Quantitative Susceptibility Mapping to Assess Cerebral Vascular Compliance

Abstract

This study explored whether autoregulatory shifts in cerebral blood volume induce susceptibility changes large enough to be depicted by quantitative susceptibility mapping. Eight healthy subjects underwent fast quantitative susceptibility mapping at 3T while lying down to slowly decrease mean arterial pressure. A linear relationship between mean arterial pressure and susceptibility was observed in cortical and subcortical structures, likely representing vessels involved in autoregulation. The slope of this relationship is assumed to indicate the extent of cerebral vascular compliance.

Fig 1.

Representative T1-weighted image, quantitative susceptibility map, and the corresponding CVC map of an axial section from a single subject (from left to right). Additional axial sections of the same subject are shown in On-line Fig 4.

Fig 2.

Schematic drawing of pial and subcortical blood vessels. The longest vessels with a high capability to modulate the diameter are the medullary arterioles and venules. According to Duvernoy type 5, these vessels follow the course of the subcortical interface over long distances before they branch into white matter.

Fig 3.

CVC map with a semicortical mask (A) and a zoomed inlay (B) showing regions with mainly arterial (arrow 1), venous (arrow 2), and pial arterial (arrow 3) contributions. In regions with predominantly arterial vessels (arrow 1), the susceptibility increases with increasing MAP (C), while it decreases in regions with predominantly venous vessels (arrow 2) with increasing MAP (D). The slope of the regression lines in C and D represents the CVC. rsq indicates the square of the correlation coefficient.