bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐EE‐A4‐02: Modeling Contrast Agent Extravasation in Dynamic Susceptibility Contrast MRI of Very Leaky Brain Tumors
Authors: Liu H , Wu Y , Yang W , Hsu Y
Published: July 2008

Purpose: In dynamic susceptibility contrast MRI, when there is a disruption of the BBB, as is frequently the case with brain tumors, contrast agent leaks out of the vasculature and causes additional T1 and T2 effects. In slightly leaky conditions, previous studies successfully modeled the T1 effect and were able correct it for better perfusion quantifications. However, in very leaky conditions, the T2 effect can be significant and needs to be taken into account. This study proposed a two‐compartmental model that is able to describe the combined T1 and T2 effects in the measured signals. Method and Materials: Our model considered different tracer residue functions for brain tissues and leaking tumors. They were then incorporated in both T1 and T2 changes in the MR signal equation. Three unknown variables were introduced: K1, K2 and K3, and the K2 directly related to the permeability. We used the model to fit measured ΔR2* curves and corrected the contrast leakage in the patient data with heavy T2 effect. Results: The proposed model was able to fit well the leaking ΔR2* curves and better correct them comparing to the previous model. The GM/WM CBV ratios were comparable before (1.26) and after (1.19) the correction. However, Tumor/WM CBV ratio was 42.6% decreased after the correction (2.25 v.s. 5.27). The K2 map was able to describe regions with significant contrast extravasation, whereas the previous model failed due to the additional T2 effect. Conclusion: The model proposed in this study was able to correct both T1 and T2 effects of contrast extravasation in DSC MRI. The T2 component significantly overestimated rCBV in very leaking brain tumors, which was not considered in the previous model with T1 effect only. In addition to better correct the rCBV maps, our model successfully extracted the regional permeability changes of the tumors.
SU‐EE‐A4‐04: Accelerating Breast Dynamic Contrast Enhanced MRI with Efficient Multiple Acquisitions by SPEED Using Shared Information
Authors: Chang Z , Craciunescu O , Yin F
Published: July 2008

Purpose: The efficient multiple acquisition method using Skipped Phase Encoding and Edge Deghosting (SPEED) has been successfully demonstrated with a dynamic contrast enhanced (CE) mice tumor study; however, it has not been tested with any human subjects. In this work, this technique is further developed to accelerate breast dynamic CE MRI. Method and Materials: In dynamic CE‐MRI, a series of images are acquired within different time frames, which contain highly similar spatial information. The strong structural similarity is used to accelerate imaging by SPEED with factors greater than that achievable with a single acquisition. It was tested in this work with an in vivo breast dynamic CE MRI study. The dynamic CE scan was performed on a GE 1.5T system using a T1‐weighted gradient echo sequence (matrix 256×256, FOV 20cm × 20cm, TR = 5.5 ms, TE = 1.5 ms, flip angle = 30°, slice thickness = 4 mm, the number of frames = 7). Results: Reference images are first reconstructed from full k‐space data. The corresponding deghosted images are then reconstructed from partial data, with undersampling factors of 3/5 for one frame and 2/5 for all other frames, resulting in an acceleration factor of 2. In other words, the total scan time is 3.5 times that of a single acquisition. The images reconstructed from partial data by the proposed method show comparable quality as those reference images. Conclusion: In this work, the technique of efficient multiple acquisitions by SPEED is further developed to accelerate breast dynamic CE MRI. By using shared spatial information, a breast dynamic CE MRI study is accelerated by SPEED with a factor of 2, which is greater than that achievable with a single acquisition. This saving can be used to double the image resolution, or to increase the frame rates of dynamic sequence.
SU‐GG‐I‐02: Evolution of Adrenal Gland Perfusion with Anti‐Angiogenic Therapy: A CT‐Based Approach
Authors: Roberts R , Armato S , Starkey A , Sensakovic W
Published: July 2008

Purpose: In radiology it is important to understand and interpret anatomical changes which correlate with treatment plans. Several anticancer agents exist that affect tumor vasculature growth and normal vessel growth. Monitoring these effects with CT imaging may be useful to guide dosing of treatment. Observing perfusion of certain organs it possible to monitor vessel competency. If perfusion is constant over time, it can be assumed there is no significant change in vasculature, and no damage due to chemotherapeutics. In contrast, significant changes in perfusion over time may suggest a decrease in normal vessel growth as a result of therapy. Method and Materials: Patients receiving the vascular endothelial growth factor (VEGF) inhibitor sorafenib underwent CT imaging every six weeks, beginning with baseline studies. A “jog scan” tracked perfusion through the highly fenestrated adrenal glands. Sixteen pairs of adrenal images were contoured, with each of the sixteen scans representing different perfusion time intervals from 0–90 seconds. The mean pixel values of each gland were obtained and compared over time for any significant changes in pixel value that could indicate change in vascular perfusion over time. Further calculations were performed isolating the medullary component of the glands because of its high vascularity. Results: The average change in maximum pixel values from baseline to six weeks after treatment initiation demonstrated a 4.58% increase in peak pixel value for both adrenals, with a subsequent decrease of 3.2% in the third scan. Changes in the medullary region demonstrated a 6.1% increase in pixel value in comparison to the entire adrenal area. Conclusion: Manual contouring of adrenal glands in conjunction with calculated maximum pixel values revealed changes in adrenal perfusion between baseline and therapy‐monitoring CT scans. The continued monitoring of perfusion could prove beneficial to the radiologic diagnosis of significant anatomical changes as a result of chemotherapy.
SU‐GG‐I‐03: Self‐Assessment as a Strategy to Improve Performance of Computer‐Aided Diagnosis in Breast Ultrasound
Authors: Drukker K , Sennett C , Giger M
Published: July 2008

