SPECT/CT: Diagnostic Confidence Is on the Rise as Need for Additional Studies Falls
Philips Precedence SPECT/CT features a 16-slice CT and can be used for combination studies, as well as CT-only and SPECT-only exams.

Single-photon emission computed tomography (SPECT) coupled with computed tomography (CT) is on the cusp of defining a new standard of diagnostic imaging for a variety of indications. The modality is expanding its presence in cardiac and oncological medicine and stands ready to offer clinicians a powerful tool for musculoskeletal indications.

Since its commercial introduction by GE Healthcare in 1999, SPECT/CT has been steadily winning converts as the technology increases its deployment. The response from clinicians conducting studies with the equipment, as well as their referrers, has been nothing short of enthusiastic.

Nuclear medicine physicians utilizing SPECT/CT no longer have to hear the old bromide about “unclear medicine;” the anatomic detail of CT paired with the functional capabilities of SPECT is delivering exams that are increasing diagnostic certainty, reducing the need for additional imaging procedures, and providing precise roadmaps for surgical interventions.

Cardiac clarity

Jean Luc Urbain, MD, PhD, chief and chair of nuclear medicine at the University of Western Ontario, Schulich School of Medicine and Dentistry in London, Ontario, said the facility began its SPECT/CT program with a GE Hawkeye in 2004 and immediately saw utilization of the modality proliferate.

“We now have four units installed, and a fifth one coming on-line shortly” he says.

His practice does quite a bit of nuclear cardiac studies on the units, as many oncology exams as it can, and a fair amount of musculoskeletal imaging.

“We see 3,000 patients for stress tests with myocardial perfusion imaging (MPI) a year, mostly on SPECT/CT,” Urbain says. “Cardiology represents about 40 percent of our business annually, oncology about 30 to 40 percent, and the rest is musculoskeletal.”

The department bases its determination of SPECT/CT exam usage on whether the SPECT portion of the study will be enhanced by CT capabilities, according to Urbain.

“My estimate is about 35 percent of the time SPECT images are enhanced by the CT portion of equipment,” he notes.

One of the greatest advantages to using SPECT/CT is that the specificity of the diagnoses from the department has been greatly enhanced, Urbain says.

“Now that we have the capability to view the functional and anatomic aspects of the exam together, we are very confident about the localization of what we see,” he explains. “Overall, it has improved tremendously our ability to diagnose accurately.”

This has been most evident in the practice’s MPI studies. They’ve been able to decrease uncertainty in these exams by about 20 to 25 percent by conducting the procedures on SPECT/CT, which has led to better patient management.

“It has drastically improved our ability to diagnose, or rule out, ischemia,” he notes.

SPECT/CT has provided another benefit to the facility; by its capability to increase diagnostic certainty, physicians are now better able to provide a diagnosis without conducting additional imaging studies on other modalities. This, in turn, has allowed greater utilization of these technologies for other patients.

Urbain is particularly excited about the possibilities for the future of SPECT/CT in cardiac imaging. He and his colleagues have begun an investigation into the efficacy of SPECT/CT MPI procedures being conducted with coronary CT angiography (CTA) in a single patient session.

“We have learned so much over the past six months that we can probably begin rewriting textbooks,” he says. “We are seeing things that we never would have suspected.”

Given the capability to design an ideal SPECT/CT system, Urbain would opt for a cardiac dream machine.

“From the medical/scientific aspect, I’d like to see a CZT [cadmium zinc telluride digital detector] SPECT paired with at least a 64-slice CT to do cardiac work,” he says.

Oncologic localization

Donald Neumann, MD, PhD, director of nuclear oncologic imaging in the department of nuclear medicine at the Cleveland Clinic in Cleveland, says he was impressed with SPECT/CT from the time it was brought on-board the facility in 2005.

