Single photon emission computed tomography (SPECT) is a nuclear imaging modality that has been around for almost 50 years. In a sense, SPECT could be characterized as a medical and scientific tool that has waited a long time to be fully appreciated.

 The CardioMD fixed 90? nuclear cardiology camera from Philips Medical Systems is designed for the office-based system and can fit into a room as small as 8 x 10 feet.

Introduced in the 1950s and older than most other imaging modalities, SPECT has been a familiar and useful clinical device. But it didn’t come into widespread use until the 1980s.

Several things needed to take place to move SPECT toward broader clinical applications. The technology for creating better images had to advance first. More radioisotopes needed to be developed for use as tracers, and better engineering designs were needed to bring SPECT out of the hospital and into the office.

After some tweaking, software began featuring improved imaging options, and innovations in drugs opened new possibilities. Then another leap—fusion and hybrids, attenuation correction, and, finally, the advent of molecular medicine.

SPECT is a modality that has the advantage of many years’ experience coupled with advances that now are making it an important player in nuclear imaging. As the pharmaceutical industry creates new drugs, the most notable companies manufacturing SPECT systems—Siemens Medical Solutions (Malvern, Pa), GE Healthcare (Waukesha, Wis), and Philips Medical Systems (Bothell, Wash)—are reinventing the hardware portion of the systems (ie, the gamma cameras needed to image and then visualize the drugs in the body).

Recent advances include refinements that make SPECT significantly more user friendly for clinical end-users—both clinicians and patients. The result has been a notable growth in its presence as a member of the imaging community.

In total, about 13,000 SPECT cameras are used in the United States. In 2003, about 1,300 systems, of the approximately 2,000 total worldwide, were added to the US market. Comprising about 65% of the total world market, the United States is an important player in SPECT.

The most common SPECT system sold now, the dual-headed gamma camera, comprises about 80% to 85% of the total US market, according to Plado Kosmaoglou, manager of product and clinical marketing at Siemens Medical Solutions’ Nuclear Medicine Group (Chicago). Traditionally, when the patient is placed in the gamma camera scanner, the detector moves around the patient to cover 360? and create several images. The advantage of the dual-headed detectors is that only a 180? rotation is necessary, cutting imaging time in half.

 Toshiba’s variable gamma camera (above) uses dual detectors with 76?, 90?, and 180? angulation to provide optimal image quality for whole-body, SPECT, and general purpose scanning in a patient-friendly environment.

Matters of the Heart
As with other areas of nuclear medicine, a SPECT image is created by the body’s functioning, not the bones or structure. This distinction from other imaging modalities has contributed to SPECT’s major current role in cardiology. For example, the metabolism of the heart muscle can be easily stimulated, allowing for portions of the heart receiving or not receiving blood to be clearly identified.

“Nuclear medicine is extremely useful in being able to classify coronary artery disease in terms of not seeing the disease itself, but the result of the disease. In other words, how well is the heart muscle being fed with blood?” Kosmaoglou explains. “If you see on the image that it is not being fed, it means you have a problem before [the heart], which is usually in the arteries. Then the patient goes to catheterization in order to find out exactly where and how big the problem is.”

Indeed, most of today’s cardiology studies are performed with SPECT. “Literature out there now shows that cardiac SPECT is a more accurate technique than non-SPECT, and the sensitivity and specificity are better,” says Robert E. Henkin, MD, of the Loyola University Medical Center’s Nuclear Medicine Division (Chicago).

Consequently, a segment of the SPECT market that is likely to continue growing is that dedicated to cardiology. According to F. David Rollo, MD, PhD, of Philips Nuclear Medicine (Andover, Mass), last year alone saw 8 million to 9 million nuclear cardiology procedures performed. Presently, cardiology dominates SPECT, representing about 50% of SPECT procedures. Specifically optimized for the purpose, the SPECT cardiology systems are also more efficient, smaller, easier to use, and more cost effective.

Another factor driving nuclear cardiology is efforts at reducing the number of unnecessary procedures performed. Among those cardiac catheterizations that were based on symptoms and family history but lacked a nuclear cardiology procedure, about 40% to 50% resulted in normal studies, Rollo says. Conversely, for patients referred for a catheterization based on results from a nuclear cardiology procedure, the quantity of normal studies drops to fewer than 10%.

 The Signature Series from Siemens Medical Solutions offers high-definition dynamic digital detectors (HD4) to deliver high image quality and reliability.

