bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐FF‐I‐23: Region‐Of‐Interest (ROI) Cone‐Beam Computed Tomography (CBCT) Using Rotational Digital Subtraction Angiography (DSA) Acquisition
Authors: Patel V , More A , Hoffmann K , Bednarek D , Rudin S 
Published: July 2007

Purpose: Region‐of‐interest (ROI) cone‐beam computed tomography (CBCT) can reduce dose to the patient. To provide data outside the ROI and overcome the truncation artifacts due to lack of data, we propose a new technique in which a material filter attenuates the beam except in a central ROI. DSA is used to subtract background bone and tissue as well as much of the ROI filter. Method and Materials: A ROI filter was made by making a 1 cm diameter aperture in 0.21 g/cm2 gadolinium screens. The ROI filter was fixed to the x‐ray tube assembly of a standard C‐arm gantry. Mask and contrast acquisitions were performed. Misregistration between the mask and contrast projections were corrected to reduce artifacts at the edge of the ROI. The intensities inside and outside the ROI were further equalized to adjust for the beam hardening effects of the filter outside the ROI. After corrections, reconstruction was performed with the acquisition system's software. Results: DSA‐ROI‐CBCT data were comparable to those obtained with standard DSA‐CBCT with registration and equalization each resulting in artifact reduction at the edge of the ROI. Data outside the ROI was noisier due to fewer photons. Since the x‐ray intensity in the periphery was reduced, the contrast‐to‐noise ratio of the iodinated vessels in the projections inside the ROI was approximately 40% higher than outside. The calculated integral dose reduction for the 12″ acquisition mode with the ROI filter was approximately 85% compared to a full‐field acquisition. Conclusion: By providing data outside the ROI, the new DSA‐ROI‐CBCT technique provides reconstructions inside the ROI comparable to standard DSA‐CBCT with minimal artifacts and significantly reduced integral dose compared to full‐field acquisition. This technique may be easily implemented in the clinical environment for DSA‐ROI‐CBCT reconstruction during ROI image‐guided interventions.(Support: NIH Grants R01‐NS43924, R01‐EB002873, Toshiba Medical Systems Corporation).
SU‐FF‐I‐24: The Influence of Bowtie Filtration On Cone‐Beam CT Image Quality
Authors: Mail N , Moseley D , Siewerdsen J , Jaffray D 
Published: July 2007

Purpose: The large variation of x‐ray fluence at the detector across the imaged field‐of‐view in cone‐beam CT causes the loss of skin‐line and reduces CT number accuracy and image uniformity. We report the performance of a bowtie filter (BTF) as a compensator for improved uniformity, skin‐line and CT number accuracy. Method: Image enhancement is performed using a BT filter with a 20cm collimator. The BTF was inserted 30cm from the x‐ray source on an Elekta Synergy XVI. This filter modulates the 2D x‐ray fluence making it non‐uniform across the field‐of‐view. This compensates for the limited attenuation near the skin, resulting in enhancement of skin‐line and uniformity. Two phantoms (1) CatPhan and 2) CatPhan with irregular acrylic annulus (Cat‐Irreg) were scanned on an Elekta CBCT system. The reconstructed images with and without a BTF were analyzed. The images were transformed into polar coordinates to allow quanitfication of radial lag artifacts (radar artifact) for the Cat‐Irreg phantom. Results: The use of the bowtie filter demonstrated a considerable improvement in CT accuracy in the skin‐line region. The uniformity increases 30% for Cat‐Irreg phantom, and skin‐line edges for both phantoms are visible. CT number accuracy with the BT filter improved by 2% for the CatPhan phantom while no improvement was evident for the Cat‐Irreg phantom. The CT♯ linearity for the catphan phantom with the BT filter improved by 8%. In addition, a 45% reduction in the “radar artifact” was observed in the Cat‐Irreg phantom images acquired with the BT filter. Conclusion: The implemented BTF shows improvement in image quality including uniformity and skin‐line reconstruction. This compensator is static and makes many compromises for anatomical imaging site, patient size, and imaged field‐of‐view. The ideal compensator would optimize the fluence profile to account for numerous properties of the patient and imaging system.Research sponsored by Elekta.
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‐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‐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‐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‐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‐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‐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.
SU‐FF‐I‐111: Feasibility of Using Higher Energy Beam Pairs to Improve DXA Accuracy
Authors: Wilson C , Carrera G 
Published: July 2007

