The success of other hybrid imaging techniques has helped MR/PET gain ground, particularly for neurodegenerative diseases. Research and system advances could put the combined modality on the map within the next several years.
In brain imaging, the big advantage of MR compared with PET is that it provides excellent contrast between white and grey matter, says Ralf Buchert, PhD, Department of Nuclear Medicine, University Hospital Hamburg-Eppendorf, Hamburg, Germany. Buchert has been working with Philips Healthcare to develop systems and software for MR/PET applications in neurodegenerative disease.
Since neurodegenerative diseases are associated with a loss of grey matter tissue, the distinction is important. While CT is useful for excluding problems such as brain tumors, MR is best for conditions such as Alzheimer’s.
The combination of the sensitivity and specificity of both PET and MR might improve the accuracy of diagnosis, Buchert says. It is almost impossible to detect the loss of grey matter tissue in the early stages of neurodegenerative disease through visual analysis, he says. The use of sophisticated CAD software is needed to detect the changes that indicate disease and let clinicians start treatment as early as possible.
Alzheimer’s disease typically starts 5 to 10 years before the first clinical symptoms occur—a long time period that should be tapped for optimal treatment, Buchert says. “If the treatment starts sufficiently early, the loss of brain tissue might be stopped. You might delay dementia or even avoid dementia.” With new Alzheimer’s treatments on the horizon, early detection is more important than ever.
Research and evaluation
Siemens Medical Solutions has developed BrainPET, with research units developed for the Magnetom Trio with Tim-enabling to benefit from 3T field strength advantages and allowing uncompromised MR functionality at the same time. The company sees the benefits of MR/PET’s exceptional soft-tissue contrast and high specificity of MR together with PET’s excellent sensitivity in assessing physiological and metabolic state.
Researchers currently are working on evaluating the system, to develop advanced applications and learn about the clinical applications demand of MR/PET. “MR/PET presents a tremendous leap forward in imaging capabilities. It has the potential to become the imaging modality of choice for neurological studies, certain forms of cancer and stroke,” according to a company statement.
Buchert says the big imaging vendors are working on developing hybrid MR/PET systems. First will come a system for brain imaging and then for whole-body imaging, he says. There are oncological indications but the benefits compared with PET/CT, for example, have yet to be fully evaluated. “I think there are some special applications for this hybrid system, but I don’t think it will completely replace PET/CT.”
Buchert has been conducting retrospective research on patient data. Among cases originally diagnosed as normal with no evidence of neurodegenerative disease through visual analysis, the prototype CAD system indicates that, in fact, often there is disease at a very early stage. Patient follow-up has shown that the CAD system was correct. This still requires a prospective trial which Buchert says is in the works.
Siemens anticipates MR/PET to help clinicians gain a better understanding of the pathologies and progression of various neurological disorders. Plus, it offers “tremendous promise for emerging therapeutic research.” Because it allows for the simultaneous measurement of anatomy, functionality and biochemistry of the body’s tissues and cells, researchers can correlate MR and PET data in a way not previously possible. This correlative approach will enable a deeper understanding of, for example, stem cell migration to damaged parts of the brain, determination over a prolonged period whether cells are still alive and identification of how stem cells have been integrated into the body’s neurological network.