bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐28: Evaluation of a Noise Addition Software for Simulating Low Dose MDCT Images
Authors: Li X , Samei E , Thomas A , Colsher J , Toth T , Frush D
Published: July 2007

Purpose: To evaluate the utility of a noise addition software in simulating realistic MDCT images at reduced radiation dose levels. Methods and Materials: The utility of the software in simulating realistic low dose CT images was evaluated using a water phantom. The phantom was scanned on a GE LightSpeed VCT scanner at four different tube potentials (80, 100, 120 and 140 kVp) and eight different tube currents (400, 300, 200, 100, 80, 60, 40 and 20 mA). Actual images from the 400‐mA scans were used to create simulated images at each reduced mA. For each combination of kVp and reduced mA, a set of three actual CT slices with no identifiable structures except water were picked together with their corresponding simulated images. Sixteen regions of interest (ROIs), 64 by 64 pixels each, were identified from each slice. Normalized noise power spectra were calculated from the ROIs using Fourier analysis and averaged over the three slices in each set. Noise power spectra of the simulated images were compared with that of their corresponding actual images to evaluate the relative magnitudes and textures of the simulated noise fields. Results: The noise power spectra of the simulated low dose images of the water phantom match well those of actual images in terms of spectral shape, but exhibit lower magnitudes especially when the mA in the simulated image is much lower than the original mA. Conclusion: The close match in spectral shape between the noise power spectra of the simulated and actual low dose CT images of the water phantom demonstrates the utility of the noise addition software to emulate actual textures of the noise. Further development is required to better match the magnitudes of noise in simulated and actual images over a wider range of mA values. Research sponsored by GE Healthcare.
SU‐FF‐I‐31: Sub‐Second CT Scanner with a 64‐Row Amorphous Silicon Flat Panel
Authors: Shapiro E , Colbeth R , Job I , Mollov I , Mollov T , Pavkovich J , Roos G , Star‐Lack J , Tognina C
Published: July 2007

Purpose: To increase the data acquisition speed and detection limits of amorphous silicon flat panels for use in a low cost multidetector‐row CT (MDCT) scanner with diagnostic image quality. Methods and Materials: A bench‐top sub‐second flat panel (FP) multidetector‐row CT system has been developed using three 64‐row FP detectors. Each FP is 30 cm × 3.3 cm in active area with 576 × 64 pixels that are 0.52 mm per side. A high degree of parallel processing is used to speed the data acquisition from the panels. The FPs are overlapped slightly enabling a scan diameter of 50 cm and slice volumes up to 20 mm. The system has been tested with various detachable scintillators and scans of performance and anthropomorphic phantoms are compared with their diagnostic MDCT scans. Results: The FP MDCT system can achieve full rotation 600 projection scans in 0.5 seconds with 32 rows and 0.6 second partial rotation scans with 64 rows. The image quality of 20 cm diameter performance phantom scans is comparable to a commercial MDCT scanner with similar technique/dose. Medium sized body scans are nearly comparable except for artifacts due to the panel overlaps and lag. Thus far, large body phantom scans are less comparable due to the additional dynamic range requirement, which are not optimized with the current ASIC amplifiers. Conclusion: The results indicate the potential for FP MDCT to be used as a less expensive and less complex alternative to crystalline silicon detectors on MDCT scanners. There is pressure to increase the number of MDCT rows beyond 64 in cardiac imaging to achieve single organ coverage in one scan rotation. The use of larger area FP detectors to achieve greater than 256 rows exists and the sub second speed can be achieved with compensations and a high degree of parallel processing.
SU‐FF‐I‐32: Effects of Scatter in Dual‐Source CT
Authors: Kyriakou Y , Ertel D , Krause J , Kalender W
Published: July 2007

Purpose: To investigate the magnitude and distribution of scatter for dual‐source CT (DSCT) and its impact on image quality. Materials and Methods: Apart from forward scatter which is given for all CT scanners, the measurements at a dual‐source system is also affected by cross scattered photons from the second tube‐detector system arranged at 90°.

Simulations and measurements of homogenous phantoms of increasing diameter (100–400 mm) and of anthropomorphic phantoms were conducted for a DSCT scanner (SOMATOM Definition, Siemens Medical Solutions, Forchheim, Germany). The simulations of both forward and cross scatter were carried out using combined analytical and Monte Carlo simulation methods using a collimation of 19.2 mm for both tube‐detector systems. Measurements of cross scatter were performed by switching one tube off, still reading out the corresponding detector. Cross scatter was evaluated with respect to anthropomorphic and homogeneous phantoms for different imaging conditions such as different tube voltages, bow—tie filters. Dual‐energy scanning was included in the evaluations. Results: The forward scatter fraction increased with increasing diameter to 10% for a PMMA phantom of 400 mm diameter; for cross scatter, the mean intensity was lower or equivalent to forward scatter for small phantoms but was larger for increased phantom diameters. For large objects the ratio of cross scatter intensity to the sum of primary signal and forward scatter intensity reaches values higher than 100%. The outer dimensions of the object appear to be decisive for cross‐scatter whereas the influence of phantom inhomogeneity appears to be negligible. For dual energy — dual source scan modes the tube current setting for each tube should be adapted to achieve a minimization of cross scatter. Conclusion: The cross scatter magnitude is non‐negligible for a DSCT system and a compensation of its contribution is necessary for the assurance of high image quality.
SU‐FF‐I‐35: Suppression of Artifact in Axial Cone Beam Reconstruction Via Ray‐Wise 3D Weighting and Anisotropic Adaptive Filtering
Authors: Tang X , Hsieh J , Dong F
Published: July 2007

