In vivo estimation of water content in cerebral white matter of brain tumour patients and normal individuals: towards a quantitative brain oedema definition.

Abstract

The “building stones” in MR imaging, namely the relaxation times (RT) correlate in certain circumstances well with water content of cerebral white matter (WM). It is, therefore, possible to estimate regional in vivo water content using RT imaging with an accuracy within ±2–4%. The purpose of the present prospective investigation was to study the RT's of cerebral WM and thereby estimate normal in vivo water content. Furthermore, the method was used to study whether water content was different in the apparently normal cerebral hemisphere of brain tumour patients compared to normal individuals. RT data of the non-tumour bearing hemisphere in 42 brain tumour patients were compared to 35 normal individuals. Results: 1) Water content was significantly higher in the posterior WM as compared to frontal WM in both normal individuals and apparently normal WM in brain tumour patients and this appears to be a true physiological difference. 2) Water content of normal WM correlated positively with age. 3) There was no significant difference between RT data from the normal hemisphere in histologically different types of brain tumours. 4) Water content was significantly higher in the apparently normal WM of brain tumour patients compared to normal individuals. 5) Based on the present results, a definite lower threshold of white matter oedema could be established as 75% water content, corresponding to a T1 of 0.850 seconds.