Filtered Back-projection Technique Research Articles

Statistical Reconstruction of Material Decomposed Data in Spectral CT

Photon-counting detector technology has enabled the first experimental investigations of energy-resolved computed tomography (CT) imaging and the potential use for K-edge imaging. However, limitations in regards to detecter technology have been imposing a limit to effective count rates. As a consequence, this has resulted in high noise levels in the obtained images given scan time limitations in CT imaging applications. It has been well recognized in the area of low-dose imaging with conventional CT that iterative image reconstruction provides a superior signal to noise ratio compared to traditional filtered backprojection techniques. Furthermore, iterative reconstruction methods also allow for incorporation of a roughness penalty function in order to make a trade-off between noise and spatial resolution in the reconstructed images. In this work, we investigate statistically-principled iterative image reconstruction from material-decomposed sinograms in spectral CT. The proposed reconstruction algorithm seeks to minimize a penalized likelihood-based cost functional, where the parameters of the likelihood function are estimated by computing the Fisher information matrix associated with the material decomposition step. The performance of the proposed reconstruction method is quantitatively investigated by use of computer-simulated and experimental phantom data. The potential for improved K-edge imaging is also demonstrated in an animal experiment.

Assessment of multi-directional MTF for breast tomosynthesis

A method was developed to assess the multi-directional modulation transfer function (MTF) of breast tomosynthesis imaging systems using a sphere phantom. The method was initially developed based on a simulation dataset. Projections were simulated for a uniform voxelized breast phantom with sphere inserts using a fluence modeled from a 28 kVp beam incident upon an indirect flat-panel detector. Based on cascaded systems modeling, characteristic noise and blurring were added to each projection. The projections were reconstructed using a standard filtered backprojection technique, producing a 3D volume with an isotropic voxel size of 200 µm. ROIs that completely encompassed single spheres were extracted and conical regions were prescribed along the three major axes extending from the centroids. Pixels within the cones were used to form edge spread functions (ESFs), from which the directional MTFs were calculated. Binning size and conical range were adjusted to maximize the accuracy and to minimize the noise of the MTF. A method was further devised to remove out-of-plane artifacts from the ESF in the x–y plane. Finally, the method was applied to experimentally assess the directional MTF of a prototype tomosynthesis system. Comparisons of the sphere-based MTF along the different axes and the theoretical MTF yielded good agreement. A 30° angular cone and a 20 µm sampling were found to provide an ideal trade-off between the noise and accuracy of the measurement. The removal of artifacts in ESF yielded ‘modified’ MTFs that enabled a resolution-only characterization of the in-slice resolution of tomosynthesis. Drop-off frequencies in the x- and y-directional MTFs were 1.6 cycles mm−1 and 1.5 cycles mm−1, respectively. The presented method of separating the effective resolution and artifacts from the measured ESF was found experimentally implementable and is expected to facilitate the interpretation of MTF measurements in tomosynthesis.

Noise-reducing algorithms do not necessarily provide superior dose optimisation for hepatic lesion detection with multidetector CT

To compare the dose-optimisation potential of a smoothing filtered backprojection (FBP) and a hybrid FBP/iterative algorithm to that of a standard FBP algorithm at three slice thicknesses for hepatic lesion detection with multidetector CT. A liver phantom containing a 9.5-mm opacity with a density of 10 HU below background was scanned at 125, 100, 75, 50 and 25 mAs. Data were reconstructed with standard FBP (B), smoothing FBP (A) and hybrid FBP/iterative (iDose(4)) algorithms at 5-, 3- and 1-mm collimation. 10 observers marked opacities using a four-point confidence scale. Jackknife alternative free-response receiver operating characteristic figure of merit (FOM), sensitivity and noise were calculated. Compared with the 125-mAs/5-mm setting for each algorithm, significant reductions in FOM (p<0.05) and sensitivity (p<0.05) were found for all three algorithms for all exposures at 1-mm thickness and for all slice thicknesses at 25 mAs, with the exception of the 25-mAs/5-mm setting for the B algorithm. Sensitivity was also significantly reduced for all exposures at 3-mm thickness for the A algorithm (p<0.05). Noise for the A and iDose(4) algorithms was approximately 13% and 21% lower, respectively, than for the B algorithm. Superior performance for hepatic lesion detection was not shown with either a smoothing FBP algorithm or a hybrid FBP/iterative algorithm compared with a standard FBP technique, even though noise reduction with thinner slices was demonstrated with the alternative approaches. Reductions in image noise with non-standard CT algorithms do not necessarily translate to an improvement in low-contrast object detection.