Purpose: To identify the root causes of artifacts in axial cone beam reconstruction, propose and evaluate the solutions of suppressing artifacts for image quality optimization. Method and Materials: With increasing cone angle in volumetric CT, suppression of artifacts in axial cone beam reconstruction becomes more challenging. In the past, data insufficiency and longitudinal truncation were identified as the major causes of the artifacts. In this study, insufficient longitudinal sampling is identified as the third major cause. Based on a detailed artifact analysis, it has been experimentally verified that, (a) the artifacts caused by data insufficiency is quite acceptable at small cone angle up to 4.23°, and barely acceptable at moderate cone angle equal to 8.46°; (b) the artifacts caused by longitudinal truncation can be efficiently reduced by ray‐wise 3D weighting. A straightforward way to reduce the artifacts caused by insufficient longitudinal sampling is to increase detector's longitudinal sampling rate, but such a way degrades noise characteristics and dose efficiency. An anisotropic adaptive filtering approach is proposed to suppress the artifact caused by insufficient longitudinal sampling. An oblique wire phantom, humanoid head phantom, modified Defrise phantom and helical body phantom, are employed to analyze artifacts and evaluate the efficacy of the proposed solutions. Results: Experimental evaluation based on the phantom study shows that, the artifacts caused by longitudinal truncation and insufficient longitudinal sampling in axial cone beam reconstruction can be substantially suppressed by ray‐wise 3D weighting and anisotropic adaptive filtering, especially while the image plane is approaching the detector's longitudinal boundaries. Conclusion: It has been evaluated and verified that the combination of ray‐wise 3D weighting and anisotropic adaptive filtering can significantly improve the image quality of axial cone beam reconstruction at cone angle up to 4.23°. Moreover, it is expected that such a combination can work well at larger cone angles.
SU‐FF‐I‐36: Improving Noise‐Resolution Tradeoffs in X‐Ray CT Imaging by Statistical Image Reconstruction
Authors: Williamson J , Politte D , O'Sullivan J , Keesing D , Whiting B , Lazos D , Evans J
Published: July 2007

Purpose: To assess the potential of a statistical image reconstruction (SIR) algorithm, penalized alternating minimization (AM) [IEEE TMI 26: 283] for improving image quality, relative to filtered back projection (FBP), for a given imaging dose. Minimizing the x‐ray CT imaging dose is an important goal both for CT‐guided radiotherapy and for imaging of pediatric patients and screening healthy populations. Method and Materials: Synthetic datasets with Poisson noise were formed from cylindrical phantoms with a variety of simulated high and low contrast features. A penalized AM algorithm based on separable surrogate penalty functions was implemented and investigated for Good's roughness penalty, an edge‐preserving log‐cosh penalty, and a novel penalty on local transmission fluctuations, all of which were applied only to adjacent pixels. Simulations were performed for a Somatom Plus 4 third generation geometry. Image blur (resolution) was specified in terms of the FWHM (σ) of the Gaussian, which when convolved with the truth image, best matched the estimated image. Resolution was varied by adjusting the filter cutoff frequency for FBP and the Lagrange multiplier for AM. Noise was quantified by image intensity variance in a uniform region. Results: For a fixed photon fluence, penalized AM images had smaller variances than FBP at all image blur levels, although the differences were not significant for low spatial resolution and low contrast features. However, for clinically relevant σ < 2 mm, the advantage of AM increased with increasing spatial resolution and contrast. For example, at σ = 1 mm, FBP had 48% and 24% larger variances for 75% contrast inserts with 0.5 mm pixels and 10% contrast with 1 mm pixels. The three penalty functions had comparable performance. Conclusion: Regularized AM SIR has the potential to realize signal‐to‐noise ratio gains equivalent to 30% imaging dose increases.

Supported in part by R01 CA075371.
SU‐FF‐I‐38: Reduction of In‐Plane Breathing Motion Artifacts Using Optimized‐Angle Sinogram Reconstruction
Authors: Low D , Parikh P , Whiting B , Mutic S , Hubenschmidt J , Malinowski K , Lu W , Bradley J
Published: July 2007

