Brain MR Contribution to the Differential Diagnosis of Parkinsonian Syndromes: An Update

Table 1

Surrogate quantitative MR markers indicating different features of neurodegeneration. The main markers corresponding to the underlying pathology and the sequences needed are indicated.

	Microstructure-biochemical profile		Macrostructure
	Marker	Sequence	Marker	Sequence
Neuronal/axonal loss: degeneration	ADC, rTrace(D), MD, AD	DW Images	T2 signal intensity	T2-w sequences
	NAA	^1H-MRS	Area, diameter, volume	Volumetric T1 sequences
	MTR	MTI (T1 or PD-w sequence with off resonance saturation)
Glial reaction: gliosis	mI	^1H-MRS
Myelin disruption	FA, RD	DW Images	T2 signal intensity	T2-w sequences
	Cho	^1H-MRS	Volume	Volumetric T1 sequences
	MTR	MTI (T1 or PD-w sequence with off resonance saturation)
Iron content	T2/R2 values	T2/R2-w sequence
	Phase shift values	SWI phase images

ADC: apparent diffusion coefficient; MD: mean diffusivity; AD: axial diffusivity; DW: diffusion weighted; NAA: N-acetyl-aspartate; ¹H-MRS: proton-MR spectroscopy; MTR: magnetization transfer ratio; MTI: magnetization transfer imaging; PD: proton density; mI: myo-inositol; FA: fractional anisotropy; RD: radial diffusivity; Cho: choline; SWI: susceptibility-weighted imaging.