Quantitative single image-based magnetization transfer weighted imaging using an inter-subject normalization reference within the image
Disclosed is a system and method for generating quantitative imagery of demyelination in the spinal cord. The method includes acquiring a magnetization transfer weighted (MTw) MR image of the spinal column, identifying a reference region of interest within the image corresponding to cerebrospinal fluid (CSF), averaging the signal intensity corresponding to the reference region of interest, and computing a ratio, on a voxel-by-voxel basis, of the signal intensity of each voxel by the averaged reference signal intensity. In doing so, normalized MTw images are obtained such that detrimental artifacts such as motion-induced errors, coil loading, and RF coil sensitivity variations are obviated.
1. A method for quantifying loss of macromolecular components in tissue, comprising:
acquiring an MTw image of the tissue, the MTw image having a plurality of voxels, wherein each voxel has a corresponding MR signal;
identifying a reference region of voxels within the plurality of voxels, wherein the region of voxels corresponds to a reference material having a minimal magnetization transfer effect;
computing a reference MR signal corresponding to the region of voxels; and
computing a normalized MT weighted image, based on the ratio of the MTw image and the reference MR signal.
2. The method of claim 1 , wherein computing the reference MR signal comprises computing an average of a plurality of MR signals corresponding to the region of voxels.
3. The method of claim 1 , wherein acquiring the MTw image comprises employing an image acquisition scheme with an MT preparation pre-pulse.
4. The method of claim 1 , wherein acquiring the MTw image comprises employing a T2* weighted pulse sequence with an MT pre-pulse.
5. The method of claim 1 , wherein the tissue comprises spinal cord tissue.
6. The method of claim 5 , wherein the reference material comprises cerebrospinal fluid.
7. The method of claim 1 , wherein computing the normalized MT weighted image comprises dividing each MTw signal by the reference MR signal.
8. The method of claim 1 , further comprising:
acquiring a second MR image; and
comparing the second MR image with the MT weighted image.
9. An MRI system, comprising:
a main magnet;
a gradient coil;
an RF coil; and
a computer having a computer readable medium encoded with a program for acquiring an MTw image of the tissue, the MTw image having a plurality of voxels, wherein each voxel has a corresponding MR signal; identifying a reference region of voxels within the plurality of voxels, wherein the region of voxels corresponds to a reference material having a minimal magnetization transfer effect; computing a reference MR signal corresponding to the region of voxels; and computing an MTCSF image, based on the MR image and the reference MR signal.
10. The MRI system of claim 9 , wherein the program for computing the reference MR signal comprises a program for computing an average of a plurality of MR signals corresponding to the reference region of voxels.
11. The MRI system of claim 9 , wherein the program for computing the MTCSF image comprises a program for dividing each MTw signal by the reference MR signal.
12. A method for quantifying demyelination in a spinal cord, comprising:
acquiring an MTw image of the spinal cord, the MTw image having a plurality of voxels, wherein each voxel has a corresponding MR signal;
identifying a reference region of voxels within the plurality of voxels, wherein the region of voxels corresponds to cerebrospinal fluid;
computing a reference MR signal corresponding to the region of voxels; and
computing a normalized MT weighted image, based on the ratio of the MTw image and the reference MR signal.
13. The method of claim 12 , further comprising identifying a hyperintensity signal region within a portion of the spinal cord that corresponds to white matter.
14. The method of claim 12 , further comprising:
acquiring a conventional MR image of the spinal cord; and
comparing the normalized MT weighted image with the conventional MR image.
15. The method of claim 14 , wherein comparing the normalized MT weighted image comprises co-registering the conventional MR image and the normalized MT weighted image.