A Single-Scan, Rapid Whole-Brain Protocol for Quantitative Water Content Mapping With Neurobiological Implications
20th December 2019
Ana-Maria Oros-Peusquens, Ricardo Loução, Zaheer Abbas, Vincent Gras, Markus Zimmermann and N. J. Shah
Water concentration is tightly regulated in the healthy human brain and changes only slightly with age and gender in healthy subjects. Consequently, changes in water content are important for the characterisation of several pathologies including, alcoholism, haemodialysis, stroke, tumour, hepatic encephalopathy and multiple sclerosis. Standard MRI can be used to measure changes in brain water content, but as these changes are usually in the low percentage range, highly accurate and precise methods are required for detection.
The method proposed in this paper offers a fast, stable, easy to use, way of achieving high-quality mapping. It is based on a long-TR (10 s) multiple-echo gradient-echo measurement with an acquisition time of 7:21min. Using such a long TR ensures that there is no T1 weighting, meaning that the image intensity at zero echo time is only proportional to the water content, the transmit field, and to the receive field. In this method, the transmit and receive inhomogeneities represent a multiplicative factor, which is corrected in post processing using e.g. SPM.
Based on a cohort of 21 healthy volunteers at 3T field strength, the results demonstrate the robustness of the method and its clinical applicability. Furthermore, the distribution of water in the human cortex is investigated for the first time and found to be region-specific and highly regulated. This opens a whole range of possible applications, not only in neurodegenerative diseases but possibly also in psychiatric afflictions. It is anticipated that the short measurement time, which could be further reduced depending on the application, should facilitate the use of quantitative water mapping even in critical applications such as pre-surgical tumour investigations and acute or post-acute stroke.
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