Gaining PerSPECTive: SPECT/CT Broadening its Clinical Horizons

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 — meaning better CT resolution and shorter scanning times.”

Nagle says cost is a present factor hindering SPECT/CT’s clinical adoption. “As healthcare providers get to add new cameras or replace old ones, and if they decide to do it with SPECT/CT in particular, the CT component makes the system more expensive,” he explains. “Also, many of the nuclear medicine rooms in many hospitals are not large enough to accommodate something that is of additional size because of the CT. A nuclear medicine room does not traditionally have lead-lined walls and users will clearly need that because of the CT component.”

Boosting clinical confidence

In some cases the ends justify the means, and investing in SPECT/CT may be well worth it. “We get a tremendous referral base from orthopedists for [SPECT/CT],” says Nagle. “I am convinced that our answers we give are better answers because of the CT localization. That results in a higher confidence level of the clinicians who send us their patients.”

More clinical acceptance is helping evolve the clinical applications of SPECT/CT, and the modality is emerging out of the shadows of PET/CT, which currently has a larger clinical installation base. Clinicians have joked that while PET is married to its CT counterpart, SPECT is merely engaged. But SPECT/CT is well on its way to finding its niche — and settling down together.

“Our biggest volume of work [with SPECT/CT] has been in ankle and foot imaging,” says Stephen Scharf, MD, chief of nuclear medicine at Lenox Hill Hospital in New York City. The nuclear medicine department is using Philips Medical Systems’ Precedence SPECT/CT system. In these types of cases, Scharf says the scanner is utilized to confirm a diagnosis or plan surgery.

“If we see an abnormality on a bone scan, we then do SPECT/CT to find and localize it,” says Scharf. “We are able to distinguish between fractures in the small bones in the feet, post traumatic arthritis or other types of abnormalities. Depending on the site of the fracture, the patient may require some surgery or he or she may only require rest to let the fracture heal independently.”

SPECT/CT is broadening the department’s clinical reach, too. “We can make a contribution to a group of doctors who nuclear medicine has not spoken to in 20 years,” says Scharf.

The hybrid scanner also is being used for infection and spine imaging. “What is really scary is that I honestly do not know how I can live without the technology,” says Scharf. “That is what happens. Lenox’s nuclear medicine department has gotten used to SPECT/CT, and so have our orthopedists and surgeons.”

A clinical necessity

Clinicians on board with SPECT/CT agree. “We actually now rely on the SPECT/CT images because once you have tried it, it becomes very difficult to go back,” says Homer Macapinlac, MD, deputy chairman, department of nuclear medicine at MD Anderson Cancer Center in Houston. “Once doctors get used to it, they realize the importance of the anatomy. I think there is no turning back once you begin utilizing this modality clinically.”

MD Anderson’s nuclear medicine department, which uses Siemens Medical Systems’ TruePoint SPECT/CT system to localize the presence or absence of cancer, is benefiting from the system’s integrated platform. “It potentially improves the way we interpret these studies in oncologic imaging,” says Macapinlac.

“The traditional methods have been to use just the structural imaging modalities — CT and MR — and interpret them,” he continues. “We would do the functional imaging like SPECT separately and try to correlate them mentally. We know for a fact that this is a very difficult process. If we use software fusion, it is very tedious and time-consuming. In a single fashion, hybrid scanners are advantageous. Doctors can do the interpretation better because the images are already registered. It also is more convenient for the patient because the patient only has to come once instead of three times. In addition, you have a lesser chance of reports being in conflict with each other when the same physician interprets both studies. It gives efficiencies in terms of patient convenience and improves the accuracy and efficiency of our reporting.”

But is the technology changing treatment options for patients? “A benign finding or a negative finding verified by the CT or the SPECT study will allow us the confidence to know that the patient does not have cancer,” explains Macapinlac. “With SPECT/CT, we can identify smaller metastases and have greater confidence in identifying early progressive disease. The outcomes for patients could be better, but I think that remains to be seen. We need to gather the data to see if the survival impact of this modality will be greater. It takes time and data to justify this. But for us, the upfront things we see on a day-to-day basis are very encouraging.”

Enhancing the CT in SPECT

Vendors are making significant software and hardware improvements to their SPECT/CT systems, one of the most revolutionary being the addition of multidetector CT imaging technology to further improve attenuation correction. Some facilities may not want their SPECT/CT system to acquire diagnostic quality CT studies, while other users may. Factors must be considered before purchasing a hybrid scanner. The right SPECT/CT system depends on the needs of the institutions and the types of exams it wants to perform.

