Anatomical-based partial volume correction for low-dose dedicated cardiac SPECT/CT

Abstract

Due to the limited spatial resolution, partial volume effect (PVE) has been a major degrading factor on quantitative accuracy in emission tomography systems. This study aims to investigate the performance of several anatomical-based partial volume correction (PVC) methods for a dedicated cardiac SPECT/CT system (GE Discovery NM/CT 570c) with focused field-of-view (FOV) over a clinically relevant range of high and low count levels for two different radiotracer distributions. These PVC methods include perturbation Geometry Transfer Matrix (pGTM), pGTM followed by multi-target correction (MTC), pGTM with known concentration in blood pool, the former followed by MTC and our newly proposed methods, which perform the MTC method iteratively, where the mean values in all regions are estimated and updated by the MTC-corrected images each time in the iterative process. The NCAT phantom was simulated for cardiovascular imaging with 99mTc-tetrofosmin, a myocardial perfusion agent, and 99mTc-red blood cell (RBC), a pure intravascular imaging agent. Images were acquired at six different count levels to investigate the performance of PVC methods in both high and low count levels for low-dose applications. We performed two large animal in vivo cardiac imaging experiments following injection of 99mTc-RBC for evaluation of intramyocardial blood volume (IMBV). The simulation results showed our proposed iterative methods provide superior performance than other existing PVC methods in terms of image quality, quantitative accuracy, and reproducibility (standard deviation), particularly for low-count data. The iterative approaches are robust for both 99mTc-tetrofosmin perfusion imaging and 99mTc-RBC imaging of IMBV and blood pool activity even at low count levels. The animal study results indicated the effectiveness of PVC to correct the overestimation of IMBV due to blood pool contamination. In conclusion, the iterative PVC methods can achieve more accurate quantification, particularly for low count cardiac SPECT studies, typically obtained from low-dose protocols, gated studies, and dynamic applications.

Noise suppressed partial volume correction for cardiac SPECT/CT

“…We indicated this variation as NS-PVC (uncorrected). In the second approach, we used regional mean values computed from the images after applying a preliminary iterative based MTC (iMTC) PVC method previously proposed, 24 which has been demonstrated to yield accurate quantification of mean values for each region, although it amplifies noise on the reconstructed images and may yield negative voxels. The combination of this two-step PVC approach is denoted as NS-PVC (iMTC).…”

“…These mean activity weighted masks were forward projected and reconstructed individually to create the template response for the MTC method. 24 For the methods of Yang and NS-PVC, these mean activity weighted masks were combined together to form a complete template to generate the template response. For both type of templates the perfusion defect and normal myocardium (excluding defect) were segmented into one single region, since the perfusion defect was not visible on the contrast CT images.…”

“…18 However, most of the existing voxel based postreconstruction PVC methods amplify noise after PVC, leading to greater intervoxel variability. 4,7,18,21,23,24 This is due to the fact that both high frequency boundary information and noise are enhanced with the application of a spatially varying PVC coefficient map (template response). The noise amplification may lead to nonuniform uptake in the organ or even cause negative voxels in the final image (for the PVC methods that involve a subtraction step, i.e., MGM).…”

“…The noise amplification may lead to nonuniform uptake in the organ or even cause negative voxels in the final image (for the PVC methods that involve a subtraction step, i.e., MGM). 24 This is especially important for myocardial perfusion imaging, as an artificially patchy distribution can lead to false positive ischemic defects and affect the subregional quantifications. In addition to increased spatial variation, PVC has also been shown to increase ensemble variation, which can lead to reduced reproducibility.…”

“…In addition to increased spatial variation, PVC has also been shown to increase ensemble variation, which can lead to reduced reproducibility. 7,24,25 With the increasing interest in dose reduction for both PET/CT and SPECT/CT applications, along with advanced applications such as respiratory and/or cardiac gating 3 and dynamic SPECT imaging with tracer kinetic modeling, 26,27 the reconstructed images are already plagued with high level of noise as only a fraction of the counts are used. However, little work has been done on performing postreconstruction PVC while penalizing noise for the low counts applications mentioned above.…”