Rapid SPECT Cuts Cardiac Imaging Time in Half

June 17, 2008

June 17, 2008 (New Orleans, Louisiana) — A new means of performing gated single-photon-emission computed tomography (SPECT) myocardial perfusion produces data in half the usual acquisition time, with no sacrifice in image quality, according to the results of a prospective multicenter study presented here at the Society of Nuclear Medicine 2008 Annual Meeting.

The new approach is rapid gated SPECT myocardial perfusion upright imaging using the 3D ordered subsets expectation maximization (OSEM)-iterative image-reconstruction technique (3D rapid SPECT). 3D-OSEM was compared with the standard 2D-OSEM reconstruction technique (2D standard SPECT) in 448 patients undergoing rest and stress gated SPECT myocardial perfusion studies at 10 centers in the United States.

The data were presented by Jamshid Maddahi, MD, clinical professor of molecular and medical pharmacology (nuclear medicine) and medicine (cardiology) at the University of California School of Medicine, Los Angeles.

Dr. Maddahi explained that the 3D-OSEM reconstruction algorithm enables depth-dependent resolution recovery and improves chamber contrast in cardiac SPECT images. This lessens acquisition time while maintaining image quality.

"The rapid protocol yields diagnostically equivalent images for rest and stress studies, reliable measurement of ventricular function parameters, and reliable quantitation of perfusion-defect severity," Dr. Maddahi said during his presentation.

Investigators evaluated the diagnostic quality of the images, quantitative perfusion-defect size, and parameters of ventricular functions, including left ventricular ejection fraction, end-diastolic volume, and end-systolic volume.

Images were acquired simultaneously with both approaches using a single-isotope technetium (Tc)-99m-agent protocol. Data were gathered from 3 different Digirad cameras: single head (n = 20), dual head (n = 239), and triple head (n = 189). Of the 448 patients, normal results were observed in 60% and abnormal results were observed in 40%.

With the dual-head camera, mean total acquisition times for 2D standard imaging were 12.81 minutes at rest and 8.39 minutes with stress; acquisition times for 3D rapid imaging took 6.53 and 4.32 minutes, respectively. With the triple-head camera, acquisition times for 2D standard imaging were 9.29 minutes at rest and 8.05 minutes with stress; acquisition times for 3D rapid imaging took 4.81 and 4.18 minutes, respectively, he reported.

With the dual-head camera, times per projection for 2D standard imaging were 47 seconds at rest and 31 seconds with stress; times per projection for 3D rapid imaging were 23.5 and 15.5 seconds, respectively.

In blinded assessment, expert observers judged the resolution of the 3D rapid images to be comparable with, and in some cases better than, that of the 2D standard imaging, in spite of the fact that data were acquired in half the time.

The quality of the 3D rapid and 2D standard images was deemed equivalent in approximately 79% of cases for both stress and rest studies. In 19% of the rest studies and 19% of the stress studies, the 3D rapid images were considered superior. In fewer than 2% of cases, the 3D rapid images were deemed inferior to the 2D standard images. Diagnostic accuracy and correlation with measures of ventricular function were also similar.

Peter S. Conti, MD, PhD, professor of radiology, clinical pharmacy, and biomedical engineering at the University of Southern California School of Medicine, in Los Angeles, and past president of the Society of Nuclear Medicine, commented that rapid SPECT offers a number of advantages, including patient compliance and high patient throughput.

"These studies can run hours in length. Rapid image acquisition and turnaround could be of great advantage to patients, clinicians, and hospitals, where more patients could be seen in 1 day," he told Medscape Radiology. "In addition, the cameras may be efficient enough to reduce the radiation dose, so there could be safety advantages."

Dr. Maddahi disclosed that he has served as a consultant for Digirad, Astellas, GE Healthcare, Mallinckrodt-Tyco, and BMS Medical. Dr. Conti disclosed relationships with Fluoropharma, Inc; Molecular Imaging Corp; NuView Radiopharmaceuticals; Molecular Insights; and Siemens.

Society of Nuclear Medicine (SNM) 2008 Annual Meeting: Abstract 7. Presented June 16, 2008.

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