Table 1.
Summary of key performance characteristics of major label-free biomedical imaging approaches
| Method | Spatial resolution | Imaging depth | Speed | Main source of contrast | Main applications | System complexity and cost | In vivo? | Clinically widely avaialble? |
|---|---|---|---|---|---|---|---|---|
| PhM | Sub μm | Tens of μm | **** | Refractive index | Cell structure | * | No | Yes |
| PolM | Sub μm | Tens of μm | **** | Birefringence | Cell and tissue structure (membranes and filament arrays, e.g., collagen fibers; cell spindle) | * | Yes (togther with other methods) | Yes |
| OCT | Several μm | Several mm | **** | Refractive index, speckle/phase variance, Doppler, strain and shear stress | Tissue structure; blood circulation; biomechanics | ** | Yes | Yes |
| HGM | Sub μm | Sub mm | *** | High-order nonlinear susceptibility | Cell and tissue structure SHG: Non-centrosymmetric structures and fibrillar structures, such as collagen or elastin in connective tissues, or myosin and microtubules in muscle fibers THG: Interfaces and optical heterogeneities, such as lipid-based biological membranes | **** | Yes | No |
| aFM | Sub μm | Sub mm | *** | Endogenous fluorochromes | Cell and tissue structure, NAD(P)H, FAD, keratin and elastin; redox; metabolic dynamics | *** | Yes | No |
| IRAM | Several μm | Sub mm | **** | Absorption | Endogenous tissue chromophores (hemoglobin, melanin, water and collagen) | ** | Yes | No |
| RM | Sub μm | Sub mm | * (linear) *** (nonlinear) |
Raman scattering of molecular vibrations | Selective macro-molecular vibrations of lipids, proteins, DNA, etc. | ** (linear) **** (nonlinear) |
Yes | No |
| PAT | Scalable: sub μm – tens of μm | Scalable: Sub mm – tens of mm | **** | Absorption | Cell and tissue structure; vasculature | **** | Yes | No |
PhM: Phase microscopy; PolM: Polarization microscopy; OCT: optical coherence tomography; HGM: Harmonic-generation microscopy; SHG: Second-harmonic generation; THG: Third-harmonic generation; aFM: Auto-fluorescence microscopy; IRAM: IR-absorption microscopy; RM: Raman microscopy; PAT: photoacoustic tomography. Rapid acquisition speed (****) refers to obtaining more than ten Mega-voxel/s in reasonable, clinical attainable resources.
Note: the table refers to the common version of each method.