A VOXEL-BY-VOXEL MULTIVARIATE-ANALYSIS OF CEREBRAL PERFUSION DEFECTS IN DIVERS WITH BENDS

Past analysis of dysbaric-induced cerebral perfusion defects, demonstr ated by Tc-99(m)-hexamethylpropylene amine oxime (Tc-99(m)-HMPAO) sing le photon emission tomography in divers using quantitative and/or univ ariate techniques, has resulted in considerable controversy regarding the significance of these lesions compared to those seen in control su bjects, correlations with clinical findings and the role of Tc-99(m)-H MPAO as a prognostic indicator in decompression sickness. We tried to address these problems by using a multivariate approach to a voxel-by- voxel analysis, involving the use of principal components, to determin e ranges of normality in 50 reference controls. in subsequent images, abnormality was defined as 10 spatially connected voxels at an appropr iate significance level of three standard deviations. The images of 50 divers with clinically diagnosed 'bends' were compared with those of a further 40 normal population controls with no previous history of lo ss of consciousness, head injury or dysbarism. The results showed that 19 of 50 divers with 'bends' and 3 of 40 population controls had sign ificant perfusion defects, representing a significant difference betwe en divers with dysbarism and population controls at the level P < 0.00 2. It is concluded that dysbarism causes significant cerebral cortical perfusion defects in affected divers both in 'silent' and symptomatic (clinically correlated) areas.