Nuclear cardiology is a very mature, well-established area of diagnostic imaging. In fact, myocardial perfusion SPECT imaging has a solid 30-year history. Its diagnostic value is high, and the modality is well-accepted. One indicator of the high value of myocardial perfusion SPECT is its procedure volume in the United States, which has seen double-digit growth in the last 15 years. Given the high acceptance and clinical utility of myocardial perfusion SPECT, any new imaging technologies designed for nuclear cardiology must meet high standards and fill well-defined needs.
Despite the broad acceptance and utility of myocardial perfusion SPECT, there is room for improvement. In fact, the clinical value of cardiac SPECT can be improved in three specific areas: reduction of acquisition time, addition of hybrid or fusion imaging with CT, and through the introduction of new tracers. IQ•SPECT, a new technology under development by Siemens, is designed to address the most pressing challenge identified by cardiologists. That is,
the fairly long acquisition time for SPECT and SPECT/CT studies is associated with image quality and patient throughput issues.
To a great extent, the power of SPECT combined with true diagnostic CT is still relatively new. Even experienced nuclear medicine physicians are not fully aware of how much the technology can do before they start using it. The same is true for referring physicians who are suddenly offered much more than they could see with conventional SPECT. The result is that non-cardiac referrals tend to grow, namely in infection, orthopedic and pediatric imaging—causing competition for camera time, with referring physicians regretting when they have to send patients with clear indications for SPECT/CT to conventional SPECT. By accelerating the acquisition time of cardiac procedures (which still represent 50 percent of the studies), IQ•SPECT frees up the agenda for SPECT/CT.
The acquisition dilemma
“The major limitation of SPECT is its acquisition time,” says James Corbett, MD, director of cardiovascular nuclear medicine at University of Michigan in Ann Arbor. “It takes from 12 to 20 minutes to acquire images, which can be a long time for patients, particularly those who are heavy, in heart failure, or claustrophobic.” The lengthy acquisition time can impact overall image quality. Uncomfortable patients tend to move, and those who are short of breath may take deep breaths causing misregistration between SPECT and CT. Typically, the longer the procedure time, the greater the likelihood that patients will be uncomfortable and breathe deeply. Both patient movement and deep breathing detract from the final image quality and potentially from diagnostic accuracy. “The ability to acquire images more rapidly should be an advantage for all patients,” explains Corbett. Not only does it translate into improved image quality, but it also facilitates a less stressful, more comfortable patient experience.
More rapid image acquisition could deliver benefits beyond improved image quality. As reimbursement for myocardial perfusion SPECT is gradually diminished, any additional efficiency in the camera would allow the provider to image additional patients. A practice with access to a faster camera would enjoy a great advantage over its competitors because the faster SPECT camera could accommodate two or three patients in the same amount of camera time as a current generation system can image one patient. “Outpatient practices might be able to purchase fewer systems, or serve more patients with fewer systems,” says Corbett.
The financial benefits of a faster camera are equally appealing on the inpatient side. Patients with acute coronary syndromes and other unstable conditions generally require a nurse to accompany them during SPECT examinations. “A patient may have to be in the nuclear medicine department for several hours for stress and, if appropriate, rest SPECT studies. It adds up to a significant amount of nursing time and studies. In some cases, some one-day studies turn into two-day studies for logistical reasons,” Corbett says. Shorter studies minimize the impact on nursing staff and often reduce the length of hospital stay.
Although growth in cardiac SPECT has flattened in recent years, demographic factors point to a potential surge in demand for the study. The obesity epidemic and the aging population could make for a perfect storm with more patients requiring cardiac SPECT imaging in the coming