Objective:
To serially quantify changes of iron concentration within hematomas in the intracerebral hemorrhage (ICH) pig model using non-invasive R2* and quantitative susceptibility mapping (QSM) MRI methods.
Introduction:
Hemolysis-related release of hemoglobin/heme/free iron after ICH causes cytotoxic injury. An accurate post hemorrhage assessment of iron would be valuable to develop strategies to prevent secondary damage. The T2* relaxation rate (R2* =1/T2*) on MRI depends on the regional oxy- versus deoxyhemoglobin. Post-ICH excess of deoxyhemoglobin has been applied as a quantitative marker to estimate iron in the brain. However, quantitative susceptibility mapping (QSM) is a new MRI technique that can quantify iron concentration within the hematoma by measuring induced magnetic susceptibility. Using R2* mapping and QSM in a large animal ICH model, we measured spatiotemporal changes in iron concentration in the brain.
Methods:
Lobar ICH was induced by infusion of 2.5 ml autologous blood in 8 Yorkshire pigs with average age/wt of 4-6wk/12.5±2.5kg. MRI was obtained at days 1 and 7. A 3D anatomical and multi-echo gradient echo images were obtained on a clinical 3.0 T Philips Ingenia MRI system. Parametric R2* and susceptibility maps were generated. Regions of interest were placed within hematoma and contralesional CSF.
Results:
R2* measurements in the hematoma at day 1 and day 7 were 41.3 ± 7.3 and 37.7 ± 7.7 s
-1
, respectively, whereas the corresponding susceptibility measurements were 0.75± 0.3 and 0.70 ± 0.5 ppm. The CSF R2* were 5.53 ± 2.1 and 6.85 ± 2.4 s
-1
, whereas susceptibility showed 0.06 ± 0.16 and 0.02 ± 0.03 ppm at the two time points. Both R2* and QSM showed no significant change in iron concentration within the hematoma ROI with p-value of 0.18 and 0.72 over a week. Absence of hyperintense regions remote from the hematoma in susceptibility maps suggested lack of diffuse iron deposition. Good correlation was observed between R2* and QSM (correlation coefficient 0.83 and 0.78 within hematoma, and -0.66 and -0.07 within CSF, at day 1 and 7, respectively).
Conclusion:
R2* and especially QSM, with their ability to provide quantitative iron content, are valuable tools to test new ICH treatments particularly targeting iron in this large animal model.
Measuring iron in the brain using quantitative susceptibility mapping and X-ray fluorescence imaging