Development of a CCD-Based Optical Computed Tomography Scanner Used in 3D Gel Dosimetry

This study proposed a CCD-based (charge-coupled device) optical computed tomography scanner (CT-s2) for 3D gel dosimetry. A parallel laser light was generated to pass through the gel sample using a diffuser and collimating lens. A CCD was used to capture projection image of gel sample at each step. An image reconstruction algorithm, filtered-back projection (FBP) technique was used to reconstruct the 3D image. Two better rotational steps are suggested as 1.0 degree and 1.5 degree for considering both of angular resolution and position deviation. The un-irradiated and irradiated BANG gel samples were scanned and reconstructed using FBP technique. Some artifacts were found in reconstructed images. Some discussions for artifacts were conducted and some solutions provided by previous researches to reduce these artifacts will be evaluated in the future work.

Cable Array $Z$-Pinch Experiments at 1 MA

Individual wires in a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinch were replaced with twisted pairs of wires, i.e., “cables.” We define a cable here as two or more fine wires twisted together to form a continuous strand with a twist wavelength λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> , dependent on the number of twists per unit length. Imploding Al cable array <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinches show a λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> -dependent increase in peak power above 1 keV. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -pinch backlighter radiography of nonimploding Ni and Cu cable arrays shows axially repeating shocklike structures. We have applied a filtered backprojection technique on these images in order to reconstruct a cross-sectional density mapping.

Evaluation of metal artifacts in MVCT systems using a model based correction method

To evaluate the performance of a model based image reconstruction method in reducing metal artifacts in the megavoltage computed tomography (MVCT) images of a phantom representing bilateral hip prostheses and to compare with the filtered-backprojection (FBP) technique. An iterative maximum likelihood polychromatic algorithm for CT (IMPACT) is used with an additional model for the pair∕triplet production process and the energy dependent response of the detectors. The beam spectra for an in-house bench-top and TomoTherapy™ MVCTs are modeled for use in IMPACT. The empirical energy dependent response of detectors is calculated using a constrained optimization technique that predicts the measured attenuation of the beam by various thicknesses (0-24 cm) of solid water slabs. A cylindrical (19.1 cm diameter) plexiglass phantom containing various cylindrical inserts of relative electron densities 0.295-1.695 positioned between two steel rods (2.7 cm diameter) is scanned in the bench-top MVCT that utilizes the bremsstrahlung radiation from a 6 MeV electron beam passed through 4 cm solid water on the Varian Clinac 2300C and in the imaging beam of the TomoTherapy™ MVCT. The FBP technique in bench-top MVCT reconstructs images from raw signal normalized to air scan and corrected for beam hardening using a uniform plexiglass cylinder (20 cm diameter). The IMPACT starts with a FBP reconstructed seed image and reconstructs the final image in 150 iterations. In both MVCTs, FBP produces visible dark shading in the image connecting the steel rods. In the IMPACT reconstructed images this shading is nearly removed and the uniform background is restored. The average attenuation coefficients of the inserts and the background are very close to the corresponding values in the absence of the steel inserts. In the FBP images of the bench-top MVCT, the shading causes 4%-9.5% underestimation of electron density at the central inserts with an average of (6.3 ± 1.8)% for the range of electron densities studied. In the uniform plexiglass background, the shadow creates 0.8%-4.7% underestimation of electron density with an average of (2.9 ± 1.2)%. In the corresponding IMPACT images, the underestimation in the shaded plexiglass background is 0.3%-1.8% with an average of (0.9 ± 0.5)% and 1.4%-6.8% with an average of (2.8 ± 2.7)% in the central insert region. In the FBP images of the TomoTherapy™ MVCT, this shading creates 2.6%-6.7% underestimation of electron density with an average of (3.7 ± 1.4)% at the central inserts and 5.9%-7.2% underestimation in the background with an average of (6.4 ± 0.5)%. In the IMPACT images, the uniform background between the steel rods is restored with 0.3%-1.0% underestimation of electron density with an average of (0.7 ± 0.3)%. The corresponding underestimation at the central inserts of the IMPACT images is -0.4%-0.1% with an average of (-0.1 ± 0.2)%. The shading metal artifact has been nearly removed in MVCT images using the IMPACT algorithm with the accurate geometry of the system, proper modeling of energy dependent response of detectors, and all relevant photon interaction processes. This results less than 1% difference in electron density in the background plexiglass and less than 3% averaged over the range of electron densities investigated.

