Molecular Imaging Promises to Transform Medical Practice

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Highly targeted radiopharmaceuticals in development coupled with advances in PET/CT and SPECT/CT look to bring more personalized diagnosis and treatment.

Molecular imaging has entered a dramatic paradigm-shifting phase of development that many experts agree will revolutionize the way that healthcare is delivered.

While current imaging techniques are being refined with enhancements to equipment such as hybrid PET/CT scanners and the introduction of SPECT/CT this year, the basic science and pre-clinical activities in molecular imaging centers is guiding the direction that healthcare will assume during the next decade.

CURRENT STATE OF MOLECULAR IMAGING

By current definition, molecular imaging involves intravenous injection of a radiopharmaceutical that emits a tracer captured by either a gamma camera (single photon emission computed tomography) or positron emission tomography (PET) system.  The contrast agent FDG (fluorodeoxyglucose) has been used with PET for many years, and although it reveals glucose uptake and has proven useful in the diagnosis of cancer, it is not as capable of targeting specific lesions as some of the newer radiopharmaceuticals under development. SPECT uses radiotracers that are less costly to produce and because gamma cameras are not as expensive as PET units, the overall expenses associated with SPECT imaging has added to its appeal.

Carl Hoh, MD, associate professor of radiology at the University of California at San Diego, explains that PET has proven to be a valuable clinical tool for the past seven to eight years, but that the field is moving into developing radiopharmaceuticals that are more specific in their targeting abilities. He suggests that these agents are several years away from widespread use, because it will take that long for full assessment of safety and clinical utility.

Although nuclear medicine scans have produced remarkable images of metabolic activity, the primary drawback of their utility has always been the lack of anatomic data to pinpoint location of the identified lesion. In response to that challenge, Siemens Medical Solutions, GE Healthcare and Philips Medical Systems developed hybrid PET/CT systems and other OEMs have developed software fusion packages to co-register CT and PET as well as facilitate co-registration of images from a variety of modalities.

At the June meeting of the Society of Nuclear Medicine, Philips debuted the Precedence SPECT/CT hybrid scanner that features a diagnostic-quality CT component.  At that same meeting, Siemens introduced TruePoint SPECT-CT technology on the Symbia product family that incorporates the e.cam SPECT imaging technology with a diagnostic multislice CT capability as well. While these units provide attenuation correction as well as pinpoint accurate anatomic data coupled with current radiopharmaceuticals, their true significance may be revealed as new specific targeting molecular agents are developed.

Some confusion has arisen as the definition of molecular imaging has evolved. Some people use the term molecular imaging simply as a description of imaging molecules. Any contrast agent is actually comprised of thousands (if not millions) of small molecules, and nuclear medicine scans image its affinity for certain processes in the body, such as increased metabolic rate observed in FDG-PET scans. But today's definition involves development of a targeted molecule that is designed to reach a specific lesion, bind and interact with cells and permit imaging that reveals the reaction.

Alexander Tokman, the general manager of global molecular imaging and radiopharmacy for GE Healthcare, describes the evolving medical paradigm as moving from a "see and treat" focus where symptoms of a disease are diagnosed, and treatment applied, to a "predict and prevent" mode where the molecular basis of human development is assessed to determine risks of diseases to facilitate earlier intervention before a person becomes symptomatic.

"Molecular imaging is focused on the techniques and technologies of interrogating molecular and cellular events in the context of the whole body," says David Piwnica-Worms, MD, PhD, president of the Society for Molecular Imaging and professor of radiology, molecular biology and pharmacology at Washington University in St. Louis, where he also serves as director of their molecular imaging center. "It's a scientific discipline that embraces everything from biochemistry to cell assays and cell cultures as steps to imaging