Cutting SPECT MPI scan time in half
A novel reconstruction method of cardiac SPECT myocardial perfusion imaging (MPI) could potentially reduce scan times by 50 percent and cut 75 percent of the time it takes to reconstruct images, according to research announced by the University of Eastern Finland yesterday.
SPECT MPI is one of the most frequently performed imaging studies throughout the world, but complications of motion, image noise, scatter and attenuation, and collimator-detector response (CDR) hamper image quality. Nuclear medicine institutions have been trying to reduce these factors for decades, but a new reconstruction algorithm could go a long way toward improving MPI imaging taking all of these conditions into account, especially CDR.
PhD candidate Tuija Kangasmaa conducted her peer-reviewed doctoral study in the departments of oncology, clinical physiology and nuclear medicine at Kuopio University Hospital in Kuopio, Finland, and in the department of oncology at Vaasa Central Hospital in Vaasa, Finland. Findings of the study have been published in Nuclear Medicine Communications, International Journal of Molecular Imaging, and Annals of Nuclear Medicine.
“Recently CDR compensation has attracted considerable interest, because it allows diagnostically satisfying images to be acquired in half of the acquisition time currently in use,” Kangasmaa wrote in her published dissertation. “Shorter scan times both reduce artifacts related to patient motion and increase the patient throughput. The utilization of modern compensation methods is not always straightforward. Their application can be time consuming and they can generate new image artifacts.”
Kangasmaa and her colleagues sought through parameter optimization to improve novel SPECT reconstruction and compensation specifically for MPI. The researchers effectively halved acquisition time and compensated for scatter by enhancing a statistical method of analysis based on counts at acquisition known as Monte Carlo-based scatter compensation. However, in preliminary studies this had an unwanted effect.
“The image quality obtained with half acquisition time using CDR and MC-based scatter compensation was better than with full acquisition time and conventional reconstruction, but it did not achieve the image quality obtained with full acquisition time combined with CDR and MC-based scatter correction.”
The researchers continued to develop the technique by combining simultaneous use of dual imaging tracers Tl-201 and Tc-99m. They found that this could hone down the total acquisition time by half, because it was possible for both the stress and rest scans to be performed just one session.
“The possible increase in patient throughput and the reduction of patient discomfort are only two of the advantages conferred by the simultaneous dual-isotope MPI,” she wrote. “The protocol also provides perfect alignment and identical physiological conditions between stress and rest images, which may provide additional information to the physician.”
The resarchers then needed to optimize the MC-simulator for MPI using both tracers at once. This significantly improved image quality and scanning was completed in less than three minutes.
“Even with reduced scan times, some patients cannot stay still during the acquisition, which leads to artifacts that can be falsely interpreted as perfusion deficits,” wrote Kangamaa.
Compensation for motion artifacts was achieved with reconstruction-based motion correction in just a few minutes and with CDR based on Bayesian techniques of reconstruction. Some limitations to the study were noted.
“At the time of the patient study evaluation, the new reconstruction method had not yet been incorporated into the clinical routine in Kuopio University Hospital, where this study was conducted,” Kangamaa concluded. “This lack of experience is probably reflected in the results.”
Further research, education and training will need to be conducted to validate and build awareness of this novel SPECT protocol before it could be incorporated into general clinical use.