Gaining PerSPECTive: SPECT/CT Broadening its Clinical Horizons

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hiit040604Early pioneers on the road to discover the clinical utilities of SPECT/CT are finding that the technology is not only useful in diagnosing and treating cardiac disease, neurological disease and cancer. It’s also finding its niche in orthopedics, sports medicine and infection imaging. Despite its clinical utility, users of the hybrid imaging technology agree that the anatomical information offered by CT alonga with the sensitivity of SPECT are giving users more information to make confident, detailed diagnoses.

When William Beaumont Hospitals in Royal Oak and Troy, Mich., installed its first GE Healthcare Hawkeye SPECT/CT system five years ago, Conrad Nagle, MD, corporate chief, diagnostic imaging, says that not much literature existed as to where the modality was having the greatest amount of clinical utility and impact. “It was my feeling at the time that by better anatomic localization and by better attenuation correction, the images and the medical answers that nuclear medicine interpretations would give would be far improved and have a better medical impact.

“Now there is increasing medical literature to support the use of SPECT/CT in a variety of ways that probably were not present in the medical literature back when we first got started,” Nagle continues.Fusion imaging is not a new concept to nuclear medicine professionals, but what makes hybrid modalities, such as PET/CT and SPECT/CT unique? Before hybrid systems, individual SPECT and CT (or PET and CT) data sets were taken and compared, sometimes introducing problems when patients altered positions or when a considerable amount of time had passed between the separate studies.

Dual modalities, which on one platform use separate detectors for x-ray and nuclear imaging, acquire two datasets that are co-registered into a fused image. Users agree that the correlation of structural information acquired by the CT scan and the functional information from the radionuclide imaging improves their ability to make a detailed diagnosis, in comparison to SPECT or PET alone.

 “At the time of interpretation, the fused [SPECT/CT] image allows physicians to localize anatomically any abnormalities that we see on the nuclear medicine component of the images,” explains Nagle. “Instead of saying something is abnormal and probably at this location, by using the CT images physicians can say it is at this location anatomically. I think with time, clinicians and surgeons at William Beaumont have begun to have much more confidence in our medical answers. The other benefit is attenuation correction. By using the CT information, it allows us to better refine the images themselves.”

Is it mainstream?

Nagle points out that the early medical literature on SPECT/CT focused on areas other than bones and joints. “Research was more focused in the oncologic arena than anything else — thallium, Octreoscan studies, tumor imaging, and soft-tissue abnormalities,” he says. “In our experience, we have actually used the system far more for bone imaging in a variety of situations. We have orthopedic back surgeons who do a lot of post surgical spine fusions and in pain situations where they are reassessing if there is a re-injury or re-fracture to the back after an operation. Is it advancing arthritis, which does not require surgery? Or is it a re-injury of the fusion in which case may require another surgery.”

The precision of SPECT/CT helps clinicians answer those questions and possibly rule out unnecessary, invasive procedures. If patients do require surgery, the SPECT/CT images provide a level of detailed information that surgeons can use to help plan treatment options.

“We also have found the system extremely useful in joints given the small bones that are associated with wrists or feet,” says Nagle. “We have found that with CT, the resolution and the ability to say exactly where something is abnormal on the nuclear medicine portion is far better. In many circumstances, I think it allows us to give as good an answer as MRI or CT alone. It is not trying to replace those modalities. It just means that it allows us to do the physiological study of the bone scan and utilize the anatomy of the CT information and give a very high level medical answer.” 

However, whether or not the modality has hit the mainstream in clinical settings remains questionable. “I think SPECT/CT is not a mainstream modality but I do think that manufacturers are beginning to address some of the deficiencies of the earlier units