Xiyun Song

Iterative SPECT Reconstruction Using Matched Filtering for Improved Image Quality

SPECT images reconstructed from low count studies suffer either from high noise or poor resolution. We have developed an iterative reconstruction with matched filtering (IRMF) to control image noise while maintaining higher image resolution. IRMF involves filtering the measured projection and re-projection during iterative reconstruction with the same low-pass filter before the two are compared to generate an error projection. Another low-pass filter can be applied to the error projection before it is backprojected to update the current activity distribution estimate. The method is validated with a cardiac phantom filled with a clinical distribution of Tc-99m. A 1-second-per-frame scan was acquired to mimic a single gated segment. The image was reconstructed using ordered-subset expectation-maximization (OSEM) algorithm with depth-dependent resolution recovery. Reconstructions of similar spatial resolution with post-reconstruction Butterworth filtering (OSEM+F) and with matched filtering are compared visually and via standard deviation (SD) and signal-to-noise ratio (SNR) measurements. Results: Images reconstructed with IRMF show strong noise suppression in both the myocardium and background areas as compared to those reconstructed with OSEM+F. The SD in the background is reduced by ~30%, and the SNR is improved by ~100%. IRMF significantly improves image quality by suppressing noise in low count SPECT studies while maintaining higher image resolution.

Comparison of penetration and scatter effects on defect contrast for GE and Siemens LEHR collimators in myocardial perfusion SPECT-A simulation study

The goal of this paper was to evaluate the effects of collimator penetration and scatter on myocardial SPECT image quality. We chose two designs: a LEHR collimator for GE Millennium VG with a longer bore and thicker septa, and a LEHR collimator for Siemens E.CAM with a shorter bore and thinner septa. These two collimators have similar resolution properties, but very different penetration fractions. In particular, the Siemens collimator has higher detection efficiency. We used Monte Carlo (MC) simulation to simulate projection data from the three-dimensional (3-D) NCAT phantom. For each collimator, we generated three sets of projection data: the first one included only the geometric components of the collimator response, the second one included both the geometric and penetration components, and the third one included geometric, penetration and collimator scatter components. The resulting projections were reconstructed with the OSEM algorithm including attenuation and geometric response compensation. For each collimator and reconstruction, we computed the defect contrast in a short-axis slice. We found very small differences in defect contrast between the two collimators with and without penetration and collimator-scattered photons. Since the collimator with higher penetration had greater detection efficiency and showed little loss in defect contrast, a collimator with higher penetration fraction may be acceptable for use in Tc-99 m myocardial perfusion imaging.

Fast shift-variant resolution compensation within iterative reconstruction for fan-beam collimator

In this paper we have modeled the spatially-varying resolution of a fan-beam collimator as a function of both distance and lateral position across the imaging plane within iterative reconstruction. We demonstrate that an incremental blurring technique can be used to more efficiently model such non-stationary resolution than the straightforward non-stationary convolution methodology with a gain of 1.5X in speed and 99% less memory usage. This method can therefore be used for efficient variable resolution compensation in 3D for collimator geometries in which the detector response function varies across the imaging plane as well as with distance from the face of the collimator†.