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The emergence of application-specific 3D tomographic small animal and dedicated breast imaging systems has stimulated the development of simple methods to quantify the spatial resolution or Modulation Transfer Function (MTF) of the system in three dimensions. Locally determined MTFs, obtained from line source measurements at specific locations, can characterize spatial variations in the system resolution and can help correct for such variations. In this study, a method is described to measure the MTF in 3D for a compact SPECT system that uses a 16 x 20 [cm.sup.2] CZT-based compact gamma camera and 3D positioning gantry capable of moving in different trajectories. Image data are acquired for a novel phantom consisting of three radioactivity-filled capillary tubes, positioned nearly orthogonally to each other. These images provide simultaneous measurements of the local MTF along three dimensions of the reconstructed imaged volume. The usefulness of this approach is shown by characterizing the MTF at different locations in the reconstructed imaged 3D volume using various (1) energy windows; (2) iterative reconstruction parameters including number of iterations, voxel size, and number of projection views; (3) simple and complex 3D orbital trajectories including simple vertical axis of rotation, simple tilt, complex circle-plus-arc, and complex sinusoids projected onto a hemisphere; and (4) object shapes in the camera's field of view. Results indicate that the method using the novel phantom can provide information on spatial resolution effects caused by system design, sampling, energy windows, reconstruction parameters, novel 3D orbital trajectories, and object shapes. Based on these measurements that are useful for dedicated tomographic breast imaging, it was shown that there were small variations in the MTF in 3D for various energy windows and reconstruction parameters. However, complex trajectories that uniformly sample the breast volume of interest were quantitatively shown to have slightly better spatial resolution performance than more simple orbits. Index Terms--CZT detector, emission imaging, mammotomography, modulation transfer function, single photon computed emission tomography, three-dimensional trajectories.

In this study related to human brain SPECT imaging, simulation of half-cone-beam (HCB) collimation with different scan paths is performed and compared with simulated fan-beam and parallel-hole circular orbit acquisitions of disk-phantom projection data. Acquisition types are quantitatively evaluated based on the photon detection efficiency, the root-mean-squared error, contrast and signal-to-noise ratio measurements of the reconstructed images. We demonstrate that a triple-camera SPECT system with haft-cone-beam collimators and circle-and-helix scan paths can offer up to a 26% efficiency increase over fan-beam, and up to a 128% increase over parallel-hole collimators for equal spatial resolutions, and display no visible axial sampling artifacts in reconstructed disk-phantom images. In addition, we perform qualitative experimental evaluation of triple-HCB circle-and-helix acquisition using a Hoffman 3D brain phantom. Reconstructed brain phantom images show improved quality due to reduced noise and no apparent sampling artifacts. Triple-HCB circle-and-helix SPECT has a potential for improved brain imaging, producing higher image quality with a smaller reconstruction error and better lesion detectability due to increased efficiency for equal spatial resolution compared to conventional fan-beam and parallel-hole SPECT. Index Terms--Axial sampling, brain SPECT, circle-and-helix, half-cone-beam, helical-path, triple-camera.

In this study related to human brain SPECT imaging, simulation of half-cone-beam collimation and helical-path data acquisition is performed. We discuss problems related to circular-orbit acquisition using cone-beam collimation, such as shoulder interference resulting in object truncation, and insufficient sampling of the object resulting in axial distortions in the reconstructed images. We demonstrate that a triple-camera SPECT system with half-cone-beam collimation and single-revolution helical-path acquisition eliminates both issues and offers substantially improved sampling and almost artifact-free reconstruction of the object. Index Terms--Cone-beam, half-cone-beam, helical-path, sampling sufficiency, SPECT, triple-camera.

