Report from SNM: Wagner identifies new direction for nuclear medicine

June 12, 2006

Nuclear medicine’s growing importance to medical practice and research permeated Dr. Henry Wagner’s 29th annual meeting highlights lecture last Wednesday at the 2006 Society of Nuclear Medicine meeting.

Nuclear medicine's growing importance to medical practice and research permeated Dr. Henry Wagner's 29th annual meeting highlights lecture last Wednesday at the 2006 Society of Nuclear Medicine meeting.

Wagner, a professor of nuclear medicine at the Johns Hopkins School of Public Health, cited the 1500 oral and poster presentations presented in San Diego as evidence of molecular imaging's growing association with therapy and its influence on medicine.

"We are promoting a knowledge-based healthcare system," he said. "We cannot just consider the economic costs of space, labor, and capital investment. We must now consider the economic value of knowledge, which is what we provide."

Nuclear medicine can help the cut waste associated with the unnecessary hospitalization each year of 300,000 U.S. residents whose chest pain falsely suggests the presence of myocardial infarction. This problem inspired Wagner's selection of the image of the year: a fusion SPECT/CT cardiac volume rendering demonstrating the location of coronary artery stenosis with great sensitivity on multidetector CT and the extent and severity of myocardial ischemia shown with great specificity on perfusion SPECT.

Molecular imaging and therapy will help usher in an era of personalized medicine. In the audio excerpt, Wagner describes how molecular medicine supplies physicians with a new way to view biomolecular processes responsible for life and disease.

Molecular dysfunction is becoming the basis for diagnosis and treatment, according to Wagner. Patients are less often consigned to diagnostic boxes such as schizophrenia, depression, or arthritis.

This philosophy can be seen in the novel application of fluorine-18 fluoro-L-DOPA, a PET agent used mainly to study Parkinson's disease. It was shown to help differentiate between focal and diffusion hyperinsulinism, a genetic condition affecting the potassium channels in beta cells of the pancreas, potentially causing brain damage. Nearly complete pancreatomy is often required for diffuse disease, but principal investigator Dr. Maria-Joao Santiago-Ribeiro of the Service Hospitalier Frederic Joliot in Orsay, France, found focal uptake patterns among 14 of 40 children. The diagnosis qualified them for less invasive surgery.

Progress was reported toward a screening test for early diagnosis of Alzheimer's disease. Dr. Victor L. Villemagne of the University of Melbourne in Australia confirmed that carbon-11 Pittsburgh Compound B can measure the neocortical accumulation of beta-amyloid in the brains of Alzheimer's patients. Differing uptake patterns distinguished Alzheimer's patients from patients with frontotemporal dementia. Higher uptake rates appeared in subjects with mild cognitive impairment than in normal controls.

Dr. Kai Kendziorra of the University of Leipzig in Germany demonstrated the relevance of nicotinic acetylcholine receptors in dementia. The scarcity of nAChRs in the cortical regions of patients with Alzheimer's disease and vascular dementia may cause the deficient cholinergic neurotransmission underlying the loss of cognitive functions associated with both diseases. Vascular dementia patients appear to have lost these receptors in their periventricular white matter, although nAChRs remain normally abundant in Alzheimer's patients. The distinction may aid diagnosis of the two conditions.

Pulmonary ventilation also remains alive and well despite the popularity of MDCT perfusion for diagnosing pulmonary emboli, Wagner said. Dr. Ben Harris of Royal North Shore Hospital in Sydney, Australia, demonstrated how readings of fusion SPECT/V/Q scintigraphy scans reclassified three of 30 patients diagnosed with perfusion CT alone from being at intermediate risk of PE to unlikely risk.

Fusion PET/CT and SPECT/CT are the big trends in nuclear cardiology. Wagner was impressed by the 58% growth in the number of SPECT/CT abstracts presented at the SNM this year. He attributed that growth to Dr. Martin P. Sandler, incoming SNM president and radiology director at Vanderbilt University. Sandler's work with cardiac fusion SPECT/CT stirred interest in applying the technology to myocardial infarction. A study presented in San Diego by Dr. Ora Israel and colleagues at the Rambam Health Campus in Haifa, Israel, for example, found a good marriage between high-sensitivity CT angiography and high-specificity SPECT for the condition.

More prospective multicenter trials involving hundreds of patients were presented in San Diego than at any SNM conference in recent memory. Dr. Hans C. Steinert and colleagues at the University Hospital Zurich in Switzerland described their experience with FDG-PET/CT for staging 205 consecutive melanoma patients. On a per-patient basis, the combination of PET/CT with dedicated CT interpretation was 98% sensitive and 94% specific for detecting distant metastases.

Predicting patient prognosis with hybrid PET and SPECT was also considered in numerous studies. Dr. Wei Chen of the University of California, Los Angeles used F-18 FLT and F-18 FDOPA to predict the response of malignant brain tumor to bevacizumab and radiotherapy. In another trial, FDG-PET was more sensitive than MRI by 10 percentage points (80% versus 70%), and PET's negative predictive value was 20 percentage points higher (83% versus 63%) for detecting recurrent high-grade gliomas.

Abstracts presented at the 2006 SNM meeting reflect nuclear medicine's growing influence on drug research. SPECT is beginning to replace autoradiography in preclinical drug trials, Wagner said. Dedicated small-animal imaging systems have now been applied to PET, SPECT, and CT, including dedicated fusion SPECT/CT, PET/CT, and MR/CT scanners. Wagner showed an exquisite 1-mm-resolution skeletal image of a mouse injected with 1 mCi of technetium-99m MDP performed on a dedicated microSPECT camera. Another paper example presented by Duke University's Dr. Bennett Chin demonstrated the ability to image a left ventricular aneurysm in a mouse brain.

Nuclear medicine's advocates could possibly exploit its use in pharmaceutical research to break through the regulatory logjam that has limited the clinical introduction of new radiopharmaceuticals, according to Wagner.

"Big Pharma likes therapeutic drugs that are administered over long periods of time. They hesitate to invest in diagnostic tracers used only once or twice. If you can combine the two, it may result in safer, more effective, and cheaper pharmaceuticals and radiopharmaceuticals," he said.

The general public should be made aware of growing evidence showing that PET/CT and SPECT/CT improve diagnosis and treatment, Wagner said.

"It is time to educate the public about how we prevent, diagnose, and treat disease and assess the effectiveness of treatment. We need to interact with other specialists more than ever before and to develop and assess our competence," he said.