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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. [ABSTRACT FROM AUTHOR]

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]

In an effort to image smaller breast lesions, two compact gamma cameras with different intrinsic NaI(Tl) 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 × 1.3 × 6 mm³ or 2.0 × 2.0 × 6 mm³ 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 99mTc (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 99mTc filled mini cold-rod phantom was imaged at S cm ROR with a simple circular orbit. Finally, a freely suspended and uniformly filled 950 mL breast phantom containing four fillable 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 <4% variability; and mean energy resolutions of each camera were ⩽ 12 % full-width at half-maximum (FWHM). The planar spatial resolutions correspond to calculated values, with smaller pixels yielding 2%-13% better resolution with decreasing separation distance; tomographic results ranged from 3.2-5.2 mm FWHM at 3-7 cm, with nominally better contrast-resolution for the smaller pixel camera. Consistent with signal detection characteristics for these measurement conditions, quantitative SNRs and contrasts from lesion imaging with the uniform breast background illustrate better overall performance under nearly all conditions and for all lesions for the larger pixel camera. [ABSTRACT FROM AUTHOR]

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 stied 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 Sd 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. [ABSTRACT FROM AUTHOR]

A novel tomographic gantry was designed, built and initially evaluated for single photon emission imaging of metabolically active lesions in the pendant breast and near chest wall. Initial emission imaging measurements with breast lesions of various uptake ratios are presented.Methods: A prototype tomograph was constructed utilizing a compact gamma camera having a field-of-view of <13×13 cm2 with arrays of 2×2×6 mm3 quantized NaI(Tl) scintillators coupled to position sensitive PMTs. The camera was mounted on a radially oriented support with 6 cm variable radius-of-rotation. This unit is further mounted on a goniometric cradle providing polar motion, and in turn mounted on an azimuthal rotation stage capable of indefinite vertical axis-of-rotation about the central rotation axis (RA). Initial measurements with isotopic Tc-99 m (140 keV) to evaluate the system include acquisitions with various polar tilt angles about the RA. Tomographic measurements were made of a frequency and resolution cold-rod phantom filled with aqueous Tc-99 m. Tomographic and planar measurements of 0.6 and 1.0 cm diameter fillable spheres in an available ∼950 ml hemi-ellipsoidal (uncompressed) breast phantom attached to a life-size anthropomorphic torso phantom with lesion:breast-and-body:cardiac-and-liver activity concentration ratios of 11:1:19 were compared. Various photopeak energy windows from 10–30% widths were obtained, along with a 35% scatter window below a 15% photopeak window from the list mode data. Projections with all photopeak window and camera tilt conditions were reconstructed with an ordered subsets expectation maximization (OSEM) algorithm capable of reconstructing arbitrary tomographic orbits.Results: As iteration number increased for the tomographically measured data at all polar angles, contrasts increased while signal-to-noise ratios (SNRs) decreased in the expected way with OSEM reconstruction. The rollover between contrast improvement and SNR degradation of the lesion occurred at two to three iterations. The reconstructed tomographic data yielded SNRs with or without scatter correction that were >9 times better than the planar scans. There was up to a factor of ∼2.5 increase in total primary and scatter contamination in the photopeak window with increasing tilt angle from 15° to 45°, consistent with more direct line-of-sight of myocardial and liver activity with increased camera polar angle.Conclusion: This new, ultra-compact, dedicated tomographic imaging system has the potential of providing valuable, fully 3D functional information about small, otherwise indeterminate breast lesions as an adjunct to diagnostic mammography. [Copyright &y& Elsevier]