Toward truly combined PET/CT imaging using PET detectors and photon counting CT with iterative reconstruction implementing physical detector response

This paper intends to demonstrate the feasibility of truly combined PET/CT imaging and addresses some of the major challenges raised by this dual modality approach. A method is proposed to retrieve maximum accuracy out of limited resolution computed tomography (CT) scans acquired with positron emission tomography (PET) detectors. A PET/CT simulator was built using the LabPET™ detectors and front-end electronics. Acquisitions of energy-binned data sets were made using this low spatial resolution CT system in photon counting mode. To overcome the limitations of the filtered back-projection technique, an iterative reconstruction library was developed and tested for the counting mode CT. Construction of the system matrix is based on a preregistered raster scan from which the experimental detector response is obtained. PET data were obtained sequentially with CT in a conventional manner. A meticulous description of the system geometry and misalignment corrections is imperative and was incorporated into the matrix definition to achieve good image quality. Using this method, no sinogram precorrection or interpolation is necessary and measured projections can be used as raw input data for the iterative reconstruction algorithm. Genuine dual modality PET/CT images of phantoms and animals were obtained for the first time using the same detection platform. CT and fused PET/CT images show that LabPET™ detectors can be successfully used as individual X-ray photon counting devices for low-dose CT imaging of the anatomy in a molecular PET imaging context.

Effects of Iterative Reconstruction Technique on Image Quality in Cardiac CT Angiography: Initial Experience

Objective: Iterative reconstruction algorithms offer potential radiation dose reduction while maintaining image quality. We attempted to compare image quality parameters of iterative reconstruction and conventional filtered back-projection (FBP) quantitatively in cardiac CT angiography, using second generation dual-source CT technology. Methods: Ten patients were scanned using retrospective ECG-gated dual-source CT for assessment of native coronary artery disease. Multiphase datasets were reconstructed using FBP and iterative reconstruction techniques. Image noise was measured throughout 20 phases of the cardiac cycle (at varying tube currents). Contrast-to-noise ratios (CNR) were compared at 9 specific coronary artery locations in diastole. Results: In all evaluated coronary artery locations, the CNR was significantly improved with iterative reconstruction when compared to conventional FBP (improvement: 39.5 ± 2.8%, p &lt;0.05). Iterative reconstruction demonstrated less image noise across all cardiac phases (reduction: 22.1 ± 4.0%, p &lt;0.05). Conclusions: Iterative reconstruction offers the potential to increase CNR in cardiac CTA. Our experience suggests that iterative reconstruction algorithms have the potential to reduce radiation doses while maintaining similar objective image quality measures such as CNR and noise levels versus standard FBP reconstructions. Further work with comparison to invasive coronary angiography is needed to ensure maintained diagnostic accuracy.

ALICE tomography section: measurements and analysis

The ALICE tomography section at Daresbury is a diagnostic setup in the injection line of EMMA, the world's first non-scaling FFAG accelerator.We present our measurements and analysis of the transverse emittance, Twiss parameters and phase space distribution of the electron beam that is injected into EMMA. The measurements are carried out at 12 MeV, for bunch charges from 20 to 80 pC. Quadrupole scans and tomography are used. The results show that space charge effect does not change the beam emittance significantly over the length of the tomography section. Starting from projections of the beam images, the quadrupole scan technique can be applied to give the emittance and Twiss parameters. The same projections can be processed using tomography to give the phase space distribution. A careful treatment of the background noise is required to produce consistent emittances between quadrupole scans at different locations. Extending this in a natural way to tomography, we are also able to remove most of the the streaking artefacts from reconstructions obtained using the Filtered Back Projection technique.

