4D-CTA in neurovascular disease: a review

Abstract

CT angiography is a widely used technique for the noninvasive evaluation of neurovascular pathology. Because CTA is a snapshot of arterial contrast enhancement, information on flow dynamics is limited. Dynamic CTA techniques, also referred to as 4D-CTA, have become available for clinical practice in recent years. This article provides a description of 4D-CTA techniques and a review of the available literature on the application of 4D-CTA for the evaluation of intracranial vascular malformations and hemorrhagic and ischemic stroke. Most of the research performed to date consists of observational cohort studies or descriptive case series. These studies show that intracranial vascular malformations can be adequately depicted and classified by 4D-CTA, with DSA as the reference standard. In ischemic stroke, 4D-CTA better estimates thrombus burden and the presence of collateral vessels than conventional CTA. In intracranial hemorrhage, 4D-CTA improves the detection of the "spot" sign, which represents active ongoing bleeding.

Fig 1.

Schematic diagram of 4D-CTA imaging techniques. The x-axis represents the time domain. The y-axis represents the z-dimension. The light-gray horizontal bar represents the area that needs to be covered in the z-dimension. A, Shuttle mode: the sinus represents continuous table movement back and forth in the z-axis dimension to provide adequate coverage of the region of interest at multiple points in time. Notice that the temporal resolution is a function of the speed of table movement, typically 2–4 seconds depending on coverage. B, Toggling-table technique: the bars represent table repositioning in the z-axis dimension to provide adequate coverage of the region of interest at multiple points in time. Notice that the temporal resolution is a function of the speed of table repositioning, typically 3–4 seconds. C, Volume scanning: complete coverage of the region of interest (horizontal bar) with 1 gantry rotation. Notice that the temporal resolution is a function of the scanning interval settings because each rotation provides full coverage. Volume CT scanning enables (D) continuous volume scanning. Temporal resolution is limited by the gantry rotation speed.

Fig 2.

4D-CTA demonstrating a Borden type I dural arteriovenous fistula of the left sigmoid sinus. Selected 4D-CTA subtraction MIP images of a continuous 4D-CTA volume acquisition (320–detector row CT) in lateral (A) and oblique (B) projections in a patient presenting with left-sided tinnitus. Branches of the occipital artery are identified as arterial feeders of the dAVF. There is normal antegrade venous return. The 3D image (C) demonstrates the advantage of 4D-CTA to study vessels in relation to surrounding structures.

Fig 3.

Timing-invariant CTA better estimates the extent of collateral circulation in a patient with right middle cerebral artery occlusion. The left image is a conventional CTA showing poor collateral circulation and suggests a poor prognosis. The right image is a TI-CTA image from a 4D-CTA acquisition (ie, temporal MIP), which shows good collateral filling and suggests a good prognosis. In this case, the patient had a good recovery.

Fig 4.

4D-CTA image demonstrating recurrence of an arteriovenous malformation. The arrow indicates the nidus, which is fed by arterial feeders from the anterior cerebral artery. There is cortical venous drainage toward the rostral superior sagittal sinus.