The development and initial evaluation of a realistic simulated SPECT dataset with simultaneous respiratory and cardiac motion for gated myocardial perfusion SPECT

Abstract

We developed a realistic simulation dataset for simultaneous respiratory and cardiac (R&C) gated SPECT/CT using the 4D NURBS-based Cardiac-Torso (NCAT) Phantom and Monte Carlo simulation methods, and evaluated it for a sample application study. The 4D NCAT phantom included realistic respiratory motion and beating heart motion based on respiratory gated CT and cardiac tagged MRI data of normal human subjects. To model the respiratory motion, a set of 24 separate 3D NCAT phantoms excluding the heart was generated over a respiratory cycle. The beating heart motion was modelled separately with 48 frames per cardiac cycle for each of the 24 respiratory phases. The resultant set of 24×48 3D NCAT phantoms provides a realistic model of a normal human subject at different phases of combined R&C motions. An almost noise-free SPECT projection dataset for each of the 1,152 3D NCAT phantoms was generated using Monte Carlo simulation techniques and the radioactivity uptake distribution of 99mTc sestamibi in different organs. By grouping and summing the separate projection datasets, separate or simultaneous R&C gated acquired data with different gating schemes could be simulated. In the initial evaluation, we combined the projection datasets into no gating, 6 respiratory-gates only, 8 cardiac-gates only, and combined 6 respiratory-gates & 8 cardiac-gates projection datasets. Each dataset was reconstructed using 3D OS-EM without and with attenuation correction using the averaged and respiratory-gated attenuation maps, and the resulting reconstructed images were compared. These results were used to demonstrate the effects of R&C motions and the reduction of image artifact due to R&C motions by gating and attenuation corrections. We concluded that the realistic 4D NCAT phantom and Monte Carlo simulated SPECT projection datasets with R&C motions are powerful tools in the study of the effects of R&C motions, as well as in the development of R&C gating schemes and motion correction methods for improved SPECT/CT imaging.

Cardiac and Respiratory Motion-induced Artifact in Myocardial Perfusion SPECT

“…Lee et al. also performed digital phantom study to evaluate the respiratory motion-induced artifacts, and the anterior artifacts disappeared in the end-inhalation and end-exhalation phases (8). SPECT acquisitions at end-inhalation and end-exhalation phases can be helpful to rule out respiratory motion induced artifacts when we can perform high-speed cardiac MPS imaging by using the cadmium zinc telluride gamma camera.…”

“…Moreover, digital phantom study has also been performed to demonstrate motion-induced artifacts, and this study characterized the extent and severity of motion-induced artifacts (8). The digital phantom study is especially important for assessment of relationship between the amplitude of respiratory motion and motion-induced artifacts as well as the development and evaluation of a motion-correction method.…”

Image reconstruction in higher dimensions: myocardial perfusion imaging of tracer dynamics with cardiac motion due to deformation and respiration

“…We felt for this application the best regularization would be the basis functions themselves, because not knowing the correct motion of the heart it then becomes difficult to know a priori what prior to implement. However, efforts are being pursued to better model motion for improved imaging results (Lee and Tsui, 2015). Since the heart is primarily incompressible, the velocity field must satisfy incompressibility or divergence-free constraints (Liu et al , 2012), which could be very useful in constraining possible solutions.…”

4-D Reconstruction With Respiratory Correction for Gated Myocardial Perfusion SPECT

“…We note that dual gating has been studied for correction of respiratory motion in other modalities such as PET or PET/CT [23], [24], [25], [26]. For example, in [27], both cardiac and respiratory gating was used in cardiac PET imaging and was found to improve the anatomical details of the heart in reconstruction.…”