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The purpose of the study is to investigate the imaging characteristics of scintimammography (SM) using parallel-hole (PR) and pinhole (PN) collimators in a clinical setting. Experimental data were acquired from a phantom that models the breast with small lesions using a low energy high resolution (LEHR) PR and a PN collimator. At close distances, the PN collimator provides better spatial resolution and higher detection efficiency than the PR collimator, at the expense of a smaller field-of-view (FOV). Detection of small breast lesions can be further enhanced by noise smoothing, field uniformity correction, scatter subtraction and resolution recovery filtering. Monte Carlo (MC) simulation data were generated from the 3D MCAT phantom that realistically models the Tc-99m sestamibi uptake and attenuation distributions in an average female patient. For both PR and PN collimation, the scatter to primary ratio (S/P) decreases from the base of the breast to the nipple and is higher in the left than fight breast due to scatter of photons from the heart. Results from the study add to understanding of the imaging characteristics of SM using PR and PN collimators and assist in the design of data acquisition and image processing methods to enhance the detection of breast lesions using SM.

Patient anatomy has complicated effects on cardiac SPECT images. We investigated reconstruction methods which substantially reduced these effects for improved image quality. A 3D mathematical cardiac-torso (MCAT) phantom which models the anatomical structures in the thorax region were used in the study. The phantom was modified to simulate variations in patient anatomy including regions of natural thinning along the myocardium, body size, diaphragmatic shape, gender, and size and shape of breasts for female patients. Distributions of attenuation coefficients and Tl-201 uptake in different organs in a normal patient were also simulated. Emission projection data were generated from the phantoms including effects of attenuation and detector response. We have observed the attenuation-induced artifacts caused by patient anatomy in the conventional FBP reconstructed images. Accurate attenuation compensation using iterative reconstruction algorithms and attenuation maps substantially reduced the image artifacts and improved quantitative accuracy. We conclude that reconstruction methods which accurately compensate for non-uniform attenuation can substantially reduce image degradation caused by variations in patient anatomy in cardiac SPECT.

The goal of our investigation was to study the effectiveness of the corrective reconstruction methods in cardiac SPECT using a realistic phantom and to qualitatively and quantitatively evaluate the reconstructed images using bull's-eye plots. A 3D mathematical phantom which realistically models the anatomical structures of the cardiac-torso region of patients was used. The phantom allows simulation of both the attenuation distribution and the uptake of radiopharmaceuticals in different organs. Also, the phantom can be easily modified to simulate different genders and variations in patient anatomy. Two-dimensional projection data were generated from the phantom and included the effects of attenuation and detector response blurring. The reconstruction methods used in the study included the conventional filtered backprojection (FBP) with no attenuation compensation, and the first-order Chang algorithm, an iterative filtered backprojection algorithm (IFBP), the weighted least square conjugate gradient algorithm and the ML-EM algorithm with non-uniform attenuation compensation. The transaxial reconstructed images were rearranged into short-axis slices from which bull's-eye plots of the count density distribution in the myocardium were generated. The FBP reconstructed images clearly demonstrated the effects of attenuation on the myocardial distribution caused by anatomical structures and the inadequacy of the algorithm to provide accurate quantitative reconstructions. The images reconstructed using the Chang, IFBP, and ML-EM methods with attenuation compensation showed substantial improvement in terms of reduction in artifacts and improvement in quantitative accuracy. The results also demonstrate that the ML-EM method is the most robust in attenuation compensation for a wide range of anatomical variations when compared to the Chang and IFBP methods. The combination of the 3D mathematical phantoms and bull's-eye plots provides an effective tool for evaluation of corrective reconstruction methods for quantitative cardiac SPECT.

We have studied reconstruction methods currently available for use in quantitative brain SPECT imaging. The conventional reconstruction methods are based on the filtered backprojection algorithm. Assuming uniform attenuation, the Chang algorithm is effective in attenuation compensation. The collimator response can be compensated for by restoration filter with an average collimator response function. Scatter compensation can be achieved by the dual window subtraction method or by incorporating an average scatter response function in the restoration filter. The dual window subtraction method is an approximate but efficient means of providing scatter compensated projection data. Iteration reconstruction method can be applied to these data for addition compensation for attenuation and the spatially variant collimator response. The latter is accomplished by incorporating the exact model of attenuation and detector response function in the projector/backprojector of the iterative algorithm. A three-dimensional brain phantom was used in the evaluation study. Projection data were collected into the photopeak and a lower scatter energy windows for scatter compensation. The images obtained from various reconstruction methods were compared for quantitative accuracy with respect to the known 3D phantom activity distribution.