Getting the Full Picture

A 58-year-old patient with a history of Rt tubular cancer and no lymphatic involvement underwent: A. a mammography, which declared the breast benign; B. a scintimammography scan, which also found the breast benign; and, finally, C. a scan with the LumaGem from Gamma Medica-Ideas, employing new CZT technology, which found a positive small lesion in the left breast (the bright mass in the upper portion of the breast).

The gamma camera has been around since the 1950s, says Samir Chowdhury, PhD, VP of clinical imaging for Gamma Medica-Ideas Inc (Northridge, Calif, and Oslo, Norway). But as nuclear medicine transforms into molecular imaging, the gamma camera’s role in medicine is expected to expand. Advanced technologies are improving this tool’s performance, while the promise of new radiopharmaceuticals and hybrid systems is expected to expand its application. Within the next decade, nuclear medicine will begin a new stage in which its clinical impact will be profound. Here, three experts discuss the nuts and bolts of this instrument and how it is evolving.

The Basics

Traditionally, medical-imaging tools?such as X-ray, CT, MRI, and ultrasound?have helped healthcare providers to image anatomy. Tools in nuclear medicine and molecular imaging help to visualize function, capturing metabolic processes within the body that provide clues to disease states.

Patients typically are administered a small radioactive isotope that is tagged to a biomarker or molecule associated with a specific body process. Examples include technetium 99, ammonia N 13, fluorodeoxyglucose F 18, and sodium chromate Cr 51. The substance, which accumulates within the structure being studied, emits gamma rays that are captured by the gamma camera to image actual function.

The gamma camera typically features:

1. The collimator, traditionally lead or tungsten, which absorbs gamma rays; holes throughout the material allow photons moving in a particular direction to pass.
2. The detection crystal, often made from thallium-activated sodium iodide; it absorbs the gamma photons that have passed through the collimator and converts them to light.
3. Photomultiplier tubes (PMT), which amplify the light and create electrical pulses.
4. The computer, which uses the data to create an image of activity within the patient.

So, for example, cancerous tumors appear brighter because they have a higher metabolic activity, Chowdhury explains.

The Advances

A woman undergoes a gamma camera scan on her breast via the LumaGem from Gamma Medica-Ideas.

With all of its plus points, the gamma camera does have its limitations, some related to its construction. The collimator, for instance, is partly responsible for poor resolution and the length of time required for the acquisition of images, considered by today’s standards to be “long.” Says Chowdhury, “CT is very quick, while nuclear medicine is much slower?it can take 20 to 30 minutes for an acquisition.”

Newer materials and geometric configurations, however, are improving this parameter. New detector materials also offer improvement; one new material under investigation is cadmium zinc telluride (CZT). According to Chowdhury, CZT directly converts gamma photons into electrical energy. Solid-state detectors (direct conversion) can allow for higher-resolution systems, which produce better image quality.

Advances in PMTs and computer algorithms have resulted in even greater improvements, significantly reducing time or improving resolution. New software offerings re-interpret the information on both new and existing systems to produce clearer images or faster acquisition. For example, the new Xpress.cardiac and Xpress.bone from UltraSPECT Inc (Brookfield, Wis) cut scan time by two using wide-beam reconstruction (WBR), a resolution recovery technology.

“On the application side, we are making it easier to manipulate the process and visualize the exam results,” says Michael Reitermann, president of the molecular imaging division at Siemens Medical Solutions (Malvern, Pa). This makes it easier for the physician to perform his diagnostic work, he adds.

Application-specific systems also bring improvements. “It’s easy to design a gamma camera for a specific application,” says Karthik Kuppusamy, general manager of molecular imaging for GE Healthcare (Waukesha, Wis), offering as an example the company’s new Ventri, designed for private-practice cardiac offices. “The system fits in a nine-by-twelve-foot room and offers greater patient and user comfort. Because 30 to 40 percent of studies are repeat patients, comfort is fundamentally important.” Greater patient comfort means less movement and a better image.

Improved throughput is another benefit of application-specific systems. “One of the advantages to the development of application-specific systems is that they can be dedicated for use in patients who require that particular scan. Instead of using the large multipurpose scanner for everyone, even a simple wrist scan, you can use the smaller system and lighten the load of the larger one, increasing efficiency,” says Chowdhury, who expects dedicated systems to become more popular for that reason. Current application-specific systems focus on cardiac, neurology, bone, and breast imaging.

The Hybrids

The compact LumaGem 3200S from Gamma Medica-Ideas attaches to upright mammography systems and uses CZT technology to perform molecular imaging of breast lesions.

Even greater benefit can be gained by combining molecular imaging with another modality that images anatomy, such as CT or MRI, to better enable localization. “Nuclear medicine images do not visualize anatomy, so it requires a lot of knowledge and experience to read them. But if you can combine it with an anatomical image, you can read it much better because you know what you’re looking at and where it is in the body,” Chowdhury says.

Prior to hybrids, the images were fused with software; in many instances, this is still the case. However, because the images are taken at different times and the patient might be in a different position, registering the two can be a challenge?hence, the development of machines that acquire the images sequentially, as in PET/CT, or simultaneously, as in some newer SPECT/CT systems.

For example, Siemens Medical’s Symbia TruePoint SPECT/CT and Biograph PET/CT hybrid imaging families seamlessly co-register the patients’ functional and anatomical data in just one exam and have been influential in more accurate disease localization and treatment planning.

Reitermann says that the trend has gained momentum over the past 18 months. MRI/PET hybrids are still in development, but adoption of PET/CT and SPECT/CT hybrids in the marketplace is increasing. Mobile units increase their use even more.

Traditionally, molecular imaging has been the drag on these exams, taking much longer to complete less-detailed images than the newest CT machines. Even 16-slice CT provides submillimeter resolution in a short time frame. But with the advances that speed acquisition and improve image quality, these disadvantages begin to disappear.

The Guidelines

It’s important for users to pay attention to all of these factors when purchasing a gamma camera. What is the hardware? The software? What type of resolution can be achieved, and in what time? How long does it take to reconstruct the images? What is the system’s usability, encompassing such aspects as ease of use and patient positioning?

And then, of course, there are the usual questions: Is the vendor reputable? What is the typical downtime? What does the service contract cover? Does it include new offerings, such as remote monitoring? What is the cost of ownership?

The questions are banal, but the answers can be revolutionary. “Nuclear medicine is going through a revolution,” Chowdhury says. “Advances in camera technology are being implemented now, and the advances in pharmaceuticals will be apparent in clinics in 10 years.”

Renee DiIulio is a contributing writer for Medical Imaging.