Correlation between hepatorenal index and attenuation imaging for assessing hepatic steatosis

Abstract

Introduction: Hepatic steatosis screening is required to assess high-risk populations, identify those for intervention, monitor response and prevent disease progression and complications. Liver biopsy and magnetic resonance imaging proton density fat fraction are current gold standards, but are limited by biopsy risk factors, patient tolerance and cost. Non-invasive, cost-effective, semi-quantitative and quantitative ultrasound assessment exists. The aim of this study was to assess the correlation between the semi-quantitative hepatorenal index (HRI) to assess hepatic steatosis using the quantitative attenuation imaging (ATI) as a reference standard, in adults with varied suspected liver pathologies.

Methods: Data were collected prospectively between April 2019 and March 2020 at a tertiary institution on any patient >18 years referred to US assessment of suspected liver pathology. The only exclusion criteria were absent or invalid HRI or ATI measurements. Three hundred fifty eight patients were included.

Results: There was a significant weak positive correlation between HRI and ATI (r = 0.351, P < 0.001) and between HRI steatosis grade (SG) and ATI SG (r = 0.329, P < 0.001), using previously established cut-off values. With ATI as the reference standard, there was no significant correlation between HRI and hepatic steatosis within steatosis grades, nor for no (SG = 0) or any (SG > 0) hepatic steatosis.

Conclusions: Our study in a typical heterogeneous clinical population suggests the semi-quantitative HRI is of limited use in hepatic steatosis imaging. As HRI is the objective measure of the subjective brightness (B)-mode assessment, this imaging feature may not be as reliable as previously thought. Quantitative ATI may be the preferred non-invasive technique for hepatic steatosis assessment.

Keywords: attenuation imaging; hepatic steatosis; hepatorenal index; steatosis grade.

Figure 1

Flow chart of study population. ATI, attenuation imaging (dB/cm/MHz); HRI, hepatorenal index; N, number. [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 2

Hepatorenal index (HRI) calculation. Liver region of interest (ROI) (A); renal ROI (B); liver echo intensity histogram (EIH) (CH A); renal EIH (CH B). Abbreviations: N, number; MAX, percentage; M, median; SD, standard deviation. [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 3

Good quality attenuation imaging (ATI) measurement using an intercostal window during suspended respiration displaying the region of interest (ROI) with a minimum of 4 x 2 cm sector size placed within homogeneous hepatic parenchyma, more than 2 cm from the liver capsule, with the top margin of the ROI parallel to the liver capsule (to avoid reverberation artefact), within 8‐10 cm of the skin surface and avoiding vessels and focal lesions. The R² values of >0.90 indicate a highly reliable and high‐quality measurement. The software automatically displays the attenuation value in white (and not yellow or red) font providing real‐time visual feedback to the sonographer of a diagnostic measurement. The 0.88 dB/cm/MHz value correlates with Brunt steatosis grade S3 (>66%). [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 4

Correlation between HRI (Mean gray‐scale intensity) and ATI (dB/cm/MHz) for the total population. ATI, attenuation imaging; HRI, hepatorenal index; P, p‐value; r, Spearman's correlation coefficient.

Figure 5

Bland–Altman comparison of HRI (Mean gray‐scale intensity) and ATI (dB/cm/MHz). Abbreviations: ATI, attenuation imaging; HRI, hepatorenal index. [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 6

Correlation between HRI (Mean gray‐scale intensity) and ATI (dB/cm/MHz) for no (SG = 0) hepatic steatosis. Abbreviations: ATI, attenuation imaging; HRI, hepatorenal index; P, p‐value; r, Spearman's coefficient; SG, steatosis grade.

Figure 7

Correlation between HRI (Mean gray‐scale intensity) and ATI (dB/cm/MHz) for any (SG > 0) hepatic steatosis. Abbreviations: ATI, attenuation imaging; HRI, hepatorenal index; P, p‐value; r, Spearman's coefficient; SG, steatosis grade.