In emission tomography, iterative reconstruction is usually followed by a linear smoothing filter to make such images more appropriate for visual inspection and diagnosis by a physician. This will result in a global blurring of the images, smoothing across edges and possibly discarding valuable image information for detection tasks. The purpose of this study is to investigate which possible advantages a non-linear, edge-preserving postfilter could have on lesion detection in Ga-67 SPECT imaging. Image quality can be defined based on the task that has to be performed on the image. This study used LROC observer studies based on a dataset created by CPU-intensive Gate Monte Carlo simulations of a voxelized digital phantom. The filters considered in this study were a linear Gaussian filter, a bilateral filter, the Perona-Malik anisotropic diffusion filter and the Catte filtering scheme.
The 3D MCAT software phantom was used to simulate the distribution of Ga-67 citrate in the abdomen. Tumor-present cases had a 1-cm diameter tumor randomly placed near the edges of the anatomical boundaries of the kidneys, bone, liver and spleen. Our data set was generated out of a single noisy background simulation using the bootstrap method, to significantly reduce the simulation time and to allow for a larger observer data set. Lesions were simulated separately and added to the background afterwards. These were then reconstructed with an iterative approach, using a sufficiently large number of MLEM iterations to establish convergence.
The output of a numerical observer was used in a simplex optimization method to estimate an optimal set of parameters for each postfilter.
No significant improvement was found for using edge-preserving filtering techniques over standard linear Gaussian filtering.
The main goal of this work is to assess the overall imaging performance of dedicated new solid state devices compared to a traditional scintillation camera for use in SPECT imaging. A solid state detector with a rotating slat collimator will be compared with the same detector mounted with a classical collimator as opposed to a traditional Anger camera. A better energy resolution characterizes the solid state materials while the rotating slat collimator promises a better sensitivity-resolution tradeoff. The evaluation of the different imaging modalities is done using GATE, a recently developed Monte Carlo code. Several features for imaging performance evaluation were addressed: spatial resolution, energy resolution, sensitivity, and a ROC analysis was performed to evaluate the hot spot detectability. In this way a difference in perfromance was concluded for the diverse imaging techniques which allows a task dependent application of these modalities in future clinical practice.