Problems and pitfalls of 3-D TOF magnetic resonance angiography of the intracranial circulation.

3-D Time of flight (TOF) Magnetic resonance angiography (MRA) is being increasingly adopted as a technique for assessment of the intracranial circulation in neuroradiological practice. We describe our recent experience of 3-D time of flight Magnetic resonance angiography. We describe some of the problems and potential pitfalls that we have experienced employing 3-D TOF MRA in these circumstances, and the diagnostic dilemmas that have arisen. A range of problems have been encountered. When performing 3-D TOF MRA, other phenomena such as sub-acute thrombus and high signal structures may be incorporated into the Maximal Intensity Projection (MIP) reconstruction and masquerade as vascular abnormalities. Interpretation of MIP reconstructions can also be difficult or impossible in the presence of sizeable haematoma. Conversely, vascular structures may not be appreciated because of loss of signal from saturation effects or dephasing due to slow or complex flow. Local susceptibility artefacts, from aneurysm clips or coils, may reduce the signal from vascular structures. Interpretation of 3-D TOF MRA must take account of potential pitfalls which can be minimized by adoption of appropriate imaging and review strategies. This requires careful consideration of MRA source data, the spin-echo axial images as well as the MIP reconstructions.