Most of the following ratios and indices can be computed using planimetric and volumetric approaches, and the prefix 2D- and 3D- can be used respectively. Also, most of these parameters refer to double structures, therefore the suffix l or r can be used to denote left or right.


  • Temporal horn index (Ti)
  • Medial Temporal-Lobe ratio (MTLr)
  • Hippocampus ratio (Hr)
  • Hippocampus-Ventricle index (HVi)
  • Medial Temporal Lobe Atrophy index (MTAi)
  • Percentage of Brain Parenchyma Volume (PBV)

Rates of atrophy (indices)

ROIAbsolute Rate of AtrophyRelative Rate of Atrophy
Telencephalic ROI
Cortical Gray MatteryrA-CGMyrRA-CGM(Ref)
Whole Brain HemisphereyrA-WBHpyrRA-WBH(Ref)
Brain Hemispheric-Cortical Gray MatteryrA-BHpCGMyrA-BHCGM(Ref)
Lobar Cortical Gray Matter (frontal, temporal, parietal, occipital and insular lobes)yrA-LCGMyrA-LCGM(Ref)
Gyri (the name of any girus is suitable, following international nomina anatomica)yrA-"Gyrus name"yrRA-"Gyrus name"(Ref)
Forebrain ParenchymayrA-FPyrRA-FP(Ref)
Medial temporal lobe (hippocampus + parahippocamal gyrus)yrA-MTLyrRA-MTL(Ref)
Striatum (Caudate+Putamen)yrA-StyrRA-St(Ref)
Lenticularis nucleus (Putamen+Pallidum)yrA-LenyrRA-Len(Ref)
Diencephalic ROI
Subthalamic nucleusyrA-SubTyrRA-SubT(Ref)
ROI in the posterior fossa
Whole CerebellumyrA-WCeryrRA-Cer(Ref)
Whole Cerebellar HemisphereyrA-WCerHpyrRA-HCer(Ref)
Whole Cerebellar Cortical Gray MatteryrA-WCerCGMyrRA-WCerCGM(Ref)
Cerebellar Hemispheric  Cortical Gray MatteryrA-CerHpCGMyrRA-CerHCGM(Ref)
Midbrain (Mesencephalon)yrA-MidByrRA-MidB(Ref)
Olivary bodyyrA-OByrRA-OB(Ref)
Substantia NigrayrA-SnyrRA-Sn(Ref)
Red NucleusyrA-RnyrRA-Rn(Ref)
Table 1: Nomenclature of Regions of Interest (ROI) and related indices of regional atrophy
Brain StructureInitials or Symbol
To be used with Telencephalic ROI
Whole BrainWB
Brain HemisphereBHp
Cortical Gray MatterCGM
Lateral VentriclesI-II
To be used with Diencephalic ROI
Whole BrainWB
Third VentricleIII
To be used with ROI in the posterior fossa
Whole BrainWB
Parenchyma in the posterior fossaPpf
Cerebellar HemisphereCerHp
Fourth VentricleIV
Table 2: Nomenclature of Structures Used as Reference

We propose a standardized, comprehensive terminology for naming the absolute and relative rates of atrophy of every ROI. The proposed nomenclature for the most frequently used ROI can be found in Table 1.
The first two letters denote the “temporal lapse”, this way all indices start with “yr” for “yearly rate”. Then we place the letter “A” if we are referring to an absolute rate of atrophy or the letters “RA” if we are referring to a relative rate of atrophy. Then a hyphen “-” separates the “yrA” or “yrRA” from the name of the ROI. Thus, the hyphen is followed by the initials of the anatomic structure used as ROI. When the ROI is a paired structure, the letter l (left) or r (right) must precede the initials of the structure if we are measuring side by side; otherwise, it will be understood that it is referred to both sides together. Finally, in rates of relative atrophy only, we add the initials of the referenced measure between parenthesis at the end “(Ref)”, where (Ref) is the short name of the parameter or structure used as measure of reference (Table 2). 
Following this nomenclature, it is easy to read any index. For instance, the “yrA-Rn” reads “yearly rate of atrophy of the red nucleus“ -and we understand it is a measure of absolute atrophy of both red nuclei- and the “yrRA-lT(WB)” reads “yearly rate of relative atrophy of the left thalamus referred to whole brain“.  

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