TABLE 1

Overview of Optical Imaging Methods in Relation to PET and MRI

				Optical methods
Parameter	Feature	PET	MRI	Confocal, multiphoton microscopy	Reflectance and raster scan	DOT
Contrast	Sensitivity to probes	High fM–pM	Low μM–mM	High fM–pM	High pM–nM	High pM–nM
	Activating probes	No	No	Yes	Yes	Yes
	Intrinsic	No	Yes	Yes
	Nonionizing	No	Yes	Yes
Imaging	Resolution	1–5 mm	40 μm–1 mm	∼0.3–10 μm	0.1–3 mm	0.1–10 mm
	Depth	Not limited	Not limited	0.01–0.5	0.1–2 mm	0.1–50 mm
	Tomography/sectioning	Yes	Yes	Yes	No	Yes

Optical methods have many flexible and powerful modes of molecular and functional contrast. Effect of depth on imaging performance is dramatic.