Table 1.

Characteristics and Trade-offs of Major Functional Neuroimaging Technologies

	Measurement	Technology	Strengths	Limitations	Notes
EEG	Electrical activity measured at scalp.	Electro-encephalogram; 8 to >200 scalp electrodes.	Noninvasive, well-tolerated, low cost, sub-second temporal resolution.	Limited spatial resolution compared to other techniques.	Tens of thousands of EEG/ERP findings reported in the literature.
MEG	Magnetic fields measured at scalp, computed from source-localized electric current data.	Superconducting quantum interference device (SQUID); ∼80–150 sensors surrounding the head.	Noninvasive, well-tolerated, good temporal resolution.	Cost, extremely limited market and availability.
PET	Regional absorption of radioactive contrast agents yielding measures of metabolic activity and blood flow.	Ringed-shaped PET scanner; several hundred radiation detectors surrounding the head.	Highly evolved for staging of cancers, measuring cognition function and evolving to a reimbursable imaging tool for predicting disease involving neurocognition such as Alzheimer's Disease.	Requires injection or inhalation of contrast agent such as glucose or oxygen; lag time of up to 30 minutes between stimulation and data acquisition, limited availability (fewer than 100 PET scanners exist in US today) given short half-life of isotopes and few locations with cyclotrons to produce them; cost.
SPECT	Like PET, another nuclear medicine technique that relies on regional absorption of radioactive contrast to yield measures of metabolic activity and blood flow.	Multidetector or rotating gamma camera systems. Data can be reconstructed at any angle, including the axial, coronal and sagittal planes, or at the same angle of imaging obtained with CT or MRI, to facilitate image comparisons.	Documented uses mapping psychiatric and neurological disease including head trauma, dementia, atypical or unresponsive mood disorders, strokes, seizures, the impact of drug abuse on brain function, and atypical or unresponsive aggressive behavior.	Requires injection of contrast agent through intravenous line; cost.	Currently available in two states (CA and CO) for purchase without physician referral; emphasis is on ADHD and Alzheimer's Disease (approx. out-of-pocket cost: $3,000 per study).
fMRI	Surplus of oxygenated blood recruited to regionally activated brain.	MRI scanner at 1 Tesla to 7 Tesla and higher; 1.5T most common because of its wide clinical availability.	Noninvasive, study repeatability, no known risks. New applications of MR in imaging diffusion tensor maps (DTI)—namely, the microstructural orientation of white matter fibers—has recently been shown to have good correlation with IQ, reading ability, personality and other trait measures (Klingberg et al. 2000).	Cost of equipment and physics expertise to run and maintain systems.	Rapid proliferation of research studies using fMRI alone or in combination with other modalities, growing from 15 in 1991 (13 journals) to 2,224 papers in 2003 (335 journals), representing an average increase of 56% per year.

Note: Combined modality systems such as EEG and fMRI are becoming increasingly common. PET and SPECT are forerunners to frontier technology in molecular imaging.