Purpose: Breathing motion mapping utilizes 4‐dimensional computed tomography (4DCT) which is typically acquired either in ciné or helical mode. Even with rapid CT scanners, tissues can move across a space of multiple pixels during image acquisition, causing motion artifacts. We are investigating a method to reduce the in‐plane motion artifacts using 180° reconstruction with CT gantry angles whose orientation is matched to the tissue motion vectors. Method and Materials: To model vessels and bronchial branches, CT scans were simulated with small cylindrical targets. The targets were moved at constant velocities during image acquisition and both 360° and 180° filtered back projection reconstructions were employed. The start angles of the 180° reconstructions were varied to examine the effect of the relative orientation between the start gantry angle and the motion vectors. Single and multiple targets were examined, including targets that moved orthogonally. Results: In all but static cases, 360° reconstruction provided the worst image quality. 180° reconstruction quality depended heavily on the relative orientation of the motion vector and the start CT gantry angle (α). When α was 0° (parallel), the image quality was good and when α was 90° (perpendicular), the image quality suffered. The image quality remained high when α was less than 45°. When multiple non‐parallel moving targets were studied, each was imaged well when its motion vector was parallel to the gantry start angle. A single good quality image could be pieced together from multiple image reconstructions created using multiple gantry start angles. Conclusion: Improving the quality of reconstruction for CT scans acquired during free breathing is possible using tuned gantry start angles even when using multiple patched image datasets. It is possible to compensate for potentially increased statistical noise due to the sub‐360° reconstruction by increasing the scanner's mA. This work supported in part by NIHR0196679.
SU‐FF‐I‐40: A Novel Gantry‐Free DBT System Using a Stationary Multi‐Beam Field Emission X‐Ray Source Array Based On Carbon Nanotubes (CNTs)
Authors: Yang G , Rajaram R , Zhang J , Sultana S , Cao G , Lalush D , Lu J , Zhou O
Published: July 2007

Purpose: To test the feasibility of a novel gantry‐free digital breast tomosynthesis (DBT) system using a stationary multi‐beam field emission X‐ray source array based on carbon nanotubes (CNTs) and to compare the system performance with the conventional devices. Method and Materials: Two tomosynthesis imaging systems have been built: a compact model and a full scale model, which contain 9 and 25 individual X‐ray pixels, respectively. The compact model can only image a partial breast phantom due to the limited span of the X‐ray source array and the small FOV of the detector. The full scale system is capable of full field digital mammography by utilizing a detector with 20‐cm FOV. The geometry of the full scale system is also comparable to the conventional DBT devices (refer to the supporting material). The system geometry, such as the source to detector distance (SDD) and X‐ray source position, is calibrated. The slice images at different depths are reconstructed using ordered subset convex (maximum likelihood) method. The system performance is evaluated by measuring parameters such as MTF and SNR. Results: By eliminating the rotary gantry, the system design is simplified and the issue if image blurring due to x‐ray source motion is removed. The total scan time can potentially be further shortened with a faster detector readout speed. Conclusion: By eliminating the rotary gantry, the system noise and equipment cost of the tomosynthesis imaging system are reduced. The total scan time can be further shortened with faster detector readout speed. The novel stationary tomosysthesis system shows great potential in clinical imaging.
SU‐FF‐I‐41: Effect of Room Setting On Object Dectectability for Two Different AMLCD Displays
Authors: Nemmers S , Mitchell C , Thomas J , Chakrabarti K , Kaczmarek R , Romanyhukha A
Published: July 2007

Purpose: The purpose of this study was to estimate the effect of viewing room setup on the reader's ability to detect subtle details in radiographic images displayed on two different active matrix liquid crystal displays (AMLCD). Method and Materials: Two viewing rooms were used in the study: one of them having a standard setup with white ceiling, light walls and furniture, and other monitors. The other room was a specially designed with black walls and ceiling and no other equipment except the monitors under study. Two different monitors, a standard IBM flat panel T‐221 and an experimental high‐bright IBM flat panel T‐221 were used in this study. In order to evaluate the effect of the different viewing room setups on the results of image reading, a computer generated 11×11 test pattern with two circular objects in every square cell were used. Each object of the pattern is defined by two parameters: diameter (number of pixels used for its generation) and contrast (number of digital driving levels). Five medical physicists were requested to read these contrast‐detail patterns at three different room illuminances (0, 5 and 20 lux) and four different backgrounds surrounding the entire test pattern (0%, 5%, 20% and 50% of max luminance) on both monitors. Results: At all conditions (room illuminance and surround) and on both flat panels, reader performance was significantly better in the specially designed dark room than in the typical viewing room. Conclusion: Higher diagnostic quality is realized in the room specially designed to minimize reflections.
SU‐FF‐I‐45: Evaluation of Age‐Dependant Dose and Image Quality for CT
Authors: Lin Y C , Tsai H Y , Chiang‐Hsieh C C , Tung C J
Published: July 2007

Purpose: To evaluate the age‐dependent CT dosimetry for the Reference Man of ICRP, the Reference Asian Man of IAEA, the mathematical phantoms of MIRD, and the Taiwan reference man established according to the data of weight and height published by the Department of Health in Taiwan. To determine size‐dependent technique factors for head and body CT scans using both traditional and novel CT scanners. Methods and Materials: Five methods were established to investigate the relation between phantom diameters and ages for above references. Five phantom cylinders in 10 to 32 cm diameters represented for the measurements of various CTDI (central, peripheral and weighted) and the cylinder in 5 cm stands for the trend between CTDIair and CTDIC in 10 cm phantom. All measurements were conduted in one single‐row and four multi‐row CT scanners across a range of energy (80–140 kVp), and slice collimation (1–40 mm). The noise, SNR and uniformity were estimated using four 2‐cm diameter ROIs in CT images. Results: These phantoms with diameters in 10, 16, 20, 24 and 32 cm represented patients of age groups of newborn, 1–5, 5–10, 10–15 and 18 (adult) years. The calculated ImPACT factor and matching MC data set for each scanner compared with ImPACT library data. The primary and scattered beam percentages were analyzed according to CTDI values. Measured CTDIs and image indicators showed that the CTDIW per 100 mAs varied with scanner, scan mode, beam quality and depended strongly on phantom size. Conclusion: Relationship between the phantom diameter and age were found. Tube voltage at 80 kVp was suggested for pediatric body scan in stead of using the same protocol as adults. This adjustment could reduce dose for 69% without sacrificing diagnostic image quality. Measured CTDIs were applied to establish pediatric diagnostic reference dose, and to determine collective effective dose.
SU‐FF‐I‐46: Measuring Kerma‐Area Products (KAP) in CT
Authors: Huda W , Ogden K
Published: July 2007

