Dynamic and simultaneous MR measurement of R1 and R2* changes during respiratory challenges for the assessment of blood and tissue oxygenation

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Abstract
This work presents a novel method for the rapid and simultaneous measurement of R1 and R2* relaxation rates. It is based on a dynamic short repetition time steady‐state spoiled multigradient‐echo sequence and baseline R1 and B1 measurements. The accuracy of the approach was evaluated in simulations and a phantom experiment. The sensitivity and specificity of the method were demonstrated in one volunteer and in four patients with intracranial tumors during carbogen inhalation. We utilized (ΔR2*, ΔR1) scatter plots to analyze the multiparametric response amplitude of each voxel within an area of interest. In normal tissue R2* decreased and R1 increased moderately in response to the elevated blood and tissue oxygenation. A strong negative ΔR2* and ΔR1 response was observed in veins and some tumor areas. Moderate positive ΔR2* and ΔR1 response amplitudes were found in fluid‐rich tissue as in cerebrospinal fluid, peritumoral edema, and necrotic areas. The multiparametric approach was shown to increase the specificity and sensitivity of oxygen‐enhanced MRI compared to measuring ΔR2* or ΔR1 alone. It is thus expected to provide an optimal tool for the identification of tissue areas with low oxygenation, e.g., in tumors with compromised oxygen supply. Magn Reson Med, 2013.

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