Molecular imaging enjoys progress on multiple fronts

From a pivotal study that may broaden Medicare's acceptance of FDG-PET to Raman spectroscopic techniques that promise a 1000-fold improvement in sensitivity compared with fluorescence imaging, the first half of 2008 will be remembered for fruitful molecular imaging research.

As of June 1, the Centers for Medicare and Medicaid Services was weighing the evidence from an application to grant routine Medicare coverage for FDG-PET to diagnose, stage, restage, and evaluate patients for suspected recurrence of brain, cervical, ovarian, pancreatic, small cell lung, and testicular cancers. Approval could mean the procedures would no longer be subject to monitoring through the National Oncologic PET Registry, a research effort deemed necessary in 2005 to study their impact on patient management.

The registry's first-year results were published online in the Journal of Clinical Oncology on March 24, a day before the Medicare application was filed. The results note that FDG-PET findings led referring physicians to change treatment strategy in 36.5% of cases. CMS has until October to announce whether the results are strong enough for a positive ruling.

Progress continued simultaneously on a broad front with the development of new MI applications. In March, Stanford scientists, led by Dr. Sam Gambhir, described their early work with Raman spectroscopy, a new technique that opens the door to real-time noninvasive observation of subcellular events, such as the migration of labeled peptides.

Dr. Mukesh G. Harisinghani, a senior researcher at the Center for Molecular Imaging Research at Massachusetts General Hospital, demonstrated in nine patients with renal masses that MRI enhanced with lymphotropic iron oxide nanoparticles (ferumoxtran-10) reliably identifies malignant spread to lymph nodes. The pilot study, presented at the 2008 International Society for Magnetic Resonance in Medicine meeting, found the technique was 100% sensitive and 95.7% specific for identifying malignant nodal involvement.

Also at the ISMRM conference, Jeff W.M. Bulte, Ph.D., director of MR research at Johns Hopkins University, introduced magnetic particle imaging, an iron oxide-enhanced technique involving an oscillating magnetic field that promises to add new capabilities to the use of MR for cell tracking. Still in the ex vivo stage of development, magnetic particle imaging may someday reduce the number of labeled cells needed for detection with MRI. It may also enable the quantification of labeled cells, a task that until now has been difficult to perform with MRI, he said.

"The probe behaves like a radiotracer," Bulte said. "The signal only originates where the particles are located. There is no anatomical background signal."