Experimental hypoxemic hypoxia: Changes in R2* of brain parenchyma accurately reflect the combined effects of changes in arterial and cerebral venous oxygen saturation
✍ Scribed by Weili Lin; Richard P. Paczynski; Azim Celik; Karthikeyan Kuppusamy; Chung Y. Hsu; William J. Powers
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 912 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0740-3194
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✦ Synopsis
Abstract
A two‐dimensional T~2~*‐weighted gradient‐echo sequence was used to image the rat brain before and during graded hypoxemia. Changes in R~2~* (δ__R__~2~*) with respect to the control state were calculated for brain parenchyma and were compared with changes in hemoglobin saturation measured from both arterial and jugular venous blood samples. δ__R__~2~* was first correlated with the changes in arterial (δ__Y__a) and venous (δ__Y__v) hemoglobin saturations individually. Although a general trend toward a linear relationship with δ__R__~2~* was observed for both δ__Y__a and δ__Y__v, neither alone was strong (correlation coefficients r = 0.71 and 0.75 for δ__Y__a and δ__Y__v, respectively, and standard errors of the regression (SER) = 0.52 and 0.48 for δ__Y__a and δ__Y__v, respectively). However, when an “effective” cerebral blood hemoglobin saturation change (δ__Y__b) was constructed that takes into account the approximate weighting of the contributions from the arterial and venous phases of the circulation (δ__Y__b = 0.75 × δ__Y__v + 0.25 × δ__Y__a), a stronger correlation with δ__R__~2~* was obtained and there was less variance (r = 0.87 and SER = 0.35). It is concluded that an appropriate weighting of the contributions of arterial and venous phases of the circulation must be taken into account in modeling the volume susceptibility effects of deoxyhemoglobin on R~2~* of brain parenchyma. In this way, a more accurate relationship between δ__R__~2~* and δ__Y__b can be obtained.