Comparison of adaptive statistical iterative and filtered back projection reconstruction techniques in brain CT

PurposeTo compare image quality and visualization of normal structures and lesions in brain computed tomography (CT) with adaptive statistical iterative reconstruction (ASIR) and filtered back projection (FBP) reconstruction techniques in different X-ray tube current–time products. Materials and methodsIn this IRB-approved prospective study, forty patients (nineteen men, twenty-one women; mean age 69.5±11.2 years) received brain scan at different tube current–time products (300 and 200mAs) in 64-section multi-detector CT (GE, Discovery CT750 HD). Images were reconstructed with FBP and four levels of ASIR-FBP blending. Two radiologists (please note that our hospital is renowned for its geriatric medicine department, and these two radiologists are more experienced in chronic cerebral vascular disease than in neoplastic disease, so this research did not contain cerebral tumors but as a discussion) assessed all the reconstructed images for visibility of normal structures, lesion conspicuity, image contrast and diagnostic confidence in a blinded and randomized manner. Volume CT dose index (CTDIvol) and dose-length product (DLP) were recorded. All the data were analyzed by using SPSS 13.0 statistical analysis software. ResultsThere was no statistically significant difference between the image qualities at 200mAs with 50% ASIR blending technique and 300mAs with FBP technique (p>.05). While between the image qualities at 200mAs with FBP and 300mAs with FBP technique a statistically significant difference (p<.05) was found. ConclusionASIR provided same image quality and diagnostic ability in brain imaging with greater than 30% dose reduction compared with FBP reconstruction technique.

Spot distribution measurement using a scanning nanoslit

A scanning and rotating nanoslit is used to measure submicrometer features in focused spot distributions. Using a filtered backprojection technique, a highly accurate reconstruction is demonstrated. Experimental results are confirmed by simulating the scanning slit technique using a physical optics simulation program. Analysis of various error mechanisms is reported, and the reconstruction algorithm is determined to be very resilient. The slit is 125 nm wide and 50 μm long and is fabricated on a 120 nm thick layer of aluminum. The size of the image field is 15 μm, and simulations indicate that 200 nm Rayleigh resolution is possible with an infinitely narrow slit.

Evaluation of Heavily Calcified Vessels with Coronary CT Angiography: Comparison of Iterative and Filtered Back Projection Image Reconstruction

To prospectively compare traditional filtered back projection (FBP) and iterative image reconstruction for the evaluation of heavily calcified arteries with coronary computed tomography (CT) angiography. The study had institutional review board approval and was HIPAA compliant. Written informed consent was obtained from all patients. Fifty-five consecutive patients (35 men, 20 women; mean age, 58 years ± 12 [standard deviation]) with Agatston scores of at least 400 underwent coronary CT angiography and cardiac catheterization. Image data were reconstructed with both FBP and iterative reconstruction techniques with corresponding cardiac algorithms. Image noise and subjective image quality were compared. To objectively assess the effect of FBP and iterative reconstruction on blooming artifacts, volumes of circumscribed calcifications were measured with dedicated volume analysis software. FBP and iterative reconstruction series were independently evaluated for coronary artery stenosis greater than 50%, and their diagnostic accuracy was compared, with cardiac catheterization as the reference standard. Statistical analyses included paired t tests, Kruskal-Wallis analysis of variance, and a modified McNemar test. Image noise measured significantly lower (P = .011-.035) with iterative reconstruction instead of FBP. Image quality was rated significantly higher (P = .031 and .042) with iterative reconstruction series than with FBP. Calcification volumes measured significantly lower (P = .019 and .026) with iterative reconstruction (44.3 mm(3) ± 64.7 and 46.2 mm(3) ± 68.8) than with FBP (54.5 mm(3) ± 69.5 and 56.3 mm(3) ± 72.5). Iterative reconstruction significantly improved some measures of per-segment diagnostic accuracy of coronary CT angiography for the detection of significant stenosis compared with FBP (accuracy: 95.9% vs 91.8%, P = .0001; specificity: 95.8% vs 91.2%, P = .0001; positive predictive value: 76.9% vs 61.1%, P = .0001). Iterative reconstruction reduces image noise and blooming artifacts from calcifications, leading to improved diagnostic accuracy of coronary CT angiography in patients with heavily calcified coronary arteries.

