clinical application. In this presentation we will give a general review of the nanotechnology and its applications in the development of novel devices including CT imaging, tomosynthesis, and cancer research radiation delivery systems. Method and Materials: Carbon nanotube field emission is a based on the unique properties of a nanomaterial called carbon nanotubes (CNT). CNT is the newest carbon allotrope discovered in 1991 and it is comprised of either a single graphene shell, called the single‐wall carbon nanotube, or multiple concentric graphene shells termed a multi‐wall carbon nanotube. The signature feature is a very large aspect ratio (ratio of diameter to length) that is typically is on the order 103. The high aspect ratio makes CNTs a practical and excellent field emitter that can produce high current density with intrinsically small divergence and extremely high temporal resolution. More importantly, its unprecedented flexibility in cathode design has launched new creativity in imaging and therapy system development. Results: We will show examples of our research development on CNT field emission based imaging and irradiation systems that include 4D micro‐RT, stationary tomosynthesis, multi‐pixel electron microbeam cellular irradiator under real time microscope observation, and multi‐pixel x‐ray micro‐CT‐RT image‐guided and intensity‐modulated radiation for small animal tumor models. The technical challenges of the CNT field emission technology will also be discussed. Conclusion: Carbon nanotube field emission technology has shown great promise in developing novel imaging and radiation systems that can potentially advance cancer research and improve the quality and efficiency of cancer diagnosis and treatment.
SU‐GG‐J‐45: CBCT Based Quality Assurance for Optically Guided Patient Positioning and Monitoring
Authors: Maxim P , Hsu A , Hristov D
Published: July 2008

Purpose: To provide image based quality assurance procedure to evaluate and eliminate systematic discrepancies between an optical positioning system and Cone Beam CT (CBCT). Materials/Method: An optically‐guided positioning system (Varian Medical Systems, Palo Alto, CA) is routinely used to setup and monitor patients undergoing fractionated and hypo‐fractionated head and neck treatments at Stanford University. We have typically assessed the accuracy of this positioning with matching of (CBCT) images acquired in treatment position to the patients planning CT scans. When the two positioning systems did not agree, the optical one was recalibrated via CBCT using a custom made imaging device consisting of the reference fiducial frame mounted to a cube phantom that is used for routine OBI QA. A CT scan of this system was acquired and exported to the Son Array workstation where the registration of the CT was performed. Phantom positioning was achieved using optical guidance. Setup was verified by volumetric matching of CBCT images to the CT. Results: To date, three patients have been treated in our clinic using the combined frameless array/CBCT positioning systems. In two cases, the solutions of the frameless and CBCT systems coincided within <1 mm and <1° rotations. In one case, differences of 3 mm were observed. The application of the above QA procedure ruled out systematic discrepancies related to system performance. It was concluded that for this patient the bite block positioning varied significantly between planning and setup. In this case positioning of the patient was based on volumetric anatomical matching via CBCT. Conclusion: The use of CBCT for both positioning and verification provides an ideal quality assurance procedure for frameless patient setup as it permits calibration of the frameless array and direct visualization of the proposed re‐positioning shifts.
SU‐GG‐J‐61: Correcting For Missing Data In 4D‐MVCT
Authors: Green A , Ramsey C , Usynin A
Published: July 2008

Purpose: A technique has been developed to retrospectively sort helical tomotherapy sinogram detector data based on the respiration phase. It is not possible to obtain complete sinograms for multiple respiration phases without delivering excessive imaging doses. As such, the sinogram detector data for each respiration phase will be missing projection data necessary to reconstruct an image. The purpose of this study was to develop and test a technique for replacing these missing projections. Method and Materials: An algorithm has been developed that re‐bins raw detector data into specific respiration phases. Redundant rays are used to further complete missing sinogram data. In CT imaging, the attenuation along a ray through a medium can be assumed to be independent of the direction it originates. In rigid slip‐ring geometry, the detector data from the opposite direction may be used in place of the missing projections. To fill in the remaining missing data, In‐Painting is used. In‐Painting is a technique that has been used for many years in the restoration of photographs and museum artwork. Digital In‐Painting, however, is a newer technique that has been used in this study to complete missing sinogram data. Results: The incorporation of redundant ray data and In‐Painting showed a considerable improvement in image quality, especially during periods of fast movement (mid‐inspiration, mid‐cycle, mid‐expiration). The resulting increase in image quality represents a significant improvement over previous 4D‐MVCT techniques. Conclusion: A custom 4D‐MVCT application was developed that retrospectively sorts the sinogram detector based on the measured respiration cycle, calculates and adds redundant rays into the reconstruction, and uses iterative In‐Painting to fill any additional gaps. Tests performed with a moving CT resolution plug indicate that the image quality could be increased without additional dose delivered to the patient. Conflict of Interest : Research sponsored by TomoTherapy, Inc.
SU‐GG‐J‐62: Correlation of White Blood Cell Count with Radiation Therapy Outcome for Cervical Cancer
Authors: Zhang D , Wang J , Derrow A , Patel R , Montebello J , Yuh W , Mayr N
Published: July 2008

