Table 2.

Strengths and weaknesses of various imaging modalities in RTT with MECP2 mutation^*.

Imaging modalities	Strengths	Weaknesses
Morphologic MRI
Structural analysis	High spatial resolution and contrast, great gray/white matter delineation	Poor contrast in younger population, especially children
Quantitative analysis	Find changes in surface or volume of multiple brain regions	under 1 year old, so disadvantageous for whole-brain analysis
Diffusion MRI
DTI	Accurately characterize brain microstructure in vivo, high sensitivity	Non-specific, can't adequately model biological system
NODDI	More precise delineate microstructure, high sensitivity and specificity	High requirements on machine, sequence and image capture
Tractography	More precise delineation of specific fiber pathway	High requirements on image captures and post-processing
CBP imaging
SPECT/PET	Excellent method for measuring CBF, semi-quantitative analysis	Radioactivity limits its use in young children, low resolution
ASL	No radioactivity, noninvasive, repeatability, quantitative	High image require, whole-brain coverage scan takes long time
Metabolism imaging
SPECT/PET	High sensitivity and specificity, target imaging, quantitative	Radioactivity, specific imaging agents are difficult to develop
MRS	No radioactivity, noninvasive, high specificity, quantitative	Difficult to develop imaging sequences for specific substances

^*ASL, arterial spin labeling; CBF, cerebral blood flow; CBP, cerebral blood perfusion; DTI, diffusion tensor imaging; MECP2, methyl-CpG binding protein gene 2; MRI, magnetic resonance imaging; MRS, magnetic resonance spectroscopy; NODDI, neurite orientation dispersion and density imaging; PET, positron emission tomography; RTT, Rett syndrome; SPECT, single positron emission CT.