Purpose. To determine Kerma‐Area Product (KAP) for head and body CT examinations, and compare these with KAP of common radiographic and fluoroscopy examinations. Method. A single projection in CT is analagous to a conventional radiograph; for both exposures, the average incident air kerma may be multiplied by the corresponding cross‐sectional area that intercepts the patient to obtain the projection KAP. Summing all projections in a CT examination enables CT examination KAP to be determined. Measurements of the absolute intensity of the CT beam was obtained at the scanner isocenter (CTDIair), together with relative intensities on a line perpendicular to the long patient axis (z‐direction). The beam cross‐sectional area was determined using the known geometry of the CT scanner combined with eliptical shaped head and body dimensions of adult patients. Results: CT KAP values for head and body examinations were ∼10 Gy‐cm2 and ∼25 Gy‐cm2, respectively. For comparison, average values in the 2000 UNSCEAR report were: (a) ∼1 Gy‐cm2 for head/chest radiographic examinations; (b) ∼5 Gy‐cm2 for abdominal radiographic examinations; (c) ∼20 Gy‐cm2 for barium studies; (d) ∼100 Gy‐cm2 for interventional procedures. Conclusion: Measurement of the CT output, and the corresponding x‐ray beam profile transmitted through the beam shaping filter, permits the determination of KAP values for CT examinations. Specifying KAP as a measure of the radiation incident on patients undergoing CT examanitions would unify CT dosimetry with current practice in radiography and fluoroscopy.
SU‐FF‐I‐47: Free in Air Characterization of Metal Oxide Semiconductor Field Effect Transistor (MOSFET) Dosimeters Using Computed Tomography Radiation Beam Delivery System
Authors: Hussain I , Anderson S , Yee B , Kaufman R
Published: July 2007

Purpose: To study MOSFET radiation response characteristics for CT dosimetry applications, using CT as radiation source. Method & Materials: We used five Thomsen‐Nielsen MOSFETs with reader and wireless communication system to a laptop computer, GE Light Speed Ultra‐8 CT scanner, Siemens Sireskop radiographic unit (Polydoros‐SX80), Radcal 9095 dosimeter with 6 cc ionization chamber and kVp sensor, aluminum plates, ready pack films & styrofoam support.

Each MOSFET was placed separately at isocenter for characterization. An exposure of approximately 1000 mR (996 mR to 1015 mR) was delivered to each MOSFET. Exposures were determined using 6cc ionization chamber at isocenter, oriented with its long axis parallel to the long axis of CT collimation, to ensure complete irradiation of the chamber. Sensitivity was compared with that of a general purpose overhead x‐ray tube. MOSFET energy dependence, linearity of response, sensitivity with CT X‐ray tube in stationary position and with tube in rotate mode, and angular dependency of MOSFETS was studied. Results: MOSFETS' response (in mV, averaged for 5 MOSFETS) changed by 12% when kVp varied from 80 through 140. Linearity of response was good for all the energies selectable. Sensitivity was obtained in the range of 25.5 to 32.5 mV for the all the MOSFETS studied. The average sensitivity for the five MOSFETs with the overhead x‐ray tube was 26.58 mV/R. The difference in sensitivity between CT tube in stationary position and CT tube in rotate mode was about 3%, compared with that of overhead radiographic tube at 8.2%. The averaged maximum variation of all MOSFETS as a function of tube angle was within 5%. Conclusion: When using MOSFETS for CT dosimetry, use of a CT x‐ray source in rotate mode is recommended for calibration purposes.
SU‐FF‐I‐49: Daily Patient Dose From Kilo‐Voltage Cone‐Beam Computed Tomography: A Comparison Between XVI and OBI
Authors: Song W , Ozawa S , Alani S , Liu C , Chvetsov A , Bhandare N , Palta J , Li J
Published: July 2007

