PET-MRI hybrid imaging scanner - an emerging new tool for molecular neuroimaging

Summary form only given. Increased interest in molecular imaging encouraged us to develop high resolution-high sensitivity PET (Positron Emission Tomograph) scanners as well as high field MRI (Magnetic Resonance Imaging), especially in the area of brain imaging. In the field of neuroimaging, both high molecular specificity and high spatial resolution are the essential requirements to meet the brain´s delicate structures and neurochemical activities. In spite of these high molecular specificity and spatial resolution requirements of neuroimaging, actual molecular imaging have been limited in resolution due to several factors, such as the physical limitations involved in PET scanner design, i.e., spatial and temporal resolution and poor sensitivity of currently available low or intermediate field MRI. In the area of MRI, high spatial and temporal resolution have been the limited, especially for the low and intermediate high field MRI systems. More recent developments in this area are the emergence of the ultra high field (UHF) MRI such as 7.0 T. Unique features of these ultra high field MRI are the improved sensitivity which enable us to improve either temporal resolution or spatial resolution. For example, with 7.0 T MRI, one can improve spatial resolution as high as 200 □m or better so that neuroscientists can examine even the cortical laminae in the human brain in-vivo. In the field of PET development, recent developments include the brain dedicated high resolution PET scanner such as the HRRT (High Resolution Research Tomograph). This brain dedicated PET (HRRT) scanner is designed to meet the resolution requirement of human brain imaging with molecular specificity, that is as good as 2.5 mm fwhm. First time in history, together with the appearance of these new developments, i.e., UHF-MRI and HRRT-PET scanners, neuroscientists began to search for a brain dedicated high resolution-high sensitivity imaging scanner that can be used for the simultaneous imaging of both the morphological and molecular or neurochemical activities with substantially increased temporal and spatial resolution than what is available today, that is the molecular neuro-images of spatial resolution as high as 200 □m, the resolution that can be obtained only with th- e ultra high resolution MRI. This new hybrid PET-MRI scanner with HRRT-PET and UHF-MRI will provide us a fused PET-MRI image, the molecular specific high resolution image, that is a truly integrated image, both in space and time. Physical design concepts and potentials of this hybrid PET-MRI scanner in neuroscience applications will be discussed and some of the preliminary results will be presented.