Scanning slit chest radiography: a practical and efficient scatter control design.

PURPOSE: To design a chest radiography unit that eliminates scatter. MATERIALS AND METHODS: A scanning slit radiography unit that also incorporates a conventional grid was designed. The scanning slit geometry defined a 10-mm-wide beam at the image receptor. RESULTS: With a typical heavy-duty radiographic tube, the proposed system was capable of delivering an entrance skin exposure of up to 32 microC/kg for a 1-second scan. Monte Carlo simulations indicated that the scatter-to-primary ratio (S/P) imaged with the scanning slit system alone was 0.125 for a 35 x 43-cm, 23-cm-thick Lucite phantom imaged at 140 kVp. When the system was coupled with 4:1, 8:1, and 12:1 grids, S/P decreased to 0.063, 0.055, and 0.054, respectively. CONCLUSION: A scanning slit system coupled with a conventional grid is a practical and highly efficient method of controlling scatter and will result in minimal soft-tissue and bone measurement errors in dual-energy chest radiography.

The effects of a simplified mechanical oral hygiene regime plus supragingival irrigation with chlorhexidine or metronidazole on subgingival plaque.

23 patients with pockets greater than or equal to 4 mm and evidence of bone loss on radiographs received thorough scaling and root planing followed by instruction in Bass brushing. They refrained from routine interdental cleaning for the first 28 days. A pulsating jet irrigator was used once daily supragingivally with 0.02% chlorhexidine (CH) 0.05% metronidazole (MD) or 0.01% quinine sulphate inactive control (PL), on a randomized double blind basis. Molar sites were not irrigated and served as control sites; they were only mechanically cleaned. For each patient, subgingival plaque samples were obtained from 2 test and 1 control sites at baseline (day 0), and on days 7, 28, 56 and 84. Plaque samples were monitored by darkfield microscopy on the basis of morphological characteristics of 4 types of bacteria: cocci, motile cells, spirochaetes and "others" (nonmotile rods, filaments and fusiforms). The simplified oral hygiene regime of scaling, root planing and Bass toothbrushing combined with interdental supragingival pulsating jet irrigation with CH, MD or PL appeared superior to a system of simplified oral hygiene alone, particularly during the first 4 weeks. However, at most time-points, the benefits were not statistically significant except for metronidazole. By day 84, the end of the experimental period, all groups approximated baseline levels. The results indicate that supragingival pulsated jet irrigation has limited effects on the composition of subgingival plaque. More marked changes occur when the irrigation fluid contains a chemical agent such as metronidazole known to be effective against important subgingival organisms, but probably not to such an extent as to change the composition of the flora from one associated with diseased sites to one associated with healthy sites.