A study of functional MRI on whole brain measured by EPI sequence

(1) 1.5T和1.5T的功能MRI比较了同一受试者使用4T和1.5T仪器的成像结果和强度的时间过程。同样进行了统计分析，并根据磁场强度的不同考虑了合适的阈值。短期记忆任务是在不同的日子用两种工具对同一受试者进行的。4T时的BOLD效应大于1.5T时，但小于理论表达式。然而，两种仪器的大脑激活区呈现的模式几乎相同，并且在4T和1.5T时观察到时间信号强度过程的多相模式。我们认为，即使1.5T也能像4T一样有效地检测大脑的功能活动。(2) fMRI强度的1/f波动对MRI时间强度过程进行频率分析，研究其与倒频的关系。人与人的MRI单次信号的频率分量与频率和频率功率成反比。任务学习的激活引起了这种反向频率关系的扰动。我们认为，从反向频率关系的偏离显示功能活性，这种偏离的程度将反映激活的强度。

(1) functional MRI of 1.5T and 4TWe compared mapping results and time courses of intensity in same subjects using 4T and and 1.5T insturments. The statistical analysis was also conducted in the same manner and suitable thresh hold depending on differences of magnetic field strength was considerdd. The short memory task was applied to the same subjects on different days using two instruments. The BOLD effect at 4T was larger than that at 1.5T,but less than the theoretical expression. However the cerebral activated areas were presented in the almost same pattern two instruments and the multiphasic pattern of time signal intensity course was observed on 4T and 1.5T.We considered that even 1.5T would be as useful as 4T to detect function activity of the brain.(2) 1/f fluctuation of fMRI intensitiesThe frequency analysis was conducted to the time intensity courses of MRI and the relationship with the inverted frequency was studied. The frequency component of MRI single on both phantom and human had the inverted proportional part to the frequency and the power of frequency. The activation by task study caused perturbation from such a inverted frequency relationship. We considered that the deviation from the inverted frequency relationship showed functional activity and the extent of this deviation would reflect strength of activation.