Dependence of the MR signal on the magnetic susceptibility of blood studied with models based on real microvascular networks
Berman, Avery J. L.
Polimeni, Jonathan R.
Buxton, Richard B.
Boas, David A.
MetadataShow full item record
Citation (published version)X. Cheng, A.J.L. Berman, J.R. Polimeni, R.B. Buxton, L. Gagnon, A. Devor, S. Sakadzic, D.A. Boas. 2019. "Dependence of the MR signal on the magnetic susceptibility of blood studied with models based on real microvascular networks." Magn Reson Med, Volume 81, Issue 6, pp. 3865 - 3874. https://doi.org/10.1002/mrm.27660
PURPOSE: The primary goal of this study was to estimate the value of beta , the exponent in the power law relating changes of the transverse relaxation rate and intra-extravascular local magnetic susceptibility differences as Delta R 2 * proportional, variant ( Delta chi ) beta. The secondary objective was to evaluate any differences that might exist in the value of beta obtained using a deoxyhemoglobin-weighted Delta chi distribution versus a constant Delta chi distribution assumed in earlier computations. The third objective was to estimate the value of beta that is relevant for methods based on susceptibility contrast agents with a concentration of Delta chi higher than that used for BOLD fMRI calculations. METHODS: Our recently developed model of real microvascular anatomical networks is used to extend the original simplified Monte-Carlo simulations to compute beta from the first principles. RESULTS: Our results show that beta = 1 for most BOLD fMRI measurements of real vascular networks, as opposed to earlier predictions of beta = 1 .5 using uniform Delta chi distributions. For perfusion or fMRI methods based on contrast agents, which generate larger values for Delta chi , beta = 1 for B 0 </= 9.4 T, whereas at 14 T beta can drop below 1 and the variation across subjects is large, indicating that a lower concentration of contrast agent with a lower value of Delta chi is desired for experiments at high B0. CONCLUSION: These results improve our understanding of the relationship between R2 (*) and the underlying microvascular properties. The findings will help to infer the cerebral metabolic rate of oxygen and cerebral blood volume from BOLD and perfusion MRI, respectively.