Refinement of exclusionary criteria for lithotripsy

This paper reports gallstones from 200 cholecystectomy patients examined with CT, US, and MR imaging. On CT scans, stones of over 50 HU had a mean bilirubinate content of 23%, versus 6.2% in those less than 50 HU. Forty-four percent of stones had MR signal on both T1- and T2-weighted images. When compared with stones without signal, these also has significantly higher CT numbers. Chemical shift imaging identified the signal as water protons. Therefore, stones above 50 HU are probably poor candidates for lithotripsy because of the increased concentrations of calcium bilirubinate and carbonate. The associated increased incidence of MR signal may be attributed to layers of water associated with bilirubinate salts