In standard DXA the fat content of the soft tissue containing the bone is assumed to be the same as the soft tissue in the baseline region of the scan adjacent to the bone. Unfortunately, this assumption is rarely correct and inaccuracies in BMD can exceed 20 % in clinically realistic cases. Moreover, changes in fat content resulting from weight loss or gain makes interpretation of changes seen in BMD problematic. The cause of the inaccuracy is the large difference in the attenuation characteristics of fat and lean tissues at the effective energy of the low energy beam used in standard DXA. A mathematical simulation of DXA using monoenergetic photon beams was performed using beam energy pairs higher than used for standard DXA. In the simulation the low energy beam was varied from 80 to 110 keV with the high energy beam held constant at 140 keV. The entrance doses of the simulations were varied to maintain a measurement precision equivalent to that of standard DXA. For simulated DXA using higher beam energy pairs the BMD error due to inhomogeneities in the fat content of soft tissue was eliminated. The entrance skin dose for the higher energy beam pairs needed to be increased to achieve the same measurement precision as standard DXA.Thus, the accuracy of BMD measurements can be improved by using higher energy beam pairs with a modest increase in entrance dose. This improvement in accuracy allows the accurate assessment of BMD changes in patients experiencing weight change.
SU‐FF‐J‐26: A Phantom Study to Assess the Feasibility of Using ExacTrac for Patient Setup for Fractionated Stereotactic Radiotherapy (SRT) Technique
Authors: Gete E , Moiseenko V 
Published: July 2007

Purpose: To investigate the feasibility of using ExacTrac for setup error correction for patients treated with fractionated stereotactic (SRT) technique with the BrainLab relocatable mask system. Method and Materials: A phantom study designed to evaluate setup accuracy of the ExacTrac system was performed. An actual treatment process, from making immobilization mask to treatment setup, was simulated. A 3.8 mm diameter lead bb was inserted in a Rando head phantom to represent a mid‐brain target. The phantom was CT scanned with 1 mm slice thickness and 1 mm slice index. A treatment plan was created using BrainScan, with an isocenter placed at the center of the bb. The phantom was setup for treatment with the following two methods:1. Phantom setup with the BrainLab localizer box.2. Phantom setup with ExacTrac.Electronic portal images of a treatment field defined by M3 MLC (12×12 mm2) were taken at various gantry and couch angles. Setup accuracies for the above two methods were calculated from the positions of the bb relative to field center. A Lutz test was performed prior to portal image acquisitions to correct for gantry flex. Results: Setup with ExacTrac showed consistently better accuracy compared with the Localizer box setup. Specifically, in Sup‐Inf direction mean deviations of the center relative to the center of the field were 0.3mm (standard deviation 0.1mm) with ExacTrac setup and 0.4mm (0.5mm) for localizer box. For Left‐Right direction deviations were −0.2 (0.3) and 0.4 (0.5); Ant‐Post 0.2 (0.2) and 0.5 (0.2) mm, for ExacTrac and localizer box, respectively. Conclusions: The BrainLab ExacTrac system has a great potential for setup verification and setup‐ error correction for the fractionated SRT technique with the BrainLab relocatable mask system.
SU‐FF‐J‐35: Clinical Implementation and Initial Experience with Calypso 4D Tracking System for Prostate Cancer Treatment
Authors: Cao D , Ye J , Afghan M , Wong T , Shepard D 
Published: July 2007

Purpose: The Calypso 4D tracking system can detect real‐time intra‐fractional tumor motion based on RF signals from the implanted beacons. The initial clinical experience on tracking prostate motion during the treatment is reported. We performed a series of tests to evaluate the calibration accuracy and stability of the system. Material and Methods: The first FDA approved clinical Calypso 4D tracking system was installed and used for this work. With three beacons implemented in the prostate, the system reports the target location in a real time fashion. Seven patients with prostate cancer were localized/tracked using this system. The vender provided a monthly calibration phantom and an in‐house developed stereotactic cone based alignment tool that were used to test the calibration accuracy of the Calypso 4D tracking system. The system stability was also studied using the monthly calibration phantom. Results: For the seven patients treated so far, the average initial setup shifts from the external tattoos were 1.1, 2.2 and 4.0 mm along lateral, longitudinal and vertical directions, respectively. For one patient, the observed maximum shifts along the above three axes were 4.6, 10.9 and 29.2 mm. The range of target motion during treatment was found to be 3.4 (Right‐Left), 9.9 (Superior‐Inferior) and 12.3 (Anterior‐Posterior) mm. The average patient setup time was less then 5 minutes. The daily QA of the system takes around 5 minutes on average.The vender provided system calibration procedure is based on room lasers with 2 mm error tolerance, which may potentially decrease the overall system accuracy. Our stereotactic cone based alignment tool can achieve sub‐millimeter accuracy. Repeated monthly calibration procedures showed that the system stability is within 1 mm. Conclusion: Calypso system provides efficient and accurate patient setup for prostate treatment. The current calibration procedure can be improved to achieve better accuracy.