The department uses a 6-slice Siemens Medical Solutions Symbia T6 TruePoint SPECT·CT system to conduct a variety of studies including: MPI, thyroid and parathyroid, brain (cerebrovascular disease and seizure imaging), a variety of octreotide exams, gastrointestinal, ProstaScint (a Cytogen-developed murine monoclonal antibody conjugated to a linker-chelator for prostate imaging), and sentinel node localization for biopsy with lymphoscintigraphy.

“The plastic surgeons and the ENT physicians just love the SPECT/CT lymphoscintigraphy studies,” Neumann says. “Before SPECT/CT, I could tell them, ‘I think there’s a sentinel node on the right side of the neck, somewhere.’ Now we can co-register with the CT and I can say, ‘Yes, there’s a 2-mm sentinel lymph node on the right at level 2b.’ I can tell them exactly where it is and I can give them 3D images.”

Physician satisfaction is not confined solely to surgical specialties, although they have been the most enthusiastic about adopting the modality, Neumann says. The vast majority of his referral base also has welcomed the capabilities of SPECT/CT.

“The coupling of the CT information with the SPECT not only increases the diagnostic confidence of the interpreting physician, it also increases the diagnostic confidence of our referring physicians,” he notes. “Overall, it’s a win-win situation and, above all, the patient benefits.”

Diagnostic efficiency also has increased thanks to SPECT/CT, Neumann says. The modality provides functional and anatomic information at such an exquisite level of detail that additional imaging studies are rarely needed to make a diagnosis. In addition, the multidetector capability of the equipment allows the department to conduct contrast-enhanced CT procedures as part of the SPECT/CT exam.

Provided with the opportunity to design the next-generation of SPECT/CT systems, Neumann says he would like to work with a dual-source CT unit coupled with SPECT equipment.

“I can envision a lot of potential applications with that technology,” he says.

MSK power

Unlike his colleagues in Canada and Ohio, Stephen Scharf, MD, chief of nuclear medicine at Lenox Hill Hospital in New York City, does not perform cardiac studies with the facility’s 16-slice Philips Medical Systems Precedence SPECT/CT system, as those are performed elsewhere. However, he has filled the practice’s schedule on the modality for the past two plus years with a breadth of oncologic and musculoskeletal exams.

“An area that we’ve done a lot of work with SPECT/CT is in orthopedics,” he says. “We do a fair amount of individual lesion localization.”

The equipment has provided interpreting physicians at the facility with the capability to distinguish fracture from degenerative disease in one exam.

“Being able to say that activity is in an articular surface rather than the mid-shaft of a bone [particularly in the foot] is helpful,” he notes. “A lot of [planar SPECT] images are difficult to interpret because the hot area is so much hotter than normal bone that you really can’t see the normal bone. Of course, with SPECT/CT you don’t have that problem.”

Foot imaging wouldn’t even be considered for SPECT alone, Scharf says, because a fracture of the foot looks like a dot rotating in space—there’s not really anything there to help the physician localize it. Whereas with SPECT/CT the interpreting physician can localize things extremely well, he says.

The group has used SPECT/CT in spinal workups for tasks such as distinguishing fractures, arthritis, and planning vertebroplasty.

“We can tell which part of a specific vertebral body needs to be pumped up,” Scharf notes.

Another orthopedic area in which the facility’s SPECT/CT system has enjoyed tremendous success is with prosthetic imaging. In these cases, the practice is looking for infection as well as the deterioration or failure of the implanted prosthesis. Cases have ranged from joint replacement hardware to cosmetic cheek implants and the modality has been able to vastly increase diagnostic confidence because of its anatomic and functional capabilities.

“In orthopedics, we’ve been able to pinpoint abnormalities so well that we can do things like actually limit surgery,” he notes.

Scharf says that he would like to see the capabilities of SPECT/CT data interpretation software expanded for the current generation of the technology.

“What I would love to be able to do is take these pictures that, right now, are incredible and blow the oncologic surgeons away by showing them exactly what their surgical field is going to look like,” he says. “The data to do that are already there, the software isn’t.”