Scott Quadrelli1,2, Carolyn Mountford3, and Saadallah Ramadan2
1Queensland University of Technology, Brisbane, Australia, 2The University of Newcastle, Newcastle, Australia, 3The Translational Research Institute, Brisbane, Australia
Synopsis
Whilst many studies have detailed the impact of
partial volume effects on proton magnetic resonance spectroscopy quantification,
there is a paucity of literature explaining how voxel segmentation can be
achieved using freely available neuroimaging packages. Here we aim to demonstrate
a practical guide to magnetic resonance spectroscopy (MRS) voxel segmentation,
partial volume correction and detail how to extract other MR metrics (such as
DTI, fMRI) from a MRS voxel. Purpose
A practical introduction to: co-registration of a MRS
voxel mask; segmentation of a voxel prescription image; calculating tissue
fractions within single voxel spectroscopy (SVS) voxel; absolute metabolite
quantification for 1D and 2D MR spectroscopy and quantification of other MRI
metrics (such as fractional anisotropy) within a SVS voxel.
Outline of Content
Proton MRS in the brain allows
for non-invasive quantification of tissue metabolites that are visible on the
MR time scale, using a conventional MRI scanner. In the brain MRS has been
applied to many different disease processes such malignancy, multiple
sclerosis, cognitive impairment and stroke (1).
The most common methods (water
signal referencing) for absolute quantification is reliant upon tissue water
concentration as an internal reference (2). The concentration of water
varies according to the tissue compartments contained within the spectroscopy
voxel. Variations in tissue and CSF
contents within the voxel effect quantification in two main ways: the relative
water content varies according to the tissue type (i.e. CSF has a greater
concentration of pure water compared to same volume of grey or white matter) (3) and the majority of
metabolites are contained within the GM and WM (partial volume effects) with
extremely low contribution from CSF.
Therefore, partial volume effects should be considered for accurate
quantification. If the water concentration isn’t corrected prior to metabolite
quantification, metabolite concentrations will be underestimated (4). Despite partial volume correction being a
recommended step for absolute quantification of metabolites (5), there is a paucity of
literature describing precisely how voxel segmentation can be achieved from a
practical standpoint.
Multi-parametric MRI can be
useful in increasing the sensitivity and specificity of a biomarker or to
confirm MRS findings. Therefore, it is useful to have an understanding of how
non-spectroscopic parameters (DTI, fMRI, structural) can be determined within
the MRS voxel. We will outline the basic steps required to determine alternate
MR metrics from within a MRS voxel.
During this educational poster
the following topics will be covered (from a practical perspective):
co-registration of a voxel mask; segmentation of a voxel prescription image;
calculating tissue fractions within SVS voxel; absolute metabolite quantification
for 1D and 2D spectroscopy and quantification of other MRI metrics within a SVS
voxel.
Summary
Partial volume effects need to be considered to
accurately quantify in-vivo metabolites. Here we propose to teach a practical
approach to partial volume correction, using freely available neuroimaging
packages.
Acknowledgements
No acknowledgement found.References
1. Oz G, Alger JR, Barker PB, et al. Clinical proton MR
spectroscopy in central nervous system disorders. Radiology [Internet]
2014;270:658–679. doi: 10.1148/radiol.13130531.
2. Gussew A, Rzanny R,
Gullmar D, Scholle HC, Reichenbach JR. 1H-MR spectroscopic detection of
metabolic changes in pain processing brain regions in the presence of
non-specific chronic low back pain. Neuroimage [Internet] 2011;54:1315–1323.
doi: 10.1016/j.neuroimage.2010.09.039.
3. Ernst T, Kreis R,
Ross BD. Absolute quantitation of water and metabolites in the human brain. I.
Compartiments and water. J. Magn. Reson. B 1993;102:1–8.
4. Lee H, Caparelli E,
Li H, Mandal A, Smith SD, Zhang S, Bilfinger T V, Benveniste H. Computerized
MRS voxel registration and partial volume effects in single voxel (1)H-MRS.
Magn. Reson. Imaging [Internet] 2013;31:1197–1205. doi:
10.1016/j.mri.2013.04.001.
5. Jansen JFA, Backes
WH, Nicolay K, Kooi ME. 1H MR spectroscopy of the brain: absolute
quantification of metabolites. Radiology [Internet] 2006;240:318–332. doi:
10.1148/radiol.2402050314.