Lower scan time, dose in SPECT MPI

A new SPECT protocol allows researchers to not only cut scan times down to a quarter of the average time, but it could also be used to lower dose, according to a study published Nov. 20 in the Journal of Nuclear Medicine.

Federico Caobelli, MD, from the department of nuclear medicine at Fondazione Poliambulanza in Brescia, Italy, and colleagues evaluated the trade-off of scan times to dose reduction in phantom models using an IQ SPECT protocol, which combines new software and hardware in a retrofit package. The researchers found that they could use IQ SPECT to scan to an eighth of the time with a full dose or to a quarter of the time (12 seconds per view) at a reduced dose without compromising image quality.

“The new IQ SPECT with multifocal collimators, which can be applied as a plug-in on multipurpose cameras, has a favorable performance regarding sensitivity and contrast-to-noise ratio when compared with conventional cameras equipped with low-energy and high-resolution collimators,” wrote the authors. “The unique geometry of the collimator, with holes focused at the center and near-parallel at the edge, facilitates enhanced sensitivity for the cardiac region while permitting acquisition of untruncated projection data.”

Researchers simulated MPI rest scans using with a full dose of Tc-99m tetrofosmin (740 MBq) and also at reduced levels equal to 50 percent, 25 percent and 18 percent of the full dose and at variable acquisition times. Images were evaluated both quantitatively and qualitatively for left ventricle wall thickness, left ventricle wall cavity contrast and transmural defect. Findings of the study showed very high quality imaging at 100 percent dose and all scan times except those obtained at four seconds per view or fewer and at reduced doses at six seconds per view or fewer. These were prone to false positive results.

“Acquiring data of good quality with lower radioactivity would reduce patients’ effective dose to approximately 2.5–3 mSv for a stress–rest study with Tc-99m labeled tracers, much lower than current protocols with general-purpose low-energy and high-resolution collimator cameras (about 9–10 mSv) and similar to those obtained with the new cadmium-zinc-telluride cameras.”

Such improvements could ease the pressure of technetium shortages and aid in industry-wide dose reduction campaigns. However, in vivo data in larger populations is needed to account for limitations such as patient motion and scatter.