. 2013 Sep 6;10(86):20130263. doi: 10.1098/rsif.2013.0263

Table 1.

Imaging methods used in TE. Physical principle and wavelength range of tissue imaging techniques are stated and methods are compared in terms of their tissue penetration (imaging depth), lateral and axial resolution and other important aspects with ratings from very low/bad (↓↓), low/bad (↓), medium (↔), high/good (↑) to very high/good (↑↑). Invasiveness means destructiveness to tissues and cells. Time and effort means time and work-consumption as well as costs (↑ means that the technique is good in this respect). Additional comments are given for each technique. WL, wavelength; MRI, magnetic resonance imaging; µCT, micro-computed tomography; OCT, optical coherence tomography; LM, light microscopy; CFM, confocal fluorescence microscopy; NLOM, nonlinear optical microscopy; 1-/2-PF, 1-/2-photon fluorescence; SHG, second harmonic generation; CARS, coherent anti-Stokes Raman scattering; EM, electron microscopy; ET, electron tomography; n.a. not applicable.

method	physical principle	WL range	imaging depth	lateral resolution	axial resolution	three-dimensional imaging	acquisition speed	invasive-ness	specificity	time and effort	comments	reference
MRI/µCT	NMR/X-ray diffraction	radio frequency/X-rays	whole body	approximately 100 µm/>1 µm	approximately 100 µm	↑↑/↑↑	↓/↔	↑/↓	↔/↔	↓↓/ ↓↓	low biological specificity	[17–21]
											MRI: low resolution and speed, applicable for soft tissue imaging
											µCT: medium resolution, preferentially used for hard tissue imaging
OCT	low coherence interferometry	NIR (800–1300 nm)	<2 mm	3–4 µm	>10 µm	↑↑	↑	↔	↑	↓	owing to limited resolution only indirect cell imaging possible	[22–24]
LM	light diffraction and interference	Vis (380–760 nm)	n.a.	200–350 nm	n.a.	↓	↑↑	↑	↔	↑	very easy, cheap and fast method, but low specificity (if used without staining)	[25,26]
CFM	fluorescence (1-PF)	UV/Vis (340–780 nm)	<100 µm	200–500 nm	500–1000 nm	↑↑	↑	↓	↑↑	↔	bleaching, low imaging depth and signal intensity, stainings required. Increase in resolution and speed possible with STED, 4Pi and spinning disc techniques	[25–28]
SEM/TEM/ET	electron diffraction	approximately 100.000× shorter than visible light	n.a./ <200 nm/ <200 nm	1–5 nm/>0.2 nm/ 5–20 nm	n.a.	↓↓	↓↓	↓↓	↑↑	↓↓	sample destruction, artefacts, time-consuming (histology)	[28–30]
SEM/TEM/ET	electron diffraction	approximately 100.000× shorter than visible light	n.a./ <200 nm/ <200 nm	1–5 nm/>0.2 nm/ 5–20 nm	n.a.	↓↓	↓↓	↓↓	↑↑	↓↓	ET: three-dimensional imaging possible	[28–30]
NLOM	2-PF/SHG/CARS	NIR	usually <1000 µm	200–500 nm	approximately 1400 nm	↑↑	↑	↑	↑↑	↓	2-PF: thermal damage, accelerated bleaching in the focal point	[27,31–38]
NLOM	2-PF/SHG/CARS	NIR	usually <1000 µm	200–500 nm	approximately 1400 nm	↑↑	↑	↑	↑↑	↓	SHG: limited to selected molecules	[27,31–38]