Ultrasound studies of the gallbladder can be successfully performed the same day as intravenous urography or contrast-enhanced CT exams, according to research published in the Journal of Ultrasound in Medicine.
It's important to wait two hours after contrast administration, however, to allow for gallbladder volume to be restored to pre-contrast values, according to researchers from the University of the West Indies in St. Augustine, Trinidad. The study was conducted prospectively on 153 patients referred for excretory urography or abdominal CT (JUM, August 2002, Vol.21:9, pp. 977-981).
The patient cohort was split into two groups. Sixty-six patients received IV contrast agents, and 87 were given oral contrast media. Of the IV group, 38 patients received a low-osmolar contrast agent, while 28 got a standard ionic agent. In the second group receiving oral contrast media, 48 received a low-osmolar agent, and 39 used the standard ionic agent.
The same sonographer, blinded to whether the patient had received oral or IV contrast, performed ultrasound studies on all of the patients before contrast administration, and at half-hour intervals up to two hours afterwards. Change in gallbladder volume was judged in terms of percentages before and after contrast administration at various intervals.
In the IV group, nonionic contrast patients had a mean gallbladder volume of 70.1% at 30 minutes, 77.9% at 60 minutes, 87.8% at 90 minutes, and 100.5% at two hours. Subjects receiving ionic agents had a mean gallbladder volume of 72.1% at 30 minutes, 79.4% at 60 minutes, 87.5% at 90 minutes, and 100.5% at two hours.
In the oral group, nonionic contrast patients had a mean gallbladder volume of 70.7%, 77.4%, 84.9%, and 98.1% at 30 minutes, 60 minutes, 90 minutes, and two hours, respectively. In the same time periods, patients with administered ionic media had mean volumes of 68.1%, 78.3%, 84.5%, and 99.4%.
"The sequential volume change as a function of time reveals that renormalization of gallbladder only occurs two hours after contrast agent administration and is independent of the route of administration or contrast agent osmolarity," the authors wrote. "Thus any strategy involving same-day sonographic or CT assessment of the gallbladder after iodinated contrast-enhanced studies should ideally wait until this period has elapsed."
As an alternative, the researchers suggested that ultrasound be considered as the initial imaging modality for the gallbladder whenever iodinated contrast-enhanced investigations are anticipated.
By Erik L. RidleyAuntMinnie.com staff writer
September 20, 2002
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