中文摘要：

目的探讨人脑嗅觉fMRI实验中改变和优化层厚及回波时间（TE）参数对降低磁敏感性伪影和提高信噪比（SNR）的价值。方法10例健康志愿者,使用GESigna1.5TMR成像仪,标准正交头线圈。采用GRE-EPI序列分别对不同层厚（2、3、4、5、6mm）和固定层厚为6mm与2mm,同时改变不同回波时间（20、25、30、35、40、45、50、55、60ms）而进行脑功能成像扫描,以观察扫描参数的变化对图像信噪比（SNR）的影响。数据处理应用MATLAB5.3与AFNI软件。在额叶底部、右侧海马区及左枕叶划定感兴趣区（后者为对照）,SNR值=兴趣区信号强度（SI）/颅外空间噪声标准差（SD）。结果①改变扫描层厚时,磁敏感性脑区额叶底部及海马区SNR值随层厚的增加呈明显下降趋势（r1=-0.994,P〈0.01,r2=-0.999,P〈0.01）,而非磁敏感性脑区左枕叶区SNR值呈轻度上升趋势（无统计学意义）。②改变回波时间时,绝大多数被试磁敏感区（额叶底部与海马区）的SNR值在层厚为6mm时较层厚为2mm时明显下降;同时,当层厚为2mm时,SNR值随TE时间的延长呈轻度升高或无明显变化;当层厚为6mm时,SNR值随TE时间的延长而下降。结论在嗅觉fMRI实验中,可通过优化改变层厚与TE来降低磁敏感性伪影和提高SNR;层厚及TE对SNR的影响是相互影响、相互制约的,选择2mm层厚和TE30～40ms可获得理想的功能图像质量。

英文摘要：

Objective To investigate the values of changing and optimum of thickness and TE to decrease susceptibility artifact and increase SNR on the olfaction fMRI research. Methods Ten healthy volunteers were recruited in the study. All MR scans were performed on a GE signa 1.5T MR/i scanner using a standard quadrature head coil. Consecutive single-shot GRE-EPI scans were performed with changed thickness selected as 2, 3, 4, 5, 6 mm respectively and different echo time （TE） as 20, 25, 30,35, 40, 45, 50, 55, 60 ms on the different thickness of 2 mm and 6 mm respectively, to study the effects of changed thickness and TE on SNR of the EPI image. The data was processed with MATLABS. 3 and AFNI software. The volume of interest （VOI） was designed at three consecutive sections of inferior frontal lobe near the base of anterior cranial fossa, the volume is about 800-900 mm^3. The other two VOI were designed at right hippocampus and left occipital lobe （as contrast） with the same volume. On EPI image, every VOI signal intensity （SI） and standard deviation （SD） of the extra-cranial noise were calculated using AFNI software. The SNR value was finally acquired according to the equation SNR=SI/SD. Results （1） The SNR values in the area of inferior frontal lobe and hippocampus are negative-correlated with thickness （r1 = -0. 994, P〈0.01 ; r2 = -0. 999, P〈0. 01）, whereas in left occipital lobe, SNR raises slightly with the increasing of thickness, and there is no statistical significance. （2）With changing of TE, to most subjects, SNR value in the area of inferior frontal lobe and hippocampus decreased apparently when the thickness is 6 mm compared to that when the thickness is 2 mm. Scanning with thickness of 2 mm, the SNR value of most subjects in the area of inferior frontal lobe and hippocampus rose slightly or no significant changed with the increasing of TE; but with thickness of 6 mm, the SNR value was slightly decreased with the increasing of TE. Conclusion On olfactory fMRI research, suscepti