Nuclear medicine scans that employ SPECT to detect disruptions in myocardial perfusion and other cardiac events have advanced with refinements to the equipment that have improved techniques and increased physician confidence in the value of these studies.
Jack Ziffer, MD, PhD, chairman of radiology at Baptist Hospital of Miami and director of cardiac imaging for the Baptist Cardiac and Vascular Institute, describes the protocol they adopted 10 years ago to incorporate into routine evaluation of patients with chest pain, possibly of cardiac origin, in whom an electrocardiogram (EKG) did not confirm an acute myocardial infarction (MI).
With a practice focused predominantly in a 500-bed community hospital that serves as a referral center for patients with cardiac disease, he relates that they see a tremendous number of patients in their emergency department with chest pain.
Using their Philips Medical Systems SKYLight SPECT system to evaluate those patients (74 percent of whom experienced resolved chest pain by the time they reached the hospital) resulted in a 16-fold reduction in undiagnosed MIs and a substantial decrease in the "total length of stay" for those hospitalized patients. The system enabled them to streamline the process in the ED, and admit patients who required further treatment.
Ziffer's department has ordered two hybrid Precedence SPECT/CT systems from Philips, which they anticipate will be installed within the second quarter of 2005. They envisage that the primary benefits of adding these hybrid scanners will include providing enhanced attenuation correction to the SPECT studies, allow calcium scoring on patients to exclude acute coronary syndrome from the differential diagnosis, and for those patients who experience an equivocal scan, they will perform a CT angiogram. Therefore, they expect the addition of the Precedence will enable a comprehensive cardiac imaging workup in one place.
Attenuation correction at the heart of accuracy
In June 2003, the two premier nuclear medicine associations issued a joint statement outlining the clinical significance of attenuation correction: "It is the position of the American Society of Nuclear Cardiology and Society of Nuclear Medicine that incorporation of attenuation correction in addition to ECG-gating with SPECT myocardial perfusion images will improve image quality, interpretive certainty, and diagnostic accuracy. These combined results are anticipated to have a substantial impact on improving effectiveness of care and lowering healthcare costs."
Gary V. Heller, MD, PhD, professor of medicine at the University of Connecticut and director of nuclear cardiology at Hartford Hospital, describes a practice that performs 6,000 cardiac SPECT studies annually with Philips CardioMD scanners, in addition to a laboratory that is involved in multiple research projects designed to move the field of nuclear cardiology forward. He asserts that although attenuation correction has been used for several years, recent advances permit techniques to improve enough so that clinicians are beginning to accept that this is a reasonable solution to a difficult problem. Attenuation correction on the system involves both hardware and software components.
"It uses a different line source, gadolinium, which scans the patient's body at the same time that the other data are being obtained, with a very low radiation dose," Heller explains. "Using the software, the transmission data and emission data are analyzed to provide one solution."
Without attenuation correction, many patients require additional procedures such as cardiac catheterization, which Heller describes as a "downtick for nuclear cardiology." In other words, if further evaluation is required due to lack of confidence in the SPECT results, eventually referring physicians will not request nuclear scans.
GE Healthcare approaches the issue of attenuation correction using another methodology via their hybrid Infinia Hawkeye dual-detector SPECT/CT system. This combined SPECT camera and GE single-slice CT scanner registers CT transmission attenuation correction and functional anatomical mapping. It is the same concept as PET/CT that combined anatomy and physiology.
Jesus Bianco, MD, professor of radiology at the University of Wisconsin in Madison, describes their use of the Infinia Hawkeye to accomplish myocardial perfusion with attenuation correction and gating studies, risk stratification for patients with recent acute coronary