Table 1.

General advantages and disadvantages of each MRI method

Methods	Advantages	Disadvantages
Phase-contrast MRI [6–8, 16–19]	Allows quantitative velocity measurements Good motion specificity Easy to apply in conventional MRI	Indirect measurement of displacement Sensitive to phase errors arising from eddy currents and gradient non-linearities Requiring numerical integration steps to quantify displacement data Requires multiple velocity encoding gradient directions and values to capture motion in all relevant directions, which can lead to long scan times Limited signal-to-noise ratio (SNR)
Complementary Spatial Modulation of Magnetization (CSPAMM) [20]	Quantitative method to measure motion in term of displacement Allows direct quantification of periodic caudal brain tissue displacement with no need to numerical integration steps Insensitive to phase-related image artefacts	Limited SNR Limited displacement sensitivity and spatial resolution when measuring very small displacements Limited to only quantify brain motion measurement in the cranial–caudal direction Reduced reproducibility of displacement measurements occurs at later cardiac phases because of tag fading caused by T1 relaxation decay Spatial blurring of the displacement in edges of structures moving independently
Displacement Encoding with Stimulated Echoes (DENSE) [3, 4, 21–26]	Quantitative method to measure motion in terms of displacement and strains Direct measurement of the displacement High spatial and temporal resolution Sensitive to very small (0.01 mm) brain displacements with good reproducibility	Long scan time Causes ghosting artefacts Limited SNR Limited accuracy in dynamic displacement
Anatomical landmark motion tracking using pixel-shifting analysis [27, 28]	Quantitative method to measure motion in term of velocity and displacement Good for analysis neural structure within the intracranial CSF Sensitive to detect cephalad and caudad cerebellar tonsil motion	Long scan time Less accuracy and precision for measuring soft-tissue displacements Accuracy of timing parameter may be affected if lengths of trigger parameter delay Not very sensitive to sub-voxel motion
Amplified MRI (aMRI) [5, 29–31]	Qualitative method to visualise displacement Short scan time compared to phase-contrast MRI Ability to reveal smaller motions Does not require phase-encoding in multiple directions to capture the full extent of brain motion Can achieve higher spatial resolution compared to DENSE High SNR Easy to implement using existing scan sequences	Currently lacks the ability to directly quantify motion