Journal of Ultrasound in Medicine, Vol 18, Issue 12 799-803, Copyright © 1999 by American Institute of Ultrasound in Medicine
Effect of ultrasound transducer frequency on the appearance of the fetal bowel
N. S. Vincoff, P. W. Callen, R. Smith-Bindman and R. B. Goldstein
Department of Radiology, University of California, San Francisco 94143, USA.
We evaluated how ultrasound transducer frequency affected the appearance of
the fetal bowel. One hundred women with singleton pregnancies, who were
undergoing routine ultrasonographic examination, were assessed at a single
institution. Patients with known fetal anomalies, abnormal biochemical
screening results, or a history of cystic fibrosis were excluded. Images of
the fetal abdomen were obtained in all patients using a single multi-Hertz
transducer, with transducer frequencies set at 5 MHz and 8 MHz. Images were
read separately by two radiologists, blinded to patient name and transducer
frequency. Observers rated the presence or absence of echogenic bowel,
defined as bowel with echogenicity greater than or equal to that of
adjacent bone. Using the 8 MHz frequency, the radiologists interpreted 31%
of the cases as having echogenic bowel, whereas using the 5 MHz frequency,
the radiologists interpreted only 3% of the cases as having echogenic bowel
(P<0.0001). A fetus was 10 times as likely to be given a diagnosis of
echogenic bowel by both observers when the 8 MHz transducer was used than
when the 5 MHz transducer was used by one observer (relative risk 10, 95%
CI 3-11). Furthermore, using the 8 MHz frequency transducer, at least one
of the radiologists interpreted echogenic bowel in 62% of the cases. We
concluded that echogenic fetal bowel is a very common observation when
imaging is performed with an 8 MHz transducer, and thus echogenic bowel
diagnosed with an 8 MHz transducer is unlikely to reflect underlying
abnormality. Identification of echogenic bowel with an 8 MHz transducer
should not prompt further testing.
