RELEVANCE OF SONOGRAPHIC ARTIFACTS OBSERVED DURINGIN VITROCHARACTERIZATION OF UROCYSTOLITH MINERAL COMPOSITION

Abstract

Nine pure mineral type canine uroliths (bladder or urethral origin only) were imaged ultrasonographically using 3.5 MHz, 5.0 MHz, and 7.5 MHz fixed focus, mechanical sector transducers in a urinary bladder phantom. The uroliths studied were those composed of 100% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, and calcium hydrogen phosphate dihydrate (brushite), ammonium acid urate, sodium acid urate, cystine, and silica. The occurrence of both reverberation/streak and acoustic shadowing artifacts were compared to urocystolith mineral type (classified by effective atomic number), urocystolith width, urocystolith height (thickness), and ultrasonographic imaging frequency. No predictable relationship was found between either of the artifacts seen beyond the urocystolith (reverberation/streak or the acoustic shadowing) and urocystolith mineral type. There was no statistical relationship between the occurrence of reverberation/streak artifact and the size (width or height) of the urocystolith or the ultrasonographic frequency. There was, however, a statistically relevant relationship between ultrasonographic imaging frequency and the occurrence of acoustic shadowing and between urocystolith height (thickness) and the occurrence of acoustic shadowing. However, regardless of ultrasound frequency, acoustic shadowing was observed less than 35% of the time in any of the urocystolith mineral types examined. Based on the imaging of the bladder phantom supporting apparatus (7.0 mm bolts covered by plastic), the accurate characterization of a curved object surface directly facing the transducer was found to be directly related to the frequency of sound used for imaging and at best predictably limited to curved vs flat. Accurate measurement of the maximum transverse dimension of an echogenic curved object or accurate characterization of the lateral borders of such an object was considered unlikely with general ultrasonographic equipment of the frequencies studied. Therefore, detailed architectural characterization of urocystoliths suitable for mineral composition prediction is considered highly unlikely with general pulse-echo ultrasonographic techniques.

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

“…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. This had been reported in another in vitro study 8 involving bladder phantoms and is consistent with in vivo observations that cystolith shadowing is an inconsistent feature of ultrasonography of the urinary bladder. On ultrasonographic images, however, the bladder phantom wall appeared to be more hyperechoic than the normal canine bladder.…”

“…[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.…”

“…Thus, accurate estimates of cystolith size are critical in determining whether specific cystoliths are In vitro comparison of plain radiography, double-contrast cystography, ultrasonography, and computed tomography for estimation of cystolith size For each image, cystolith size was measured by 2 radiologists with computerized calipers, and size estimates were compared with actual cystolith size. However, that study did not assess the ability of various imaging modalities to accurately estimate cystolith size, and in a subsequent study, 8 ultrasonography was found to substantially overestimate the size of a plastic-covered metal bolt that was part of the bladder model. However, for ultrasonographic images, mean ± SD difference between actual and estimated cystolith size (2.95 ± 0.73 mm) was significantly higher than mean difference for radiographic, cystographic, and computed tomographic images.…”

Fundamentals of Diagnostic Ultrasound

“…On occasion, gas produces a sharp, clean shadow, and conversely, calcified structures can create dirty shadows. 31,32 The calculus must be near the focal zone of the transducer and be at least as wide as the incident beam to create an obvious acoustic shadow.…”