The combination of oxygen extraction fraction (OEF) and neural tissue susceptibility (𝛘n) brain mapping can be used to quantify the metabolic activity of active multiple sclerosis (MS) brain lesions, according to a new article published in the Journal of Cerebral Blood Flow & Metabolism.

The study found that lesion rims had higher OEF and 𝛘n values compared to the lesion cores, -6.6±7.0% vs -9.8±7.8% (P <.001) and 33.9±20.3 ppb vs 25.7±20.5 ppb (P =.017), respectively. The differences between the rim and core of the lesions were attributed to a higher density of iron-rich microglia in the rim and irreversible tissue damage in the core leading to less oxygen use.

“These promising results suggest that OEF derived from [multi-echo gradient echo (mGRE)] data may serve as a sensitive marker of tissue oxygen metabolism in [quantitative susceptibility mapping] rim+ lesions, which can be important for lesion status monitoring and development of novel MS therapeutic targets,” the authors mentioned.

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The study also compared MS scans of the whole brain with healthy controls and found that MS patients had lower OEF values (P <.001) and higher 𝛘n (P =.018). The authors hypothesized that the lower OEF values in MS brains may represent a unique tissue injury mechanism, possibly related to impaired mitochondrial function which induces chronic oxygen deprivation in neurons.

“Brain OEF mapping is feasible in MS brains and can detect within lesion difference between the rim and core regions of MS lesions with QSM hyperintense rim as well as global and regional gray matter differences between MS and HC,” the authors concluded.

To extract OEF values, mGRE data were extracted using a QSM plus quantitative blood oxygenation level-dependent magnitude signal (QSM+qBOLD, or QQ) algorithm. The QQ algorithm is able to separate the effect of OEF from the 𝛘n.

For the study, a total of 22 relapsing-remitting MS patients (17 female, 5 male) and 11 age-matched healthy controls (1 female, 10 males) were included. All MRI images were captured using a 3T scanner. 

Reference

Cho J, Nguyen TD, Huang W, et al. Brain oxygen extraction fraction mapping in patients with multiple sclerosis. J Cereb Blood Flow Metab. Published online September 24, 2021. doi: 10.1177/0271678X211048031

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