The 7.0T MRI and HRRT-PET fusion system amalgamates molecular and genetic information (PET) into ultra-high resolution anatomical images (MRI) of the in vivo human brain. With this high-end fusion system, we will venture into the unknown territory of the human brain with unprecedented chemical specificity and spatial resolution!
• World's First HRRT-7.0T MRI Fusion System for Molecular Imaging
Fig. 1. Diagram and photograph of the newly installed HRRT-PET and 7.0T MRI fusion system – truly the first PET-MRI fusion system in the world (2005)
The successful combination of a molecular image and a high resolution anatomical image has long been the dream of neuroscientists. Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) are the two most widely used imaging tools in both the clinical arena and neuroscience research. These images provide clues for brain diseases and the mysteries of the mind, but aspects of their physical performance, such as spatial resolution and signal-to-noise ratio (SNR), are still far from the exacting demands of neuroscientists. Currently, the state-of-the-art PET and MRI are the High Resolution Research Tomograph (HRRT)-PET and the 7.0T-MRI, respectively. The HRRT can measure not only the traditionally used glucose metabolism but also ligand-receptor interactions with a resolution down to 2.5 mm full width at half maximum (FWHM), compared with the typical 5–6 mm FWHM available with existing scanners. The 7.0T MRI can also visualize various structures of the human brain in vivo with a resolution as fine as 0.2 mm FWHM. In spite of this remarkable progress, molecular imaging alone is still unable to visualize the desired localization of activity in the brain. On the other front, MRI has yet been able to provide molecular and chemical signatures of the human brain. The desire to combine the two modalities, PET and MRI, has been accute. The combination of HRRT-PET and 7.0T-MRI appears to promise the state-of-the-art PET-MRI fusion system with desired spatial resolution and chemical specificity.
• First PET-MRI fusion imaging - Metabolic activities in the hippocampus
Fig. 2. Experimentally obtained PET-MRI image of a human subject showing the details of the hippocampus and localized metabolic activity – this the first of its kind submillimeter details of the hippocampus and local metabolic activity is achieved with NRI's PET-MRI fusion system.
A human subject was scanned in the calibrated PET-MRI hybrid system. Uptake of fluorodeoxyglucose (FDG) was measured using the HRRT-PET and the 7.0T MRI image was acquired, and then the two images were fused. In this experiment, the subject was moved to the HRRT-PET scanner via the shuttle system after the MRI exam, and PET imaging followed. As pictured, in Fig.2 the scanned FDG PET image shows spatially matched metabolic functions to the various gray matters in the hippocampal image, such as the CA4, subiculum, and parahippocampus, among others.
• Advanced PET-MRI Fusion Algorithm
Fig. 3. PET-MRI fusion algorithm used for the PET-MRI system at the Neuroscience Research Institute.
The PET system can be assumed to be a spatially invariant system and system blurring is defined as a point spread function (PSF). Once the exact PSF of the system is estimated, it can be used for the image deblurring operation, also known as deconvolution. The PET image deblurring operation is performed using a number of parameters that are extractable from neurochemical and molecular information, as well as image resolution information obtainable from MRI. For example, we can assume that the glucose utilization of the cell takes place in the gray matter area rather than in the white matter area or in the CSF. Therefore, in the PET-MRI, the segmented gray matter is used as the basis of image fusion, from which one can confine blurred molecular image data of PET only onto the gray matter (boundary) of the MRI by a process termed “confinement.” In other words, the segmented gray matter image from the MRI is projected onto the PET image of the same geometrically assigned location and is then “confined” to the molecular image data from the well-defined morphological data of the MRI.
- Zang-Hee Cho, Young-Don Son, Hang-Keun Kim, Kyoung-Nam Kim, Se-Hong Oh, Jae-Yong Han, In-Ki Hong, Young-Bo Kim. A hybrid PET-MRI: An integrated molecular-genetic imaging system with HRRT-PET and 7.0-T MRI. International Journal of Imaging Systems and Technology. 17(4):252-265 (2007)
- Z. H. Cho, Y. D. Son, H. K. Kim, K. N. Kim, S. H. Oh, J. Y. Han, I. K. Hong, and Y. B. Kim, “A fusion PET-MRI system with a high-resolution research tomograph-PET and ultra-high field 7.0 T-MRI for the molecular-genetic imaging of the brain,” Proteomics. 8(6),1302-1323 (2008).
• Research Interests
1. Development of PET-MRI Fusion System
2. Development of PET-MRI Fusion Algorithm
3. Applications of PET-MRI Fusion System
(1) Early diagnosis of Alzheimer’s Diseases using PET-MRI Fusion System
(2) Early diagnosis of Parkinson’s Diseases using PET-MRI Fusion System
(3) Study of mechanism of learning and memory using PET-MRI Fusion System