SPECT also is a relatively cost-efficient modality. Its gamma cameras don’t require the shielding and room preparation necessary for other modalities, such as CT and MRI. The SPECT equipment is also less expensive. Additionally it doesn’t require the expensive disposable parts required, for example, by the CT X-ray tube. This cost advantage has made it an attractive imaging modality, especially for certain specialties, including cardiology.

Kosmaoglou estimates that departments using dedicated cardiology SPECT could break even within 2 or 3 years at approximately three patients a day. A busy department could see a higher number of patients, reaching the break-even point more quickly, he suggests.

Most of these systems are purchased for use in private cardiology practices. Reimbursement for procedures performed with these imaging systems also are very favorable at this time, Kosmaoglou says, which adds to the systems’ attractiveness.

“[The patient has] immediate access to the availability of nuclear cardiology [for when] the diagnostic cardiologist says, ‘This looks like cardiac disease,’” Rollo explains. “What [the cardiologist] would like to have is the diagnosis within minutes. Then, if the patient has cardiac disease, he/she can be sent to the hospital; if the patient doesn’t have the disease, he/she can be sent back to the referring physician, replete with the information that the physician needs to look for other causes for the pain.”

Attenuation correction is a sophisticated solution for potential false results in SPECT studies. The correction compensates for tissues or materials that lie between the detector and the organ of interest, which cause the absorption of photons emitted by the organ. Particularly important in decision-making in cardiology, this burgeoning area has significant promise. New and better software continues to be developed to address the issue. And gamma systems incorporate methods designed to reduce this effect. For example, the Infinia Hawkeye from GE Healthcare was introduced last year; it performs a new and quite effective attenuation correction, according to the manufacturer.

On to Oncology
The second major clinical use for SPECT is oncology. “What [physicians] are looking for is that a tumor has a much higher intensity function than the rest of the body does. It consumes more energy because it grows very fast,” Kosmaoglou explains. With the correct radiopharmaceutical, the SPECT image will show the tumor as a center that consumes much more of this drug than its surroundings.

Estimates of SPECT use for oncology range from 30% to 50%. The balance is made up of general imaging—lungs, kidneys, brains, and thyroids. Brain scans in particular are an important application. “Cerebral perfusion studies must be performed with SPECT, because there is no other way to do them,” says Henkin of Loyola University.

Two significant advances in SPECT have been the combination of functional and anatomical views through fusion and hybrid systems. Time has shown that it makes sense for diagnosticians to see combined information received from both functional modalities (like SPECT) and anatomical modalities (like CT).

Supporting this practice has been image fusion, which occurs when images from two separate scans—SPECT and CT, for example—are mixed together via a computer. One image, then, enables physicians to see both the functional information of nuclear medicine and the anatomical information of CT. This process has become an important diagnostic advance, used primarily for oncology studies at present.

The Infinia Hawkeye joins a nondiagnostic CT with a SPECT gamma camera to combine anatomical and functional imaging. A major contribution of this system is its localization of disease as well as improved image quality, notes Michelle Heying, general manager of global nuclear medicine at GE Healthcare.

And this month, Philips is launching the SkyLight, a SPECT/CT device that brings a new hybrid into the market to further evolve this innovative approach.

The Future of SPECT
SPECT is revealing its strengths both clinically and in the marketplace. As a less-expensive technology compared to other modalities, SPECT also offers lower setup costs for facilities. Additionally, SPECT has the ability to be narrowly applied and optimized for specific organs—the heart, for example, with cardiology. So the question arises: What does the future hold?

“One of the real advantages of [this modality] is the large number of SPECT cameras that are available,” Philips’ Rollo says. Virtually every hospital has SPECT as do several thousand outpatient diagnostic centers. “We have 13,000 SPECT cameras in the United States; therefore, the issue of access to care allows anyone to have a SPECT scan available to them,” he says. By comparison, about 600 PET systems exist, and most of them are in fairly large hospitals.

Another advantage, Rollo notes, is the large number of radiopharmaceutical agents already available as well as the number of new agents that are in the process of being cleared by the FDA for specific applications. Citing the more than 4 million bone scans performed each year for a variety of reasons, he says that by far, “the most sensitive method of looking [at a bone] is the use of the bone agents and the unique advantages of SPECT bone scans. Plus, we have some new software that allows us to see even the smallest areas of abnormality much better, and we can localize them better than we ever have in the past.”

Rollo notes that Philips has a number of new cerebral imaging agents that are in development and will be cleared soon. The conditions addressed include Alzheimer’s disease, Parkinson’s disease, and attention deficit disorders. “Obviously, to have an accurate diagnosis and, therefore, be able to apply therapy becomes extremely important to patients. Heretofore, most of what we’ve done is a neurological examination, a family history, and then [explained why we think a patient has a certain disease],” he says. “We want to have an agent that allows physicians to make a picture of the brain and have a pattern that allows them to specifically determine the disease type and then treat the patient appropriately. Better yet, we’d like physicians to be able to say, ‘No, you don’t have the disease’ and then look for other causes.”

