Alternative Neuroimaging Techniques

PETTMS

SPECTEEG

Positron Emission Tomography (PET)• Relies on injection of a radioactive isotope to measure cerebral blood flow.

• Whereas fMRI images rely on the interaction of multiple factors (different tissue proton densities, relaxation times, a combination of CBF, CBV, CRMO and CRMGl) PET relies only on only one factor for a given experiment (e.g., usually CBF – but can be CBV or CRMO)

Transcranial magnetic stimulation (TMS)• Typically an interruption of function – creating temporary lesions in the healthy brain.

• Great for pinpointing regions involved in specific components of tasks or for mimicking neurological disorders.

• Single vs. rapid-pulse TMS – inherent dangers in rapid-pulse TMS

• Poor spatial resolution – vitamin E tablets and MRI help! (and magnetic dipole modeling as in VEPs)

Single Photon Emission Computed Tomography (SPECT)

SPEC T

PET

Less spatial resolution than PET – but far less expensive

Often used for early detection of dementias – evidenced by hypoperfusion in a given area

http://imasun.lbl.gov/~budinger/medTechdocs/SPECT.html

Electro-encephalogram (EEG)• Scalp potentials – EEG used clinically but from this we can get visually evoked potentials (VEPs) and the like.

• Dipole modeling used to locate the source of the VEP

• Requires many trials – poor spatial but great temporal resolution.

128 electrode array

Combinations

• fMRI and single cell in monkeys (Logothetis)

• Non-pherous EEG recordings with fMRI in humans

• TMS and PET (Paus, 1999; Desmurget et al. 1999)