. Author manuscript; available in PMC: 2013 Nov 5.

Published in final edited form as: Ann N Y Acad Sci. 2008 Nov;1144:10.1196/annals.1418.025. doi: 10.1196/annals.1418.025

TABLE 1.

Comparison of brain imaging modalities used for drug development in brain-gut disorders

Imaging modality	Method	Measurement	Advantages	Disadvantages
HUMAN STUDIES
PET	Measures emissions from radiolabeled chemical injected into the bloodstream	H₂O¹⁵ – blood flow F¹⁸ Fluorodeoxyglucose (FDG) – cellular metabolism	• Can directly show blood flow (H₂O¹⁵) or glucose metabolism (FDG) in brain tissues	• Variable temporal resolution (tracer dependent) • Radiation exposure
PET ligand		Radiolabeled drug/molecule of interest	• Can observe regional receptor occupancy	• Ligand availability • Radiation exposure
fMRI	Measures magnetic variations due to the amount of oxygenated and deoxygenated hemoglobin	Blood oxygen level dependence (BOLD), which correlates with blood flow	• Noninvasive • Good spatial resolution • Good temporal resolution	• BOLD is an indirect measure of blood flow • Some regions of the brain are poorly visualized due to technical artifacts
ANIMAL STUDIES
fMRI	Measures magnetic variations due to the amount of oxygenated and deoxygenated hemoglobin	Blood oxygen level dependence (BOLD), which correlates with blood flow	• Good spatial and temporal resolution • Able to accommodate repeated studies in a single animal	• Requires sedation and restraint of the animal to avoid movement
microPET	Measures emissions from radiolabeled tracers injected into the bloodstream	H₂O¹⁵ – blood flow ¹⁸F Fluorodeoxyglucose (FDG) – cellular metabolism	• Uptake of radiotracer may take place in ambulatory animals (FDG) • Able to accommodate repeated studies in a single animal	• Poor spatial resolution for brain imaging in small animals • Requires sedation and restraint of the animal to avoid movement
c-fos	Evaluates early response genes	c-fos mRNA or protein	• Spatial resolution at the cellular level	• Poor temporal resolution • Poor ability for 3D mapping • Requires animal sacrifice so repeated studies cannot be performed
Autoradiography	Injection of radiotracer and exposure of the cryosectioned brain to photographic film or a phosphor imager	Cerebral blood flow, Cerebral metabolism	• Good spatial and temporal resolution • Imaging in nonrestrained, nonsedated animals	• Requires animal sacrifice so repeated studies cannot be performed.