Wolfgang R. Bauer

Theory of the BOLD effect in the capillary region: An analytical approach for the determination of T*2 in the capillary network of myocardium

This article presents an analytical approach for the quantification of the blood oxygen level dependent (BOLD) effect in the capillary region. The capillary geometry of myocardium is considered. The relaxation rate R u2009*2 is determined as a function of the capillary radius Rc, the intracapillary volume fraction RBV, and the diffusion coefficient D. When the intracapillary volume fraction is small, the approximation R u2009*2 = RBV · τ−1 · (√1u2009+u2009(τδω)2u2009−u20091) is valid, with the correlation time τ = (R u2009c2 /4D) · (|ln RBV|/(1u2009−u2009RBV)). The predictions of this model agree well with numerical simulations and experimental data of others and with data recently measured by our group. Magn Reson Med 41:51‐62, 1999.

Theory of Coherent and Incoherent Nuclear Spin Dephasing in the Heart

We present an analytical theory of susceptibility induced nuclear spin dephasing in the capillary network of myocardium. Using a strong collision approach, equations are obtained for the relaxation rate of the free induction and the spin echo decay. Simulation and experimental data are well predicted by the theory. Since paramagnetic deoxyhemoglobin as the origin of nuclear spin dephasing has a higher tissue concentration in myocardium supplied by a stenotic, i.e., significantly narrowed, coronary artery, spin dephasing might serve as a diagnostic tool. Our approach can be modified for capillary networks in other tissues than myocardium and may be applied in material science.

In Vivo Assessment of Rat Hearts with and without Myocardial Infarction by Cine NMR - Comparison of the NMR Method to Invasive Techniques and Application to Intervention Studies

Aim of the study was to test the feasibility of cine-NMR for assessment of the infarcted rat heart and to compare the results to established methods. Thereafter, the value of cine-NMR was tested in studies investigating interventions to change the course of the remodeling process. NMR was performed for determination of left ventricular (LV) volumes and mass, MI-size and cardiac output. After MRI rats underwent conventional hemodynamic measurements for determination of cardiac output and LV volumes by electromagnetic flowmeter and pressure-volume curves. LV wet weight was determined. MI-size was determined by histology. MRI-acquired MI-size (18.5±2%) was smaller than histology (22.8±2.5%, p<0.05) with close correlation (r=0.97). There was agreement in LV mass between MRI and wet weight (r=0.97, p<0.05) and in the MRI- and flowmeter measurements of cardiac output (r=0.80, p<0.05). Volume by MRI differed from pressure-volume curves with good correlation (r=0.96, p<0.05). In conclusion, cine-NMR is a valuable diagnostic tool applicable to the rat model of MI. Being non-invasive and exact it offers new insights in the remodeling process after MI because serial measurements are possible.