Contrast-enhanced magnetic resonance angiography of the carotid bifurcation using the time-resolved imaging of contrast kinetics (TRICKS) technique

The time-resolved contrast-enhanced magnetic resonance (MR) angiographic technique TRICKS (time-resolved imaging of contrast kinetics) reconstructs a temporal series of three-dimensional (3D) images. The temporal resolution is increased by using a short TR (<8 ms) and TE (<2 ms), zero filling, partial echo sampling, view sharing, and temporally sampling k-space at variable rates. TRICKS allows reconstruction of multiple sequential 3D volumes following bolus injection of a gadolinium chelate (0.2 mmol/kg body weight up to 40 ml, injection rate ∼2 ml/s). The resulting temporally defined datasets are conceptually similar to a catheter-based intra-arterial digital subtraction angiographic series, except that they are 3D volumes and not projection images. Similar to other contrast-enhanced MR angiographic methods, TRICKS improves delineation of carotid artery stenosis by minimizing saturation effects. TRICKS and other contrast-enhanced MR angiographic techniques use short echo times and small voxels, thus reducing intravoxel dephasing. Surface morphology of atherosclerotic plaque and slow flow in nearly occluded vessels ("string sign") are well delineated. The major advantage of the TRICKS technique is that the timing of the acquisition in relation to the passage of the contrast bolus occurs automatically, allowing for consistent capture of the arterial phase, and eliminating the need for sophisticated synchronization methods.