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The common imaging practice of each detector on a multidetector SPECT imaging system to acquire only a fraction of the total number of projections in a 360/spl deg/ projection set introduces the possibility of imbalances in system response which can cause artifacts and changes in image quality. Here we evaluate the effect of variations in detector sensitivity caused by differences in the position of the photopeak window, window width, and different collimators on reconstructed image quality. Analytical simulations of cardiac phantom geometries and experimental measurements with Data Spectrum's Cardiac and Deluxe SPECT phantoms on a three detector SPECT imaging system were used in the evaluation. The relative efficiency of one of three detectors was changed over a series of values between 100 and 0%, while the efficiency of the remaining two detectors was maintained at 100%. The results show that decreased activity and geometric distortions occur along directions perpendicular to the projections with altered sensitivity. The degree of distortion and decrease of activity depends on the geometry of the activity distribution and the reduction in sensitivity. The relative count ratios in the regions with decreased activity varied over a range of 1.0 to 0.59 as the detector sensitivity is decreased from 100 to 0% of the full energy window. Variations in detector sensitivity can degrade spatial resolution and uniformity and create artifacts in reconstructed tomographic slices.

In SPECT imaging, a cylindrical detector geometry offers many advantages. Because the detector completely surrounds the patient, the cylindrical system geometry should provide more detector coverage than the rotating camera SPECT systems. This increased coverage means increased sensitivity, or improved resolution, and better image quality. Because the cylindrical detector system is stationary and the projection data is acquired through collimator rotation, this geometry simplifies system design and allows very stable imaging performance. The authors propose a cylindrical system geometry that features a large number of projections for a small FOV located at the center of the gantry. This geometry has potential for cardiac SPECT imaging, provided that the patient's body can be offset properly and reliably to place his heart in the specified FOV. General design issues and potential configurations for such a cardiac SPECT system are presented.

The authors describe a new technique that uses simultaneous transmission and scatter SPECT imaging for determination of segmented attenuation /spl mu/-maps. These /spl mu/-maps could provide the basis for attenuation correction and quantification of radiopharmaceutical uptake in cardiac SPECT. For transmission imaging, a line source and a fan-beam collimator on one head of a triple-head SPECT system are used. For scatter imaging, two external ring sources and parallel collimators on one or two of the other heads are used. The fan-beam transmission data are truncated, while the parallel-beam data are not. The proposed technique uses both sets of tomographic data to complement each other and to obtain a composite image. A /spl mu/-map with three segmented regions of distinct /spl mu/-values could be derived from the composite image. This final /spl mu/-map can then be used as the basis for attenuation correction. >

A study was conducted to evaluate the feasibility of simultaneous dual radionuclide brainimaging with 123I and 99m Tc using photopeak image subtraction techniques or offset photopeak image acquisition. The contribution of the photons from one radionuclide to a second radionuclide’s photopeak energy window (crosstalk) was evaluated for SPECT and planar imaging of a brain phantom containing 123I and 99m Tc for a range of activity levels and distribution properties approximating those in rCBF images of the adult human brain. Crosstalk was evaluated for 10% symmetrical energy windows centered on the 123I and 99m Tc photopeaks and for 10% energy windows asymmetrically placed to the left and right of the center of the respective photopeaks. Major observations include: (1) in the centered photopeak windows, 99m Tc crosstalk in the 123I window is 8.9% of the 99m Tc seen in the 99m Tc window and ranges from 37.5% to 75.0% of the 123I in the 123I window. 123I crosstalk is 37.8% of the 123I seen in the 123I window and ranges from 4.4% to 8.9% of the 99m Tc seen in the 99m Tc window; (2) the spatial distribution of a radionuclide’s crosstalk photons differs from that observed in the radionuclide’s photopeak window; (3) a 99m Tc photopeak window offset to the left does not decrease 123I crosstalk, and the percentage of 99m Tc scatteredphotons is significantly increased in the window. Offsetting the 123I window to the right decreases 99m Tc crosstalk to 9.0% to 17.9% of the 123I counts, but decreases 123I sensitivity by 39.9%; and (4) offsetting both photopeak windows to the right decreases the 99m Tc scatteredphotons in the 99m Tc window, but increases 123I crosstalk to 17.0% to 33.8% of the 99m Tc counts. The findings show that image quality, spatial resolution, and quantitative accuracy are degraded to unacceptable levels with the combinations of energy windows tested for dual radionuclide imaging of 99m Tc and 123I. This indicates that dual radionuclide imaging must be thoroughly tested and validated before use in clinical studies.

Since many different configurations of brain SPECT systems are available for clinical imaging recently, it is informative to investigate if there are much differences in their performance potential. However, the variation of system configurations and performance characteristics make direct comparisons difficult. To clarify the confusion, the authors have developed a method to analyze the relative merits of different basic system geometries and evaluating the potential for different system configurations. This method is based on the calculated system geometric efficiency (SGE) of each configuration under the condition that the reconstructed spatial resolution are normalized. In the normalization process, the design parameters and performances of the collimators were iteratively adjusted to match the reconstructed resolution of an appropriately defined reference specifications. After the collimator was normalized, the geometric efficiency (GE) of the collimator was calculated by integrating the point source geometric efficiency (PSGE) over a brain source model with narrow-beam attenuation effect imposed. Based on the calculated GE for each collimator, the SGE is derived for each system configuration. This analysis was performed for many existing geometries of brain SPECT systems with different detector-collimator configurations of commercial interest. >

Conventional partial orbit SPECT acquisition (90/spl deg/, 120/spl deg/ or 180/spl deg/ depending on number of camera heads) on multihead cameras enhance the problems caused by patient motion or change in organ position ("cardiac creep"), since the misplaced data are present at several intervals in the projection set. The authors investigated the effects of source motion and developed new image motion correction methods based on 360/spl deg/ acquisition of each detector on a three camera SPECT system. Experimental measurements with point sources and cardiac phantom were used to evaluate the influence of source motion on SPECT images. A point source phantom was rotated 5-30/spl deg/ CCW and moved axially 0.5-4.0 cm. A cardiac phantom was moved in laterally (0.5-4.0 cm) and in the axial direction (0.5-4.0 cm). Cross-correlation of images from different heads at the same angular position is used to detect and correct for motion. Two correction methods were investigated: (1) summation of complete 360/spl deg/ projection sets without correction, (2) time normalization of projection frames without motion to replace frames affected by motion. The first method corrects for small displacement of the source (

In this paper we are presenting a method for achieving strain analysis of cardiac tissues from 3D ultrasound images. First of all, the left ventricle was segmented by an iterative snake algorithm which exploits the gradient vector flow field estimated from the 3D images. Once the ventricle was segmented, a set of points located on the external surface of the ventricle was selected. The movement of all these points along the entire cardiac cycle was calculated by using speckle tracking techniques based on the minimization of a Sum of Absolute Differences. The strain of all the segments connecting two of the considered points was computed, together with the rotation of the points along the long axis of the ventricle. The method was tested on images acquired from 10 patients: 3 with heart pathologies, 5 healthy subjects, and 2 patients with mild hypertrophy. The segmentation of the left ventricle with iterative methods demonstrated to be able to delineate the external surface of the ventricle in a consistent way. Preliminary results showed the feasibility of characterizing healthy subjects and patients with well-defined heart pathologies by using the outcomes achieved with the strain analysis.