Our laboratory and others have reported the ability to detect individual Alzheimer's disease (AD) amyloid plaques in transgenic mouse brain in vivo by magnetic resonance imaging (MRI). Since amyloid plaques contain iron, most MRI studies attempting to detect plaques in AD transgenic mouse brain have employed techniques that exploit the paramagnetic effect of iron and have had mixed results. In the present study, using five-way anatomic spatial coregistration of MR images with three different histological techniques, properties of amyloid plaques in AD transgenic mouse brain were revealed that may explain their variable visibility in gradient- and spin-echo MR images. The results demonstrate differences in the visibility of plaques in the cortex and hippocampus, compared to plaques in the thalamus, by the different MRI sequences. All plaques were equally detectable by T2SE, while only thalamic plaques were reliably detectable by T2*GE pulse sequences. Histology revealed that cortical/hippocampal plaques have low levels of iron while thalamic plaques have very high levels. However, the paramagnetic effect of iron does not appear to be the sole factor leading to the rapid decay of transverse magnetization (short T2) in cortical/hippocampal plaques. Accordingly, MRI methods that rely less on iron magnetic susceptibility effect may be more successful for eventual human AD plaque MR imaging, particularly since human AD plaques more closely resemble the cortical and hippocampal plaques of AD transgenic mice than thalamic plaques.
Bibliographical noteFunding Information:
The authors would like to thank Karen Duff for providing the PS1 transgenic breeder mice, Gregor Adriany for developing the MRI coil, and Dawn Gregor and Jennifer Scott for their expert technical assistance. The authors would also like to thank Thomas Moyer, Ph.D., and Darcy Fjosne from the Metals Laboratory in the Mayo Department of Laboratory Medicine and Pathology. This work was supported by NIH grants R01 AG22034 , P30 NS057091 , and P41 RR008079 , the Minnesota Biotechnology Partnership , the MIND Institute , and the Mayo Foundation .
- Alzheimer's disease
- Magnetic resonance imaging
- Thioflavine S