Purpose: The aim of this work was to develop and apply a computerized auto‐assessment method in which a computer‐aided diagnosis (CADx) system itself provides a level of confidence for its output for each radiologist‐identified lesion. Method and Materials: We investigated the potential of computer‐derived confidence levels both 1) as an output aid to radiologists indicating a confidence level for the computer‐estimated probability of malignancy and 2) as an automated method to improve the computer classification performance — in the task of differentiating between cancerous and benign lesions — without eliminating any lesions from the database. For the former, the CADx cancer classification performance was assessed within 3 confidence categories where each category included a range of confidence levels. For the latter, the computer‐derived confidence levels were used as an automated criterion in the determination of the computer‐estimated probability of malignancy for each actual lesion based on probabilities obtained from different views. The stand‐alone computer performance was assessed within a leave‐one‐case‐out protocol using a database of sonographic images from 542 patients (19% cancer prevalence). Results: The classification performance increased substantially from an area under the ROC curve (AUC value) of 0.66 to 0.72 to 0.92 for confidence categories ‘Poor’, ‘Fair’ and ‘Good’, respectively. The use of the auto‐assessment method in an automated classification‐improvement protocol resulted in a modest but statistically significant increase in the AUC value with respect to the performance obtained using the ‘traditional’ CADx approach, increasing the AUC value from 0.89 to 0.90 (p‐value 0.03) for the entire database. Conclusion: We believe that computer‐provided confidence levels may be helpful to radiologists who are using CADx output in diagnostic image interpretation. Conflict of Interest: This work is supported in parts by the NIH. Some authors stockholders of, grant support of, and/or royalties from R2 Technology/Hologic Inc.
SU‐GG‐I‐10: An Evaluation of a Solid State Dosimeter in Direct Measurement of CT Dose
Authors: Lu Z , So J , Nickoloff E , Dutta A
Published: July 2008

Purpose: Our group presented in the past the results of pediatric CT dose monitoring using a small volume solid state dosimeter (SD). This paper studies the responses of such a dosimeter with various technique settings and the limitations implied. Method and Materials: A variety of phantoms has been involved, including anthropomorphic adult head, chest and abdomen phantoms as well as pediatric head and body phantoms. In addition, cylindrical acrylic phantoms are utilized with varying diameters from 6 cm to 32 cm. A pediatric 64 slice VCT scanner is utilized in this study. We evaluate the angle and energy dependence of the SD dosimeter and the effect on dose measurement. Result: The results measured with the SD dosimeter are compared to the CTDI measurements by a pencil ion chamber (IC). The SD energy response is within +/− 10%. It is angle dependent which affects CT dose measurement. It is shown that the IC results are higher than those of SD. The discrepancy increases with kVp, e.g., 20% at 80 kVp, 36% at 100 kVp, 49% at 120 kVp and 61% at 140 kVp using a 16 cm diameter phantom. In addition, the variation appears to be more significant as the phantom size reduces, e.g., 12% at 120 kVp for a 32 cm diameter phantom, 39% for 24 cm, 49% for 16 cm and 77% for 10 cm. Similar trends are observed with anthropomorphic phantoms. This leads us to adjust the setting and use the SD sensors in pair with one facing up and the other facing down. Corrective factors are calculated to compensate for the angle dependence. Conclusion: The angular sensitivity in the SD dosimeter affects the ultimate dose reading and needs correction factors. Overall, the SD dosimeter provides a new tool for direct and instantaneous measurement of CT dose.
SU‐GG‐I‐12: Effect of Geometric Unsharpness On the Reconstructed Image in Region of Interest (ROI) μCT
Authors: Wang W , Patel V , Keleshis C , Bednarek D , Hoffmann K , Rudin S
Published: July 2008

Purpose: To demonstrate the effects of variation of focal‐spot size and magnification on the spatial resolution of reconstructed images of a micro‐computed tomography (μCT) system which is attached to a standard angiographic C‐arm gantry to enable Region‐of‐Interest cone‐beam CT (ROI‐CBCT). Method and Materials: High‐resolution ROI projection data of a vascular phantom were acquired using a new high‐sensitivity, microangiographic fluoroscope (HSMAF) detector (35 μm pixels), which was attached to the C‐arm gantry and able to be positioned in front of a standard full field‐of‐view, low‐resolution commercial flat‐panel detector (FPD) (194 μm pixels). The HSMAF consists of a CsI phosphor viewed by a 4‐cm diameter light image‐intensifier with large variable dynamic range whose output is coupled via a fiber‐optic taper to a CCD camera. The test objects in the vascular phantom were a stent (100 micron struts) inside of a catheter in a cylindrical water bath. The phantom was placed on a portable test platform (PTP) enabling CBCT image acquisition by the HSMAF every 1°. Six μCT runs were performed using two focal‐spot sizes (0.3 and 0.6 mm) and three magnification factors (1.15, 1.29, and 1.48). Profiles were extracted from the reconstructed struts, and the full width half‐maximum (FWHM) were measured. Results: The reconstructed data show that using the optimal configuration (smallest magnification with small focal spot) compared to the worst configuration (largest magnification and the large focal spot) resulted in a 47% reduction in the FWHM in the object plane (175 μm versus 375 μm). Conclusion: Micro‐CBCT can provide more accurate visualization of fine device features; however, geometric unsharpness and/or large focal spots can substantially degrade resolution reducing the quality of the μCBCT reconstructions.

