Table 1.

Comparison of different elastography imaging modalities.

Modalities	Manual palpation	USE	OCE	CTE	MRE	SCE	PAE
Features
Interrogating signal or mechanism	External mechanical stress (by examiner’s hand)	Acoustic waves	Optical waves [generally, in near-infrared region (NIR)]	X-rays	Magnetic waves	Optical waves [generally, in near-infrared region (NIR)]	Optical waves [generally, in near-infrared region (NIR)]
Detection mechanism	Sense of touch (by examiner’s hand)	Acoustic waves	Optical waves [generally, in near-infrared region (NIR)]	X-rays	Magnetic waves	Optical waves [generally, in near-infrared region (NIR)]	Acoustic waves (frequency range in MHz)
Signal contrast	Mechanical strain	Acoustic impedance	Optical property	X-rays attenuation coefficient	Magnetic property	Optical property	Optical and acoustic properties
Spatial resolution	Not deterministic (subjective)	$\sim 500\mu \mathrm{m}$	$\mu \mathrm{m}$	$\sim 300\mu \mathrm{m}$	$\sim 500\mu \mathrm{m}$	$\mu \mathrm{m}$	$\sim 50\mu \mathrm{m}$
Penetration or imaging depth	Not deterministic (subjective)	cm (whole body)	$\sim 1\mathrm{mm}$	cm (whole body)	cm (whole body)	$\sim 1\mathrm{mm}$	cm
Historical advent	Since centuries	$\sim 1991$	$\sim 1998$	$\sim 2004$	$\sim 1995$	$\sim 2012$	$\sim 2011$
Noninvasive and nondestructive	Yes	Yes	Yes	Yes	Yes	Yes	Yes

Notes: CTE, computed tomography elastography; MRE, magnetic resonance elastography; SCE, speckle contrast elastography.