Article

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

Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA 19104, USA.
Magnetic Resonance in Medicine (Impact Factor: 3.4). 08/2009; 62(2):333-40. DOI: 10.1002/mrm.21981
Source: PubMed

ABSTRACT 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 degrees . 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.

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    • "MR susceptometry-based oximetry is a recently developed method for quantifying SvO2, measured in units of percent-oxygenated hemoglobin (%HbO2) [10,24,33,34]. Because deoxyhemoglobin is paramagnetic, a magnetic susceptibility difference exists between deoxygenated blood and oxygenated blood or tissue. "
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    • "Functional magnetic resonance imaging offers multiparametric and noninvasive measurements of blood flow, and relative changes in blood oxygenation, blood volume, and oxygen metabolism (Davis et al, 1998; Mandeville et al, 1998) without depth limitations . However, it is still challenging to isolate pure hemoglobin oxygen saturation (SO 2 ) changes without administration of exogenous contrast agents, especially when measuring a transient functional hemodynamic response in single cerebral vessels (Langham et al, 2009). "
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