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Accuracy and precision of MR blood oximetry based on the long paramagnetic cylinder approximation of large vessels
Author(s) -
Langham Michael C.,
Magland Jeremy F.,
Epstein Charles L.,
Floyd Thomas F.,
Wehrli Felix W.
Publication year - 2009
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21981
Subject(s) - biomedical engineering , reproducibility , nuclear magnetic resonance , tilt (camera) , accuracy and precision , coefficient of variation , cylinder , saturation (graph theory) , pulse sequence , repeatability , materials science , field strength , concordance correlation coefficient , chemistry , magnetic field , physics , medicine , mathematics , geometry , statistics , chromatography , quantum mechanics , combinatorics
An accurate noninvasive method to measure the hemoglobin oxygen saturation (% HbO 2 ) of deep‐lying vessels without catheterization would have many clinical applications. Quantitative MRI may be the only imaging modality that can address this difficult and important problem. MR susceptometry–based oximetry for measuring blood oxygen saturation in large vessels models the vessel as a long paramagnetic cylinder immersed in an external field. The intravascular magnetic susceptibility relative to surrounding muscle tissue is a function of oxygenated hemoglobin ( HbO 2 ) and can be quantified with a field‐mapping pulse sequence. In this work, the method's accuracy and precision was investigated theoretically on the basis of an analytical expression for the arbitrarily oriented cylinder, as well as experimentally in phantoms and in vivo in the femoral artery and vein at 3T field strength. Errors resulting from vessel tilt, noncircularity of vessel cross‐section, and induced magnetic field gradients were evaluated and methods for correction were designed and implemented. Hemoglobin saturation was measured at successive vessel segments, differing in geometry, such as eccentricity and vessel tilt, but constant blood oxygen saturation levels, as a means to evaluate measurement consistency. The average standard error and coefficient of variation of measurements in phantoms were <2% with tilt correction alone, in agreement with theory, suggesting that high accuracy and reproducibility can be achieved while ignoring noncircularity for tilt angles up to about 30°. In vivo, repeated measurements of % HbO 2 in the femoral vessels yielded a coefficient of variation of less than 5%. In conclusion, the data suggest that % HbO 2 can be measured reproducibly in vivo in large vessels of the peripheral circulation on the basis of the paramagnetic cylinder approximation of the incremental field. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.