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Erschienen in:
01.08.2015 | Research Article
IVIM analysis of brain tumors: an investigation of the relaxation effects of CSF, blood, and tumor tissue on the estimated perfusion fraction
Erschienen in: Magnetic Resonance Materials in Physics, Biology and Medicine | Ausgabe 4/2015
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Object
We sought to investigate the dependence of intravoxel incoherent motion (IVIM)-related perfusion fraction (f) estimates on the transverse relaxation of brain tissue, blood, and cerebrospinal fluid (CSF), attempting to overcome the influence of CSF on conventional f maps.
Materials and methods
Eighteen patients with gliomas underwent DWI with 14 b-values (0–1,300 s/mm2) and two distinct echo times (TEs). Regions of interest representing tumour and normal brain tissue were analysed by calculating the f values for both TEs. A mask for pixels with relevant CSF partial volume was subsequently created. The f values were tested for significant differences.
Results
We found statistically significant differences between the two TEs in the f values for cortical and juxtacortical structures and non-enhancing areas of the tumour /oedema. Normal white matter and gadolinium-enhancing tumour tissue appeared insensitive to TE variation. In all tissue types examined, the masking of voxels with considerable CSF content was able to overcome issues of erroneous f estimation and calculation of f values insensitive to TE changes was feasible.
Conclusion
Due to the complex interaction in the relaxation rates of CSF, blood, and tumour tissue, the estimation of f values is affected by the choice of TE. Only f values in normal white matter and tumour tissue—which largely comprise blood voxels with minor CSF partial volume—may be clinically applicable in the present form of IVIM-based DWI analysis. Going a step further, and after removing voxels with heavily TE-susceptible f values, we were able to obtain accurate and TE-independent f values in contrast-enhancing tumour tissue, white matter, and grey matter, which were essentially consistent with those reported in the literature.