Zhiliang Wei1,2, Jiadi Xu1,2, Peiying Liu1,2, Lin Chen1,2, Wenbo Li1,2, Peter van Zijl1,2, Hanzhang Lu1,2,3. 1. Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. 2. F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA. 3. Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Abstract
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.
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.
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