title: Differentiation of calcified regions and iron deposits in the ageing brain on conventional structural MR images.
abstract: OBJECTIVE
  In the human brain, minerals such as iron and calcium accumulate increasingly with age. They typically appear hypointense on T2*-weighted MRI sequences. This study aims to explore the differentiation and association between calcified regions and noncalcified iron deposits on clinical brain MRI in elderly, otherwise healthy subjects.
  
  
  METHODS
  Mineral deposits were segmented on co-registered T1- and T2*-weighted sequences from 100 1.5 Tesla MRI datasets of community-dwelling individuals in their 70s. To differentiate calcified regions from noncalcified iron deposits we developed a method based on their appearance on T1-weighted images, which was validated with a purpose-designed phantom. Joint T1- and T2*-weighted intensity histograms were constructed to measure the similarity between the calcified and noncalcified iron deposits using a Euclidean distance based metric.
  
  
  RESULTS
  We found distinct distributions for calcified regions and noncalcified iron deposits in the cumulative joint T1- and T2*-weighted intensity histograms across all subjects (correlations ranging from 0.02 to 0.86; mean = 0.26 ± 0.16; t = 16.93; P < 0.001) consistent with differences in iron and calcium signal in the phantom. The mean volumes of affected tissue per subject for calcified and noncalcified deposits were 236.74 ± 309.70 mm(3) and 283.76 ± 581.51 mm(3); respectively. There was a positive association between the mineral depositions (β = 0.32, P < 0.005), consistent with existing literature reports.
  
  
  CONCLUSIONS
  Calcified mineral deposits and noncalcified iron deposits can be distinguished from each other by signal intensity changes on conventional 1.5T T1-weighted MRI and are significantly associated in brains of elderly, otherwise healthy subjects.
authors.affiliation: Brain Research Imaging Centre, Department of Neuroimaging Sciences, University of Edinburgh, Edinburgh, United Kingdom; Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh, Edinburgh, United Kingdom; SINAPSE (Scottish Imaging Network, A Platform for Scientific Excellence) collaboration, Scotland, United Kingdom.
authors.forename: Maria del C
authors.initials: Mdel C
authors.lastname: Valdés Hernández
authors.forename: Andreas
authors.initials: A
authors.lastname: Glatz
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Kiker
authors.forename: David Alexander
authors.initials: DA
authors.lastname: Dickie
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Aribisala
authors.forename: Natalie A
authors.initials: NA
authors.lastname: Royle
authors.forename: Susana
authors.initials: S
authors.lastname: Muñoz Maniega
authors.forename: Mark E
authors.initials: ME
authors.lastname: Bastin
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Deary
authors.forename: Joanna M
authors.initials: JM
authors.lastname: Wardlaw
mesh_terms: D000368:Aged; D000375:Aging / Q000378:metabolism* / Q000473:pathology; D001921:Brain / Q000033:anatomy & histology; D001923:Brain Chemistry; D002118:Calcium / Q000032:analysis*; D002119:Calcium Carbonate / Q000032:analysis*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007501:Iron / Q000032:analysis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution
chemical_list: D007501:Iron; D002119:Calcium Carbonate; D002118:Calcium
keywords: MRI; ageing; brain; calcium; iron; segmentation