(Research sponsored by: NIH Grants R01‐NS43924, R01‐EB002873, Toshiba Medical Systems Corporation)
SU‐GG‐I‐25: An Image Quality Comparison Study Between XVI and OBI CBCT Systems
Authors: Kamath S , Song W , Chvetsov A , Li J , Ozawa S , Liu C , Palta J
Published: July 2008

Purpose: To evaluate image quality on the X‐ray Volumetric Imager (XVI®, Elekta Medical Systems) and the On‐Board Imager (OBI®, Varian Medical Systems) using a CatPhan® phantom in a single institution setting. Method and Materials: We evaluated four major image quality indices, including high and low contrast resolution, noise, and contrast‐to‐noise (CNR) ratio. For the XVI unit, the four manufacturer‐supplied protocols were measured. For the OBI unit, full bow‐tie and half bow‐tie filters were used in combination with the “full‐fan” and “half‐fan” modes. The mAs was varied for each protocol. High contrast resolution was evaluated using number of line pairs visible per cm and low contrast resolution was evaluated using the visibility of low resolution disks. Noise was computed over circular regions of interest (ROIs) on the uniformity module. CNR was calculated using a polystyrene insert and the background of module CTP404. The images were analyzed using MATLAB. Results: Up to 10 line pairs per cm are visible on OBI for high mAs settings and so are most low contrast discs. 2 line pairs per cm and none of the low contrast discs are visible on XVI. Noise values fall from 35 to 6 on OBI and vary between 10 and 3 for “prostate” protocol on XVI with increasing mAs. On OBI, CNR steadily increased from 4 to 20 with increasing mAs. For the “prostate” protocol on XVI, CNR varies from 10 to 23 and generally increases with mAs. For the four XVI protocols evaluated, mean pixel values in ROIs are found to decrease with mAs. Conclusion: Image quality parameters are generally found to be better on OBI as compared with XVI for clinical protocols. However, this is important to be viewed in the context of the observation that OBI generally delivered higher doses than XVI.

Research sponsored by Elekta Inc.
SU‐GG‐I‐26: A Simple Technique to Improve Image Quality of CBCT for Brain
Authors: Duvvuri S , Palta J , Malyapa R , Mendenhall N , Huh S
Published: July 2008

Purpose: Improve the image quality of Cone‐Beam CT from the Elekta Synergy Linear Accelerator for its use for radio surgery system or external radiation therapy for small brain tumors. Method and Materials: The image quality of the CBCT images using manufacturer‐recommended preset value are not adequate to take full advantage of image fusion with planned CT and CBCT images for daily setup, especially for small targets or organs with low contrast in the brain. To resolve this issue various parameters, including the gantry rotational settings and the XVI image panel are experimentally optimized to improve image contrast in the CBCT images of the brain. Results: Choosing a voltage of 120KVp instead of 100KVp reduced the bony artifacts, especially in the region of skull base. Increasing gantry rotation from 200° to 300° reduced streak artifacts. Increasing the x‐ray tube current by a factor of 2 or 4 increased the signal‐to‐noise ratio (SNR) while minimizing the radiation dosage to a patient. Reducing the collimator setting for x‐ray generator from a size of ∼25cm by 25cm (at the Isocentre) to 25cm by 10cm minimized scattered radiation and radar artifacts, while covering whole brain independent of tumor position in the brain. Using 0.1 to 2mm thick aluminum filter effectively reduced scattered radiation from the head of the patient. Conclusion: New protocol qualitatively improves low contrast of the brain. This setup is especially useful to correlate the targets in the middle of the brain when there are rotational discrepancies between CT and CBCT images. Further investigation of the this technique is required to qualitatively improve the CBCT image quality.
SU‐GG‐I‐28: Performance Comparison of Two Different Cone‐Beam CT Systems
Authors: Chan P , Li S , Chan M
Published: July 2008

