Table 1.

Property summary of the biomedical imaging modalities.

Imaging modality	Contrast mechanism	Typical spatial resolution	Typical penetration depth	Advantages	Disadvantages	Representative applications
US	Acoustic reflection (back scattering)	0.3 mm	10 cm	Non-invasive, high speed, deep penetration	Low resolution, low chemical sensitivity, coupling medium needed	Mechanics, flow dynamics, scaffold cavitation
MRI	Proton magnetization and relaxation (spinning frequency)	1 mm	50 cm	Non-invasive, deep penetration	Expensive, low imaging speed	Water content and transport
MPM CM	Fluorescent emission, optical scattering	1 μm	1 mm	Non-invasive, cellular-level resolution, high chemical sensitivity	Superficial penetration	Cell attachment of scaffolds, gene expression
OCT	Optical back scattering	10 μm	2 mm	Non- invasive, cellular-level resolution, high imaging speed	Superficial penetration, low chemical sensitivity	Vascularization, cell tracking, scaffold degradation
PAT	Optical absorption	0.1 mm	10 cm	Non-invasive, high functional and chemical sensitivity deep penetration	Coupling medium needed	Vascularization, oxygenation, cell tracking
X-ray imaging	X-ray absorption	0.1 mm	40 cm	Non-invasive, deep penetration, high resolution	Ionizing radiation, low chemical sensitivity	Engineered bone, pore structures
TEM/SEM	Electron scattering	1 nm	0.1 μm	Nano-scale resolution	Invasiveness (needing sample fixation), complex sample preparation, superficial penetration	Cell-material interaction, mineralization
PET/SPECT	Gamma emission	5 mm	50 cm	Non-invasive, deep penetration, high molecular sensitivity	Low resolution, radiative labelling	Cell metabolism, cell tracking

US, ultrasound imaging; MRI, magnetic resonance imaging; CM, confocal microscopy; MPM, multi-photon microscopy; OCT, optical coherence tomography; PAT, photoacoustic tomography; TEM, transmission electron microscopy; SEM, scanning electron microscopy; PET, positron-emission tomography; SPECT, single-photon emission computed tomography