Short versus long echo time for cranial MR angiography in children and adults.

PURPOSE To evaluate the ability of short-echo-time (TE) versus long-TE three-dimensional time-of-flight MR angiography sequences to decrease phase-related signal loss and refocus signal from blood in intracranial MR angiography of adults and children.

METHODS We evaluated 3-D time-of-flight cranial MR angiography in 33 cases (18 children and 15 adults) using two sequences. The longer-echo reference sequence had a TE of 8.0 milliseconds and a field echo of 6.5 milliseconds; the shorter-echo sequence had a TE of 5.1 and a field echo of 4.2 milliseconds. Repetition time, flip angle, and matrix were constant. The bandwidth for the longer-echo sequence was 130 Hz, 195 Hz for the shorter-echo sequence.

RESULTS The greatest improvement in diagnostic images was for children; significant and mildly improved signal recovery was demonstrated in 15 and 2 cases, respectively, of a total of 18 studies. This allowed improved diagnostic assessment. However, in the adult group significantly and mildly improved signal recovery were present in only 2 and 6 cases, respectively, of a total of 15 studies. In the group of children and adults combined, decreased lumen definition and peripheral vessel visibility were present in 24 and 30 of 33 cases, respectively, because of higher signal from background tissue when the shorter-TE field-echo sequence was used and, hence, reduced vascular contrast.

CONCLUSION The use of a short-field-echo/TE sequence is therefore recommended as the initial study in children but as a secondary examination in areas of abnormality in adults. This study illustrates the improved signal recovery from phase-related sources and improved visibility of intracranial stenosis in children with the use of a short-echo sequence. In adults, the short-echo sequence should not be used for the initial screening but reserved for secondary evaluation.