Andrew Alexander, PhD

Slide of the Week: Andrew Alexander, PhD

Title: Multiple contrast MRI with retrospective motion correction

Legend:  Representative example of multiple image contrasts from a new brain imaging technique MPnRAGE developed in the Alexander Lab in the Waisman Brain Imaging Core.  The MPnRAGE method can generate multiple inversion recovery contrasts, quantitative T1 relaxometry, and tissue specific (gray matter or white matter) maps.  Whole brain three-dimensional images are acquired in roughly 8 minutes with 1 mm isotropic resolution.

Citations:  Kecskemeti, S., Samsonov, A., Hurley, S. A., Dean, D. C., Field, A. and Alexander, A. L. (2015), MPnRAGE: A technique to simultaneously acquire hundreds of differently contrasted MPRAGE images with applications to quantitative T1 mapping. Magnetic Resonance in Medicine. doi: 10.1002/mrm.25674

Alexander, A. L., Kecskemeti, S. R.  Improved Dual White Matter and CSF Suppression using MPnRAGE.  2014 Proceedings of the International Society for Magnetic Resonance in Medicine.  Abstract 416.


Purpose:  To introduce a new technique called MPnRAGE, which produces hundreds of images with different T1 contrasts and a B1 corrected T1 map.

Theory and Methods:  An interleaved 3D radial k-space trajectory with a sliding window reconstruction is used in conjunction with magnetization preparation pulses.  This work modifies the SNAPSHOT-FLASH T1 fitting equations for radial imaging with view-sharing and develops a new rapid B1 correction procedure. MPnRAGE is demonstrated in phantoms and volunteers, including 2 volunteers with 8 scans each and 8 volunteers with 2 scans each.   T1  values from MPnRAGE were compared with those from fast spin echo inversion recovery (FSE-IR) in phantoms and a healthy human brain at 3T.

Results: The T1 fit for human white and gray matter was T1MPnRAGE=1.00 · T1FSE-IR + 24 ms, r2=0.990.  Voxel-wise coefficient of variation in T1 measurements across 8 times points was between 0.02 and 0.08.  ROI based T1 values were reproducible to within 2% and agree well with literature values.

Conclusions:  In the same amount of time as a traditional MPRAGE exam (7.5 minutes), MPnRAGE was shown to produce hundreds of images with alternate T1 contrasts as well as an accurate and reproducible T1 map that is robust to B1 errors.

About the Lab: Alexander’s research focuses on the use of magnetic resonance imaging (MRI) for mapping and measuring the functional and structural organization of the human brain. These techniques are used to investigate the brain in both typically developing individuals and subjects with developmental disorders including autism. Functional MRI (fMRI) is used to assess brain regions associated with cognition and affect and their dysfunctions in these populations. Diffusion tensor MRI (DT-MRI) is used to study the patterns of structural connectivity between brain activity regions. Anatomic imaging methods are used to assess longitudinal structural changes in brain regions. These measurements are ultimately compared with measures of affect, behavior and cognition in specific population groups.

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