Measuring consciousness in coma and related states

Table 2 Main strength and limits of the different techniques

Technique	Strenght	Limits
PET	Relatively direct measure of brain activity	Ionizing, radioactive tracer, low spatial and temporal resolution expensive
MRI	No use of ionizing. Permits both high resolution study of structural brain (DTI) and fMRI employing active, passive and resting state paradigms	Indirect measure of brain activity (functional) Sensitive to movement and artifacts, impractical (application precluded in patients with contraindication), expensive
TMS-EEG	Practical (no important contraindications) gives information at single subject level	Sensitive to muscle artifacts

PET: Positron emission tomography; MRI: Magnetic resonance imaging; TMS-EEG: Transcranial magnetic stimulation coupled with electroencephalography; DTI: Diffusion tensor imaging; fMRI: Functional magnetic resonance imaging.