Fig. 4.

Schematic diagram showing the multiple in vivo ¹⁷O measurements at 9.4T for determining CMRO₂ using the complete model according to the mass balance equation of Eq. [7] which links C_b(t), C_a(t), CBF and n with CMRO₂. To simplify the equation, three known constants of 2αf₁, mf₂ and m/λ used in Eq. [7] are replaced by k₁, k₂ and k₃, respectively. (A) Stacked plot of the ¹⁷O spectra of cerebral H₂¹⁷O tracer from one representative voxel as indicated by the circle in the anatomical brain image (low center insert). The spectra were acquired before and after a bolus injection of H₂¹⁷O for CBF measurements. (B) Stacked plot of the ¹⁷O spectra of the metabolic H₂¹⁷O from the same voxel acquired before (natural abundance), during (as indicated by the gray bar under the stacked plot) and after a 2-minute ¹⁷O₂ inhalation. (C) Measurement of C_a(t) by using an implanted ¹⁷O RF coil (the left insert). The middle insert illustrates an ¹⁷O spectrum of natural abundance H₂¹⁷O obtained from the rat carotid artery blood with the implanted coil before ¹⁷O₂ inhalation. The right insert shows the time course of C_a(t) (circle symbol) and C_b(t) from a representative 3D ¹⁷O CSI voxel (square symbol) in the same rat during the ¹⁷O₂ inhalation. Finally, the ratio between the ¹⁷O signal decay detected after a bolus injection of H₂¹⁷O (see Fig. 4A) versus the ¹⁷O signal decay detected after the cessation of ¹⁷O₂ inhalation (see Fig. 4B) gives the constant of n. Adapted from Zhu et. al. PNAS 2002; 99: 13194–13199.