Accuracy and precision of MR blood oximetry based on the long paramagnetic cylinder approximation of large vessels

Michael C. Langham, Jeremy F. Magland, Charles L. Epstein, Thomas F. Floyd, Felix W. Wehrli

Research output: Contribution to journalArticle

40 Scopus citations

Abstract

An accurate noninvasive method to measure the hemoglobin oxygen saturation (%HbO2) 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 (HbO2) 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 %HbO2 in the femoral vessels yielded a coefficient of variation of less than 5%. In conclusion, the data suggest that %HbO2 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.

Original languageEnglish (US)
Pages (from-to)333-340
Number of pages8
JournalMagnetic resonance in medicine
Volume62
Issue number2
DOIs
StatePublished - Aug 2009

Keywords

  • Blood oxygen saturation
  • Demagnetizing field
  • Magnetic resonance oximetry
  • Magnetic resonance susceptometry
  • Phase imaging

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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