Optimizing three-dimensional time-of-flight MR angiography with variable repetition time.

PURPOSE: To implement and evaluate a variable repetition time (TR) modification of three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography. MATERIALS AND METHODS: Variable- and constant-TR 3D TOF MR angiography of the intracranial vasculature was performed in 20 healthy volunteers and 10 patients with known or suspected cerebrovascular disease. Total acquisition time was short and held constant for all studies. Frequency-selective fat saturation (FS) and magnetization transfer saturation (MTS) pulses were applied. The associated maximum-intensity projection (MIP) images were evaluated quantitatively for contrast-to-noise (C/N) and qualitatively for depiction of vessels that exhibit slow flow. RESULTS: Variable-TR MIP images exhibited improved C/N and depiction of small peripheral vessels and venous structures when compared with constant-TR MIP images. These observations were consistent for all studies. CONCLUSIONS: The variable-TR modification improved the depiction of intracranial vessels that exhibit slow flow.