Biomarkers

Diagnosis and treatment of AD relies on imaging of beta amyloid (Aβ) plaques in the brain using PET with radiotracer injection, and brain structural changes using MRI-two imaging modalities with extremely high costs. We have demonstrated that Aβ-plaques can be seen with MRI in high spatial resolution images in brain histological samples using a high field (7T and above), and with long acquisition times (7+ hours), which is too long for clinical human imaging studies. To address this technological challenge, we explored the feasibility of an MRI method (multiple-echo frequency-domain image contrast (MEFIC), which could improve signal-noise-ratio for high spatial resolution while optimizing T2* contrast, to image Aβ-plaques in living human brains at 3T.

Eighteen mild cognitive impaired (MCI) and twelve normal (CN) subjects took part in the study. MEFIC images were acquired on a Siemens Prisma-Fit 3T scanner with a 64-channel head coil in a resolution of 0.4 x 0.4 x 0.7 mm³ and scan time of 12:49. Aβ-PET scan was conducted on a Siemens Biograph mCT 20 PET/CT scanner with Florbetapir. Clinica software was used to calculate the standardized uptake value ratio (SUVr) with SUVr ≥ 1.11 as positive. PET and MEFIC images were co-registered in the patients' native space with SPM12.

Figures 1-2 show evident correspondence between MRI-Aβ map (MEFIC) and the PET-Aβ (SUVr) map from one Aβ+ (MCI) and one Aβ- (CN) subjects. The prominent contrast between gray matter (GM) and white matter (WM) in the Aβ- subject was diminished in the Aβ+ subject mainly due to the Aβ load in the GM. MEFIC imaging provides a greater (10x) T2* contrast to noise ratio over conventional T2* imaging, which allows for high spatial resolution in-vivo brain imaging at 3T. There was a significant negative correlation between the Aβ-PET SUVr value and MEFIC signal in cortical GM (Figure 3).

We have shown that Aβ-plaque can be detected in T2* MRI images with MEFIC in the human brain at 3T. We have confirmed that MRI T2* in GM negatively correlates to SUVr of Aβ PET.