Fast functional MRA using time-resolved projection MR angiography with correlation analysis.

Most recently, time-resolved 2D MRA after injection of a contrast agent bolus for various applications has been proposed. Similar to conventional digital subtraction angiography (DSA), 2D MR DSA offers the ability to observe the dilution of the bolus in the vascular system during the passage with a temporal resolution considerably below 1 sec. The purpose of this paper is to present strategies to improve the inherent low signal-to-noise ratio of 2D angiograms while retaining some temporal resolution. This can be achieved by applying algorithms for time series analysis as used in functional MRI. The significantly improved image quality is demonstrated on examples from clinical studies from bronchial MRA as well as cardiovascular MRA. In addition to the increased signal-to-noise ratio, correlation analysis leads to suppression of background signals and to a better discrimination of overlapping vessels. Further improvements in the temporal discrimination of vessels is afforded by the use of consecutive multiple contrast agent boli as demonstrated by numerical simulations and experiments.