Purpose: To assess the impact of circulating white blood cell (WBC) counts during the treatment course for local tumor control in patients treated with radiation therapy (RT) for cervical cancer. Method and Materials: Forty‐two advanced cervical cancer patients (FIGO stage IB2‐IVA) were studied as a part of IRB‐approved protocol. The standard RT for cervical cancer included ∼5 weeks of external beam RT, followed by brachytherapy within 3 weeks. Blood tests, including white blood cell counts, were collected approximately once per week longitudinally during the two month RT course. For each patient, the mean (mWBC) and median of white blood cell counts were evaluated across the RT course. The outcome endpoints, local (pelvic) tumor recurrence (LR) and death of disease (DOD), were determined by long term patients follow‐up 3.9 ∼9 years (median 7.5 years). Cox proportional hazards model was applied to correlate of WBC parameters with RT outcome. Survival analysis was carried out with Kaplan‐Meier method. Results: The parameter mWBC correlated with RT outcome including LR (p= 0.004) and DOD (p= 0.032). The median of mWBC in patient subgroup with LR (13 patients, median= 6.2×109/ l) was higher than that in the subgroup with local tumor control (29 patients, median= 5.5×109/ l). Kaplan‐Meier analysis confirmed higher LR rate of 47% for mWBC >5.4×109/ l versus LR rate of 7% for mWBC < 5.4×109/ l (p= 0.017). The sensitivity, specificity, and accuracy of high mWBC to predict LR were 85%, 48%, and 60%, respectively. Correlation of high mWBC with higher DOD rate was marginally (p= 0.059). Conclusions: Our preliminary results suggest that higher white blood cell counts during the course of radiation therapy correlate with higher local tumor recurrence rate. The etiology is unknown, however, may be related to inflammatory changes and tumor necrosis, and requires further investigation e.g. imaging assessment.
SU‐GG‐J‐68: Developing Contrast Enhanced Biodegradable Markers to Enhance Image Guided Radiation Therapy
Authors: Monroe JI , Exner A , Sohn JW
Published: July 2008

Purpose: Surgical markers implanted during the removal of tumors prior to radiation treatment are used to guide radiation therapy. Current markers are permanent and frequently difficult to image. Our purpose is to develop and analyze contrast enhanced bioabsorbable polymer markers which are detectable in both planning CT images and the delivery verification images from Electronic Portal Imaging Devices (EPID), MegaVoltage Computed Tomography (MVCT), and Cone‐beam CT (CBCT). Method and Materials: We created bioabsorbable, radio‐opaque surgical markers formed into either small cylinders or as a quick‐setting injectable liquid that solidifies. Contrast agent was blended with PLGA (poly lactic‐co‐glycolic acid) polymer, a bioabsorbable polymer approved for surgical usage. Percent composition of was varied to optimize imaging visibility. Four blends of PLGA cylindrical polymer markers with 5%, 10%, 20%, and 25% loading densities of were made for preliminary measurements. Markers were imaged with EPID, CBCT, CT, and MVCT in various phantoms for image quality analysis. The injectable formulation was made by dissolving the PLGA in N‐methyl pyrrolidone (NMP), a low‐toxicity, organic solvent at concentrations ranging from 20–40% PLG. To study degradation rates polymer implants with contrast were implanted into 10% gelatin phantoms. CT scans were acquired periodically over 5 weeks to monitor marker stability. Final candidate blends were implanted in rats for testing imaging, biocompatibility, and material stability. Results: Results show biodegradable polymer can be blended with contrast, producing markers which can be imaged with CBCT, MVCT, EPID, and CT modalities. Markers are stable and biocompatible in test animals. Conclusion: The blends of 20 – 25% additive bioabsorbable markers were visible in all imaging modalities and therapy sites tested. In vivo animal testing demonstrated stability and biocompatibility. Contrast enhanced markers show great promise and further investigations should be pursued, especially with the increased emphasis on partial breast treatments.