The forces that are moving medicine toward molecular diagnoses and treatments will undoubtedly include SPECT. “The SPECT world is changing,” says Jody Garrard, product manager for gamma cameras at Philips Medical Systems. “We’re no longer just taking pictures; we’re trying to provide the doctors with more information than just whether it’s positive or negative for, let’s say, cancer. We want to give quantification; we want to give quantifiable data that can calculate how much radiation delivery could kill this tumor.” Garrard cites the SkyLight as a product that addresses these informational needs.

The relationship between gamma camera companies and pharmaceutical companies is also likely to change, with greater incentives to work cooperatively and in tandem. The creation of GE Healthcare from GE Medical Systems and Amersham Health, for instance, just might herald a new paradigm for the future.

A good example of that collaboration among drug and camera companies is with Philips. The company is looking to use the ability of a gamma camera to separate agents with different energy windows and then characterize tumors with “essentially a battery of tracer tests,” Garrard says. SPECT can image at a range of different energies, which allows separation of different tracers. Injecting the patient with a combination of tracers, each at a different energy and each tagged to a different array of pharmaceuticals, provides information that will give the physician better data in order to tailor the treatment.

“We’re going to be a lot more creative in the way that we apply these energy windows, in order to get the most information possible,” Garrard says. She also adds that Philips is focusing on an acquisition protocol that optimizes image quality and concurrently provides accurate quantitative results. By using multiple isotopes, the patient is able to undergo just one procedure while the physician obtains optimal image and quantitative information.

Loyola University’s Henkin believes that SPECT has a lot of potential. “The biggest advances could stand to be in SPECT because the pharmaceuticals for SPECT are easier to make and easier to label, and a lot of researchers are [exploring with this modality].”

In fact, Henkin believes that during the next 5 years, much more will be happening in SPECT than has occurred to date. Citing a new class of drugs in clinical trials now that will measure cell death, he notes that the organs or tumors will be imaged using SPECT. These will be a very powerful class of drugs that, he believes, will change how medicine looks at tumors and cardiac disease.

Perhaps this new century, with molecular medicine close on the horizon, portends a new and significant role for nuclear medicine. And maybe SPECT will be an important part of that future. It certainly looks promising.

Ellen Zagorin is a contributing writer for Medical Imaging.

PET and SPECT Shopping

by Laura Gater and Ellen Zagorin

Is your facility thinking of adding PET and/or SPECT to its repertoire of services? Use this product roundup as a guide for some of what’s currently available.

AutoQUANT Plus from Philips Medical Systems—AutoQUANT Plus is a comprehensive review and quantification solution for nuclear cardiology. It facilitates the most efficient workflow for study interpretation with exclusive integration of perfusion (Quantitative Perfusion SPECT), function (Quantitative Gated SPECT), and reporting (Automatic Report Generation). Seventeen-segment scoring is now available.

AVIA Workstation from Hitachi Medical Systems America—The AVIA workstation is designed for processing and viewing DICOM data from any diagnostic imaging modality. It allows centralized diagnostic interpretation of discrete and/or fused images in display formats that are selected or customized by the user. And a comprehensive library of visualization and quantitative analysis tools has been seamlessly integrated with the revolutionary Fusion7D software. Integrated Fusion7D software provides speed, flexibility, and accuracy for improving lesion localization and diagnostic interpretation. The workstation includes an extensive tool kit of both modality- and application-specific algorithms designed to improve the accuracy of electronic fusion.

Biograph family of PET/CT systems from Siemens Medical Solutions—The new Biograph PET/CT family incorporates a range of performance options to enhance image quality, resolution, and throughput as well as new information technology (IT) solutions for multimodality integration. Key new features include a high-resolution PET option, image-quality enhancement, a 6-slice CT biograph companion to existing 2- and 16-slice configurations, and further integration into the Siemens Leonardo postprocessing IT workplace. The biograph PET/CT family’s technological advancements are built upon its ultrafast LSO crystal technology, which delivers exceptional images in the shortest scanning time possible today—less than 15 minutes. The new Pico 3-D option provides ultrafast detector electronics that improve image quality with up to 70% better count-rate performance. LSO-based Biograph systems are now available with new Hi-Rez technology, which is supported by a new LSO crystal, thus, it can provide greater than 250% improvement in volumetric image resolution.

