Abstract
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).
