Time-resolved MRA sequences are widely used wherever circulation is rapid (carotids, cardio-pulmonary system) or unpredictable (extremities)
The method is particularly useful for evaluating collateral or retrograde flow around stenosesand in the work up of arteriovenous malformations
It can also be useful in assessing arterial feeders, AV fistulas, stenosis of vessel supplying tumors while simultaneously evaluating enhancement characteristics.
The centre of k-space contains the image contrast information, during the passage of the contrast bolus, the centre of k-space is sampled eliptically(purple region) more frequently than the periphery (grey)
The data from the different k-space samplings are combined to create a series of images which are then automatically subtracted.
Parallel imaging can be used to increase spatial resolution and/or coverage without increasing scan tim
We used a 3T scanner (GE Discovery MR750W 32 channel GEM) with a 24 channel head and neck coil. Our neck protocol includes a STIR and T1w coronal, T2w sagittal, T1w, T2w and DWI axial and axial TRICKS followed by T1w fat sat axial and coronal post gadolinium.
TR 3.9, TE 1.5, FA 20, FOV 24, temporal resolution 4.7, matrix 256x256, slice thickness 6mm, 48 phases with no gap, 20 seconds/phase, total scan time 4 mins 8 secs. No parallel imaging was used.
TWIST (Time resolved angiography With Stochastic Trajectories) - Siemens use this acronym
TRICKS (Time-Resolved Imaging of Contrast KineticS) - GE
4D-TRAK (4D Time-Resolved Angiography using Keyhole) - Philips sequence
Freeze Frame - Toshiba
TRAQ (Time-ResolvedAcQuisition) - Hitachi