Time-resolved contrast-enhanced MR angiography creates a series of 3D images during the passage of a contrast agent. The principle clinical application is to demonstrate dynamic vascular events such as arterial-venous malformations, fistulas, shunts, and many congenital diseases. Additionally, this method is ideal for demonstrating non-symmetric filling defects typical in pulmonary diseases and peripheral atherosclerotic diseases. Another clinical application is to determine the optimal bolus arrival time for conventional, high-resolution contrast-enhanced MR angiography techniques, a.k.a. the “bolus timing test” technique. In general, time-resolved methods provide improved temporal resolution (faster) with some compromise in spatial resolution (detail) as compared to conventional MR angiography techniques, although these compromises are often acceptable from a clinical perspective, especially when assessing dynamic vascular events.
This comprehensive syngo TWIST Users Guide describes the basics of the TWIST principle. The given acquisition strategies have been clinically optimized to consider the clinical requirements for spatial and temporal resolution, optimal PAT factors, and coil combinations. No distinction was made between 1.5T and 3T. Each of the clinical applications offer protocols for high temporal resolution and high spatial resolution:
- Head (intracranial)
- Carotid (aortic arch and carotids)
- Thorax (pulmonary, aorta, and subclavians)
- Abdomen (aorta, renals, and iliacs)
- Thigh (runoff thighs)
- Calf (runoff calves and feet)
- Hand (extremity)
Since higher acceleration factors (PAT) generally require more coil elements and RF channels, the protocols are also organized according to RF configuration:
- PAT 2 + 08 channels
- PAT 3 + 18/32 channels
Appendix 1 of the syngo TWIST Users Guide contains a more detailed discussion of optimized clinical protocols.
Appendix 2 contains a more detailed discussion of the sequence implementation and caveats.