Purpose: To make a comprehensive set of absolute dose measurements from the X‐ray Volumetric Imager (XVI®, Elekta Medical Systems) and the On‐Board Imager (OBI®, Varian Medical Systems) on cylindrical phantoms using a calibrated ion chamber. Method and Materials: Two cylindrical (acrylic) phantoms with diameters of 18 cm (head phantom) and 30 cm (body phantom) were used for all measurements. Each phantom has a hole in the center and 2 cm below the phantom surface. For the XVI unit, the four manufacturer‐supplied protocols were measured, namely, “head & neck”, “prostate”, “pelvis”, and “pelvis — large”. The total mAs settings were also varied for each protocol to verify the dose linearity. For the OBI unit, full bow‐tie, half bow‐tie, and no bow‐tie filters were used in combination with the two scanning modes, namely, “full‐fan” and “half‐fan”. Results: For the XVI unit, the (isocenter) doses range between 0.1 and 2.2 cGy for the “head & neck” and “prostate” protocol, respectively, and agree well with the “Nominal Scan Dose” supplied by the manufacturer. The measured doses were highly linear with the total mAs settings. For the OBI unit, the (isocenter) doses range between 0.9 and 8.5 cGy. In the full bow‐tie with the “full‐fan” mode, the head phantom central dose was 8.5 cGy. This is significantly larger than a similar protocol scan measured with the XVI unit (“head & neck”). Half value layers were between 4.6 to 7.0‐mm‐Al for the two x‐ray units. Conclusion: A comprehensive series of dose measurements were made on the XVI and OBI CBCT imagers. It was observed that the OBI unit generally results in higher dose with up to 8.5 cGy measured with the head phantom. More studies are required to determine the increase in image quality expected from the increase in patient dose from the OBI unit.
SU‐FF‐I‐53: X‐Ray Scattering and Fluorescence Spectroscopy as a Possible Tool for KVp Monitoring
Authors: Krmar M , Shtykov A , Ganezer K , Ma G
Published: July 2007

Small changes in the peak voltage of a diagnostic x‐ray tube can cause significant modifications in the absorbed dose or degrade the contrast of an x‐ray image. It has been suggested that kVp should be monitored routinely however a standardized noninvasive technique for kVp monitoring has yet to be developed. A number of x‐ray beam‐related quantities depend upon the endpoint energy including, intensity, penetrability and dosage. However, none of these parameters can be used to determine kVp for x‐ray tubes in general.

If a material is irradiated by an x‐ray beam, spectra for Compton scattered photons as well as x‐ray fluorescence lines that are a characteristic of the target material can be simultaneously collected. The ratio of the integral number of Compton scattered photons and the number of fluorescent x‐ray photons is a function of the maximal beam energy and same time independent of the tube current, measurement geometry, and other quantities that are related to the experimental setup.

CdTe detectors having sufficient energy resolution to distinguish individual x‐ray fluorescence lines and high efficiency for energies in the 10‐keV region were used in our measurements. Several materials covering a wide range of atomic numbers from Copper (Z=12) to lead (Z=82) were used as the medium for fluorescence and for scattering. A variety of scattering angles and detection geometries were tested.

Our measurements have demonstrated that the ratio of the integral number of Compton scattered photons to that of fluorescent photons using a fixed geometry is a sensitive index of kVp (peak tube voltage).
SU‐FF‐I‐54: Use of Wisconsin Test Cassette with CR System
Authors: Liang Y , Chu R , Rutel I
Published: July 2007

Purpose: The Wisconsin Cassette had been widely used for beam quality measurements of the screen‐film radiographic systems. We explore the possibility of modifying this tool to use CR imaging plate instead of film and the application to the state‐of‐the‐art radiographic systems. Method and Materials: When using a Wisconsin Cassette to survey the beam quality, one compares the adjacent dots in the testing and reference regions of the exposed film to find the location of equal optical density, and checks the appropriate calibration curve. In this preliminary study, we removed the back cover of the cassette and placed it on a CR imaging plate. The amount of radiation exposure under the interesting region of the cassette was chosen to be about 1 mR. During the kVp and HVL testing, we added additional copper and aluminum to the reference region until the cassette's original calibration curves became usable. The imaging plate was processed by a Fuji FCR 5000 plus CR reader with S value fixed to 200 under Test/Sensitivity menu option. We analyzed the image by comparing the pixel value of dots in the testing and reference regions. Results: With the modified Wisconsin Cassette and CR system, kVp tests at 60, 80, 100, and 120 KVp, as well as the HVL tests at 60 and 80 kVp, were performed at four radiographic systems. The results agree with the recent measurements by noninvasive kVp electronic sensor to within 4% for kVp values, and the measurements by ionization chamber to within 8% for HVL values. Conclusion: The modified Wisconsin Cassette can be used with CR as a QA testing tool for radiographic systems with high frequency converters. It will allow for more frequent evaluation of beam quality, and the possibility of finding tube problems associated with kVp and HVL degradation sooner.
SU‐FF‐I‐59: A Machine Independent Threshold Method for PET Target Delineation
Authors: Zheng Y , Syh J , Greskovich JF , Kunos C , Wessels BW
Published: July 2007

Purpose: We have developed a PET image segmentation method for accurate target delineation and volume estimation and compared the performance with other published methods without prior volume estimates from CT or MR. Method and Materials: Eight spheres containing a uniform concentration of FDG and ranging in size from 1 cc to 95 cc were imaged in a Jaszczak phantom. The spheres to background concentration ratio were variable from 3:1 to 12:1. Our hypothesis is that the optimal threshold depends on target volume and target/background concentration ratio and can be derived only from PET image. However, the target volume and concentration ratio both can not be obtained from image directly. For this work, a mean intensity segmentation method was used to obtain an initial target volume. Based on this initial volume estimate and source/background ratio, the concentration ratio was computed. This ratio combined with initial volume provided enough information to derive desired threshold to segment PET image and outline target volume. These volumes were compared with the actual measured sphere volumes. To determine the performance of this method, we also compared the segmentation results from adaptive thresholding, mean SUV and spatial derivative segmentation methods. Preliminary patient studies of lung lesion were also conducted. Results: The overall average error for sphere volume estimation was 8.7%. The performance was robust and uniform for all spheres in wide range of size and concentration ratio. Preliminary patient studies showed substantial clinic utility. Conclusions: This method results a high‐quality and uniform performance for PET image segmentation with acceptable clinic delineation. The method was shown to be superior compared to other methods in phantom studies overall, especially for small volumes.
SU‐FF‐I‐62: Automatic Quantitative MRI Technique as a Biomarker for AD Tracking
Authors: Alyassin A
Published: July 2007

