Non-invasive evaluation of liver steatosis with imaging modalities: New techniques and applications

Table 3 Summary of techniques for liver fat quantification and their mechanisms

Technique	Mechanism for liver fat quantification	Principle of the techniques
CAP	Spectral based technique (AC)	CAP measures the attenuation of or reduction in the amplitude of the ultrasound waves on their way through the liver
ATI	Spectral based technique (AC)	ATI quantifies the degree of the ultrasound beam attenuation. The attenuation of the ultrasound beam is calculated by analyzing echo signals received by the transducer
ATT	Spectral based technique (AC)	Two ultrasonic waves of different frequencies (F0, F1; F0 < F1) are transmitted to the same beamline and the received signal is obtained. ATT estimates the attenuation coefficient it by calculating the slope of the received signal ratio (F0/F1)
UGAP	Spectral based technique (AC)	UGAP compares the measured liver signal and the referential signal (measured on the reference phantom with known attenuation and backscatter coefficients)
Att. PLUS	Spectral based technique (AC)	Att. PLUS measures the decrease in amplitude of ultrasound waves as they propagate throughout the tissue
TAI	Spectral based technique (AC)	TAI is determined based on the attenuation properties of different frequency components in the tissue, and the spectrum of radiofrequency signals provides a downshift of the center frequency according to depth. The TAI parameter indicates the slope of the ultrasound center frequency downshift
BSC	Spectral based technique (BSC)	BSC measures the ultrasound energy returned from the tissue
UDFF	Spectral based technique (BSC)	UDFF is obtained by combining both AC and BSC and the result is presented as the percentage of hepatic steatosis. Reference phantom data is integrated into the ultrasound system and fixed-acquisition region of interest is applied
TSI	Envelope Statistic based technique	The TSI is based on the shape parameter of the Nakagami distribution which reflects the local concentration and arrangement of ultrasound scatterers
ASQ	Envelope Statistic based technique	ASQ measures the FD ratio, which is based on the difference between theoretical and real echo amplitude distributions
NLV	Envelope Statistic based technique	NLV parameter was derived from ASQ, which analyzed ultrasound amplitudes sampled from gray-scale ultrasound images
SS	Envelope Statistic based technique	SS calculates the speed of sound through the liver
SSp.PLUS	Envelope Statistic based technique	SSp.PLUS is a novel technique that allows quantification of the intrahepatic speed of sound which is correlated with the liver fat content

AC: Attenuation coefficient; BSC: Backscatter coefficient; CAP: Controlled attenuation parameter; ATI: Attenuation imaging; ATT: Attenuation measurement function; UGAP: Ultrasound-guided attenuation parameter; Att.PLUS: Attenuation plane-wave ultrasound; TAI: Tissue attenuation imaging; UDFF: Ultrasound-derived fat fraction; TSI: Tissue scatter distribution imaging; ASQ: Acoustic structure quantification; NLV: Normalized local variance; SS: Speed of sound; SSp.PLUS: Sound speed plane-wave ultrasound; FD: Focal disturbance.