In an effort to image smaller breast lesions, two compact gamma cameras with different intrinsic NaI(TI) pixel sizes are evaluated for use in the application specific emission tomography (ASET) system for dedicated mammotomographic emission imaging. Comparison measurements were made with two scintillator arrays having 1.3 x 1.3 x 6 [mm.sup.3] or 2.0 x 2.0 x 6 [mm.sup.3] elements on exactly the same set of PMTs, electronics and control/processing hardware. Uniformity, sensitivity and energy resolution were assessed with flood field phantoms. Spatial resolution measurements included: a [sup.99m]Tc (140 keV) activity filled capillary tube imaged in planar mode from 1-10 cm distance; two such tubes separated by 2 cm were also imaged with simple circular tomography from 3-7 cm radii-of-rotation (RORs); and a [sup.99m]Tc filled mini cold-rod phantom was imaged at 5 cm ROR with a simple circular orbit. Finally, a freely suspended and uniformly filled 950 mL breast phantom containing four tillable lesions (4-10 mm dia) was imaged with a lesion-to-uniform-background activity concentration ratio of 15:1, using simple and complex three-dimensional (3-D) orbits and minimal RORs. The measured sensitivity varied by the crystal fill-factor; uniformity had Index Terms--Breast imaging, gamma camera, mammotomography, quantized detector, SPECT.

A compact, dedicated cadmium zinc telluride (CZT) gamma camera coupled with a fully three-dimensional (3-D) acquisition system may serve as a secondary diagnostic tool for volumetric molecular imaging of breast cancers, particularly in cases when mammographic findings are inconclusive. The developed emission mammotomography system comprises a medium field-of-view, quantized CZT detector and 3-D positioning gantry. The intrinsic energy resolution, sensitivity and spatial resolution of the detector are evaluated with Tc-99m (140 keV) filled flood sources, capillary line sources, and a 3-D frequency-resolution phantom. To mimic realistic human pendant, uncompressed breast imaging, two different phantom shapes of an average sized breast, and three different lesion diameters are imaged to evaluate the system for 3-D mammotomography. Acquisition orbits not possible with conventional emission, or transmission, systems are designed to optimize the viewable breast volume while improving sampling of the breast and anterior chest wall. Complications in camera positioning about the patient necessitate a compromise in these two orbit design criteria. Image quality is evaluated with signal-to-noise ratios and contrasts of the lesions, both with and without additional torso phantom background. Reconstructed results indicate that 3-D mammotomography, incorporating a compact CZT detector, is a promising, dedicated breast imaging technique for visualization of tumors < 1 cm in diameter. Additionally, there are no outstanding trajectories that consistently yield optimized quantitative lesion imaging parameters. Qualitatively, imaging breasts with realistic torso backgrounds (out-of-field activity) substantially alters image characteristics and breast morphology unless orbits which improve sampling are utilized. In practice, the sampling requirement may be less strict than initially anticipated. Index Terms--Breast imaging, CZT detector, emission imaging, mammotomography, single photon emission computed tomography, SPECT, three-dimensional orbits.

While contemporary clinical single photon emission computed tomography (SPECT) scanners are limited to a horizontal axis of rotation about the patient, the compact application specific emission tomography (ASET) system overcomes physical proximity limitations of clinical scanners and allows for fully three-dimensional movement in an inverted hemisphere about the pendant breast through combined variable radius of rotation (ROR) and polar and azimuthal angular positioning. With these three degrees of freedom, the ASET can provide trajectories that satisfy Orlov's sampling criterion while maintaining a small ROR, necessary to minimize resolution degradation. One class of orbits investigated here consists of combinations of circular orbits and up to 60[degrees] arcs. Orbits are evaluated for image quality, including sampling and resolution characterization, utilizing both cold disk and cold rod emission phantoms, and quantitated contrasts and signal-to-noise ratios (SNRs) of small lesions located in a breast phantom with and without additional torso phantom backgrounds. The reconstructed cold disk and cold rod results indicate that all tested orbits in this class completely sample the volume and provide near equal resolution recovery. Furthermore, results from all orbits yielded higher contrasts and/or SNRs for the breast lesions compared with simple vertical-axis-of-rotation acquisitions, and nearly an order of magnitude better than those from uncompressed planar imaging. Index Terms--Breast imaging, mammotomography, single photon emission computed tomography, three-dimensional orbits.

