Table 1.

Classical imaging modalities of transpathology in clinical practice

Imaging technique	Source of imaging	Spatial resolution	Tissue penetration depth	Sensitivity	Examples for probes	Ref
Single-photon emission computed tomography (SPECT)	γ-ray	8–10 mm	No limit	pM	Radionuclides (99mTc, 201Tl, 111In, 131I, 123I, 67Ga)	[56]
Positron emission tomography (PET)	Positron emitters	4–5 mm	No limit	pM	Radionuclides (18F, 11C, 13N, 15O, 64Cu, 68Ga)	[57]
Computed tomography (CT)	X-ray	1–2 mm	No limit	mM	High-atomic-number atoms (iodine, barium sulfate)	[58]
Magnetic resonance imaging (MRI)	Radiofrequency waves	0.5–1 mm	No limit	mM to μM	Para-(Gd3+) or superparamagnetic (Fe3O4) materials	[59]
Ultrasound (US)	Ultrasound waves	0.3–1.1 mm	Few centimeters	n.c.	Microbubbles	[60]
Optical coherence tomography (OCT)	Light waves	10–20 μm	Few millimeters	n.c.	Albumin microsphere, near-infrared dyes, gold nanoshells	[61]
Confocal microscopy (CM)	Light waves	0.5–1.25 μm	200–300 μm	n.c.	Aluminum chloride, indocyanine green, sodium fluorescein	[62]

pM, pmol/L; mM, mmol/L; μM, μmol/L; n.c., not well characterized