Comparison of PET and Functional MRI

The advantages and disadvantages of PET versus fMRI are summarized in Table 10-3.

TABLE 10-3. Advantages and disadvantages of positron emission tomography (PET) versus functional magnetic resonance imaging (fMRI)

Advantages of PET versus fMRI

Quiet (good for acoustic stimulation); fMRI may have noise >90 dB Less sensitive to movement artifact Allows metabolic and receptor mapping

Allows imaging of brain regions that are typically difficult to image with fMRI because of the presence of a susceptibility artifact (orbitofrontal cortex, inferior temporal lobe) that causes both distortion and loss of signal

Allows the use of standard measurement devices (physiological, behavioral) inside the scanner (i.e., avoids the complication for the need of specially designed MRI-compatible hardware)

(In the MRI environment, the presence of a very strong static magnetic field commands the use of diamagnetic components; moreover, every electric device in the scanner room needs to be carefully shielded to prevent interference problems to and from the scanner. Scanning is not used in patients who have pacemakers or ferromagnetic metal parts in their bodies.)

Disadvantages of PET versus fMRI

Injection of a radioactive isotope precludes the use of PET for longitudinal studies in which the same subjects are scanned repeatedly over an extended period of time.

PET provides an integral measure (over time) of brain activity (for activation techniques), with a temporal resolution on the order of minutes because of the lifetime of the isotope. By comparison, fMRI has a temporal resolution on the order of seconds. This prevents the use of sophisticated, event-related designs with PET. Also, the number of images typically collected with PET on a single subject rarely exceeds a dozen, thereby limiting the statistical treatment in the analysis of the data.

Spatial resolution is more limited with PET than with fMRI. Cyclotron must be located nearby.

PET is more expensive than fMRI (utilization costs per hour: fMRI, ~$500; PET, ~$2,000).

The acquisition procedure is time-consuming and requires more resources. (One scan typically lasts ~3 hours [fMRI typically lasts <1 hour]. In comparison, the MRI experimental setup is easier to perform and can be operated by just one person.)

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