Intracranial MR angiography: a direct comparison of three time-of-flight techniques

During the past few years, several time-of-flight MR angiographic techniques have been described for rapid, reliable, noninvasive vascular evaluation. This investigation was performed to directly compare three time-of-flight methods in imaging the intracranial vasculature: a single-volume method, a sequential two-dimensional slice technique, and a technique using the sequential acquisition of multiple thin volumes. Thirty-two normal volunteers were imaged, and direct comparisons of the three techniques were performed in 20 subjects. Analysis of the resulting images revealed optimal depiction of large vessels with the single-volume and multiple thin-volume methods, small vessels with the multiple thin-volume technique, and venous structures with the sequential two-dimensional slice acquisition. The effects of progressive spin saturation in time-of-flight MR angiography are discussed along with the individual benefits and disadvantages of each method. We conclude that the diagnostic value of intracranial time-of-flight MR angiography can be maximized through tailoring the angiographic method to the suspected abnormality based on the requirements for spatial resolution and slow-flow sensitivity, as suggested by the clinical history or prior imaging studies.