Purpose: A newly automatic segmentation technique was developed to measure the percent brain parenchyma (PBP) with a high degree of precision. The purpose was to provide a simple yet a robust biomarker to track automatically and accurately over time the progression of early stages of Alzheimer Disease (AD). Method and Materials: The PBP was calculated as the percent difference between the brain intra‐dural volume (IDV) and the cerebral spinal fluid (CSF) volume over the IDV. The developed automatic segmentation technique is composed of two main stages of image processing methods. The first stage uses multi‐spectral analysis where the brain and CSF clusters are delineated automatically and accurately based on known information of tissue relaxations, optimal MR parameters, as well as T2 median filter. The T2 Median filter is used to reduce the spread of the clusters thus improves the reproducibility of the segmentation technique. The second stage is composed of a special region growing technique in combination with logical image processing operators. The technique requires dual spin echo MR T2 weighted images of the whole brain. To test the precision of the technique, two normal subjects were scanned on a GE 1.5 Tesla MR Scanner seven times over a month period with the same MR spin echo pulse sequence. The pulse sequence generated a voxel size of 0.859×1.719×2 mm3. Results: The percent brain parenchyma was calculated for these two subjects. The percent change in PBP was less than 0.3%. The technique ran automatically without any user interaction under a minute using a standard personal computer. Conclusion: This research provides a newly fast technique that can be used as to track automatically and accurately the progression of early stages of AD patients. Conflict of Interest: “Research sponsored by General Electric Corporation”.
SU‐FF‐I‐65: Evaluation of Four Volume‐Based Image Registration Algorithms
Authors: Chu J , Zhang Y , Hsi W , Khan A , Mehta P , Bernard D , Abrams R
Published: July 2007

Purpose: To evaluate four different, volume‐based, automatic image registration algorithms from two commercially available treatment planning systems (Philips Syntegra, BrainLab BrainScan). Methods and Materials: Philips Syntegra provides Cross Correlation (CC), Local Correlation (LC) and Normalized Mutual Information (NMI) as optimization metrics. BrainScan applies Mutual Information (BSMI) as an optimization metric. These algorithms were evaluated with: 1) synthesis images, i.e., the images obtained by applying known transformations to a set of original CT images, 2) CT and MR phantom images, and 3) CT and MR head images from 12 different patients with brain tumors. Results: For synthesis images, the registration results were compared with known transformation parameters and all algorithms achieved sub‐millimeter accuracy in translation and sub‐degree accuracy in rotation. For phantom and patient images, the registration results were compared with those provided by manual registration. The mean and standard deviation of translation and rotation errors for the phantom study were 2.0±1.1 mm and 1.7±1.0 degree respectively. For the 12 sets of head images in this study, NMI algorithm, with registration accuracy within 1.5mm and 1 degree, performed better than other algorithms (p‐value 0.005). CC and BSMI performed poorly with potential errors close to 4mm and 3 degrees. We also noticed that LC and CC algorithms were much less robust and may fail to register when large translation and rotation were required. Conclusion: All algorithms themselves can achieve sub‐voxel accuracy for CT to CT registration of synthesis images. For clinical MR and CT image registration, the accuracy is much reduced, probably due to the intensity and voxel size differences between those images. In addition, Normalized Mutual Information based model appears to outperform other algorithms for registering MR and CT images of the brain.
SU‐FF‐I‐66: An Interactive Deformable 3D/3D Image Registration System: Radial Basis Functions
Authors: Kim J , Li S , Zhao Y
Published: July 2007

Purpose: Deformable image registration becomes challenging in the existence of noise and/or extrinsic objects such as rectum fillings or gas, and subject to failure. When the registration is unsatisfactory the result needs to be corrected. For this purpose we have developed an interactive 3D/3D deformable registration system that allows users to easily modify the registration using computer input devices. Method and Materials: The system uses radial basis functions to deform one of the input volumes. Users can edit control points on three orthogonal sectional views: selecting, moving, adding, and removing control points. As the function status changes the renderer updates the views real‐time to feed the change back to the user. The system also has automatic local registration features, which utilize box or mask ROI based rigid body registrations to establish correspondences of the selected points. Results: Real‐time rendering is very important for interactive editing. The editing of radial basis functions was possible up to 125 control points without major noticeable delay. The computer was equipped with one 3.0GHz CPU, 2GB system memory, and an NVidia GeForce 6800 graphics adaptor with 512MB GPU memory. Conclusion: We have developed an interactive deformable 3D/3D image registration system that allows editing radial basis functions interactively. We find this system is useful to correct registration errors after an automatic registrations session.
SU‐FF‐I‐67: Conventional CT to Cone‐Beam CT Image Registration Using Combination of Intensity‐ and Landmark‐Based Deformable Image Registration Methods
Authors: Gao S , Wang H , Zhang L , Zhang Y , Mohan R , Dong L
Published: July 2007

