Magnetic resonance angiography of cerebral arteriovenous malformations

Contrast-enhanced magnetic resonance angiography of cerebral arteries. A review

The loss of blood vessel visibility due to the signal saturation of slow flow can be partially overcome by the T1 reduction that occurs with the use of contrast agents such as Gd-DTPA during magnetic resonance angiography (MRA) studies. Dynamic-imaging techniques that have been applied successfully in abdominal imaging may also be useful for intracranial applications. However, the time between arterial and venous enhancement is very short during intracranial circulation. This limits the spatial resolution that can be obtained between arterial and venous enhancement. Fortunately, the blood-brain barrier and the relatively long duration of significant decrease in blood T1 has led to the development of very high resolution intracranial MRA techniques. Knowledge of the contrast-agent dilution factors and the ultimate resulting relaxation rates can be used to optimize the imaging parameters to maximize vessel signal relative to the background signal (the signal-difference-to-noise ratio). The additional venous vascular detail in the contrast-enhanced study can be spatially resolved in the 3D image data and determined by incorporating information from both high-resolution precontrast and postcontrast studies. In this article, the history, development and application of contrast agents in MRA are presented.

Usefulness of three-dimensional phase contrast MR angiography on arteriovenous malformations

Prospective three-dimensional phase contrast (3D-PC) MR angiography was obtained in 34 patients with arteriovenous malformations (AVM) and comparison was made between digital substraction angiography (DSA) and three-dimensional time-of-flight (3D-TOF) methods. Velocity encoding (VENC) for 3D-PC was adjusted to 60 and 10 cm/sec., and was changed only when adequate information was not obtained. VENC 60 cm/sec, demonstrated the main feeders in 100% of cases and the nidus in 86% of cases whereas VENC 10 cm/sec. showed the draining vein in 78% of cases. The detection rate of feeder, nidus and drainer was 60%, 40% and 13% respectively by the TOF technique. The mean size of the nidus as compared with DSA as standard was 130% with MRI, 108% with 3D-PC and 92% with the TOF technique and this difference was not statistically significant. 3D-PC was clearly superior in detecting AVM in the presence of hemosiderin, hematoma or surgical clips. It also showed gradual disappearance of the lesion after radiosurgery. We found 3D-PC superior to 3D-TOF in the diagnosis, therapeutic planning and follow-up of AVM.