Nomenclature

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.

Ratios

• 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)

ROI	Absolute Rate of Atrophy	Relative Rate of Atrophy
Telencephalic ROI
Cortical Gray Matter	yrA-CGM	yrRA-CGM(Ref)
Whole Brain Hemisphere	yrA-WBHp	yrRA-WBH(Ref)
Brain Hemispheric-Cortical Gray Matter	yrA-BHpCGM	yrA-BHCGM(Ref)
Lobar Cortical Gray Matter (frontal, temporal, parietal, occipital and insular lobes)	yrA-LCGM	yrA-LCGM(Ref)
Gyri (the name of any girus is suitable, following international nomina anatomica)	yrA-"Gyrus name"	yrRA-"Gyrus name"(Ref)
Forebrain Parenchyma	yrA-FP	yrRA-FP(Ref)
Hippocampus	yrA-H	yrRA-H(Ref)
Medial temporal lobe (hippocampus + parahippocamal gyrus)	yrA-MTL	yrRA-MTL(Ref)
Amygdala	yrA-Amy	yrRA-Amy(Ref)
Caudate	yrA-Cau	yrRA-Cau(Ref)
Putamen	yrA-Pu	yrRA-Pu(Ref)
Striatum (Caudate+Putamen)	yrA-St	yrRA-St(Ref)
Pallidum	yrA-Pa	yrRA-Pa(Ref)
Lenticularis nucleus (Putamen+Pallidum)	yrA-Len	yrRA-Len(Ref)
Diencephalic ROI
Thalamus	yrA-T	yrRA-T(Ref)
Hypothalamus	yrA-HypoT	yrRA-GypoT(Ref)
Subthalamic nucleus	yrA-SubT	yrRA-SubT(Ref)
ROI in the posterior fossa
Whole Cerebellum	yrA-WCer	yrRA-Cer(Ref)
Whole Cerebellar Hemisphere	yrA-WCerHp	yrRA-HCer(Ref)
Whole Cerebellar Cortical Gray Matter	yrA-WCerCGM	yrRA-WCerCGM(Ref)
Cerebellar Hemispheric  Cortical Gray Matter	yrA-CerHpCGM	yrRA-CerHCGM(Ref)
Midbrain (Mesencephalon)	yrA-MidB	yrRA-MidB(Ref)
Pons	yrA-Pons	yrRA-Pons(Ref)
Medulla	yrA-Med	yrRA-Med(Ref)
Olivary body	yrA-OB	yrRA-OB(Ref)
Substantia Nigra	yrA-Sn	yrRA-Sn(Ref)
Red Nucleus	yrA-Rn	yrRA-Rn(Ref)

Table 1: Nomenclature of Regions of Interest (ROI) and related indices of regional atrophy

Brain Structure	Initials or Symbol
To be used with Telencephalic ROI
Whole Brain	WB
Brain Hemisphere	BHp
Cortical Gray Matter	CGM
Lateral Ventricles	I-II
To be used with Diencephalic ROI
Whole Brain	WB
Third Ventricle	III
To be used with ROI in the posterior fossa
Whole Brain	WB
Parenchyma in the posterior fossa	Ppf
Cerebellar Hemisphere	CerHp
Fourth Ventricle	IV

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 most frequently used ROI with the corresponding nomenclature for absolute and relative rates of atrophy. The letters "Ref" refer to the structure or parameter used as measure of reference.

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). 

Structures frequently used as reference in indices of relative rate of regional atrophy. Structures are arranged by the location of the ROI that will be used along.

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“.