WE‐A‐301‐03: Enhancement of Four‐Dimensional Cone‐Beam Computed Tomography by Compressed Sensing with Bregman Iteration

Purpose: In four‐dimensional (4D) cone‐beam computed tomography (CBCT), there is a spatio‐temporal tradeoff. The aim of this study is to develop a Bregman iteration based formalism for high quality 4D CBCT image reconstruction from low‐dose projections. Methods: The 4D CBCT problem is first divided into multiple 3D CBCT subproblems by grouping the projection images corresponding to the phases. To maximally utilize the information from the under‐sampled projection data, a compressed sensing method is employed for solving each subproblem. We formulate an unconstrained lasso (least absolute shrinkage and selection operator) problem based on least‐square criterion regularized by total‐variation. The least‐square criterion reflects the inconsistency between the measured and the estimated line integrals. Furthermore, the unconstrained lasso problem is updated and solved repeatedly by Bregman iterations. Results: The performance of the proposed algorithm is demonstrated through a series of phantom experiments, and the results are compared to those of conventional filtered back‐projection (FBP). The simulation studies have shown that artifact suppressed images can be obtained with as small as 41 projections per phase, which is adequate for clinical 4D CBCT reconstruction without slowing down the gantry rotation. With such small number of projections, the conventional FBP failed to yield meaningful 4D CBCT images. Conclusions: The proposed method significantly reduces the radiation dose and scanning time to achieve the high quality images compared to the conventional 4D CBCT imaging based on FBP technique.

WE‐G‐110‐03: Directional MTF Measurement of Tomosynthesis Images Using a Cone‐Based Technique

Purpose: To develop a cone‐based modulation transfer function (MTF) measurement technique for tomosynthesis using a sphere phantom. Methods: Projections were simulated for a voxelized breast phantom with 12 mm sphere inserts using a fluence modeled from 28 kVp beam and incident upon an indirect flat‐panel detector with 200 um pixel size. Characteristic noise and blurring for each projection were added using cascaded systems analysis. The projections were reconstructed using standard filtered backprojection techniques, producing a 3D volume with an isotropic voxel size of 200 um. ROIs that completely encompassed single spheres were extracted, and conical regions were prescribed along the three axes extending from the centroids. Pixels within the cones were used to form edge spread functions (ESF), from which directional “raw” MTFs were calculated. Binning size and conical range were considered for maximizing accuracy and minimizing noise of the MTF. A method for removing out‐of‐plane artifacts of the ESFs in x and y directions was investigated and yielded an “effective” MTF. Results: Comparisons of the cone‐based MTF along the different axes and the true 3D MTF yielded good agreement. A 30 degree angle was found to provide ideal trade‐off between measurement noise and accuracy. Drop‐off frequencies in the x‐ and y‐directional “raw” MTFs were 1.5 cycles/mm and 2.5 cycles/mm, respectively. As expected, the z‐directional MTF had a much lower drop‐off due to the lack of angular sampling. The removal of artifacts in ESF yielded a “modified” MTFs which enabled a novel characterization of in‐slice resolution for tomosynthesis. Conclusion: The directional MTF of tomosynthesis reconstruction with FBP was determined by using the cone‐based MTF technique. The presented method of separating the effective resolution and artifacts from the measured ESF is expected to facilitate the interpretation of MTF measurements in tomosynthesis.

A compressed sensing-based iterative algorithm for CT reconstruction and its possible application to phase contrast imaging

BackgroundComputed Tomography (CT) is a technology that obtains the tomogram of the observed objects. In real-world applications, especially the biomedical applications, lower radiation dose have been constantly pursued. To shorten scanning time and reduce radiation dose, one can decrease X-ray exposure time at each projection view or decrease the number of projections. Until quite recently, the traditional filtered back projection (FBP) method has been commonly exploited in CT image reconstruction. Applying the FBP method requires using a large amount of projection data. Especially when the exposure speed is limited by the mechanical characteristic of the imaging facilities, using FBP method may prolong scanning time and cumulate with a high dose of radiation consequently damaging the biological specimens.MethodsIn this paper, we present a compressed sensing-based (CS-based) iterative algorithm for CT reconstruction. The algorithm minimizes the l1-norm of the sparse image as the constraint factor for the iteration procedure. With this method, we can reconstruct images from substantially reduced projection data and reduce the impact of artifacts introduced into the CT reconstructed image by insufficient projection information.ResultsTo validate and evaluate the performance of this CS-base iterative algorithm, we carried out quantitative evaluation studies in imaging of both software Shepp-Logan phantom and real polystyrene sample. The former is completely absorption based and the later is imaged in phase contrast. The results show that the CS-based iterative algorithm can yield images with quality comparable to that obtained with existing FBP and traditional algebraic reconstruction technique (ART) algorithms.DiscussionCompared with the common reconstruction from 180 projection images, this algorithm completes CT reconstruction from only 60 projection images, cuts the scan time, and maintains the acceptable quality of the reconstructed images.

