Diffusion-weighted imaging in the evaluation of watershed hypoxic-ischemicbrain injury in pediatric patients

The purpose of our study was to determine the usefulness of echo-planar dif fusion-weighted imaging (EPDI) in the evaluation of watershed hy oxic-ische mic brain injury in pediatric patients. Eighteen patients ranging in age fr om 3 weeks to 12 years were evaluated for evidence of ischemic/infarction c hanges on conventional MR and EPDI. Included in the study group were five p atients with sickle cell disease. four with congenital heart disease, four with hypotensive episodes with various etiologies, three with sepsis, and t wo with encephalitis or meningitis. Patients were examined 2 h to 6 days af ter the initial insult, with follow-up studies in four patients at 1 to 62 days after the initial examination. After conventional MR imaging (Tl, FSE T2, and FLAIR), diffusion-weighted MR imaging was performed using high-spee d, single-shot EP techniques with TR 6000, TE 144, matrix 96 x 128, FOV 23. 3 x 31 and five b values of 0, 160, 360, 640,and 1,000 s/mm(2). EPDI demons trated abnormally increased signal in watershed ischemic/infarction zones i n all initial cases. Apparent diffusion coefficients (ADC) were obtained in 59 lesions. When compared with radiographically normal (on EPDI) contralat eral brain parenchyma, 45 demonstrated a relatively decreased ADC, while ei ght had normal (+/- 10 %) and six had increased ADC. In four cases, signal abnormalities on EPDI were not seen or exceeded that seen with conventional MR imaging. In the remaining cases, signal abnormalities were obvious on E PDI and more subtle on conventional MR imaging. Follow-up studies demonstra ted resolution of abnormal EPDI signal with persistent abnormalities on con ventional imaging in some cases, while others revealed an increase in size or number of EPDI signal abnormalities, suggesting ongoing acute ischemic/i nfarctive changes. EPDI is a rapid., sensitive technique for detecting wate rshed ischemic/infarction changes in pediatric patients with hypoperfusion episodes, at times before such changes are apparent on conventional MR imag es and/or are clinically apparent.