Purpose: A hybrid deformable registration approach was proposed to combine the landmark‐based compact support radial basis functions (CSRBFs) spline registration with the automatic intensity‐based diffusion registration. The goal was to gain more local control of the region that cannot be handled properly with intensity‐based automatic image registration for cone beam CT (CBCT) images with local image artifacts. Method and Materials: The hybrid registration takes the advantage of both methods: the diffusion registration for automatic registration of the entire image and the CSRBFs spline method with limited landmark points to control the local deformation for special situations. For registration of CT image with the CBCT image of head and neck cancer patient, the air cavity and the image artifacts in CBCT image are the major concern of the local CSRBFs spline registration. The control points were usually selected on the boundary of those correspondence ambiguity regions in both images. Due to the limited range of the CSRBFs, the registration will not affect the area outside of the region where the landmark points were placed. The constraint of the topology preservation involved in this algorithm ensures that the transformations are reliable and accurate. Results: we register CT image to CBCT images of head and neck cancer patients, and map the manual contours to daily CBCT image using three different registration approaches. The performances of the registration algorithms were evaluated by visually assessing the agreement of the structures with the deformed contours in the CBCT image. We found that the hybrid registration gave a better result. Conclusion: The hybrid method can handle correspondence ambiguity problem in image registration cause by air cavity and image artifacts in CBCT images. It can also improve the registration accuracy without significantly increasing the registration time.

Research is sponsored in part by Varian.
SU‐FF‐I‐85: Development of a Cone‐Shape Phantom for Multi‐Voxel MR Spectroscopy
Authors: Woo D , Choe B , Kim B , Jung S , Park H , Rhim H , Jahng G
Published: July 2007

Purpose: The purpose of this study was to develop a cone‐shape phantom for multi‐voxel magnetic resonance spectroscopy (MRS) and to evaluate MR spectra using the cone‐shape phantom we developed in this study. Method and Materials: A cone‐shape MRS phantom was developed with a combination of cone‐shape vials. The cylindrical main body was made of acrylic resin and the cone‐shape vials were fabricated from poly‐ethylene cones. Each cone of the phantom was filled with various metabolite materials (The solution mimicked human brain). 1.5T GE and 3T Philips systems were used for the single voxel spectroscopy (SVS) as well as for the multi‐voxel spectroscopy (MVS). Identification and quantification of the metabolite materials in the cone‐shape phantom were done by the SAGE post‐program. Results: The MR images and spectra of the cone shape phantom were obtained from the assigned slice position. The high order shimming control provided enhanced resolution in the SVS and MVS. The area and amplitude were proportional to the metabolite volume in the voxel. We confirm that the analyzed results are reasonable and the present study demonstrated that the cone‐shape phantom was useful for the metabolite quantification. Conclusion: We propose that the cone‐shape phantom can be used for the evaluation of quality control of the MR spectra obtained from SVS and MVS.
SU‐FF‐I‐86: MRI and MRS Assessment of Bone Marrow Cellularity
Authors: Pichardo J , Bourke V , Bolch W
Published: July 2007

Purpose: Bone marrow cellularity is an important parameter in the diagnosis and treatment of bone marrow disease, as disease affects marrow cellularity and marrow adipocyte concentration significantly alters beta‐ or alpha‐particle energy deposition from radiopharmaceuticals to radiosensitive hematopoietic cells. The current “gold standard” for the assessment of cellularity is the histological analysis of painful bone marrow biopsies of the iliac crest. There have been a few limited attempts to quantify cellularity non‐invasively by MR Chemical Shift Imaging (CSI), but the accuracy of this technique has never been validated. Here we demonstrate a method to correlate ex‐vivo CSI cellularity values to the results obtained by standard histological methods, using stereotactic image co‐registration. Method and Materials: Cellularity phantoms were created by preparing a series of lipid/water emulsions in which the water fractions (WFs) ranged from 0% to 100%, and were precisely known a priori. WFs were then measured in each phantom by CSI using a Phillips 3T horizontal bore scanner. Following this, tubular Silicon fiducials were inserted into the spongiosa of an excised canine limb using a Teflon template guide. Ex‐vivo cellularity measurements were obtained by 3T‐CSI within the fiducial region, and then bone cores were extracted with the fiducial systems intact for subsequent histological analysis and digital microscopy imaging using standard protocols. The accuracy of the CSI cellularity was then evaluated by co‐registration of the MR spectroscopy to the histological ‘gold‐standard’. Results and Conclusions: Here we demonstrate a novel technique to co‐register NMR Spectroscopy with standard digital imaging methods, in phantoms and histological specimens in which the lipid to water fraction is precisely quantifiable. Further studies are suggested, but these results imply that it may be possible to accurately sample bone marrow cellularity in both healthy and diseased individuals, for improved prognostic outcome in the treatment of metastatic bone disease.
SU‐FF‐I‐87: Qualifying Magnetic Moments in Small Cylindrical Objects by Complex Sum Method
Authors: Hsieh C , Cheng Y , Neelavalli J , Haacke E
Published: July 2007