Parallel-beam tilted-head single photon emission computed tomography (TH-SPECT) was previously implemented a SPECT system for its potential to image breast lesions and nearby axilla of seated, upright women. All TH-SPECT reconstructions will contain artifacts since the tilted orbit does not satisfy the Orlov sampling criteria. However, it is not clear which reconstruction method, if any, is better suited for TH-SPECT data. Here a geometric derivation of the ramp filter for tilted parallel-beam geometries is presented. A filtered backprojection (FBP) algorithm, using this filter, was then implemented and compared with an iterative ordered subsets expectation maximization (OSEM) algorithm, using TH-SPECT data. A breast scan at various tilt angles was simulated and used to generate a noise versus bias study for both methods. Contrast and signal-to-noise ratio (SNR) values, as well as axial elongation present in all TH-SPECT reconstructions, were characterized using a mini-Defrise disk phantom placed inside a tillable breast phantom and imaged from 0 to 15[degrees] head tilt. A tillable breast phantom containing lesions was also imaged with a system dedicated to prone breast SPECT from 0 to 30[degrees] to evaluate the effects of incomplete sampling due to greater tilt angles. FBP noise versus bias studies indicated a greater increase in bias with tilt angle compared to OSEM reconstructions. At small tilt angles about the mini-Defrise disk phantom, poorer contrasts were obtained with FBP compared to OSEM at similar noise levels. All reconstructions of the fillable breast phantom indicated axial elongation at greater tilt angles, although FBP reconstructions displayed an increase in stretching distortions of the breast. OSEM SNR and contrast values were higher at all degrees of tilt. In conclusion, measured results indicate OSEM TH-SPECT reconstruction provides better contrast and SNR values and may offer better shape and uniform activity distribution of the breast compared to FBP methods. Index Terms--Breast imaging, filtered backprojection (FBP), ordered subsets expectation maximization (OSEM), Orlov, single photon emission computed tomography (SPECT).

The primary goal of this work has been to develop a processing method for gated cardiac emission computed tomography (ECT) that simultaneously reconstructs the pixel intensities of the gated images and estimates the motion of the cardiac wall. The simultaneous reconstruction and motion estimation is achieved using conjugate gradient optimization with an objective function that is dependent on the gated reconstructed images at two time frames and the estimated motion of the object between the two frames. The method was evaluated on simulated phantom data both with and without Poisson noise. With noise-free data, the accuracy of the motion estimate and the quality of the reconstructed images were found to be dependent on the hyperparameter selection. With noisy data, the simultaneous method produced reconstructed images with smaller squared error compared with images reconstructed without motion estimation. In a patient gated myocardial perfusion study, the estimated motion between two frames agreed with subjective assessment of wall motion.

The purpose of this study is to evaluate cardiac lesion detectability with triple-head 360[degrees] versus dual-head 180[degrees] myocardial perfusion SPECT scans with equal acquisition time. The channelized Hotelling observer (CHO) and human observers were used. A male and a female voxelized cardiac-torso phantoms were used to generate the 360[degrees] and the 180[degrees] projection data. A cold lesion was placed in eight different locations of myocardium and had a lesion contrast of 25%. Sixteen time frames of the cardiac cycle were averaged to create the cardiac motion blurring to simulate the clinical ungated scan. Sufficient Poisson noise was added to set the area under the receiver operating characteristic (ROC) curve ([A.sub.z]) to be between 0.75 and 0.85 in a pilot study and to simulate the clinical case where dual-head 180[degrees] and triple-head 360[degrees] scans both have the same total acquisition time. For each lesion location, multiple realizations of lesion-present and of lesion-absent data were generated. Five-iteration ordered subsets expectation maximization with eight subsets was used to reconstruct the data. There was no attenuation correction (AC) in reconstruction with images used in the human study, while CHO was applied on images both reconstructed with and without AC. A three-dimensional Hann filter with 0.7 times the Nyquist frequency was used to smooth the reconstructed images. For images reconstructed without AC, both the CHO and the human observer study showed better detection performance for the 180[degrees] scan, especially for the female phantom. For images reconstructed with AC, the CHO study showed better detection performance for the 360[degrees] scan, especially for the female phantom. The CHO results demonstrated the detection performance with 360[degrees] scan was improved more than with 180[degrees] scan after AC. Index Terms--Myocardial perfusion imaging protocol, observer study, receiver operating characteristic, SPECT acquisition.

