Quantitative assessment of fetal bowel echogenicity: comparison of harmonic, compound, and fundamental sonographic images.

Purpose: The aims of this study were to assess normal fetal bowel echogenicity quantitatively and to compare the levels of bowel echogenicity observed with the use of 3 different sonographic image-processing techniques-harmonic plus compound imaging, harmonic imaging alone, and fundamental imaging-and 2 different broadband transducers.

Methods: Women with normal singleton second-trimester fetuses underwent sonographic scanning with both a 2-5-MHz and a 4-7-MHz transducer. The use of the 3 imaging techniques and the 2 transducers resulted in 6 types of images: 2-5-HC (harmonic plus compound images), 2-5-H (harmonic images), and 2-5-F (fundamental images), and 4-7-HC, 4-7-H, and 4-7-F images. The relative echogenicities (brightness) of the fetal bowel and iliac bone were measured, and bowel echogenicity ratios (bowel echogenicity/iliac bone echogenicity x 100) were calculated using graphics software. The resulting data were analyzed to evaluate differences in echogenicity ratios between the 6 types of images.

Results: We examined 37 fetuses during the study period. The bowel echogenicity ratios were highest on the images obtained with harmonic and compound-imaging techniques (2-5-HC, 84.7 +/- 23.4%; 4-7-HC, 98.5 +/- 36.4%). The bowel echogenicity ratio for the 2-5-HC images was significantly higher than those for the 2-5-H and the 2-5-F images (p < 0.01 and p < 0.001, respectively), and those for the 4-7-HC and 4-7-H images were higher than that for the 4-7-F images (p < 0.01 for both comparisons).

Conclusions: A sonographic finding of echogenic fetal bowel should be interpreted cautiously because the use of special image-processing techniques can artificially enhance the apparent level of echogenicity of the bowel. We recommend rescanning without the use of those techniques if the fetal bowel appears to have an increased level of echogenicity.