Related Experiment Video
Updated: Mar 3, 2026
A Dual Tracer PET-MRI Protocol for the Quantitative Measure of Regional Brain Energy Substrates Uptake in the Rat
Published on: December 28, 2013
Manganese concentration mapping in the rat brain with MRI, PET, and autoradiography
Geoffrey J Topping1,2, Andrew Yung3, Paul Schaffer4
1Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T 2B5, Canada.
Purpose:
Mn2+ is used as a contrast agent and marker for neuronal activity with magnetic resonance imaging (MRI) in rats and mice, but its accumulation is generally not assessed quantitatively. In this work, nonradioactive Mn and 52 Mn are injected simultaneously in rats, and imaged with MRI, positron emission tomography (PET) and autoradiography (AR). Mn distributions are compared between modalities, to assess the potential and limitations on quantification of Mn with MRI, and to investigate the potential of multimodal measurement of Mn accumulation.
Methods:
MRI (in vivo), PET (in vivo and post mortem), and AR (ex vivo) were acquired of rat brains, for which animals received simultaneous intraperitoneal (IP) or intracerebrovertricular (ICV)-targeted injections containing the positron-emitting radionuclide 52 Mn and additional nonradioactive MnCl2 , which acts as an MRI contrast agent. Pre and postinjection MR images were fit for the longitudinal relaxation rate (R1), coregistered, and subtracted to generate R1 difference maps, which are expected to be proportional to change in Mn concentration in tissue. AR and PET images were coregistered to smoothed R1 difference maps.
Results:
Similar spatial distributions were seen across modalities, with Mn accumulation in the colliculus, near the injection site, and in the 4th ventricle. There was no 52 Mn accumulation measurable with PET in the brain after IP injection. In areas of very highly localized and concentrated 52 Mn accumulation in PET or AR, consistent increases of R1 were not seen with MRI. Scatter plots of corresponding voxel R1 difference and PET or AR signal intensity were generated and fit with least squares linear models within anatomical regions. Linear correlations were observed, particularly in regions away from very highly localized and concentrated Mn accumulation at the injection site and the 4th ventricle. Accounting for radioactive decay of 52 Mn, the MnCl2 longitudinal relaxivity was between 4.0 and 5.1 s-1 /mM, which is within 22% of the in vitro relaxivity.
Conclusions:
This proof-of-concept study demonstrates that MR has strong potential for quantitative assessment of Mn accumulation in the brain, although local discrepancies from linear correlation suggest limitations to this use of MR in areas of inflammation or very high concentrations of Mn. These discrepancies also suggest that a combination of modalities may have additional utility for discriminating between different pools of Mn accumulation in tissue.
Insights
This study shows magnetic resonance imaging (MRI) can quantify manganese (Mn2+) brain accumulation. Multimodal imaging revealed limitations in high-concentration areas, suggesting combined approaches for precise Mn2+ measurement.
Area of Science:
- Neuroimaging
- Biomedical Engineering
- Radiochemistry
Background:
- Manganese (Mn2+) is a contrast agent for neuronal activity in MRI.
- Quantitative assessment of Mn2+ accumulation is challenging.
- Simultaneous nonradioactive Mn and radioactive 52 Mn offer multimodal analysis potential.
Purpose of the Study:
- To compare Mn distribution across MRI, PET, and autoradiography (AR).
- To assess MRI's potential and limitations for quantitative Mn accumulation.
- To investigate multimodal measurement of Mn accumulation.
Main Methods:
- Rats received simultaneous intraperitoneal (IP) or intracerebroventricular (ICV) injections of 52 Mn and nonradioactive MnCl2.
- In vivo MRI, PET, and ex vivo AR were used to image Mn distribution.
- R1 difference maps from MRI were coregistered with PET and AR images.
Main Results:
- Similar Mn spatial distributions were observed across MRI, PET, and AR.
- MRI showed limitations in quantifying Mn in areas of very high concentration.
- Linear correlations between MRI R1 difference and PET/AR signals were found, except near injection sites.
Conclusions:
- MRI shows significant potential for quantitative Mn brain accumulation assessment.
- Limitations exist in areas of inflammation or very high Mn concentrations.
- Multimodal imaging may improve discrimination of Mn accumulation pools.