Purpose: To evaluate and compare the imaging performance of two popular cone‐beam CT (CBCT) systems used for image‐guided radiation therapy. Method and Materials: The study was carried out on Varian Clinac iX equipped with OBI/CBCT and Elekta Synergy equipped with XVI/CBCT. The performance evaluation involved comparison of volumetric image data taken from two systems. Two CT phantoms (Catphan‐504 and 600, Phantom Laboratory, Salem, NY) were scanned using the Varian CBCT with standard half and full fan setup, and Catphan‐600 was also scanned on Elekta CBCT with half and full circle scans at different resolutions and field‐of‐view (FOV). In‐house image analysis software was used to measure the mean CT numbers, standard deviations, and image noise for 5×5 mm ROI in seven different density materials. Image quality, reproducibility, position correction, and geometric accuracy were also evaluated with markers in a small alignment phantom. The image quality measurements included uniformity, linearity, image resolution, density accuracy, and image noise. Results: The linearity for both phantoms was fairly consistent using the Varian CBCT. The Elekta CBCT with half circle 27×27 FOV had higher CT numbers as compared to its other three modes. With the same phantom for low‐density materials, the CT numbers with Varian CBCT were 300–600 units lower than those with Elekta CBCT. The image noise of full and half circle 27×27 FOV were about 5 and 2 times, respectively, higher than for the Varian CBCT, while the image noise levels in its other modes were similar. The accuracy of the image systems was comparable. Conclusion: This study confirmed the comparability of imaging performance of both systems. While the Elekta CBCT provided timely image reconstruction, relatively higher image noise was observed. Our objective evaluation of imaging performance demonstrated that the volumetric data rendered from both CBCT systems is accurate as compared with conventional CT.
SU‐GG‐I‐32: Optimization of Dose Efficiency in Helical Scan and Image Reconstruction at Dynamically Variable Pitches
Authors: Tang X , Hsieh J , Dong F , Licato P , Toth T
Published: July 2008

Purpose: To present a cone beam helical image reconstruction algorithm for CT diagnostic imaging at dynamically variable pitches and its optimization in dose efficiency. Method and Materials: The ray‐wise 3D weighted helical cone beam filtered backprojection (CB‐FBP) algorithm is extended to carry out image reconstruction at dynamically variable helical pitch, in which the filtering process is carried out in the cone‐parallel geometry along the tangential direction of the helical source trajectory. Consequently, the filtering paths are straight lines at dynamically invariable pitch, but become curves at dynamically variable helical pitches. In addition, since the pitch variation may be caused by either acceleration or deceleration, the filtering paths can be curves containing inflexions. The FORBILD head and thorax phantoms are utilized to evaluate the performance of the extended algorithm. The dynamical variation range of normalized helical pitch in the evaluation is between 0.5:1 and 1.5, which is quite large from the perspective of clinical applications. Moreover, the optimization in dose efficiency is studied by evaluating the noise characteristics at various transitions of helical pitches. Results: The phantom study shows that, at a wide variation of helical pitches, the extended ray‐wise 3D weighted helical CB‐FBP algorithm can provide a well‐balanced imaging performance over reconstruction accuracy, spatial resolution and noise characteristics, while a large field of view can be maintained. Meanwhile, the noise uniformity of the presented algorithm can be improved by optimizing the ray‐wise 3D weighting parameters with the dynamic variation of helical pitch during the scan. Conclusion: Based on the experimental evaluation, especially its robustness over a large variation range of helical pitches, it is expected that the extended ray‐wise 3D weighted CB‐FBP algorithm can meet the challenges posed by advanced clinical applications, in which helical scanning and image reconstruction at dynamically variable pitches and maintenance of noise characteristics are demanded.
SU‐GG‐I‐37: Organ and Effective Dose in Pediatric Patient in 64‐Slice Computed Tomography
Authors: Chen H , Lamba M , Alsip C , Lemen L
Published: July 2008

Purpose: The absorbed dose for the pediatric patient has been reported to be 1 to 2.6 times higher than in the adult using Monte Carlo simulations of head, chest, abdomen and pelvis examinations on single and/or 16‐slice computed tomography (CT) scanners. In the UK, a study investigated the effective dose for studies on a 4‐slice CT scanner using thermoluminescent dosimeters (TLDs). Our goal was to measure the organ dose and calculate the effective dose from clinical pediatric chest‐abdomen‐pelvis (CAP) and chest examinations on 64‐slice CT scanners. Method and Materials: An ATOM one year old anthropomorphic phantom with mimic biological tissue (Model 704‐D, CIRS, VA; phantom loaned courtesy of T. Yoshizumi, Duke University) was scanned using clinical protocols on two 64‐MSCT scanners (GE LightSpeed VCT and Toshiba Aquilion). Absorbed dose and effective dose were measured by loading 19 TLDs inside and 1 on the surface of the phantom at selected radiation sensitive organs according to ICRP publication 60 methodology, including TLDs to estimate the remainder tissues, and using the published tissue weighting factors. Results: Standard pediatric clinical protocols with adaptive mAs methods were utilized on each scanner (120kVp, mAs of 22–55, and collimation of 32 and 40 mm). Doses to the lens of the eye were 0.4 to 1 mGy in CAP examination. The effective doses were 7 to 16.5 mSv in CAP examination and 4.5 mSv in chest examination and 2.3 to 6.4 mSv in chest examination. Conclusion: Our study results for effective dose and organ absorbed doses, including to the eye, for a one year old anthropomorphic phantom may help in the evaluation of radiation risk in any clinical studies of small children undergoing 64‐slice CT examinations.
SU‐GG‐I‐47: A New Limited‐Angle CT Reconstruction Method Based On Total‐Variation Minimization
Authors: Zhang J , Ren L , Zhou S , Yin F
Published: July 2008

Purpose: To develop a new CT reconstruction algorithm based on Total‐Variation (TV) minimization. The new algorithm is specifically designed for limited angle reconstruction to alleviate volume information loss caused by incomplete projections. Method and Materials: TV is defined as the summation of the gradients between adjacent pixels. A nonlinear conjugate gradient algorithm is used to minimize TV and projection error simultaneously. Pixel Signal‐to‐Noise Ratio (PSNR) was used to quantitatively evaluate reconstruction quality of a Shepp‐Logan phantom. Head and neck CT images were reconstructed from simulated projections to demonstrate reconstruction quality at different scan angle. The effects of weighting factors for TV and projection frequency were investigated. Results: The algorithm can reconstruct good quality images with the scan angle as low as 60 degree. With 90‐degree projections, the reconstructed Shepp‐Logan phantom has a high PSNR of 17 dB. Weighting factors for TV were determined through simulations. Image qualities were improved by weighting more high frequency of the projection data. In simulation tests using head/neck simulated projections, volume information can be recovered accurately from 60‐degree projections. Conclusion: The TV‐based reconstruction algorithm improves the quality of limited angle CT reconstruction.

