High temporal and high spatial resolution MR angiography (4D-MRA)

In the first decade of the twenty-first century, whole-body magnetic resonance scanners with high field strengths (and thus potentially better signal-to-noise ratios) were developed. At the same time, parallel imaging and echo-sharing techniques were refined to allow for increasingly high spatial and temporal resolution in dynamic magnetic resonance angiography (time-resolved = TR-MRA). This technological progress facilitated tracking the passage of intra-venously administered contrast agent boluses as well as the acquisition of volume data sets at high image refresh rates (4D-MRA). This opened doors for many new applications in non-invasive vascular imaging, including simultaneous anatomic and functional analysis of many vascular pathologies including arterio-venous malformations. Different methods were established to acquire 4D-MRA using various strategies to acquire k-space trajectories over time in order to optimize imaging according to clinical needs. These include keyhole - based techniques (e.g. 4D-TRAK), TRICKS-both with and without projection - and HYPR-reconstruction, TREAT, and TWIST. Some of these techniques were first introduced in the 1980 s and 1990 s, were later enhanced and modified, and finally implemented in the products of major vendors. In the last decade, a large number of studies on the clinical applications of TR-MRA was published. This manuscript provides an overview of the development of TR-MRA methods and the 4DMRA techniques as they are currently used in the diagnosis, treatment and follow-up of vascular diseases in various parts of the body. Key statements 4D-MRA, which differs according to manufacturer, generates high temporal and spatial resolution MRA volume data sets. Key differences in 4D-MRA techniques concern the sequence of the acquisition of k-space portions. Central k-space portions define image contrast and are thus repetitively scanned with 4D-MRA. Numerous clinical applications of 4D-MRA are already documented in the literature. Citation Format: Hadizadeh DR., Marx C, Gieseke J et al. High temporal and high spatial resolution MR angiography (4D-MRA).