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Keywords:
Liver, Ultrasound physics, Elastography, Diagnostic procedure, Cirrhosis
Authors:
L. Chami1, C. Pellot-Barakat1, M. Lefort1, A. Ayed2, I. Huynh-Charlier1, S. Egels1, O. Lucidarme1; 1Paris/FR, 2Paris /FR
DOI:
10.1594/ecr2014/C-2180
Methods and materials
This study was approved by our institutional review board.
70 patients (47 men,
23 women,
mean age : 53,9 yr ; range 22-91 yr) have been prospectively included in a single center study.
These patients were referred for abdominal ultrasound with normal as well as pathological conditions of liver : 49 patients with known chronic liver disease,
21 without known liver disease.
US examinations were performed by two experienced operators in liver elastography.
Clinical indexes :
Patient morphotype and body shape were determined as follow:
- Body Mass index: calculated from weight and height using the NIH calculator (National Institutes of Health).
BMI categories were defined as follow: underweight ≤ 18,5 ; normal weight = 18,5-24,9 ; overweight=25-29,9 ; obesity= BMI of 30 or greater
- Skin-to-liver thickness: length measured from the skin to liver capsule (mm)
Pathological conditions of liver were associated with:
- Liver heterogeneity: evaluated by US operator at the time of examination using four grade scales (from 0: homogeneous to 3: strongly heterogeneous)
- Degree of elasticity: average value of 3 measurements of elasticity expressed in kilopascals in selected frames
Shearwave elastography acquisition :
SWE was performed using a conventional ultrasound probe during a standard intercostal examination of the right lobe of the liver.
For each patient the SWE acquisitions were performed as follow and repeated with an abdominal (convex) probe (1-6 Mhz) as well as with a linear probe (10 Mhz) :
- an average value of 3 SWE measurements (kilopascals) was calculated after selection of 3 different frames at the time of examination and the manual determination of a Region Of interest (ROI) by the operator
- a SWE video clip (10 seconds) was additionally recorded
SWE quality parameters :
Three qualitative parameters were extracted from SWE video clips (10 seconds) using a homemade automatic algorithm :
- Temporal Variability (TV) : averaged frame to frame,
pixel to pixel differences.
This parameter reflects the stability of the elasticity measurements from frame to frame along the clip.
- Percentage of Non Filling (PNF) : percentage of non colored pixels into the whole SWE box.
This parameter reflects the propagation of shear waves.
- Spatial Variability (SV) : standard deviation of the elasticity values into the whole SWE box in an automatically selected frame.
This parameter reflects the spatial homogeneity of the elasticity values.
Analysis
Elasticity values and quality parameters were compared to clinical indexes as well as probes performances were compared and correlation coefficients (r) were calculated.