Research sponsored by a Varian research grant.
SU‐GG‐I‐48: Performance Evaluation of Three Algorithms for Metal Artifact Reduction in CT Imaging
Authors: Du G , Prevrhal S
Published: July 2008

Purpose: To provide a reference for clinical applications by investigating the performance of three metal artifact reduction (MAR) methods for CT imaging. Method and Materials: The expectation maximization (EM) algorithm, algebraic reconstruction technique (ART), and a MAR method based on filtered back projection (FBP) were tested with Shepp‐Logan phantom in noise free and additive Gaussian noisy environments. A small disk of metal was added to the phantom to simulate the metal effect, and the projection data were obtained by parallel beam projection. In each projection data set, there were 180 views and 367channels. Noise was simulated by adding Gaussian noise (μ = 0.5, σ = 0.5) to the projection data. Computational experiments were performed to demonstrate and compare effectiveness of artifact reduction. Essential characteristics such as reconstruction accuracy, convergence, computational costs, have been evaluated. In addition, the robustness of MAR algorithms to variations of the threshold for detecting metal region in implementation was also investigated. Results: Simulations with Shepp‐Logan phantom in noise free and additive Gaussian noisy environments show that all of these methods can provide high‐quality reconstruction images. In comparison, EM obtains the most accurate reconstruction image and shows highest robustness to parameter variation. In addition, EM converges faster than ART. As for computational costs, FBP removes metal artifacts most efficiently. Conclusion: Simulations have shown that all of three methods can finish artifact reduction task effectively. In comparison, EM can provide most accurate reconstruction image and FBP remove the effect of metal most efficiently. The studies presented herein would provide a reference for clinical use. Future work involves comparison of MAR techniques based on real raw data.
SU‐GG‐I‐50: Breast Tissue Classification in Digital Breast Tomosynthesis Images Using Texture Features
Authors: Kontos D , Bakic P , Maidment A
Published: July 2008

Purpose: Breast density is a known breast cancer risk factor. Digital breast tomosynthesis (DBT) is a tomographic x‐ray breast imaging modality with superior breast tissue visualization in comparison to mammography. The goal of our on‐going study is to evaluate the performance of DBT texture features in distinguishing between dense and fatty breast tissue regions. Our hypothesis is that DBT texture analysis could result in more discriminative features to characterize breast density in comparison to mammography, and ultimately yield more accurate measures of risk. Method and Materials: DBT images and digital mammograms (DM) from 39 women were analyzed. DBT and DM acquisition was performed with a GE Senographe 2000D FFDM system modified to allow positioning of the x‐ray tube at 9 locations by varying the angle from −25° to +25° in increments of 6.25°. Filtered‐backprojection was used to reconstruct DBT tomographic planes in 1 mm increments. The dense tissue area was delineated within each breast image using a widely validated thresholding technique (Cumulus Ver. 4.0, University of Toronto). Two regions of interest (ROIs) were manually selected in each breast image: one within the dense tissue region and another within the fatty region. Texture features of skewness, coarseness, contrast, fractal dimension, energy and homogeneity were computed from all available ROIs. Two‐tailed paired Student's t‐test was applied to compare the means of the texture feature distributions from the dense versus the fatty ROIs. Results: Coarseness, contrast, energy and homogeneity were statistically significantly different (p⩽0.001) between dense and fatty ROIs. Dense ROIs have lower coarseness, higher contrast, higher energy and lower homogeneity. Conclusion: X‐ray image texture differs between dense and fatty breast tissue regions. Further work is underway to fully compare the relative performance of texture features in classifying dense versus fatty tissue regions using DM, DBT source projections, and reconstructed DBT images.
SU‐GG‐I‐52: Conversion of On‐Board Digital TomoSynthesis (DTS) to HU Values
Authors: Yoo S , Wu Q , Godfrey D , Ren L , Yin F
Published: July 2008

Purpose: To investigate a method to convert the pixel values of DTS images to HU values with reference HU values from CT images. Method and Materials: This study included CT and DTS images of two phantoms (Catphan and a chest phantom) and three patients (prostate, head‐and‐neck, and lung). Cone‐beam radiograph projections were acquired to reconstruct the limited angle DTS images, which were expressed in arbitral pixel values after a Feldkamp‐type technique. Regions of interest (ROIs) in the CT images were selected for low‐ and high‐density areas, and HU values were measured in the ROIs. DTS pixel values were measured for the corresponding ROIs in the DTS images. A linear regression was performed using the DTS pixel values (D) as the dependent variable in terms of the HU (H) for each phantom and patient independently. The linear regression was applied to the DTS images in order to convert the DTS pixel values into HU values. DTS images expressed in HU values were compared to CT images. Results: The method proposed in this study is simple and feasible to convert DTS images in HU values. However, the DTS image slices certainly contain different image contents than corresponding CT image slices. The out‐of‐plane objects smear into the plane of interested in DTS images and affect HU values of in‐plane objects. Thus, HU values do not represent correct tissue materials due to underlying/overlaying tissues. Conclusion: This method could be used to convert DTS images in HU values and useful to understand DTS images for positioning purpose. However, DTS images in HU values should not be used for planning purposes due to smearing effect of underlying/overlaying objects.