A two-layer model which includes a channelized Hotelling observer (CHO) followed by a Hotelling observer (HO) is proposed to operate on three-dimensional images containing multiple slices and multiple views similar to clinical displays of SPECT myocardial perfusion images. The observer was applied to simulated data of an idealized heart model. The task is the detection of cold defects in the myocardial wall. A CHO was computed for each slice of the multislice image and an HO was then applied on the decision variable arrays to obtain a multislice CHO-HO lesion detectability index. Results are compared to those of a single-slice CHO applied to the slice through the center of the lesion and also to human-observer results. The result suggests the ability of the multislice method to separate better these images into their correct classes as compared to the single-slice method, by combining information from multiple slices. The multislice method provides a single detectability scalar for studies in which the lesion could be present in multiple slices. It may be that a multislice CHO-HO model could more closely predict the performance of radiologists in tasks where the radiologist evaluates multislice and multiview images. Index Terms--Mathematical observer, multislice observer, myocardial perfusion imaging, SPECT.

In recent years, many investigators have proposed Gibbs prior models to regularize images reconstructed from emission computed tomography data. Unfortunately, hyperparameters used to specify Gibbs priors can greatly influence the degree of regularity imposed by such priors and, as a result, numerous procedures have been proposed to estimate hyperparameter values from observed image data. Many of these procedures attempt to maximize the joint posterior distribution on the image scene. To implement these methods, approximations to the joint posterior densities are required, because the dependence of the Gibbs partition function on the hyperparameter values is unknown. In this paper, we use recent results in Markov chain Monte Carlo (MCMC) sampling to estimate the relative values of Gibbs partition functions and using these values, sample from joint posterior distributions on image scenes. This allows for a fully Bayesian procedure which does not fix the hyperparameters at some estimated or specified value, but enables uncertainty about these values to be propagated through to the estimated intensities. We utilize realizations from the posterior distribution for determining credible regions for the intensity of the emission source. We consider two different Markov random field (MRF) models - the power model and a line-site model. As applications we estimate the posterior distribution of source intensities from computer simulated data as well as data collected from a physical single photon emission computed tomography (SPECT) phantom. Index Terms -Bayesian reconstruction, emission tomography, Markov chain Monte Carlo, Markov random fields, normalizing constants.

This study evaluated 123I SPECT volume and activity quantitation in terms of accuracy and precision using experimental phantom data. Two reconstruction methods were considered. The filtered backprojection (FB) method with 2D Metz pre-filtering and single iteration Chang attenuation compensation was compared with an iterative ML-EM method that used Gaussian post-filtering and incorporated the 3D divergent detector response and attenuation in the detection kernel. Both methods were examined over a range of resolution and noise characteristics. An ensemble of 21 SPECT data sets were acquired of a cylindrical phantom that contained spheres of size 21.4, 12.0, and 5.7 ml, filled with high purity 123I in a uniform background (5:1 uptake ratio). Each data set was reconstructed by both methods, and sphere volume and activity measurements were obtained from the reconstructions using a semi-automatic method that defines the region-of-interest based on the intensity gradient in the area of increased 123I concentration. The mean and standard deviation of the 21 measurements provided accuracy and precision indices, respectively. For the 21.4 ml sphere, the measured volume with either reconstruction method was accurate to within 5% of the true volume with a standard deviation of approximately 8% of the true volume. For the 12.0 ml sphere the measured volume with the iterative method exhibited substantially smaller standard deviation for equal accuracy compared with the FB method. Sphere activity was underestimated with both methods due to spatial resolution effects. The 5.7 ml sphere was generally below the size limit for volume and activity quantitation by these methods.