Reducing Abdominal CT Radiation Dose With Adaptive Statistical Iterative Reconstruction Technique

To assess radiation dose reduction for abdominal computed tomography (CT) examinations with adaptive statistical iterative reconstruction (ASIR) technique. With institutional review board approval, retrospective review of weight adapted abdominal CT exams were performed in 156 consecutive patients with ASIR and in 66 patients with filtered back projection (FBP) on a 64-slice MDCT. Patients were categorized into 3 groups of <60 kg (n = 42), 61 to 90 kg (n = 100), and >or=91 kg (n = 80) for weight-based adjustment of automatic exposure control technique. Remaining scan parameters were held constant at 1.375:1 pitch, 120 kVp, 55 mm table feed per rotation, 5 mm section thickness. Two radiologists reviewed all CT examinations for image noise and diagnostic acceptability. CT dose index volume, and dose length product were recorded. Image noise and transverse abdominal diameter were measured in all patients. Data were analyzed using analysis of variance. ASIR allowed for an overall average decrease of 25.1% in CT dose index volume compared with the FBP technique (ASIR, 11.9 +/- 3.6 mGy; FBP, 15.9 +/- 4.3 mGy) (P < 0.0001). In each of the 3 weight categories, CT examinations reconstructed with ASIR technique were associated with significantly lower radiation dose compared with FBP technique (P < 0.0001). There was also significantly less objective image noise with ASIR (6.9 +/- 2.2) than with FBP (9.5 +/- 2.0) (P < 0.0001). For the subjective analysis, all ASIR and FBP reconstructed abdominal CTs had optimal or less noise. However, 9% of FBP and 3.8% of ASIR reconstructed CT examinations were diagnostically unacceptable because of the presence of artifacts. Use of ASIR reconstruction kernel results in a blotchy pixilated appearance in 39% of CT sans which however, was mild and did not affect the diagnostic acceptability of images. The critical reproduction of visually sharp anatomic structures was preserved in all but one ASIR 40% reconstructed CT examination. ASIR technique allows radiation dose reduction for abdominal CT examinations whereas improving image noise compared with the FBP technique.

Clinical correlation of the binding potential with 123I-FP-CIT in de novo idiopathic Parkinson’s disease patients

The aim of this study was to evaluate the accuracy of different single-photon emission computed tomography (SPECT) reconstruction techniques in measuring striatal N-omega-fluoropropyl-2beta-carbomethoxy-3beta-4-[(123)I]iodophenyl-nortropane ((123)I-FP-CIT) binding in de novo Parkinson's disease (PD) patients, in order to find a correlation with clinical scales of disease severity in the initial phases of disease. Thirty-six de novo PD patients underwent (123)I-FP-CIT SPECT and MRI scan. SPECT data were reconstructed with filtered back projection (FBP), with an iterative algorithm (ordered subset expected maximization, OSEM) and with a method previously developed in our institution, called least-squares (LS) method. The ratio of specific to non-specific striatal (123)I-FP-CIT binding (binding potential, BP) was used as the outcome measure with all the reconstruction methods (BP(FBP), BP(OSEM), BP(LS)). The range of values of striatal BP(LS) was significantly greater than BP(FBP) and BP(OSEM). For all striatal regions, estimates of BP(FBP) correlated well with BP(OSEM) (r = 0.84) and with BP(LS) (r = 0.64); BP(OSEM) correlated significantly with BP(LS) (r = 0.76). A good correlation was found between putaminal BP(LS) and Hoen and Yahr, Unified PD Rating Scale (UPDRS) and lateralized UPDRS motor scores (r = -0.46, r = -0.42, r = -0.39, respectively). Neither putaminal BP(FBP) nor putaminal BP(OSEM) correlated with any of these motor scores. In de novo PD patients, (123)I-FP-CIT BP values derived from FBP and OSEM reconstruction techniques do not permit to differentiate PD severity. The LS method instead finds a correlation between striatal BP and disease severity scores. The results of this study support the use of (123)I-FP-CIT BP values estimated with the LS method as a biomarker of PD severity.

