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Absolute quantitation of brain metabolites with respect to heterogeneous tissue compositions in 1H-MR spectroscopic volumes

  • Alexander GussewEmail author
  • Marko Erdtel
  • Patrick Hiepe
  • Reinhard Rzanny
  • Jürgen R. Reichenbach
Research Article

Abstract

Object

Referencing metabolite intensities to the tissue water intensity is commonly applied to determine metabolite concentrations from in vivo 1H-MRS brain data. However, since the water concentration and relaxation properties differ between grey matter, white matter and cerebrospinal fluid (CSF), the volume fractions of these compartments have to be considered in MRS voxels.

Materials and methods

The impact of partial volume correction was validated by phantom measurements in voxels containing mixtures of solutions with different NAA and water concentrations as well as by analyzing in vivo 1H-MRS brain data acquired with various voxel compositions.

Results

Phantom measurements indicated substantial underestimation of NAA concentrations when assuming homogeneously composed voxels, especially for voxels containing solution, which simulated CSF (error: ≤92%). This bias was substantially reduced by taking into account voxel composition (error: ≤10%). In the in vivo study, tissue correction reduced the overall variation of quantified metabolites by up to 35% and revealed the expected metabolic differences between various brain tissues.

Conclusions

Tissue composition affects extraction of metabolite concentrations and may cause misinterpretations when comparing measurements performed with different voxel sizes. This variation can be reduced by considering the different tissue types by means of combined analysis of spectroscopic and imaging data.

Keywords

1H-MRS Absolute quantitation Brain Tissue segmentation Partial volume effect correction 

Abbreviations

1H-MRS

Proton magnetic resonance spectroscopy

rf

Radiofrequency

T1 and T2

Longitudinal and transversal relaxation time constants

CM, CW

Absolute concentrations of metabolites and water

IM

Quantitated intensity of metabolite

IW

Quantitated intensity of water

NMprot

Number of hydrogen nuclei within the metabolite molecule

GM, WM, CSF

Brain’s grey and white matter and cerebrospinal fluid

S1, S2, S3

Phantom solutions 1, 2 and 3

fGM, fWM, fCSF

Relative volume fractions of GM, WM and CSF within a voxel

fS1, fS2, fS3

Relative volume fractions of GM, WM and CSF within a voxel

R

Factor to consider the relaxation related signal attenuation

CW0

Free water concentration

α

Relative water content in tissue

NAA, Cr, tCho

N-acetyl-aspartate, creatine, total choline

CWsolution

Nominal water concentration in a phantom solution

Cnomsolution

Nominal NAA concentration in a phantom solution

TR, TE, TI

Repetition time, echo time, inversion time

FOV

Field of view

GI, GII

Volunteer groups 1 and 2 (each consisting of seven persons)

NAS

Number of averaged single acquisitions

SNR

Signal to noise ratio

FWHM

Full width at half maximum

CRLB

Cramer Rao lower bound

Chom

Metabolite concentration calculated by assuming homogeneous tissue composition in MRS voxel

Chet

Metabolite concentration calculated by considering the heterogeneous tissue composition in MRS voxel

Notes

Acknowledgments

This study was supported by the Centre for Interdisciplinary Prevention of Diseases related to Professional Activities (KIP) founded by the Friedrich-Schiller-University Jena and the Accident Prevention and Insurance Association for Food and Restaurants (Berufsgenossenschaft Nahrungsmittel und Gaststätten, BGN, Germany). A. G. acknowledges support from a stipend provided by KIP (project 1.1.29). This project was also supported by the Deutsche Forschungsgemeinschaft (DFG 1123/11-1) and by the Bernstein Group for Computational Neuroscience Jena (BMBF 01GQ0703). We acknowledge Mary Atterbury for her support in manuscript preparation and proof reading.

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Copyright information

© ESMRMB 2012

Authors and Affiliations

  • Alexander Gussew
    • 1
    Email author
  • Marko Erdtel
    • 1
    • 2
  • Patrick Hiepe
    • 1
  • Reinhard Rzanny
    • 1
  • Jürgen R. Reichenbach
    • 1
  1. 1.Medical Physics Group, Institute of Diagnostic and Interventional Radiology IJena University Hospital—Friedrich Schiller University JenaJenaGermany
  2. 2.Department of Medical PhysicsNinewells Hospital and Medical School, University of DundeeDundeeUK

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