Acoustic liver biopsy using endoscopic ultrasound

Abstract

Background: Transabdominal ultrasound cannot be used to quantitate fibrosis in patients with cirrhosis because of variability in the abdominal wall thickness and variability in the components of the abdominal wall (fat versus muscle). Endoscopic ultrasound through the gastric wall is always at a constant distance, approximately 3 mm, away from the liver when the transducer is just below the gastroesophageal junction, thereby eliminating this variability.

Purpose: To differentiate between cirrhotic and noncirrhotic liver using endoluminal ultrasound.

Methods: Eleven patients without known liver disease and eight patients with cirrhosis underwent endoscopic ultrasound using an Olympus linear ultrasound scope. The gain, contrast, frequency, and acoustic power were kept constant on the Aloka ultrasound processor. Videotaped images of the liver were recorded and then digitized on Image-Pro Plus software. The brightness of the image was adjusted to a standard brightness for each image and an area of interest was chosen using Photoshop 7.0. Vessels and artifacts were eliminated digitally and a histogram was produced using Photoshop to quantitate the pixel density for the area of interest from 0 (black) to 255 (white). Approximately 250,000 pixels were evaluated for each subject. The mean +/- standard deviation (SD) pixel density of the noncirrhotic subjects was evaluated against the cirrhotic patients using a Student unpaired t-test.

Results: The mean echogenecity in patients with cirrhosis was 116.85 and the mean echogenecity in patients without cirrhosis was 92.75 (P < 0.002). The mean standard deviation of the pixel density in patients with cirrhosis was 19.08 and the mean standard deviation of the pixel density in patients without cirrhosis was 13.25 (P < 0.0004). Using these criteria the subjects with cirrhosis were segregated from the noncirrhotic subjects (normal subjects and the subjects with steatosis) with 100% sensitivity and 100% specificity.

Conclusion: A new method of evaluating the liver parenchyma (acoustic liver biopsy) that takes advantage of the proximity of the endoscopic ultrasound transducer to the liver and uses commercial image analysis technology that is inexpensive and widely available was developed. This is a preliminary study of this new technology, which demonstrates that endoscopic ultrasound, can be standardized in order to image, analyze, and compare the mean echogenecity and mean standard deviation of the pixel density in the liver in order to distinguish cirrhotic patients from patients without cirrhosis.