Korean J Radiol.  2016 Oct;17(5):750-757. 10.3348/kjr.2016.17.5.750.

Prospective Comparison of Liver Stiffness Measurements between Two Point Shear Wave Elastography Methods: Virtual Touch Quantification and Elastography Point Quantification

• Yoo H
• Lee JM
• Yoon JH
• Lee DH
• Chang W
• Han JK

• KMID: 2458067
• DOI: http://doi.org/10.3348/kjr.2016.17.5.750

Abstract

OBJECTIVE
To prospectively compare technical success rate and reliable measurements of virtual touch quantification (VTQ) elastography and elastography point quantification (ElastPQ), and to correlate liver stiffness (LS) measurements obtained by the two elastography techniques.
MATERIALS AND METHODS
Our study included 85 patients, 80 of whom were previously diagnosed with chronic liver disease. The technical success rate and reliable measurements of the two kinds of point shear wave elastography (pSWE) techniques were compared by χ2 analysis. LS values measured using the two techniques were compared and correlated via Wilcoxon signed-rank test, Spearman correlation coefficient, and 95% Bland-Altman limit of agreement. The intraobserver reproducibility of ElastPQ was determined by 95% Bland-Altman limit of agreement and intraclass correlation coefficient (ICC).
RESULTS
The two pSWE techniques showed similar technical success rate (98.8% for VTQ vs. 95.3% for ElastPQ, p = 0.823) and reliable LS measurements (95.3% for VTQ vs. 90.6% for ElastPQ, p = 0.509). The mean LS measurements obtained by VTQ (1.71 ± 0.47 m/s) and ElastPQ (1.66 ± 0.41 m/s) were not significantly different (p = 0.209). The LS measurements obtained by the two techniques showed strong correlation (r = 0.820); in addition, the 95% limit of agreement of the two methods was 27.5% of the mean. Finally, the ICC of repeat ElastPQ measurements was 0.991.
CONCLUSION
Virtual touch quantification and ElastPQ showed similar technical success rate and reliable measurements, with strongly correlated LS measurements. However, the two methods are not interchangeable due to the large limit of agreement.

Keyword

Liver fibrosis; Liver stiffness; Ultrasound elastography; Shear wave elastography

MeSH Terms

Adult
Aged
Aged, 80 and over
Elasticity Imaging Techniques/*methods
Female
Humans
Liver Cirrhosis/*diagnostic imaging
Male
Middle Aged
Observer Variation
Prospective Studies
Reproducibility of Results
Severity of Illness Index

Figure

• 

  Fig. 1 Flow diagram of study population. *One patient who had technical failure on VTQ also had unreliable measurement on ElastPQ. ElastPQ = elastography point quantification, LS = liver stiffness, VTQ = virtual touch quantification

• 

  Fig. 2 LS measurements by two pSWE techniques. VTQ (A) and ElastPQ (B). For both measurements, operator placed predefined measuring box in liver. ElastPQ = elastography point quantification, LS = liver stiffness, pSWE = point shear wave elastography, VTQ = virtual touch quantification

• 

  Fig. 3 Histogram showing distribution of mean LS measurements by two pSWE techniques. VTQ (A) and ElastPQ (B). Skewness/standard error of skewness was 3.10 for VTQ vs. 4.96 for ElastPQ. Black line = normal distribution fit. ElastPQ = elastography point quantification, LS = liver stiffness, pSWE = point shear wave elastography, VTQ = virtual touch quantification

• 

  Fig. 4 Bland-Altman plot shows agreement in VTQ and ElastPQ LS measurements. X-axis shows means of repeated LS measurements, and y-axis shows difference between VTQ and ElastPQ LS measurements. Red line = mean difference, Green line = 95% limits of agreement. ElastPQ = elastography point quantification, LS = liver stiffness, VTQ = virtual touch quantification

• 

  Fig. 5 Bland-Altman plot shows intraobserver agreement of ElastPQ measurement. X-axis shows means of repeated LS measurements, and y-axis shows difference between repeat ElastPQ LS measurements. Red line = mean difference, Green line = 95% limits of agreement. ElastPQ = elastography point quantification, LS = liver stiffness

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