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- SPATIO-TEMPORAL RECONSTRUCTION FOR GATED CARDIAC SPECT
- Niu, Xiaofeng
- 2011-07, 2011-07
In myocardial perfusion imaging using single photon emission computed tomography (SPECT), gated acquisition is often used in order to deal...
Show moreIn myocardial perfusion imaging using single photon emission computed tomography (SPECT), gated acquisition is often used in order to deal with blur caused by cardiac motion in the resulting images. While this can provide useful information about the myocardial function, it also inevitably leads to reduced signal-to-noise ratio in the acquired data due to gating. In this work, we aim to investigate and evaluate image reconstruction methods for improving the quality of the reconstructed images in cardiac gated SPECT imaging. First, we propose a spatio-temporal (aka 4D) reconstruction procedure for gated images based on use of discrete Fourier transform (DFT) basis functions, wherein the image activity at each spatial location is regulated by a Fourier representation along the gate dimension. The gated images are then reconstructed through determination of the coefficients of the Fourier representation. We explore two different reconstruction algorithms, one is a penalized least-square approach and the other is a maximum a posteriori approach. Our simulation results demonstrate that use of DFT-basis functions in gated imaging can improve the accuracy of the reconstruction. While in gated imaging the tracer distribution is traditionally treated as constant, a recent development is gated dynamic imaging where the goal is to obtain an image sequence from a single acquisition which shows simultaneously both cardiac motion and tracer distribution change over the course of imaging. In this work, we further develop and demonstrate a fully 5D (3D space plus time plus gate) reconstruction procedure for cardiac gated, dynamic SPECT imaging, where the challenge is even greater without the use of multiple fast camera rotations. We develop and compare two iterative reconstruction algorithms: one is based on the modified block sequential regularized EM (BSREM-II) algorithm, and the other is based on the Bsplines algorithm. Our simulation results demonstrate that the 5D reconstruction xiii procedure can yield gated dynamic images which show quantitative information for both perfusion defect detection and cardiac motion. Based upon the success of 5D reconstruction, we also study the saliency of 5D images for detection of perfusion defects. We explore efficient ways for characterization and visualization of information pertinent to perfusion defects in a 5D image sequence. We apply various metrics to quantify the degree to which perfusion deficits can be detected. We show that these metrics can be used to produce new types of visualizations, showing wall motion and perfusion information, that may potentially be useful for clinical evaluation. Finally, with the ultimate goal of effective detection of lesion defect for clinical use, we also investigate a direct reconstruction approach to determine a sequence of gated, kinetic parameter images from a single acquisition, which can provide information simultaneously for both tracer kinetics and wall motion. To combat the greatly under-determined nature of the problem, we apply smoothness constraints to exploit the similarity both among the different gates and among the local spatial neighborhood. The parameter images of the different gates are then determined jointly using maximum a posteriori estimation from all the available image data.
Ph.D. in Electrical Engineering, July 2011