Two-Dimensional-Shear Wave Elastography with a Propagation Map: Prospective Evaluation of Liver Fibrosis Using Histopathology as the Reference Standard
Dong Ho Lee, Eun Sun Lee, Jae Young Lee, Jae Seok Bae, Haeryoung Kim, Kyung Bun Lee, Su Jong Yu, Eun Ju Cho, Jeong-Hoon Lee, Young Youn Cho, Joon Koo Han, Byung Ihn Choi
Korean J Radiol. 2020 Dec;21(12):1317-1325. https://doi.org/10.3348/kjr.2019.0978
The liver responds to sustained insult by a scarring process known as fibrosis. A stiff liver can regenerate when managed appropriately in its early stages but when gone unrecognised or untreated, can progress to irreversible cirrhosis and hepatocellular carcinoma.
Transient elastography (TE), point shear wave elastography (SWE) and two-dimensional (2D) SWE of supersonic shear imaging (SSI) are ultrasound (US) techniques that have been developed to provide a reliable non-invasive measurement of liver stiffness comparable to the reference diagnostic standard which is fibrosis stage obtained from liver biopsy specimens. Accurate values for liver stiffness are achieved by using a measurement reliability index with point SWE and propagation map in 2D SWE. SWE techniques, unlike TE, can provide B-mode and elastography exams concurrently. Other limitations of TE include small sample volume and physical impediment to push-pulse technique in patients with ascites and obesity [1].
In this prospective review, fibrosis detection and staging by 2D SWE using a propagation map was compared to results of histopathological specimens obtained from the same patients. The final study population comprised of 114 patients from two separate hospitals with a male to female ratio of 0.5:1 who met the following inclusion criteria: a) age between 20 – 85 years, b) liver biopsy indicated to ascertain cause of diffuse liver disease, c) valid informed consent and d) no bleeding risk (platelet count > 80,000/mm3, INR <1.5).
One of three radiologists performed US evaluation of the liver parenchyma on all patients prior to liver biopsy. Patients were fasted for at least 6 hours before their scheduled appointment and they were scanned using a curvilinear probe in the supine position with their right arm above their head. Greyscale B-mode was first used to detect any focal lesions. 2D SWE mode was then activated, a 2 x 2 cm sample box was placed 1cm below Glisson’s capsule avoiding large vessels and a shear wave propagation was emitted using an acoustic radiation force while the patient held their breath for 1 second. Smooth parallel lines within the sample box were taken to represent stable measurement conditions. Shear wave propagation and data filling of the sample box was performed three times for each patient with one of the propagation maps having three further measurements taken from smaller 1cm-sized circular ROIs; this amounted to nine values of liver stiffness per patient. An elasticity map was then used to measure degree of liver stiffness in kilopascal (kPa).
Out of the 9 values per patient, median measurements were selected for further analysis. Values >30% of the interquartile range (IQR) were considered unreliable. The rate of unreliable measurements in this study was estimated at 7.3%, similar to another study using 2D-SWE with a propagation map which had a rate of 5.2% [2] and less than another study using 2D-SWE with SSI which had a rate of 23% [3].
The same radiologist performing the 2D SWE proceeded to perform a liver biopsy from segment V/VIII using an 18-gauge biopsy gun. Two 2.2cm long cores were obtained for each patient; these were fixed in formalin, embedded in paraffin and stained using haematoxylin and eosin as well as Masson’s trichrome stain. Two histopathologists reviewed all biopsy specimens assigning a stage of fibrosis (F0 – F4) and grade of necroinflammatory activity (A0 – A4).
According to a multivariate linear regression analysis, stage of fibrosis was the only significant factor (p <0.001) determining liver stiffness value obtained by 2D-SWE with a propagation map. The latter provided good diagnostic performance in terms of grading each stage of liver fibrosis having a sensitivity of 91.7% and specificity of 87.8% for detecting F ≥ 3 stage and sensitivity of 90.9% and specificity of 88.4% for detecting cirrhosis.
The authors highlight a number of limitations of this study namely, the heterogeneous nature of the study population with various aetiologies of chronic liver disease, uneven distribution of liver fibrosis stages, each patient was scanned by only one radiologist hence there was no assessment of interobserver agreement on liver stiffness values for individual patients and lack of head-to-head comparison with prospective studies using other elastography techniques.
This study confirms that 2D-SWE with a propagation map is a reliable and accurate non-invasive technique to evaluate liver fibrosis.
References:
- Jeong WK, Lim HK, Lee HK, Jo JM, Kim Y. Principles and clinical application of ultrasound elastography for diffuse liver disease. Ultrasonography 2014;33:149–160.
- Lee ES, Lee JB, Park HR, Yoo J, Choi JI, Lee HW, et al. Shear wave liver elastography with a propagation map: diagnostic performance and inter-observer correlation for hepatic fibrosis in chronic hepatitis. Ultrasound Med Biol 2017;43:1355–1363.
- Yoon JH, Lee JM, Joo I, Lee ES, Sohn JY, Jang SK, et al. Hepatic fibrosis: prospective comparison of MR elastography and US shear-wave elastography for evaluation. Radiology 2014;273:772–782.
Dr. Daniel Borg is a third-year radiology resident at Mater Dei Hospital, Malta. He completed his undergraduate medical degree at the University of Malta in 2016 and joined the Medical Imaging Department in 2018 where he is undertaking training in diagnostic and interventional radiology.
Comments may be sent to