World's first PET/MR images of the human brain

The world's first PET/MR images of the human brain, taken simultaneously by positron emission tomography (PET) imaging and magnetic resonance (MR), debuted during the 54th Annual Meeting of SNM.

"Here at SNM's Annual Meeting, we are showing the first simultaneously acquired PET/MR images of the human brain," noted Bernd J. Pichler, associate professor and head of the Laboratory for Preclinical Imaging and Imaging Technology in the Department of Radiology at the University of Tuebingen in Germany. "PET/MR, acquired in one measurement, presents a tremendous leap forward in imaging capabilities. PET/MR, acquired in one measurement, has the potential to become the imaging modality of choice for neurological studies, certain forms of cancer, stroke and the emerging study of stem cell therapy," he added. "We expect that PET/MR will open new doors in understanding the pathologies and progression of various neurological disorders like Alzheimer's, Parkinson's, epilepsy, depression and schizophrenia," he emphasized.

"The feasibility of simultaneous PET/MR imaging in humans opens new potentials in the emerging field of molecular imaging. Our data prove that the PET/MR scanner allows even multifunctional imaging with PET, functional MRI (fMRI) and spectroscopy," said Pichler, indicating this exciting work was made possible by a collaborative effort of researchers from the universities of Tennessee and Tuebingen (in Germany) and Siemens Medical Solutions. "PET/MR is an imaging technique that brings the exceptional soft tissue contrast and high specificity of MR together with PET's excellent sensitivity in assessing physiological and metabolic state," he added.

Combined or hybrid technologies'such as PET/CT and SPECT/CT, incorporate both imaging modalities into one machine but conduct the two scans sequentially (one after the other), explained Pichler. "This PET/MR machine, developed by Siemens and which debuted last year, acquires MR and PET scans at the same time, for the same imaging volume and, therefore, produces a higher degree of registration," he said. "The PET/MR system allows simultaneous measurement of anatomy, functionality and biochemistry of the body's tissues and cells, enabling researchers to correlate MR and PET data in a way not previously possible before," Pichler noted. "Neither the MR nor the PET imaging performance was degraded by synchronous data acquisition. The PET/MR data of the human brain revealed image qualities comparable to stand-alone systems without any significant distortions," he said.

Pichler explained some of the future possibilities with this PET/MR system. PET currently can differentiate mild cognitive impairment from early-stage Alzheimer's, but it cannot determine reduced brain volume caused by atrophy. "By combining MR and PET, clinicians may be able to make a more sound determination of both cognitive impairment and atrophy. Furthermore, combining PET/MR and new emerging neurological biomarkers has great potential to strengthen the assessment of the condition," said Pichler. Similarly, in stroke patients, the technology holds the promise of allowing doctors to study which brain tissues might be salvageable after a stroke.

PET imaging uses very small amounts of radioactive materials that are targeted to specific organs, bones or tissues. Radiotracers (such as FDG) are injected and then detected by a special type of camera that works with computers to provide precise pictures of the area of the body being imaged and molecular images of the body's biological functions. MRI uses radio waves and a strong magnetic field to provide clear and detailed pictures of internal organs and tissues. Functional MRI (fMRI) is a procedure that uses MR imaging to measure the quick, tiny metabolic changes that take place in an active part of the brain. Spectroscopy is a procedure that examines the biochemical constituents of a body part.

Siemens' PET/MR is a non-commercially available prototype dedicated brain PET scanner that is inserted into a commercial 3T MRI scanner. The prototype dedicated brain PET scanner uses a next-generation Avalanche Photodiode Detector technology. APD technology renders the PET scanner impervious to magnetic fields while providing excellent PET results.