Quantitative assessment of cerebral venous blood T₂ in mouse at 11.7T: Implementation, optimization, and age effect

Purpose: To develop a non-contrast-agent MRI technique to quantify cerebral venous T₂ in mice.

Methods: We implemented and optimized a T₂ -relaxation-under-spin-tagging (TRUST) sequence on an 11.7 Tesla animal imaging system. A flow-sensitive-alternating-inversion-recovery (FAIR) module was used to generate control and label images, pair-wise subtraction of which yielded blood signals. Then, a T₂ -preparation module was applied to produce T₂ -weighted images, from which blood T₂ was quantified. We conducted a series of technical studies to optimize the imaging slice position, inversion slab thickness, post-labeling delay (PLD), and repetition time. We also performed three physiological studies to examine the venous T₂ dependence on hyperoxia (N = 4), anesthesia (N = 3), and brain aging (N = 5).

Results: Our technical studies suggested that, for efficient data acquisition with minimal bias in estimated T₂ , a preferred TRUST protocol was to place the imaging slice at the confluence of sagittal sinuses with an inversion-slab thickness of 2.5-mm, a PLD of 1000 ms and a repetition time of 3.5 s. Venous T₂ values under normoxia and hyperoxia (inhaling pure oxygen) were 26.9 ± 1.7 and 32.3 ± 2.2 ms, respectively. Moreover, standard isoflurane anesthesia resulted in a higher venous T₂ compared with dexmedetomidine anesthesia (N = 3; P = 0.01) which is more commonly used in animal functional MRI studies to preserve brain function. Venous T₂ exhibited a decrease with age (N = 5; P < 0.001).

Conclusion: We have developed and optimized a noninvasive method to quantify cerebral venous blood T₂ in mouse at 11.7 T. This method may prove useful in studies of brain physiology and pathophysiology in animal models. Magn Reson Med 80:521-528, 2018. © 2017 International Society for Magnetic Resonance in Medicine.