Quantitative Susceptibility Mapping-Based Microscopy of Magnetic Resonance Venography (QSM-mMRV) for In Vivo Morphologically and Functionally Assessing Cerebromicrovasculature in Rat Stroke Model.

Meng-Chi Hsieh,Jyh-Horng Chen,Jenq-Lin Yang,Chia-Hao Su,Ching-Yi Tsai,Min-Chiao Liao,Quan Jiang

doi:10.1371/journal.pone.0149602

Abstract

Abnormal cerebral oxygenation and vessel structure is a crucial feature of stroke. An imaging method with structural and functional information is necessary for diagnosis of stroke. This study applies QSM-mMRV (quantitative susceptibility mapping-based microscopic magnetic resonance venography) for noninvasively detecting small cerebral venous vessels in rat stroke model. First, susceptibility mapping is optimized and calculated from magnetic resonance (MR) phase images of a rat brain. Subsequently, QSM-mMRV is used to simultaneously provide information on microvascular architecture and venous oxygen saturation (SvO2), both of which can be used to evaluate the physiological and functional characteristics of microvascular changes for longitudinally monitoring and therapeutically evaluating a disease model. Morphologically, the quantification of vessel sizes using QSM-mMRV was 30% smaller than that of susceptibility-weighted imaging (SWI), which eliminated the overestimation of conventional SWI. Functionally, QSM-mMRV estimated an average SvO2 ranging from 73% to 85% for healthy rats. Finally, we also applied QSM to monitor the revascularization of post-stroke vessels from 3 to 10 days after reperfusion. QSM estimations of SvO2 were comparable to those calculated using the pulse oximeter standard metric. We conclude that QSM-mMRV is useful for longitudinally monitoring blood oxygen and might become clinically useful for assessing cerebrovascular diseases.

Highlights

Stroke is the leading cause of long-term disability, one of the commonest causes of mortality in aging countries [1]
At baseline, the SvO2 in several major veins (MIF, longitudinal hippocampal vein (LHIV), medial collicular vein (MCOLV), thalamostriate vein (THSV), great cerebral vein (GCV), and straight sinus (STS)) had a mean of 86.23%, which was higher than other SvO2 measurements of ~70% [17,58]
We have described a quantitative susceptibility map (QSM)-based microscopic MRV combined with QSM reconstruction for in vivo quantitative visualization of the architecture of small venous vessels in rat stroke model

Summary

Introduction

Stroke is the leading cause of long-term disability, one of the commonest causes of mortality in aging countries [1]. Abnormal structure and blood oxygen saturation (SO2) of cerebral microvessels (diameter: 100 μm) [2] is a critical feature of stroke. Measuring cerebral blood oxygen saturation might be necessary for an accurate diagnosis, to predict disease outcomes, and to monitor the treatment response in stroke. The most commonly used noninvasive methodologies of medical imaging in clinical and experimental neuroscience for assessing the cerebral microvessels in cerebrovascular diseases like stroke, glioma, and vascular malformation are computed tomography angiography (CTA) and magnetic resonance angiography (MRA). CTA with a contrast agent can rapidly and accurately detect the structure of blood vessels [4], it has the potential negative side affect of ionizing radiation. TOF-MRA is limited to measuring small cerebral vessels (venules, arterioles, and capillaries) because of slow-flowing signals in the cerebral microvessels. CE-MRA uses gadolinium (Gd)-based contrast agents to detect these slow-flowing signals [6]. CE-MRA might not satisfy the long acquisition time required for high-resolution MRA application because it has a short intravascular half-life and rapidly redistributes into the extracellular space

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Conclusion