Research partially sponsored by grants from NIH and Varian Medical Systems.
SU‐GG‐I‐54: Need for the Liquid Crystal Displays Having the Capability of Rendering Higher Than 8 Bits in Grayscale
Authors: Hiwasa T , Morishita J , Higashida Y , Hatanaka S
Published: July 2008

Purpose: The purpose of this study was to examine the potential usefulness of liquid crystal displays (LCDs) having the capability of rendering higher than 8 bits in grayscale. Method and Materials: An LCD having the capability of rendering 8, 10, and 12 bits in grayscale was used. It was calibrated to the grayscale standard display function (GSDF) with a maximum luminance of 450 cd/m2 and a minimum of 0.75 cd/m2. To examine the grayscale resolution of the human visual system, various test patterns having different combinations of brightness in 8, 10, and 12 bits were displayed on the LCD. These patterns were placed on different uniform background luminance levels, such as 0%, 50%, and 100% of maximum luminance. Then, the probability of detection for various differences in 8, 10, and 12 bits was examined. Results: All observers distinguished a smaller difference of luminance than a one‐pixel value of 8 bits irrespective of background luminance levels. As a result of the adaptation processes of the human visual system, observers had a greater tendency to distinguish a small difference of luminance for the signal level of the test pattern to be nearer to the background luminance level. The smallest difference of luminance that observers were able to distinguish was a four‐pixel value difference in 12 bits, i.e. the difference of a one‐pixel value in 10 bits. Conclusion: Considering the human visual systems, medical images should be displayed on LCDs having 10 bits in grayscale or greater in order to detect low contrast objects with small differences of luminance and carry out smooth gradation expressions into practice.
SU‐GG‐I‐59: Computed Radiography Image Exposure Statistics
Authors: Yang Z , Lobick J , Nagy P
Published: July 2008

Purpose: To review computed radiographic (CR) system image exposure statistics. Method and Materials: Computed radiography image plate exposure indices were collected from six departments of the medical center over a five‐month period. A total of 40,936 exams were under 19 exam groups and 143 exposure types. Exams of low occurrence were excluded to maintain statistical significance. The remaining 40,753 exams including 15 exam groups and 93 exposure types are analyzed. Each exam was categorized by exposure type and patient age or size group. The average exposure index and the exposure index distribution are calculated for each category. A subset of the data is plotted for visualization. Results are compared with manufacturer's recommendations. Results: Nearly half of the exams are chest cases, followed by lower extremity making up 21%, upper extremity and abdominal cases each making up 10%. The average exposure indices center at 2.0 for LgM, and are in agreement of manufacturer's recommendation. Although the values of the exposure indices fit to Gaussian distribution, for some cases the variation of the index is very large. In general, more images are underexposed rather than overexposed, and chest images have less exposure than abdomen images. Conclusion: There is a higher tendency to over expose pediatric patients in abdomen exams than in chest exams. If a record of the detailed image technique and beam quality used for each case can be incorporated into the CR information file, one can better monitor and improve the clinical practice. Consistent quality control procedures for computed radiographic systems are as important as, if not more than, QC of traditional screen/film system to deliver satisfactory image quality and patient care.
SU‐GG‐I‐63: Calculations of Organ Doses From Cone‐Beam CT IGRT Procedures Using a Suite of Patient Phantoms
Authors: Gu J , Xu X , Jiang S
Published: July 2008

Purpose: Widespread uses of Computed Tomography (CT) and image‐guided radiation treatment (IGRT) can significantly increase the cumulative exposure to health tissues. AAPM TG‐75 was formed to compile data on imaging exposures and to identify ways to optimize the imaging procedure. To address the lack of organ doses and effective doses assessment in the IGRT imaging procedure, this paper describes a study to use a Monte Carlo based method to simulate kV and MV cone beam CT (CBCT) scanners and then calculate organ doses and effective doses. Method and Materials: This paper utilizes a whole‐body adult male phantom called the VIP‐Man, and Adult Male and Female that are adjusted to match with 50th percentile ICRP average population. The MCNPX code is used to simulate CT scanners and finally calculate doses. Several IGRT procedures are considered to demonstrate how this method can assess and compare various protocols. Results: For the VIP‐Man phantom, the effective dose for kV CBCT (assuming total exposure of 1350 mAs) is about 9.5 mSv for the two anatomical sites while the effective dose for MV CBCT (assuming a total of 6 MU) ranges from 5.10 mSv for the H&N case to 8.39 mSv for the prostate case. For different procedures, the effective dose data can be adjusted accordingly. Conclusion: With realistic patient phantoms and imaging scenario, organ dosees can be obtained by Monte Carlo simulation, and consequently effective doses have been calculated. The results show that showed that the effective dose is a useful quantity for the comparison of the performance and patient safety between kV CBCT and MV CBCT. These information can aid the assessment of radiation risk to the patient from imaging procedure. This study demonstrates the feasibility of determining detailed organ doses for various IGRT related cone‐beam CT procedures.
SU‐GG‐I‐66: Comparison of Use of Cs‐137 Versus Scattered X‐Ray Beam for Calibration of Diagnostic Survey Meters
Authors: Merrill R , Yester M
Published: July 2008

