T2 relaxometry of the hippocampus at 3T

Abstract

Background and purpose: T2 mapping is useful for identifying and quantifying abnormalities of the hippocampus and amygdala. It is particularly useful in the presurgical evaluation of patients with temporal lobe epilepsy and for the identification of bilateral hippocampal sclerosis (HS). The purpose of this study was to implement and validate a dual-echo method for producing coronal T2 maps with complete coverage of the hippocampus and the rest of the brain on a 3T MR imaging scanner.

Materials and methods: T2 relaxation times were estimated on 10 occasions on 3 quality assessment Eurospin II (Diagnostic Sonar, Livingstone, Scotland) test objects with the use of conventional spin-echo (CSE), fast spin-echo, and fast recovery fast spin-echo (FRFSE) sequences on a 3T Excite MR imaging scanner (GE Healthcare, Milwaukee, Wis). Hippocampal T2 relaxation times were then measured in 15 healthy subjects and 20 subjects with clear-cut HS who were scanned at 1.5 T with a previously validated dual-echo CSE sequence and 3T with an FRFSE sequence.

Results: 3T FRFSE data were as reliable as CSE data at 1.5 T. Reliability of hippocampal T2 measures was good on healthy volunteers and subjects with HS. FRFSE images were suitable for qualitative radiologic reporting and with complete brain coverage, so no additional T2-weighted sequences were required. There was good correlation between the 3T hippocampal T2 measurements and values obtained with the previously validated technique at 1.5 T, with reliable identification of all of the subjects with HS.

Conclusions: T2 mapping with an FRFSE 30/80 sequence may be readily applied at 3T and can produce reliable T2 values in vivo with contiguous 5-mm sections and in a much reduced scan time of 3 minutes 1 second compared with 10 minutes 30 seconds for the CSE sequence at 1.5 T.

Fig 1.

Subject with unilateral right-sided HS (left of image). A, FRFSE 30/80 early echo. B, FRFSE 30/80 late echo. C, FRFSE 30/80 T2 calculated image showing placement of region of interest.

Fig 2.

Scatterplot of calculated hippocampal T2 relaxation times obtained with 3T FRFSE 2000/30, 80 sequence (y-axis), and 1.5T CSE 2000/30,120 sequence (x-axis), in 15 healthy control subjects (30 hippocampi) and 20 patients with hippocampal sclerosis (40 hippocampi).