Table 1. Comparison between the Most Common Imaging Techniques Used for Theranostics and Some Examples of Nanomaterials Used As Contrast Agents (CA).

bioimaging technique	probe	source	advantages	disadvantages	NPs [ref]
optical/fluorescence imaging	photon emission	laser/lamp	high sensitivity	low penetration depth	UCNPs2
			multichannel acquisition	low spatial resolution	QDs3
magnetic resonance imaging	proton relaxation	magnetic field	high spatial resolution	high costs	IONPs4
			unlimited penetration depth	high acquisition time	Gd-MSNs5
				relative low sensitivity
computed tomography	scattered X-rays	X-rays source	unlimited penetration depth	non quantitative	Micelles6
			high spatial resolution	exposure to radiation
positron emission tomography	positron	X-rays source	high sensitivity	high cost	PEG-based NPs7
			quantitative	exposure to radioactive elements
			unlimited penetration depth