Purpose: Our ultimate goal is to quantify magnetic moments of small cylindrical objects in‐vivo from MR images, without any a priori information. We want to achieve this goal with the complex sum method [1,2]. Methods: Simulation procedures and the experimental setups were described in [1]. The magnetic moment is defined as . The magnetic moment of an object is proportional to the phase values around the object in MR phase images. Three concentric circles were chosen on a phase image with radii R1, R2 and R3. In the simulations, if the magnetic moment is known in advance, the phase values around the object can be used to determine the radii, using formulas in [3]. Each radius has to be larger than the size of the phase aliasing area[2]. Knowing the radii can be used to determine the magnetic moment of the object [2]. We also study the uncertainties of the magnetic moment with the presence of both systematic and thermal noises through error propagation methods. A gel image is also analyzed. Results: For the uncertainty studies, we found that the phase combination (φ1,φ2,φ3)=(3,2,1), in units of radians, leads to an uncertainty of the magnetic moment within 3% of the expected moment, which seems to be the lowest uncertainty. Using this phase combination and the known magnetic moment −5.78 ppm‐mm2 from gel data [1], we were able to determine those three radii and then solve the magnetic moment between the gel‐air interface. The result is −5.53 ppm‐mm2 which is within 5% uncertainty of the expected value.

Conclusions: We have shown that the current method is feasible of extracting the magnetic moment of a small cylindrical object within good accuracy.
SU‐FF‐I‐90: Automated Detection of Arterial Input Function in DSC Perfusion MRI in a Stroke Rat Model
Authors: Yeh Mai‐Yu , Lee Tsong‐Hai , Chyi Tzuu‐Kang , Liu Ho‐Ling
Published: July 2007

Introduction: Dynamic susceptibility contrast (DSC) perfusion MRI has been widely applied to assess ischemia in small animal stroke models. Quantitative CBF estimation requires deconvolution of the tissue concentration time curves with an arterial input function (AIF). However, image‐based determination of AIF in rodent is challenging due to limited spatial resolution. We evaluated the feasibility of automated AIF detection and compared the results with those obtained from commonly applied semi‐quantitative analysis. Methods: Permanent occlusion of bilateral common carotid artery was used to induce ischemia in a spontaneous hypertensive rat (240gm, 12‐week). DSC imaging was performed on a 3‐T MR scanner, using a wrist coil, with a SE‐EPI sequence (TR/TE = 700/80 ms, FOV = 41 mm, matrix = 64, 3 slices, SW = 2 mm), starting from 7 s prior to contrast injection (1.2ml/kg, Schering AG). The experiment was performed at pre‐operation, 1‐day, 1‐week and 4‐week post‐operation. For quantitative analysis, AIF was obtained from 10 voxels with greatest contrast enhancement and used for deconvolution. For the semi‐quantitative analysis, relative CBF was estimated by the integral divided by the first moment of the relaxivity time curves. Results: No significant differences were observed between the AIF obtained in three different ROIs, whole brain, hemisphere without lesion and hemisphere with lesion. Comparing the CBF ratios (lesion/normal) between quantitative and semi‐quantitative analyses, a similar trend at different operative time points was found. Discussion: The automated method was able to detect AIF with similar shapes as could be found in literatures. In this study, arterial inputs to hemispheres with and without lesion were found to be similar, thus the quantitative analysis led to comparable CBF ratios than the semi‐quantitative analysis. However, when the regional blood supply is altered, being capable of determining local AIF will be crucial for the accurate assessment of ischemia status.
SU‐FF‐I‐92: MR Vessel Size Imaging of Brain Tumors Using Double Contrast Agent Injections
Authors: Liu HL , Yang WS , Hsu YY
Published: July 2007

Purpose: Microvascular dimensions can be estimated by MR vessel size imaging (VSI) which requires measurements of and ΔR2 following contrast passage, cerebral blood volume, and apparent diffusion coefficient (ADC). Recently, this method has been applied in human subjects using a double‐echo sequence with a constant ADC. However, such sequence is not widely available in clinical scanners and may result in limited resolution. In addition, ADC can vary between different tissues and lesions. This study proposed a set of imaging protocols including double contrast injections and ADC measurement for VSI in patients with brain tumors.

Methods: Seven patients with brain tumors were examined on a 3T clinical MR scanner. VSI data were acquired during two injections of 0.2 ml/kg Gd‐DTPA (Magnevist) (4 ml/s): (1) GE‐EPI (TR/TE=1500ms/35 ms) and (2) SE‐EPI (TR/TE=1500ms/70ms), each with 60 phases, matrix size = 64, and slice thickness = 5 mm. Three‐directional diffusion‐weighted MRI was performed with b = 1000 s/mm∧2. Vessel diameters in gray matter, white matter and tumor regions were calculated with the measured ADC and compared to the results with an assumed constant ADC (800 mm∧2/s). Results: Vessel diameters in normal gray and white matters were obtained as 18.8+/− 8.4 and 15.5+/− 4.7 μm, respectively, which was in agreement with previous studies. The vessel caliber of tumors ranged from 68.0 to 179.1 μm. Results calculated with constant ADC introduced 3–24% errors in VSI of tumors, depending on the discrepancies between the true and assumed ADCs. Conclusion: This study included ADC measurements in the clinical protocol of MR VSI, which is crucial for accurate assessment of microvascular dimensions in lesions. A double contrast agent injection approach was tested and proven being capable of providing reasonable vessel calibers. This approach has potential for VSI with higher resolution, which is currently under investigation.