Clinical lymphoma I-131 radioimmunotherapy (RIT) studies are underway at our institution. The effectiveness of treatment can be evaluated through accurate time-dependent three-dimensional (3-D) dosimetry calculations based on SPECT images. We compared the absolute quantitative SPECT performance of a high-resolution rotating parallel-hole collimator (RPHC) designed to minimize septal penetration with that of a traditional medium-energy parallel-hole collimator (MEPHC). We scanned a phantom consisting of four spheres having inner diameters of 2.2 and 2.8 cm and whose activity concentration ratios with respect to the surrounding medium were between 5:1 and 17:1. Images were reconstructed using the OSEM algorithm (10 subsets, 20 iterations) with spatial resolution modeling. Quantitation of the MEPHC SPECT images yielded a large overestimation of the surrounding activity concentration (50%) due to septai penetration. Quantitation of the RPHC SPECT image yielded a surrounding medium activity concentration within 8% of the expected value, and the activity within the spheres was estimated to within 20% of their absolute expected values for the RPHC. We also investigated the effect of out of field-of-view (FOV) uncollimated gamma rays on SPECT quantitation. We conclude that for the present quantitation application, the benefits of septal penetration suppression by the RPHC outweigh the increased image noise due to low count rate. These results point to the feasibility of using a large-FOV collimator based on the imaging principles of the RPHC for accurate clinical SPECT quantitation of I-131 RIT. Index Terms--Biomedical applications of nuclear radiation, biomedical nuclear imaging, image reconstruction, nuclear tomography, single photon emission computed tomography.

A maximum-likelihood (ML) expectation-maximization (EM) algorithm (called EM-IntraSPECT) is presented for simultaneously estimating single photon emission computed tomography (SPECT) emission and attenuation parameters from emission data alone. The algorithm uses the activity within the patient as transmission tomography sources, with which attenuation coefficients can be estimated. For this initial study, EM-IntraSPECT was tested on computer-simulated attenuation and emission maps representing a simplified human thorax as well as on SPECT data obtained from a physical phantom. Two evaluations were performed. First, to corroborate the idea of reconstructing attenuation parameters from emission data, attenuation parameters ([Mu]) were estimated with the emission intensities ([Lambda]) fixed at their true values. Accurate reconstructions of attenuation parameters were obtained. Second, emission parameters [Lambda] and attenuation parameters [Mu] were simultaneously estimated from the emission data alone. In this case there was crosstalk between estimates of [Lambda] and [Mu] and final estimates of [Lambda] and [Mu] depended on initial values. Estimates degraded significantly as the support extended out farther from the body, and an explanation for this is proposed. In the EM-IntraSPECT reconstructed attenuation images, the lungs, spine, and soft tissue were readily distinguished and had approximately correct shapes and sizes. As compared with standard EM reconstruction assuming a fix uniform attenuation map, EM-IntraSPECT provided more uniform estimates of cardiac activity in the physical phantom study and in the simulation study with tight support, but less uniform estimates with a broad support. The new EM algorithm derived here has additional applications, including reconstructing emission and transmission projection data under a unified statistical model. Index Terms--Attenuation maps, EM, multiple sources, SPECT.

An experimental phantom study was performed to evaluate cardiac uniformity, contrast, and signal-to-noise ratio for two clinical cardiac SPECT imaging protocols: adjacent dual-head 180 [degrees] and triple-head 360 [degrees] scans. One head of a SPECT camera was used to acquire 180 [degrees] and 360 [degrees] projections with different times per step to simulate the clinical case where dual-head 180 [degrees] and triple-head 360 [degrees] each takes a total of 20 min. Scans were acquired with no lesion, anterior lesion, and posterior lesion in the myocardium. Maximum a posteriori reconstruction was done by an iterative coordinate descent algorithm using a quadratic convex prior. The L-curve method was used to obtain the prior strength. Some investigation was done on obtaining the L-curve and on the ways to fit the L-curve and to get the corner point. Images both with attenuation and scatter correction (ASC) and without ASC were compared. The 180 [degrees] scan shows an intensity decrease in anterior apical and posterior basal regions. The 360 [degrees] scan shows an intensity decrease in the posterior wall. For the anterior lesion, the 180 [degrees] scan has slightly better contrast, while for the posterior lesion, the 360 [degrees] scan has slightly better contrast. The difference between the 180 [degrees] and 360 [degrees] scans is subtle, and the comparison results depend on the lesion position and the view angle of the heart. A receiver operating characteristic study of 180 [degrees] versus 360 [degrees] acquisition designed based on these characterizations of contrast, uniformity, and noise will be necessary to evaluate overall performance. Index Terms--Cardiac imaging protocol, L-curve, maximum a posteriori (MAP) reconstruction, prior strength.

