IN-VITRO EVALUATION OF CONTRAST-MEDIUM CONCENTRATION AND DEPTH EFFECTS ON THE RADIOGRAPHIC APPEARANCE OF SPECIFIC CANINE UROLITH MINERAL TYPES

Nine pure mineral types of canine uroliths (bladder or urethral origin only identified in a chronologic sample from the Minnesota Urolith Ce nter mere compared to sequential dilutions of iodinated radiographic c ontrast medium in vitro. The uroliths studied mere those composed of 1 00% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, calcium hydrogen phosp hate dihydrate (brushite), ammonium acid orate, sodium acid urate, cys tine, and silica. The radiopacity of the uroliths was classified as ra diolucent, isopaque, or radiopaque, as compared to the radiopacity of the contrast medium solutions in which they were placed, using 2.0 mm and 5.0 mm depths in petri dishes radiographed using a table-top techn ique. A statistically significant relationship was found between the e ffective atomic number of the uroliths and the effective atomic number of the contrast medium solutions to which they were compared for the endpoints of isopacity, first lucency tin increasing iodine concentrat ion sequence), and optimal visualization of internal architecture. In general, uroliths isopaque or radiolucent in contrast medium solutions weaker than 23.5 mgI(2)/ml are most likely ammonium acid urate or sod ium acid urate. Uroliths isopaque or radiolucent in contrast medium so lutions between 23.5 mgI(2)/ml and 44.4 mgI(2)/ml are probably magnesi um ammonium phosphate, cystine, or silica. Uroliths that remained radi opaque in solutions stronger than 44.4 mgI(2)/ml, and particularly tho se radiopaque in contrast medium solutions stronger than 80 mgI(2)/ml, almost always contained calcium. This relative opacity assessment is proposed for use in double contrast cystography as an aid in different iating urolith mineral types clinically to facilitate appropriate use of medical protocols to dissolve uroliths or to present their growth o r recurrence.