Nuclear Cardiology’s Next Step

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 years. Sites equipped with systems capable of improved patient throughput could enjoy a competitive advantage.

Hybrid SPECT/CT: Beyond perfusion

“Myocardial perfusion SPECT is a good tool for visualization of perfusion changes,” says Torsten Kuwert, MD, director and chair of clinical nuclear medicine at the University of Erlangen-Nuremberg in Germany. “Its prognostic value is high. On the other hand, advances are possible. SPECT does not allow physicians to visualize vessels or morphology. Nor does it provide a calcium score.” Hybrid SPECT/CT cameras could rise to the challenge by providing a means to visualize morphology and perfusion in a single imaging session. 

Raising the bar in well-established myocardial perfusion SPECT imaging evaluations using hybrid SPECT/CT imaging can enable the addition of calcium scoring, for evaluating a patient’s risk of developing coronary artery disease. Adding the 30-second CT to the SPECT study adds the assessment of the buildup of calcium in the coronary arteries to the standard ischemia evaluation. Because many heart attacks occur in patients without obvious signs or risk factors, calcium scoring can add independent information in the detection of coronary artery disease.

The tracer angle

“Nuclear cardiology lacks new tracers, especially agents to enable visualization of atherosclerosis in the vessel walls,” says Kuwert. Approximately 50 percent of myocardial infarctions occur in arteries without a major occlusion before the event. The culprit is vulnerable plaque, which cannot be identified by coronary angiography. Cardiologists, thus, lack the right tool to make an accurate diagnosis. The challenge could be solved via a SPECT-specific radiopharmaceutical agent capable of identifying unstable plaque.

On the horizon

Siemens IQ•SPECT technology represents the next step in SPECT and hybrid SPECT/CT imaging. The technology will enable SPECT and SPECT/CT cameras to a comprehensive cardiac workup including perfusion, CT attenuation correction and calcium scoring in as few as five minutes: four minutes for the SPECT acquisition and one minute for re-positioning and the CT study. IQ•SPECT technology is achieved through a specially designed “smart” collimator that magnifies the heart. Typically, SPECT data are obtained through mechanically centered detector rotation, where organ-specific magnification cannot be achieved. The flexible mechanics of the Siemens’ Symbia S and T gantries allow an organ-centric detector rotation that can zero-in on the organ of interest; in this case, the heart.

Because nuclear cardiology is such a mature specialty, any
new technology needs to integrate with current systems, and IQ•SPECT is designed to connect with all standard reading and reporting packages to allow a seamless user experience. Siemens expects to unveil the technology in 2009. This new tool for cardiology is a great leap forward. With IQ•SPECT, cardiologists can look forward to improvements in image quality, patient care and the bottom line.