2D-Look-Locker sequenceを使用したT₁計測の試み

抄録

A sequence for T₁ relaxation-time measurement that allows a high resolution to be obtained within a short acquisition time is described herein and its application to the orofacial region is investigated. The sequence is based on the Look-Locker (LL) method and it employs a magnetization-preparation pulse prior to data acquisition with either a turbo field echo (TFE) or turbo field-echo echo-planar imaging (TFEPI) sequence. The sequence is implemented on a standard clinical scanner. We synchronized the data acquisition with the virtual electrocardiogram in order to set the time after the preparation pulse. Accuracy of the T₁ results obtained by the LL sequence was evaluated and compared with those by the Inversion Recovery (IR) sequence by a phantom which consisted of 10 tubes of distilled water, with each tube containing a different concentration of the contrast media. The correlation between the T₁ values obtained by the LL sequence and those by the IR sequence was high with an R² of more than 0.99. The percentage difference was less than 4% between 500ms and 2000ms of the T₁ values obtained by the IR sequence. As the flip angle increases, the difference in the percentage between the T₁ values obtained by the IR sequence and those by the LL-TFE sequence thus become larger for the slow-relaxing compartment (T₁ > 1500ms).
However, the effect of the flip angle on the percentage difference by the LL-TFEPI sequence was smaller than that by the LL-TFE sequence. We therefore applied the LL sequence to the orofacial region and calculated the T₁ value of various tissues. As a result, a close agreement was observed between the T₁ values obtained by the LL-TFE sequence and by the LL-TFEPI sequence. The T₁ values obtained with both sequences did not significantly differ (P = 0.55, paired t test).