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-T E three-dimensional time-of-flight MR angiography sequences to decreas e phase-related signal loss and refocus signal From blood in intracran ial MR angiography of adults and children. METHODS: We evaluated 3-D t ime-of-flight cranial MR angiography in 33 cases (18 children and 15 a dults) using two sequences. The longer-echo reference sequence had a T E: of 8.0 milliseconds and a field echo of 6.5 milliseconds; the short er-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 s equence. RESULTS: The greatest improvement in diagnostic images was fo r children; significant and mildly improved signal recovery was demons trated in 15 and 2 cases, respectively, of a total of 18 studies. This allowed improved diagnostic assessment. However, in the adult group s ignificantly 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 peripher al vessel visibility were present in 24 and 30 of 33 cases, respective ly, because of higher signal from background tissue when the shorter-T E field-echo sequence was used and, hence, reduced vascular contrast. CONCLUSION: The use of a short-field-echo/TE sequence is therefore rec ommended as the initial study in children but as a secondary examinati on in areas of abnormality in adults. This study illustrates the impro ved signal recovery from phase-related sources and improved visibility of intracranial stenosis in children with the use of a short-echo seq uence. In adults, the short-echo sequence should not be used for the i nitial screening but reserved for secondary evaluation.