As a test bed for dedicated breast single-photon emission computed tomography (SPECT) cameras that are under development, a general purpose SPECT system with two tiltable heads was used to image fillable breast and torso phantoms containing multiple lesions. Breast, liver, and myocardial activity were included in order to simulate direct contamination and Compton scattering expected in clinical scans. The tiltable-head SPECT (TH-SPECT) data were reconstructed using an OS-EM algorithm which accounted for the tilted geometry. High-count planar images were acquired for comparison with TH-SPECT. In order to characterize axial blurring effects inherent with TH-SPECT reconstructions, two cylindrical disk Defrise phantoms, one large Defrise phantom and one mini-Defrise phantom placed inside the fillable breast phantom, were imaged at various tilt angles. Results indicate an increase in axial blurring with greater tilt angle. Reconstructions of the combined fillable breast and torso phantoms containing two 1.15 ml lesions, one centered axially and one proximal to the anterior chest wall within the breast, were most clearly visible in the 30 [degrees] reconstructed TH-SPECT images, providing lesion signal-to-noise ratio (SNR) and contrast improvements of nearly three times compared to the high-count planar images.

An important approach to reconstructing PET and SPECT (PET/SPECT) radiotracer images is to utilize high-resolution information from registered MRI or CT (MRI/CT) images. These methods depend on accurate registration of PET/SPECT and MRI/CT images. Herein, we consider registration via optimization of a PET/SPECT image-reconstruction objective function which includes the registration parameters. Potential benefits of this approach include 1) modeling, within the registration process, of PET/SPECT noise and PET/SPECT acquisition effects such as limited spatial resolution, perhaps resulting in more accurate registration and 2) a natural framework for calculating joint uncertainties in registration parameters and radiotracer activity. In cases where the structures imaged by MRIJCT (e.g., gray matter and white matter in the brain) strongly influence the radiotracer distribution, the relatively small number of variables comprised of alignment parameters and regional radiotracer mean activities may account for, not all, but much of the estimable radiotracer distribution, and it may be useful to develop methods for rapid, highly accurate estimation of these few parameters, ultimately embedding such estimation within more general estimation of the full radio- tracer distribution. Herein we develop Levenberg-Marquardt simultaneous estimation of regional radiotracer mean activities and the six 3D rigid body translation and rotation alignment parameters. The method is tested by a computer-simulation study. With a PET/SPECT scanner spatial resolution of 0.2 cm FWHM, this study shows translational registration errors of about 0.002 cm and rotational errors which are fractions of a degree. For small regions, estimates of regional mean activities are much closer to true values than are estimates obtained by OSEM using PET/SPECT projection data only. [ABSTRACT FROM AUTHOR]

Breast SPECT imaging with pinhole collimation provides high resolution and sensitivity when the pinhole aperture is in close proximity to the breast. In this study we used clinical count density scans to analyze quantitatively the effects of three acquisition geometries. A Trionix clinical scanner was used with rotation range limited to 180 degrees to simulat the presence of a torso. An isolated breast phantom containing two spherical lesions was mounted on a tiltable platform attached to the patient bed. The orbits were: A) single half-circular orbit (single HCO); B) three parallel half circles separated axially (triple parallel HCO); and C) three half circles with the plane of rotation for two half circles tilted +30 and -30 degrees relative to the middle (triple tilted HCO). Multiple scans were taken for all orbits to perform statistical analysis. ML-EM was used for reconstruction. Our analysis shows that for the central lesion, orbits ‘B’ and ‘C’ yield 31% and 28% higher peak contrast than orbit ‘A’. For the edge lesion, orbit ‘C’ gives a 55% higher peak contrast than ‘A’ and 70% higher than ‘B’. Signal-to-noise ratios are dependent on the lesion location. The contrast analysis suggests that triple half-circular orbits are superior to the single half-circular orbit, especially, when two of the circles are tilted so that a larger part of the breast volume stays in the field of view during acquisition. [ABSTRACT FROM AUTHOR]

Deals with a study which aimed to evaluate cardiac lesion detectability with triple-head 360 ° versus dual-head 180 ° myocardial perfusion SPECT scans with equal acquisition time. Methods used in the study; Results and conclusion.