title: Intensity standardisation of 7T MR images for intensity-based segmentation of the human hypothalamus.
abstract: The high spatial resolution of 7T MRI enables us to identify subtle volume changes in brain structures, providing potential biomarkers of mental disorders. Most volumetric approaches require that similar intensity values represent similar tissue types across different persons. By applying colour-coding to T1-weighted MP2RAGE images, we found that the high measurement accuracy achieved by high-resolution imaging may be compromised by inter-individual variations in the image intensity. To address this issue, we analysed the performance of five intensity standardisation techniques in high-resolution T1-weighted MP2RAGE images. Twenty images with extreme intensities in the GM and WM were standardised to a representative reference image. We performed a multi-level evaluation with a focus on the hypothalamic region-analysing the intensity histograms as well as the actual MR images, and requiring that the correlation between the whole-brain tissue volumes and subject age be preserved during standardisation. The results were compared with T1 maps. Linear standardisation using subcortical ROIs of GM and WM provided good results for all evaluation criteria: it improved the histogram alignment within the ROIs and the average image intensity within the ROIs and the whole-brain GM and WM areas. This method reduced the inter-individual intensity variation of the hypothalamic boundary by more than half, outperforming all other methods, and kept the original correlation between the GM volume and subject age intact. Mixed results were obtained for the other four methods, which sometimes came at the expense of unwarranted changes in the age-related pattern of the GM volume. The mapping of the T1 relaxation time with the MP2RAGE sequence is advertised as being especially robust to bias field inhomogeneity. We found little evidence that substantiated the T1 map's theoretical superiority over the T1-weighted images regarding the inter-individual image intensity homogeneity.
authors.affiliation: Department of Psychiatry and Psychotherapy, University Hospital Leipzig, Leipzig, Germany.|Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors.forename: Stephanie
authors.identifier: http://orcid.org/0000-0003-1378-0053
authors.initials: S
authors.lastname: Schindler
authors.affiliation: Department of Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Schreiber
authors.affiliation: Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.|Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors.forename: Pierre-Louis
authors.initials: PL
authors.lastname: Bazin
authors.affiliation: Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Trampel
authors.affiliation: Department of Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors.forename: Alfred
authors.initials: A
authors.lastname: Anwander
authors.affiliation: Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Geyer
authors.affiliation: Department of Psychiatry and Psychotherapy, University Hospital Leipzig, Leipzig, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Schönknecht
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007031:Hypothalamus / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged