Objective: To assess the inter-and intra-observer variability of acoustic radiation force impulse (ARFI) quantification in liver segments with influence of age, body mass index (BMI) and liver capsule-to-box (CB) distance. Methods: 10 healthy volunteers were examined twice, by three experienced operators, separated by a 1-week interval. 10 readings were obtained, from segments 3, 5/6 and 7/8. Age, BMI and the CB distance were noted. The Cronbach a statistic for analysis of reliability was performed for the inter-and intra-observer studies. Multivariate linear regression models determined significance of the other parameters. . For both the inter-and intra-observer study, the Cronbach a statistic was $0.7 (reliable) when taken from segments 5/6 and 7/8 but ,0.7 (unreliable) for segment 3. BMI and age showed significant (p,0.0001) but contrasting correlation (segment 5/6: BMI r50.02, age r520.02; segment 7/8: BMI r520.01, age r50.01) with ARFI velocities when analysed for the segments deemed reliable. A weak negative correlation between ARFI velocities and liver CB distance was demonstrated for both assessed segments (segment 5/6, r520.08; segment 7/8, r520.06; p,0.001). Conclusion: With trained operators, ARFI is a reliable and reproducible method of liver stiffness quantification in segments 5/6 and 7/8 but acquisition of measurements from segment 3 should be avoided. Values obtained deeper to the liver capsule allow more reliable liver stiffness quantification.

Accurate assessment of liver fibrosis in patients with chronic liver disease is necessary to determine prognosis, monitor disease progression and formulate treatment decisions. Currently, histological staging of liver biopsy is the most widely used reference standard for this purpose. Liver biopsy, however, has recognized risks, as well as sampling and observer error. These limitations have stimulated the search for new non-invasive approaches. Numerous methodologies, including serum markers, magnetic resonance elastography and ultrasound elastography, have evolved in the last decade to predict fibrosis in those with chronic liver disease. Ultrasound elastography methods assess liver fibrosis by determining liver stiffness and translate this into a quantifiable measurement for analysis. As these tests are non-invasive, without side-effect or discomfort, it is possible to conduct repeat examinations at much closer intervals than biopsy. The three most investigated ultrasound elastography methods are transient elastography, realtime elastography and acoustic radiation force impulse. Although significant strides have been made in the development of the technology, an unequivocal advocacy of elastography as a surrogate for biopsy is still not established. The aim of this review is to evaluate the advantages, limitations and clinical relevance of the three ultrasound-based modalities. Also, the review shall assess the current and possible future clinical application the modalities may serve both separate and in conjunction with liver biopsy.

• CT signs correlate with right-sided heart catheter data in portopulmonary hypertension • CT adds to the transthoracic echocardiography detection of portopulmonary hypertension • CT may have a complementary role in pre-liver transplantation triage.