Use of spin echo T2 BOLD in assessment of cerebral misery perfusion at 1.5 T

Inadequate blood supply relative to metabolic demand, a haemodynamic condition termed as misery perfusion, often occurs in conjunction with acute ischaemic stroke. Misery perfusion results in adaptive changes in cerebral physiology including increased cerebral blood volume (CBV) and oxygen extraction ratio (OER) to secure substrate supply for the brain. It has been suggested that the presence of misery perfusion may be an indication of reversible ischaemia, thus detection of this condition may have clinical impact in acute stroke imaging. The ability of single spin echo T₂ to detect misery perfusion in the rat brain at 1.5 T owing to its sensitivity to blood oxygenation level dependent (BOLD) contrast was studied both theoretically and experimentally. Based on the known physiology of misery perfusion, tissue morphometry and blood relaxation data, T₂ behaviour in misery perfusion was simulated. The interpretation of these computations was experimentally assessed by quantifying T₂ in a rat model for cerebral misery perfusion. CBF was quantified with the H₂ clearance method. A drop of CBF from 58 ± 8 to 17 ± 3 ml/100 g min in the parieto-frontal cortex caused shortening of T₂. from 66.9 ± 0.4 to 64.6 ± 0.5 ms. Under these conditions, no change in diffusion MRI was detected. In contrast, the cortex with CBF of 42 ± 7 ml/100 g min showed no change in T₂. Computer simulations accurately predicted these T₂, responses. The present study shows that the acute drop of CBF by 70% causes a negative BOLD that is readily detectable by T₂ MRI at 1.5 T. Thus BOLD may serve as an index of misery perfusion thus revealing viable tissue with increased OER.