THE EFFECT OF STORAGE ON THE COMPUTED-TOMOGRAPHY ATTENUATION OF GALLSTONES

RATIONALE AND OBJECTIVES. The effect of storage in five media on the computed tomography (CT) attenuation of gallstones, which might be important to future in vitro studies involving gallstones and their CT characteristics, was determined. METHODS. Gallstones were obtained in bile from cholecystectomy specimens. To establish a range of normal variability in the attenuation measurements of gallstones, 24 stones were scanned three times within a 5-minute interval, with a comparison of the attenuation measurements of individual stones. To determine the effect of storage, five stones from the same gallbladder underwent CT within 48 hours of surgical retrieval and were then placed in native bile, sterile normal saline, sterile water, air, or formalin. The stones were rescanned after 1 week and 4 weeks in storage. Ten sets of five stones were evaluated with a comparison of the attenuation measurements of individual stones. RESULTS. There was an average difference of 10.2 Hounsfield Units (HU) and a maximum difference of 35 HU between the three attenuation measurements of the 24 stones that did not undergo storage. With storage, native bile was the only media where none of the 10 stones varied in attenuation by more than 35 HU. Air and saline had the greatest effect on the attenuation of stones with statistically significant differences after 4 weeks in storage (P < .02). Six of the stones stored in air and three stored in saline decreased in attenuation by more than 35 HU, with maximal decreases of 137 and 79 HU, respectively. Although not statistically significant, two stones in water and one stored in formalin showed more than 35 HU of attenuation change, varying by up to 69 and 47 HU, respectively. CONCLUSIONS. Storage may affect the CT attenuation of gallstones and needs to be considered in any in vitro experiment involving gallstones and CT correlation Native bile is the only medium where no stones varied in attenuation more than can be accounted for by normal measurement variation, and thus, is the storage medium of choice.