Direct comparison between pharmacological stress with adenosine triphosphate disodium and exercise stress myocardial perfusion imagings

To clarify the significance of adenosine triphosphate disodium stress myocardial perfusion imaging (ATP-MPI), we directly compared the findings of ATP-MPI with those of exercise stress myocardial perfusion imaging (Ex-MPI). ATP-MPI, Ex-MPI, and coronary angiography (CAG) were performed within 60 days in 17 coronary artery disease patients with mean age of 62.1+/-7.9 years. CAG revealed single-vessel disease (SVD) in 10 patients and multivessel disease (MVD) in seven patients. The summed stress score (SSS) of ATP-MPI was significantly higher than that of Ex-MPI (10.0 [7.8-14.3] vs. 8.0 [4-18], P<0.05). No difference in the SSS was observed between ATP-MPI and Ex-MPI in patients with SVD (8.0 [6.0-9.0] vs. 8.0 [6.0-10.0], NS), whereas this difference was significant in patients with MVD (15.0 [14.0-22.8] vs.9 [7.3-16.3], P<0.05). There was no difference in the summed rest score between ATP-MPI and Ex-MPI. The univariate logistic analysis showed that "MVD" was the significant factor influencing to the overt discrepancy between ATP-MPI and Ex-MPI (odds ratio: 9.0, 95% confidence interval: 1.07-75.84, P=0.043). The accuracy of ATP-MPI and Ex-MPI in detecting the territory of stenotic coronary vessel or previous myocardial infarction was 98.0% and 92.1% (NS), respectively. In conclusion, ATP-MPI is useful for detecting potential ischemic areas that cannot be detected by Ex-MPI, particularly in patients with MVD.

Three-dimensional Doppler tomograms and detection of motions beyond the orbital plane in close binary systems

The newly developed radioastronomical approach (RA) has been modified for the reconstruction of three-dimensional (3D) Doppler tomograms. The RA permits an unequal space distribution of the views of an object and a reduction in the number of required orbital phases when compared with the filtered back-projection technique. The 3D Doppler tomogram of the close binary system U Coronae Borealis was reconstructed on the basis of 47 spectra of the Hα line. The three strongest Hα emission features found on the map were the accretion annulus, the gas stream moving along the ballistic trajectory, and a high-intensity region moving at high velocity in a direction across the orbital plane. It was not possible to discover this latter feature using standard two-dimensional Doppler tomography. The new RA technique is a useful tool for the subsequent study of gas flows in close binary systems.

MO-E-I-609-03: A Volume-Of-Interest (VOI) Scanning Technique for Cone Beam Breast CT

Purpose: To demonstrate that high quality cone beam CTimages can be generated within the volume‐of ‐interest (VOI) and to investigate the dose saving with the VOI scanning technique. Method and Materials: The VOI scanning technique was investigated using both computer simulation and imaging experiments. To implement the VOI scanning technique, an additional filter is inserted between the x‐ray source and the breast. The filter has a circular or rectangular opening to deliver a higher level x‐ray exposure to a selected spherical or cylindrical VOI and a lower level exposure to the region outside the VOI. To prepare for reconstruction, a non‐uniform reference image acquired with the VOI filter in but with the object out is used to normalize the projection images and measure the object attenuation only. Since the non‐uniform attenuation by the VOI filter is modulating both the reference and projection images, it cancels out in the computed transmittance image. Regular Feldkamp filtered backprojection technique is used to reconstruct the 3‐D images. Dose saving factor was estimated by tallying x‐rays going through the VOI, thus delivered at high dose level, and dividing the result by the total number of x‐rays backprojected to an image voxel. Results:Images from both simulation and experimental studies show that during VOI scanning, an exposure reduced by a factor of up to 50 can be delivered to areas outside the VOI without compromising on the accuracy of image reconstruction, allowing for a small VOI in the breast to be imaged with more clarity or lower dose to the rest of the breast. However, dose saving becomes less significant when the distance between the voxel and the VOI decreases. (This work was supported in part by a research grant CA104759 from the NCI and a research grant EB‐00117 from the NIBIB)