Christian Federau

Measuring brain perfusion with intravoxel incoherent motion (IVIM) MRI was first proposed over 25 years ago,¹ but this idea did not translate at the time into any useful clinical application. We thought this might have been due to technical challenges, and that software and hardware improvement over the last two decades might have solved some of the issues. The method is based on the fact that at low b-values some of the drop in signal amplitude due to diffusion gradients might be due to the movements (“mixing”) of blood in the microvasculature. This elegant explanation is reasonable because the measured “diffusion” at low b-value (so called “pseudodiffusion”) is faster than thermal diffusion of water at body temperature, and therefore, external input of energy (from the heart) seems necessary to produce the measured effect. We therefore decided to revisit the method in the current technological environment.

We performed various validation studies, and found a gradual increase of IVIM perfusion parameters with a gradual hypercapnia challenge (known to increase cerebral perfusion),² as well as a dependence of those parameters on the cardiac cycle,³ while “thermal” diffusion remained mainly unchanged in both experiments. Furthermore, Iima et al found a correlation between IVIM perfusion fraction and capillary density in mice brain tumors.⁴ We then studied the applicability of the method in the current clinical setting.

In this study,⁵ we were able to demonstrate a difference in IVIM perfusion fraction between high- and low-grade gliomas, while in the same issue of AJNR, Kim et al showed the utility of the method in the assement of tumor reccurence.⁶ Furthermore, Suh et al demonstrated the utility of the IVIM perfusion fraction in differentiating between gliobastoma and lymphoma,⁷ while we found in a further study a decrease in perfusion fraction in the infarct core of acute strokes.⁸ Taken together, we think that those results are encouraging, and we hope that they will increase the general interest in this method, as it has many advantages over current perfusion methods: it is simple and fast, requires no contrast injection, and is intrinsically local and quantitative.

References

1. Le Bihan D, Breton E, Lallemand D, et al. Intravoxel incoherent motion imaging using steady-state free precession. Magn Reson Med 1988;7:46–51, 10.1002/mrm.1910070312
2. Federau C, Maeder P, O’Brien K, et al. Quantitative measurement of brain perfusion with intravoxel incoherent motion MR imaging. Radiology 2012;265:874–81, 10.1148/radiol.12120584
3. Federau C, Hagmann P, Maeder P, et al. Dependence of brain intravoxel incoherent motion perfusion parameters on the cardiac cycle. PLoS One 2013;8:e72856, 10.1371/journal.pone.0072856
4. Iima M, Le Bihan D, Okumura R, et al. Apparent diffusion coefficient as an MR imaging biomarker of low-risk ductal carcinoma in situ: a pilot study. Radiology 2011;260:364–72, 10.1148/radiol.11101892
5. Federau C, Meuli R, O’Brien K, et al. Perfusion measurement in brain gliomas with intravoxel incoherent motion MRI. AJNR Am J Neuroradiol 2014;35:256–62, 10.3174/ajnr.A3686
6. Kim HS, Suh CH, Kim N, et al. Histogram analysis of intravoxel incoherent motion for differentiating recurrent tumor from treatment effect in patients with glioblastoma: initial clinical experience. AJNR Am J Neuroradiol 2014;35:490–97, 10.3174/ajnr.A3719
7. Suh CH, Kim HS, Lee SS, et al. Atypical imaging features of primary central nervous system lymphoma that mimics glioblastoma: utility of intravoxel incoherent motion MR imaging. Radiology 2014;272:504–13, 10.1148/radiol.14131895
8. Federau C, Sumer S, Becce F, et al. Intravoxel incoherent motion perfusion imaging in acute stroke: initial clinical experience. Neuroradiology 2014;56:629–35, 10.1007/s00234-014-1370-y

Read this article at AJNR.org . . .