“Know how much it is going to cost upfront to buy the system,” says John Seitz, MD, chief of nuclear medicine at William Beaumont Hospital, as to some of the factors users must consider before purchasing a SPECT/CT scanner. “How much is it going to cost to maintain? What are the room requirements? What is it primarily going to be used for? Do we need a system with a high-end CT scanner?”

William Beaumont currently uses GE’s older generation Hawkeye but is gearing up to install GE’s newest SPECT/CT system, the Infinia Hawkeye 4. The new scanner combines GE’s Infinia gamma camera with a 4-slice CT. Seitz says the Hawkeye 4 is faster and has a smaller slice thickness capability that will aid in patient throughput.

“At the time of installation [of the first SPECT/CT system], we were not sure how much the imaging modality was going to impact, or if it would make that much of a clinical difference,” says Seitz. “As time went on, we basically have had a tremendous amount of growth in bone imaging, primarily through orthopedists and sports medicine physicians and physical medicine rehab. Most of our referrals are for bone scans, while a few years ago they were primarily for oncology.”

Siemens and Philips also have introduced next-generation SPECT/CT systems. Philips’ new Precedence SPECT/CT combines a nuclear imaging camera with the anatomical precision of a 16-slice CT scanner. In addition to oncologic and bone imaging, the system provides the ability to do a combined coronary CT angiography with SPECT myocardial perfusion imaging. 

Siemens’ TruePoint SPECT/CT integrates Siemens’ SPECT imaging with its CT technology and enables clinicians to utilize the device in three ways to perform three separate studies — SPECT, multidetector CT and SPECT/CT. The vendor offers various multidetector CT configurations with speeds of up to 0.6 seconds per rotation, allowing acquisition of a high-quality CT scan in a few seconds.

Lenox’s Sharf says that if a hospital does purchase a SPECT system with a high-end CT scanner, they always have the option of using it as a back up CT scanner on nights and weekends, and using it to cover downtime. “When we first purchased the Philips Precedence, it was the first multislice CT scanner in the institution. We actually used it for a couple weeks almost exclusively as a CT scanner.”

The Baptist Miami Cardiac Vascular Institute is using a Philips Precedence 16-slice SPECT/CT. The system is located in the hospital’s molecular imaging section of the radiology department. In addition to SPECT/CT, the department also has two PET/CT scanners. “In our department, we have four physicians who are double boarded by the American Board of Nuclear Medicine and American Board of Radiology,” says Jack Ziffer, MD, PhD, director of cardiac imaging at Baptist. “We have people who are trained expertly to read CT’s and to read nuclear. We also have a number of technologists who are dual trained.”

In general, Ziffer says the machine is fully utilized by patients needing SPECT/CT studies. “When that scanner is idle in the evening and the other CT scanners are busy throughout the hospital, and if we are caught up in nuclear, we will use it as an independent diagnostic CT scanner,” says Ziffer.

Parathyroid scanning with SPECT/CT is Baptist’s most frequent application. “Formally we used to do a nuclear parathyroid scan with a SPECT and then under the nuclear camera I would take a radioactive marker and mark the abnormal area,” explains Ziffer. “Then the patient would be brought over to CT, and we would do a CT scan to try to map where the abnormal nuclear activity was. By having this integrated piece of instrumentation we can do SPECT and CT, fuse them, and then let the surgeon know the same type of information we acquired before, but presumably better and faster.”

The crystal ball

Hybrid imaging modalities are greatly impacting the diagnostic capabilities of nuclear medicine physicians and boosting confidence levels of clinicians and surgeons. When SPECT/CT becomes mainstream still remains to be seen, but current users can not imagine their world without the hybrid scanner. As more hospitals explore the clinical utilization of SPECT/CT, the future remains bright. Some clinicians even compare SPECT/CT’s evolution to that of older sibling PET/CT.

“PET has been around for over 20 years and it is only now that its impact is being realized because of the CT component of the study,” says MD Anderson’s Macapinlac. “Research has been shown that having the PET and CT together is much better than having the PET alone, the CT alone or reading them side by side. Having them acquired simultaneously with registration has shown that the interpretation accuracy is much better. I believe that this will happen for SPECT if institutions acquire a dedicated SPECT/CT scanner. Many people initially disputed the fact that PET/CT would not work or that it was not necessary. However, multi-institution trials have shown that this not true. The same thing I think will happen to SPECT/CT.”