What is the clinical evidence from this study?

Study design: Other. Population: Myocardial perfusion imaging (MPI). Intervention: 4D spatiotemporal reconstruction algorithm with continuous acquisition vs. Conventional 4D spatiotemporal reconstruction method without gating. Primary outcome: Mean Stabilized Activity (MSA), signal to noise ratio (SNR), and Bias for myocardium activities.

July 13, 2022Open Access

Monte Carlo Simulation and Reconstruction: Assessment of Myocardial Perfusion Imaging of Tracer Dynamics With Cardiac Motion Due to Deformation and Respiration Using Gamma Camera With Continuous Acquisition

Key Result

The proposed 4D spatiotemporal reconstruction method with continuous acquisition showed better resolved myocardial walls during diastole to systole and improved bias to less than 10% compared to ungated 4D images in Monte Carlo simulations.

Structured PICO

Does a 4D spatiotemporal reconstruction algorithm with continuous acquisition improve image quality and tracer dynamics estimation compared to conventional 4D reconstruction in simulated dynamic SPECT MPI?

Population

A Monte Carlo simulation study using the 4D XCAT digital phantom to evaluate a spatiotemporal reconstruction algorithm for dynamic cardiac SPECT imaging.

Intervention

4D spatiotemporal image reconstruction algorithm using splines for continuous image acquisition with a slowly rotating SPECT camera

Comparator

Conventional 4D spatiotemporal reconstruction method (ungated 4D image)

Outcome

Mean Stabilized Activity (MSA), signal to noise ratio (SNR), and Bias for the myocardium activitiessurrogate

A novel 4D spatiotemporal reconstruction algorithm for continuous-acquisition SPECT MPI successfully resolves cardiac and respiratory motion artifacts in Monte Carlo simulations, potentially enabling better quantification of myocardial blood flow.

Limitations

Requires a very large number of views and sufficient cardiac-respiratory phases per rotation, which could increase noise if injected dose is small
Simulation ignored significant liver scattering and background activities
Not tested with real patient data because current camera systems do not provide gating information during dynamic acquisition

Abstract

Purpose Myocardial perfusion imaging (MPI) with single photon emission computed tomography (SPECT) is routinely used for stress testing in nuclear medicine. Recently, our group extended its potential going from 3D visual qualitative image analysis to 4D spatiotemporal reconstruction of dynamically acquired data to capture the time variation of the radiotracer concentration and the estimated myocardial blood flow (MBF) and coronary flow reserve (CFR). However, the quality of reconstructed image is compromised due to cardiac deformation and respiration. The work presented here develops an algorithm that reconstructs the dynamic sequence of separate respiratory and cardiac phases and evaluates the algorithm with data simulated with a Monte Carlo simulation for the continuous image acquisition and processing with a slowly rotating SPECT camera. Methods A clinically realistic Monte Carlo (MC) simulation is developed using the 4D Extended Cardiac Torso (XCAT) digital phantom with respiratory and cardiac motion to model continuous data acquisition of dynamic cardiac SPECT with slowly rotating gamma cameras by incorporating deformation and displacement of the myocardium due to cardiac and respiratory motion. We extended our previously developed 4D maximum-likelihood expectation-maximization (MLEM) reconstruction algorithm for a data set binned from a continuous list mode (LM) simulation with cardiac and respiratory information. Our spatiotemporal image reconstruction uses splines to explicitly model the temporal change of the tracer for each cardiac and respiratory gate that delineates the myocardial spatial position as the tracer washes in and out. Unlike in a fully list-mode data acquisition and reconstruction the accumulated photons are binned over a specific but very short time interval corresponding to each cardiac and respiratory gate. Reconstruction results are presented showing the dynamics of the tracer in the myocardium as it continuously deforms. These results are then compared with the conventional 4D spatiotemporal reconstruction method that models only the temporal changes of the tracer activity. Mean Stabilized Activity (MSA), signal to noise ratio (SNR) and Bias for the myocardium activities for three different target-to-background ratios (TBRs) are evaluated. Dynamic quantitative indices such as wash-in (K 1 ) and wash-out (k 2 ) rates at each gate were also estimated. Results The MSA and SNR are higher with higher TBRs while biases were improved with higher TBRs to less than 10%. The correlation between exhalation-inhalation sequence with the ground truth during respiratory cycle was excellent. Our reconstruction method showed better resolved myocardial walls during diastole to systole as compared to the ungated 4D image. Estimated values of K 1 and k 2 were also consistent with the ground truth. Conclusion The continuous image acquisition for dynamic scan using conventional two-head gamma cameras can provide valuable information for MPI. Our study demonstrated the viability of using a continuous image acquisition method on a widely used clinical two-head SPECT system. Our reconstruction method showed better resolved myocardial walls during diastole to systole as compared to the ungated 4D image. Precise implementation of reconstruction algorithms, better segmentation techniques by generating images of different tissue types and background activity would improve the feasibility of the method in real clinical environment.

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