UROCYSTOLITH DETECTION: COMPARISON OF SURVEY, CONTRAST RADIOGRAPHIC AND ULTRASONOGRAPHIC TECHNIQUES IN ANIN VITROBLADDER PHANTOM

Abstract

Urocystoliths of 9 mineral types from 437 canine patients submitted to the University of Minnesota Urolith Bank were imaged in a urinary bladder phantom. Imaging techniques simulated were survey radiography, pneumocystography, double contrast cystography (two iodine concentrations) and real-time ultrasonography (3.5 MHz, 5.0 MHz, 7.5 MHz). Imaging techniques were compared for accuracy of urocystolith detection, accuracy of urocystolith enumeration, and tendencies for over or undercounting. Across urocystolith mineral types, the false negative rates (no urocystoliths detected in a given case) for survey radiographs range from 2 to 27%. Pneumocystographic techniques are one-half as likely to yield false negative results as are survey radiographic techniques. Underestimates of urocystolith numbers and false negatives are likely using 80 mg iodine/ml double contrast cystography because calcium-based urocystoliths are isopaque in this contrast medium dilution. The 200 mg iodine/ml double contrast cystographic techniques are unlikely to yield false negative diagnoses even for very small (< or = 1.0 mm) urocystoliths and is comparable to pneumocystography for detection and slightly better for enumeration. The likelihood of an ultrasonographic false negative for urocystoliths decreases with increasing MHz. Under optimal conditions using a 7.5 MHz mechanical sector transducer, the false negative rates were comparable to double contrast cystography, but rates increased notably with lower MHz transducers.

In vitro comparison of plain radiography, double-contrast cystography, ultrasonography, and computed tomography for estimation of cystolith size

“…On ultrasonographic images, however, the bladder phantom wall appeared to be more hyperechoic than the normal canine bladder. 19 Although artifacts were present in most ultrasonographic images in the present study, they appeared to be less extensive than those reported in a previous in vitro study, 7,8 largely because of the absence of metal bolts within the phantom. A similar flattened appearance was observed in a previous in vitro study 8 in which a lower-frequency transducer (3.5 to 7.5 MHz) was used.…”

“…[7][8][9][10][11] Overall, the quality of images obtained by computed tomography, radiography, and cystography was excellent and comparable to the quality of images obtained in vivo. Despite these potential disadvantages, in vitro phantoms are well suited for imaging and have been used to evaluate the diagnostic performance of various imaging modalities for detection of cystoliths.…”

“…[7][8][9][10][11] Overall, the quality of images obtained by computed tomography, radiography, and cystography was excellent and comparable to the quality of images obtained in vivo. 7,8,15,16 Artifacts are most commonly produced when a highly reflective object (balloon wall, container, or cystoliths) is imaged adjacent to an anechoic region (urine or saline solution) and may be secondary lobe artifacts, 15,16 filling in of anechoic structures, 17 slice-thickness artifacts, 18 or range ambiguity artifacts. Cystoliths had a tendency to have a flattened appearance, and reverberation or streak artifacts were noted deep to some cystoliths.…”

“…7 The protocol used for double-contrast cystography resulted in an approximately 5-mm-deep pool of diluted contrast medium with a final concentration of 185 mg of iodine/mL in the bottom of the bladder phantom. Bladder phantoms have been used in previous in vitro studies 7-11 of cystolith imaging.…”

“…1-6,a Such techniques are typically limited to relatively small cystoliths. A previous in vitro study 7 suggested that doublecontrast cystography and ultrasonography were the most accurate diagnostic imaging methods for detecting and enumerating cystoliths. Results-Mean cystolith size estimates obtained by means of radiography, cystography, and computed tomography did not differ significantly from each other.…”