Investigation of the suitability of tissue phantoms for testing the constancy of ultrasonic transducer arrays in quality assurance.

PURPOSE: To ensure high quality ultrasound diagnostics, proper functioning of the devices used is a necessary prerequisite. Ultrasound transducers have proven to be the most failure-prone part of the signal chain. Their technical monitoring is possible in principle with the help of tissue phantoms. The background of the present study is to determine which type of phantoms and which measurement parameters are best suited to a consistency test as part of routine quality assurance of ultrasound imaging systems. MATERIALS AND METHODS: A classic wire-type phantom (ATS Mod. 539, ATS Labs Bridgeport, USA) and a 3 D cyst phantom (TCC, Timelkam, Austria) were used for the studies and comparative tests were conducted between intact transducers and those in which faults had been simulated. The collected measurement data show a relatively large scatter. Therefore, statistical analysis methods were used, and the discrimination analysis proved to be a useful tool. RESULTS: Local failures which arise, e. g. due to the breakdown of individual piezoelectric elements or element groups in the transducer array, can be detected with the help of the gray value targets of the ATS phantom, but only in those cases in which the error-affected sound field part actually overlaps with the target under consideration. The TCC phantom is not suitable for the detection of such errors. Global transducer failures, i. e. those that affect the entire array, can even be detected with both types of phantoms. CONCLUSION: When the emphasis of quality assessment is on the detection of local defects in the array that make up the largest part of the transducer faults, studies with conventional phantoms are only of limited value.

Effects of sodium selenite on deoxycholic acid-induced hyperproliferation of human colonic mucosa in short-term culture.

It has been shown that in vitro incubation of human colonic biopsies with the secondary bile acid deoxycholic acid (DCA) leads to the hyperproliferation of colonic crypt cells with an expansion of the proliferative zone, which is regarded as a biomarker of increased cancer risk. Sodium selenite (SSE), on the other hand, has been implicated as a protective agent in experimental studies, but toxic effects were reported as well, depending on the dose of SSE. To elucidate the effects of SSE on human colonic mucosa, biopsies from endoscopically normal sigmoid colon tissue of 30 subjects were incubated with 5 microM DCA or a combination of 5 microM DCA and SSE in concentrations of 5, 10, 20, 50, 80, and 100 microM, respectively. Equimolar NaCl incubations served as a control. Proliferating cells were labeled by bromodeoxyuridine immunohistochemistry, and the labeling index (LI) was computed. In the experiments using 5, 10, and 20 microM SSE, the whole crypt LI was significantly lower after DCA + SSE incubation (0.136, 0.118, and 0.110, respectively) compared to that after incubation with DCA alone (0.172, 0.157, and 0.165, respectively; P < 0.01). The corresponding LIs during DCA + SSE incubation were comparable to the LIs obtained after NaCl incubation (average LI = 0.14). Contrary to this finding, severe cell damage was observed in the biopsies that were incubated with the higher SSE concentrations of 50 microM and above. The antiproliferative effects of SSE may indicate a possible protective effect in the prevention of human colon cancer development. However, the observed toxic effects of higher SSE concentrations strongly suggest the need for additional studies before general recommendations for the use of SSE in colon cancer prevention can be made.

Effects of calcium and deoxycholic acid on human colonic cell proliferation in vitro.

A high-fat and low-fiber diet is regarded as a major risk factor for colon cancer by increasing luminal contents of secondary bile acids. Calcium, on the other hand, has been implicated as a possible preventive agent in colon tumor development. In in vitro studies with human colonic epithelium, incubation with the secondary bile acid deoxycholic acid (DCA) induced hyperproliferation of colonic crypt cells which is regarded as a sign of preneoplastic transformation. In the present study the effects of calcium chloride (CaCl2) on DCA-induced hyperproliferation were tested at different stages of DCA-induced cell injury. Colonic biopsies from 36 patients (no tumors, polyps or IBD) were incubated with CaCl2 (1 and 10 mM) and 5 microM DCA which was added to the incubation medium either together with (experiment A), after (experiment B), or before CaCl2 (experiment C). Coincubation of the biopsies with DCA and 10 mM CaCl2 at the same time (experiment A) resulted in a significant reduction of whole crypt labeling index by 12% (p < 0.05), whereas in the other incubation experiments no significant growth-inhibitory effects could be demonstrated for CaCl2. These findings may best be explained by the formation of calcium-bound bile acid salts which lost most of their toxicity for the colonic cells.