The Cardiac Gamma Camera from Siemens Medical Solutions—The is a reclining, dedicated cardiac gamma camera that enhances imaging accuracy and efficiency while delivering a small footprint and improved patient comfort. The’s myocardial viability and perfusion capabilities offers cardiologists increased diagnostic confidence, and the system’s fully integrated software allows analysis of ejection fraction and wall motion. Its reclining chair allows patients to sit back comfortably throughout the imaging procedure, decreasing movement.

CardioMD from Philips Medical Systems—CardioMD is a fixed 90? nuclear cardiology gamma camera specifically designed to meet the specialized requirements of an office-based practice. CardioMD provides high image quality and throughput as well as a small footprint. It offers complete cardiac imaging capabilities and provides an ideal combination of easy-to-use features that both enhance departmental workflow and allow for simple patient setup. With the optimized dual-head system design, CardioMD offers efficiency in nuclear cardiology scans. Prescheduling and multitasking functions provide technologists with additional flexibility and freedom.

Discovery ST PET/CT from GE Healthcare—Discovery ST is the only PET/CT system that combines a PET scanner with a 4- and 8-slice CT scanner. The system is capable of 2-D, 3-D, and 4-D imaging; a large 77-cm gantry opening accommodates larger patients and offers mobile customers a more flexible system. Discovery PET/CT with HeartFusion allows physicians to noninvasively evaluate fused coronary anatomy and myocardial perfusion information for a more comprehensive assessment of coronary artery disease.

Discovery ST PET/CT, second generation from GE Healthcare—The Discovery ST second-generation design provides 2-D and 4-D imaging modes with a 70-cm-wide patient bore as well as the highest sensitivity in 3-D mode. The 2-D mode with septa is valued by clinicians for whole-body imaging because it reduces scatter, which improves quantification. Of course, 2-D imaging is important for quantitative myocardial perfusion imaging.

The Signature Series from Siemens Medical Solutions—The Signature Series offers a host of technological advancements, including the system’s high-definition dynamic digital detectors (HD4) that deliver high image quality and reliability. These gamma cameras’ Flash 3D technology features 3-D collimator beam modeling and iterative reconstruction that improves image quality, contrast resolution, and lesion detection. The optional is an integrated audio/visual feature that can be used to improve patient comfort during an imaging session or for patient information and education.

Gemini PET/CT Scanner from Philips Medical Sysytems—Gemini is the world’s first and only open PET/CT scanner, now available with Brilliance CT 16-slice power configuration for customers requiring higher performance and a broader range of clinical applications. The PET and CT components can be used as stand-alone devices when dual-modality scans are not necessary for individual patients.

Infinia Hawkeye from GE Healthcare—A combined nuclear medicine/CT system, the Infinia Hawkeye delivers high image quality and diagnostic confidence to physicians with a proven impact on patient management.

JETStream Workspace from Philips Medical Systems—JETStream Workspace is the next-generation nuclear cardiology module. It encompasses all of the imaging elements of a nuclear cardiology laboratory into one environment. JETStream makes it possible for display, processing, review, reporting, and image archiving to exist in one environment at a single location or distributed throughout the department in multiple locations.

PEM Flex from Naviscan PET Systems Inc—This new PET device achieves spatial resolution that is unprecedented for a clinical device. The scanner’s advanced crystal components and compact design make it ideal for imaging small body parts, such as breasts, hands, heads, or feet. The PEM Flex can operate in a stand-alone configuration or correlate with digital X-ray images from other imaging modalities.

Sceptre from Hitachi Medical Systems America—The Sceptre PET imaging system combines the latest in LSO detector technology with a unique gantry architecture. High-speed LSO block detectors enable isotropic 3-D image acquisition while reducing randoms by 50%. Sceptre also uses the most advanced scatter correction, randoms correction, and iterative reconstruction algorithms to achieve image quality found in the highest end PET systems. It employs a CT-type spiral gantry design to provide an unexcelled combination of clinical performance, operational efficiency, and economics.

SkyLight Nuclear Imaging Platform from Philips Medical Systems—SkyLight is the industry’s first and only gantry-free nuclear camera. The system’s architecture allows gamma detectors to be mounted directly into a room’s structure, creating a gantry-free or “open-floor” design. By removing limitations associated with conventional floor-mounted systems, the SkyLight can image any size patient, on any bed, in any position. The platform also allows medical professionals to image two different patients simultaneously, offering unparalleled efficiency gains for busy imaging departments.

Laura Gater and Ellen Zagorin are contributing writers for Medical Imaging.