Effects of motion, attenuation, and scatter corrections on gated cardiac SPECT reconstruction

Abstract

Purpose: In gated cardiac single photon emission computed tomography (SPECT), image reconstruction is often hampered by various degrading factors including depth-dependent spatial blurring, attenuation, scatter, motion blurring, and low data counts. Consequently, there has been significant development in image reconstruction methods for improving the quality of reconstructed images. The goal of this work is to investigate how these degrading factors will impact the reconstructed myocardium when different reconstruction methods are used. Methods: The authors conduct a comparative study of the effects of these degrading factors on the accuracy of myocardium by several reconstruction algorithms, including (1) a clinical spatiotemporal processing method, (2) maximum likelihood (ML) estimation, (3) 3D maximum a posteriori (MAP) estimation, (4) 3D MAP with posttemporal filtering, and (5) motion-compensated spatiotemporal (4D) reconstruction. To quantify the reconstruction results, the authors use the following measures on different aspects of the myocardium: (1) overall error level in the myocardium, (2) regional accuracy of the left ventricle (LV) wall, (3) uniformity of the LV, (4) accuracy of regional time activity curves by normalized cross-correlation coefficient, and (5) perfusion defect detectability. The authors also assess the effectiveness of degrading corrections in reconstruction by considering an upper bound for each reconstruction method, which represents what would be achieved by each method if the acquired data were free from attenuation and scatter degradations. In the experiments the authors use Monte Carlo simulated cardiac gated SPECT imaging based on the 4D NURBS-based cardiac-torso (NCAT) phantom with different patient geometry and lesion settings, in which the simulated ground truth is known for the purpose of quantitative evaluation.Results: The results demonstrate that use of temporal processing in reconstruction (Methods 1, 4, and 5 above) can greatly improve the reconstructed myocardium in terms of both error level and perfusion defect detection. In low-count gated studies, it can have even greater impact than other degrading factors. Both attenuation and scatter corrections can lead to reduced error levels in the myocardium in all methods; in particular, with 4D the bias can be reduced by as much as four-fold compared to no correction. There is a slight increase in noise level observed with scatter correction. A significant improvement in heart wall appearance is demonstrated in reconstruction results from three sets of clinical acquisitions as correction for degradations is combined with refinement of temporal filtering. Conclusions: Correction for degrading factors such as resolution, attenuation, scatter, and motion blur can all lead to improved image quality in cardiac gated SPECT reconstruction. However, their effectiveness could also vary with the reconstruction algorithms used. Both attenuation and scatter corrections can effectively reduce the bias level of the reconstructed LV wall...

4D reconstruction for low-dose cardiac gated SPECT

“…The FBP without AC plus lowpass filtering is currently the standard as per ASNC guidelines, 32 while the additional temporal filtering is the standard employed clinically at UMass Medical School. 22,23 This method is referred to as "ST121. "…”

“…In recent years, 4D reconstruction methods that exploit the temporal correlation among the gated frames have been developed to improve image quality in GSPECT, aiming to achieve better perfusion defect detectability and functional assessment. [17][18][19][20][21][22][23] Indeed, in our recent work, 23 it was demonstrated that use of temporal processing in GSPECT reconstruction can have greater impact on the accuracy of the myocardium than correction of other degrading factors. However, all these 4D studies were conducted at the standard dose level with the focus on image quality improvement.…”

“…In addition, as preliminary demonstration, GSPECT data acquired in list-mode from two patients were used to mimic lower dose acquisitions for comparison of image quality. It is noted that the previous studies 22, 23 focused on 4D reconstruction development and the effects of different degrading factors at standard dose. The purpose of this work is to investigate the important question of whether 4D reconstruction can be utilized to significantly lower the imaging dose of GSPECT.…”

“…Based on previous reports that imaging dose can be halved using advanced 3D reconstruction 9,10 and that 4D reconstruction can achieve superior performance over 3D reconstruction, 22,23 we hypothesize that advanced 4D reconstruction can yield images at even lower (e.g., quarter) dose with comparable or even better quality to clinically reconstructed images at standard dose. To test our hypothesis, we used Monte Carlo simulation 24 to simulate GSPECT acquisition of different dose levels (standard, half, and quarter dose) with the 4D NURBS-based cardiac-torso (NCAT) phantom 25 and 99m Tc-Sestamibi as the imaging agent.…”

Gated SPECT myocardial perfusion imaging quality assurance in current and future practice

“…Most software packages simultaneously display a cinematic playback of the original rotating data during this data processing step, if data were acquired by a rotating gamma camera, and users need to inspect this cine for issues that can affect data integrity, such as patient vertical and twisting motion. 8 Even cooperative patients may be unable to control their motion, such as due to coughing or neurologic motor disorders, so that it is always important to verify the data are not compromised by patient motion, or to use post-acquisition motion correction software that can be used manipulate the vertical position of projection data. 9 Currently, efforts are underway to enable users to correct gated SPECT MPI reconstructions simultaneously for both pulmonary and cardiac motion.…”