STUDY OF SUSCEPTIBILITY-INDUCED ARTIFACTS IN GRASE WITH DIFFERENT ECHO TRAIN LENGTH

The aim of this study was to evaluate the sensitivity of gradient-and- spin-echo (GRASE) sequences to susceptibility effects. GRASE sequences with 21 and 33 echoes per echo train were compared with a T2-weighted FSE sequence with an echo train length of 5 by means of MRI in phanto ms, volunteers (n =10), and patients (n = 19) with old hemorrhagic bra in lesions. All experiments were performed on a 1.0-T clinical MR syst em (Impact Expert, Siemens AG, Erlangen, Germany) with constant imagin g parameters. Contrast-to-noise ratios (CNRs) of tubes doped with iron oxides at different concentrations, of brain areas with physiological iron deposition (red nucleus, substantia nigra), and of areas of old brain hemorrhage were calculated for FSE and GRASE pulse sequences. Ar eas of old brain hemorrhage were also qualitatively analyzed for the d egree of visible susceptibility effects by blinded reading. The CNR of iron oxide tubes and iron-containing brain areas decreased with incre asing echo trains of GRASE sequences. The CNR of GRASE sequences decre ased when compared with CNR of their FSE counterparts (GRASE 21 echo t rains 23.8 +/- 0.8, FSE 5 echo trains 26.7 +/- 0.9; p less than or equ al to 0.01). Qualitative analysis confirmed these measurements. FSE wi th an ETL of 5 demonstrated significantly stronger susceptibility effe cts than their GRASE counterpart with an ETL of 21. The results demons trate that GRASE sequences do not necessarily compensate for the reduc ed sensitivity of FSE to susceptibility effects. The complex signal be havior of GRASE makes conventional SE, gradient echo, or FSE sequences containing shorter echo trains preferable when patients with intracra nial hemorrhage are clinically evaluated.