The Comparison of Susceptibility Changes in 1.5T and 3.0T MRIs due to TE Change in Functional MRI

ABSTRACT

PURPOSE: The purpose of this study was to find the optimum TE value for enhancing T2* weighting effect and minimizing the SNR degradation and to compare the BOLD effects according to the changes of TE in 1.5T and 3.0T MRI systems. MATERIALS AND METHODS: Healthy normal volunteers (eight males and two females with 24-38 years old) participated in this study. Each volunteer was asked to perform a simple finger-tapping task (sequential opposition of thumb to each of the other four fingers) with right hand with a mean frequency of about 2Hz. The stimulus was initially off for 3 images and was then alternatively switched on and off for 2 cycles of 6 images. Images were acquired on the 1.5T and 3.0T MRI with the FLASH (fast low-angle shot) pulse sequence (TR 100ms, FA 20degrees, FOV 230mm) that was used with 26, 36, 46, 56, 66, 76ms of TE times in 1.5T and 16, 26, 36, 46, 56, 66ms of TE in 3.0T MRI system. After the completion of scan, MR images were transferred into a PC and processed with a home-made analysis program based on the correlation coefficient method with the threshold value of 0.45. To search for the optimum TE value in fMRI, the difference between the activation and the rest by the susceptibility change for each TE was used in 1.5T and 3.0T respectively. In addition, the functional T2* map was calculated to quantify susceptibility change. RESULTS: The calculated optimum TE for fMRI was 61.89+/-2.68 at 1.5T and 47.64+/-13.34 at 3.0T. The maximum percentage of signal intensity change due to the susceptibility effect in activation region was 3.36% at TE 66ms in 1.5T and 10.05% at TE 46ms in 3.0T, respectively. The signal intensity change of 3.0T was about 3 times bigger than that of 1.5T. The calculated optimum TE value was consistent with TE values which were obtained from the maximum signal change for each TE. CONCLUSION: In this study, the 3.0T MRI was clearly more sensitive, about three times bigger than the 1.5T in detecting the susceptibility due to the deoxyhemoglobin level change in the functional MR imaging. So the 3.0T fMRI is more useful than 1.5T.