Technical NotesMR-visible brain water content in human acute stroke
Introduction
An increasing number of MR spectroscopy studies deal with quantification of metabolite concentrations in brain tissue using the water signal amplitude as an internal calibration standard.1, 2, 3, 4 A basic assumption for calculation of metabolite concentrations using this method is that the water content in the brain tissue is known or at least does not differ significantly from the normal water content in healthy brain tissue. Changes in water content in ischemic brain tissue during the course of stroke will introduce errors in the calculation of metabolite concentrations using the internal water standard technique. This has implications if the concentration of N-acetyl-aspartate in infarcted brain tissue is to be used as a neuronal marker in efficacy studies of neuroprotective drugs. Recent studies using volume selective proton magnetic resonance spectroscopy (1H-MRS) demonstrated that it is possible to perform non-invasive estimates of water content in human brain tissue in vivo.5, 6 The results show that the fractional water content per unit wet tissue weight is approximately 0.70 in a region containing a mixture of gray and white matter, which is about 5% lower than expected from biochemical analyses.7 We estimated brain water content in patients with cerebral infarction using a 1H-MRS technique previously described at our institution.6 We focused on the time course of the water content serially from the acute to the chronic stage of infarction. To correlate with regional cerebral blood flow (rCBF) in the infarct region, SPECT-scanning was performed.
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Materials and methods
Fourteen patients with acute stroke (median age 68 years, range 29–80 years) and nine healthy volunteers (median age 67 years, range 58–80 years) were included in the study. All patients had large cortical infarctions (more than 2–4 cm in diameter), none of the patients had any signs of hemorrhagic transformation on standard MRI. The 1H-MRS and rCBF measurements were carried out serially within the time intervals 0–3 days; 4–7 days; 8–21 days; and more than 180 days after the stroke (Table 1 ).
Results
The results of the 1H-MRS measurements are shown in Table 1. In the controls the mean water content (SD) was 36,6 (3,1) mol · [kg wet weight]−1. In the patients the mean water content in the affected region measured between Day 0–3 after the onset of symptoms was 37.7 (5.1) mol · [kg wet weight]−1. From Day 0–3 to Day 4–7 mean water content increased significantly to 41.8 (4.8) mol · [kg wet weight]−1 (p = 0.034). The water content at Day 4–7 was significantly higher than in controls (p ≤
Discussion
We found that mean water content in ischemic brain tissue following acute stroke was 14% higher than in normal brain tissue after 4–7 days, at this time reperfusion had occurred in all but two patients. This agrees well with the study of an animal stroke model where increased water content of 13.75% was found 24 h following occlusion.15 No studies of human infarction have to our knowledge been published.
Quantification of water content in the brain depends on the experimental conditions as well
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