Multi-Component Relaxation Study of Human Brain Using Relaxographic Analysis

ABSTRACT

PURPOSE: To demonstrate that the relaxographic method provides additional information such as the distribution of relaxation times and water content which are poentially applicable to clinical medicine. MATERIALS AND METHODS: First, the computer simulation was performed with the generated relaxation data to verify the accuracy and reliablility of the relaxographic method (CONTIN). Secondly, in order to see how well the CONTIN quantifies and resolves the two different T1 environments, we calculated the oil to water peak area ratios and identified peak positions of T1-distribution curve of the phantom solutions, which consist of four centrifugal tubes (10ml) filled with the compounds of 0, 10, 20, 30% of corn oil and distilled water, using CONTIN. Finally, inversion recovery MR images for a volunteer are acquired for each TI ranged from 40 to 1160 msec with TR/TE=2200/20 msec. From the 3 different ROIs (GM, WM, CSF), CONTIN analysis was performed to obtain the T1-distribution curves, which gave peak positions and peak area of each ROI location. RESULTS: The simulation result shows that the errors of peak positions were less in the higher peak (centered T1=600 msec) than in the lower peak (centered T1=150 msec) for all SNR but the errors of peak areas were larger in the higher peak than in the lower peak. The CONTIN analysis of the measured relaxation data of phantoms revealed two peaks between 20 and 60 msec and between 500 and 700 msec. The analysis gives the peak area ratio as oil 10%: oil 20%: oil 30%=1:1.3:1.9, which is different from the exact ratio, 1:2:3. For human brain, in ROI 3 (CSF), only one component of -distributions was observed whereas in ROI 1 (GM) and in ROI 2 (WM) we observed two components of T1-distribution. For the WM and CSF there was great agreement between the observed T1-relaxation times and the reported values. CONCLUSION: we demonstrated that the relaxographic method provided additional information such as the distribution of relaxation times and water content, which were not available in the routine relaxometry and T1/T2 mapping techniques. In addition, these additional information provided by relaxographic analysis may have clinical importance.