Purpose: To determine the effect of the standard calibration of survey meters using Cs‐137 compared to the clinical measurement of radiation exposure of scattered radiation from a typical diagnostic x‐ray beam. Method and Materials: A phantom consisting of 8 inches of Lucite was used as a source of scattered radiation. A standard pancake ion chamber with a volume of 150 cc that had been recently calibrated was used as a reference. Three different survey meters (Victoreen Model 470 A Panorama, Keithley Model 36150, and Fluke 451) used in various applications of radiation surveys were placed at the same distance from the center of the scattering material as the ion chamber. Each of the test survey meters had been calibrated recently with a Cs‐ 137 source. X‐ray exposures were made as a function of kVp and additional filtration (Al and Cu). Measurements were made in the integral and rate mode. Results: There was no significant deviation noted in the rate mode of the test meters compared to the 100 cc chamber. No significant systematic deviation was noted for exposures obtained with no additional filtration and the use of external filtration of Al and Cu to simulate the types of filtration encountered in modern x‐ray and angiographic systems. Some systematic differences were noted for the integrate mode, but this appeared to be a function of the device and not the x‐ray spectrum. Conclusion: The use of Cs‐137 for calibrating survey meters used in diagnostic imaging radiation survey measurement provides an accurate calibration for diagnostic survey meters. Conversely, an x‐ray beam with scatter could be employed to calibrate survey meters for diagnostic applications.
SU‐GG‐I‐75: Discrepancies in Exposure Conditions for the EZ CR‐DIN Phantom
Authors: Willis C , Marsh R , Polman R , Shepard S
Published: July 2008

Purpose: To determine whether discrepancies between exposure conditions recommended by the manufacturer of the EZ CR‐DIN phantom, by the DIN standard, and by a user affect evaluation of phantom images. Method and Materials: Computed radiographs (CR) of the Nuclear Associates EZ CR‐DIN phantom (Fluke Biomedical, Cleveland, OH) were acquired in triplicate for three exposure conditions: 72 kVp, the manufacturer's1; 80 kVp, the user's2; and 70 kVp plus 25 mm Al added filtration, the DIN specification3. Aluminum 1100‐H14 was substituted for 99.4% Al.4 kVp was verified non‐invasively. Projections of the phantom used AEC or manual technique on STVI imaging plates (IP) at 100 cm SID in the undertable Bucky tray. IPs were developed without delay with test menus in Semi‐automatic EDR mode using a FCR5000 (FujiFilm USA, Stamford, CT) calibrated for sensitivity and uniformity. DICOM images were transmitted to the PACS system using unity rescale slope and zero intercept. Images were exported from the PACS to a PC and analyzed using MATLAB (MathWorks, Natick, MA). Spectra for the three exposure conditions were generated using a semi‐empirical method.5 Results: Evaluation of low contrast features depended on exposure conditions, test menu selection, and subject contrast values. Contrast was exaggerated using the manufacturer's exposure conditions, but was indistinguishable between user and DIN conditions. Simulated spectra attenuated by the phantom indicated an average energy of 56, 61 and 59 keV for manufacturer, user, and DIN conditions. A high‐contrast test menu improved visibility of low contrast features but did not resolve all six steps of the dynamic range feature. Detected contrasts were more consistent with the manufacturer's subject contrast values than with those in the current DIN standard. Conclusion: Comparison of QC results among institutions depends on standard test objects imaged under standardized conditions. Differences in exposure and development conditions affect evaluation of test images.
SU‐GG‐I‐77: Quality Assurance Testing for a Clinical Digital Radiography System
Authors: McUmber A , Bednarek D , Kuhls‐Gilcrist A , Rudin S
Published: July 2008

Purpose: To develop a series of tests that can be readily performed on a clinical digital‐radiography (DR) system to assess the quality of the PACS‐archived image. Method and Materials: The quality of the final, processed and archived images from a digital radiography (DR) system was assessed using several measurements. These measurements included evaluation of the intra‐image characteristic (or sensitometric) curve of the system using an exposure‐calibrated aluminum step‐wedge and its variability with mAs or “exposure index”; measurement of the relative noise in the image as a function of exposure under the steps; and determination of the square‐wave‐response function (SWRF) from a bar‐pattern image. Test‐object images were obtained using an indirect flat‐panel system, saved on the hospital PACS, and evaluated offline, using image processing software. Results: The DR system provided non‐linear (s‐shaped) curves of pixel gray‐level versus step exposure; however, the curve shape derived from the calibrated step‐wedge was invariant of exposure mAs. Relative image noise decreased almost linearly with log exposure under the steps and decreased with increasing mAs, as expected. The SWRF provided a means to quantify the resolution, as a function of spatial frequency of the archived image. Conclusion: The methods described here provide a straightforward approach for testing the performance of the total DR system by evaluating the final archived image. These measurements provide an evaluation of the basic parameters that define the image quality and may be used as a means of quality assurance.
SU‐GG‐I‐82: Contrast Detail Curves in Head CT Examinations
Authors: Frey G , Elojeimy S , Huda W , Ogden K
Published: July 2008

Purpose: To generate CT based contrast detail curve using a representative head CT image from each of five clinical head CT examinations. We measured detection of 4 to 12.6 mm sized lesions using a 2 Alternate Forced Choice (2‐AFC) experimental. In each experiment the observer identifies the lesion location in one of two regions of interest; after 128 such observations, it is possible to determine the contrast (I) corresponding to a 92% accuracy (I92%) of lesion detection. For each lesion size, we performed four repeat detection experiments, and the order of the 100 AFC experiments (i.e., 5 patients × 5 lesion sizes × 4 repeats) was randomized to eliminate experimental bias (i.e., learning curve and/or observer fatigue). Average values of I92% were obtained for one observer at each lesion size. Contrast detail curves were generated with log(I92%) plotted versus log(lesion size). There were major differences in contrast detail curves for the five patients depending on the presence of anatomical structure in the image. The coefficient of variation in lesion detection, averaged over the five images and five lesion sizes, was found to be 33%. The slope of the contrast detail curve averaged over five patients was −0.14; this slope is a factor of seven lower than the value of −1.0 predicted by the Rose model of lesion detection. Results from our pilot study of low contrast lesion detection in clinical head CT suggest that that anatomical structure is of greater importance than quantum mottle.
SU‐GG‐I‐88: Spinal Canal Segmentation with Well‐Balanced Speed and Accuracy Combination for Radiation Treatment Planning
Authors: Sawada A , Hiraoka M
Published: July 2008

Purpose: This study proposes a fast automatic spinal canal segmentation algorithm which is clinically acceptable in terms of speed and accuracy. Method and Materials: The proposed algorithm employs gray‐level thresholding, morphological operations, and distance‐transform based interpolation in the CT slice direction. The method consists of two phases: 2D extraction and 3D extraction phases. In the 2D extraction phase, smoothing and multilevel thresholding based on CT values are performed for each ROI (Region Of Interest) on all the CT images. Next, erosion followed by dilation of the extracted blobs is applied to eliminate speckle‐shaped and thin line‐shaped blobs. Subsequently, island blobs having areas less than a predetermined threshold level are removed. After that, the compactness that characterizes a disk‐shaped blob is calculated for blobs in each ROI image and the disk‐shaped blob having the maximum compactness is identified because a contour of spinal canal in axial plane is close to a ring. In the subsequent 3D extraction phase, false regions are removed by evaluating position variations of the centers of gravity of the identified blobs in the slice direction. For improperly extracted ROI images that have no reasonable blobs, interpolation in the slice direction is performed by referring to the properly extracted blobs in the adjacent slice images on both sides. Results: The false blobs in 2D extraction phase are replaced to reasonable ones in 3D extraction phase and smoother shape is clearly observed in 3D views of segmented spinal canal. The calculation time was approximately six seconds for 126 slices in lung SRT (Stereotactic radiotherapy) datasets. Conclusion: We proposed a fast automatic spinal canal segmentation approach. Verification results have showed that the proposed method is well‐balanced speed and accuracy combination, which expectedly results in significant acceleration of radiation treatment planning with reduced oncologist's workload.
SU‐GG‐I‐91: An Automatic Contouring Method That Combines Rule‐Based, Atlas‐Based, and Mesh‐Based Approaches
Authors: Gering D , Lu W
Published: July 2008

Purpose: Image segmentation technology can automate the task of contouring organs at risk for radiation treatment planning. While automatic methods tend to be rule‐based, atlas‐based, or mesh‐based, a combination of all three approaches is proposed. Method and Materials: Model‐based segmentation can be initialized by automatically positioning the adaptable meshes relative to the scan. The entire scene is segmented in order to recognize the approximate organ locations. Segmentation is accomplished by a 5‐layer hierarchy that propagates information from the voxel layer up to voxel neighborhoods, then tissues, then organs, and finally organ systems. The voxel layer treats each voxel as an independent statistical event. Bayesian classification uses an atlas in the form of a spatially varying prior constructed from training data. The classification is adaptive within an Expectation‐Maximization framework that iteratively performs segmentation and model‐estimation simultaneously. The neighborhood layer introduces local contextual constraints using Markov random fields. The tissue layer corrects mistakes using a series of logical rules. The organ layer divides tissue into different organs, or stitches different tissues together to form an organ. Organ cross‐sections are segmented in order by quantitative confidence measures. The systems layer manipulates geometric primitives that have been fit to organs in order to reconcile overlaps. Results: The automatic initialization of meshes has been trained and tested on 5 prostatic datasets. Processing time for volumes with roughly 60 slices, and 256×256 pixels per slice, is 40 seconds on a standard PC, without any human interaction. The segmentation results from the same 5‐layer hierarchy were verified by the trained experts and redeemed to be acceptable. Conclusion: A 5‐layer hierarchy can perform both recognition and delineation, seeing the big picture as well as the details. Such a framework where local decisions are supported by global properties can be useful in addressing inconsistent rectum contents.