Clinical
SMPTE test pattern Fig 9
Fig 10
Images with solid state detectors can be smaller than equivalent film or PSPs
FURTHER READING
Brettle D, Carmichael F. The impact of digital image processing artefacts mimicking pathological features associated with restorations. Br Dent J 2011; 211: 167-170.
Rout J, Brown J. Ionizing Radiation Regulations and the Dental Practitioner: 3. Quality Assurance in Dental Radiography. Dent Update 2012;39: 334-339.
Greenall C, Drage N, Ager M. Quality Assurance Tests for Digital Radiography in General Dental Practice. Dent Update 2014; 41: 126-134
Thomas B L, Davies J, Whaites E. Shall I Go Digital? Dent Update 2014;41: 314-326.
Solid state detectors bitewing holders limiting occlusion Fig 11
Continued »
Image processing artefacts are becoming more subtle with more sophisticated systems. To minimise potential misdiagnosis, it might be prudent to consider other areas unrelated to the area in question and consider if the halo effect is present.
9. Viewing conditions Many dental surgeries are bright, well-lit rooms. This can cause problems when reading images on computer monitors. It is important to ensure that optimum viewing conditions are obtained to
ABOUT THE AUTHOR
Barbara Lamb qualified as a general radiographer in 1974 and, since then, has worked exclusively as a specialised radiographer in the dental field.
allow accurate assessment of the computerised image. The monitor should be placed
in a dimly lit area where the light levels are approximately equal to those that would be normal in an overcast day or darker. A light level of about 50 to ı00 lux, the SI unit of luminescence, would be acceptable. Many surgeries are lit to a level of 300 to 500 lux, which is too bright for optimum viewing conditions. The solution is to move the monitor or place a hood around it to cut down on light pollution.
10. Monitors Test patterns that can be used to check monitor condition can be downloaded from the web: Society of Motion Pictures and Television Engineers (SMPTE) (Fig 9) and Technical Group ı8 QC (TGı8-QC). These images should be
captured and archived to be displayed at regular intervals, possibly monthly. These test the overall operation of the system and should be viewed in the same light conditions used in the surgery when viewing digital images. These images should be viewed full- screen for all tests. Whichever test pattern is used, the monitor should be checked for brightness, contrast, resolution and geometric distortion. There are two squares on
the test pattern, one black and one white, which are marked 5 per cent detail on the 0 per cent square (black) and 95 per cent detail on the ı00 per cent square (white). Both of these should be distinctly visible and if not, the monitor settings should be adjusted until they become so. Most monitors cope better with the 95/ı00 per cent than the 0/5 per cent, but if the ambient light is kept low, both should be clearly visible. (Figure 9). SSDs contain solid state
materials such as amorphous silicon or amorphous selenium
in their construction. There are two types of detectors containing either a charge coupled device (CCD) or complementary metal oxide semiconductor(CMOS). The intra-oral systems
generally have a flexible cable connecting the detector directly to the PC. Images are collected in real time and can be viewed on the monitor. The sensors are bulky
and rigid and compromised patients, children and the elderly will probably not deal well with SSDs. In comparison to conventional film or PSPs, the imaging area is smaller and, as a result, approximately three less points of interest will be captured by the direct digital sensor (Fig ı0). Consequently, accurate positioning is essential to cover the area of interest. The presence of the cable will
not allow the teeth to be in occlusion during the taking of bite wing radiographs (Fig ıı). A consequence of over-exposure could be pixel overload “blooming”, which can result in black banding on the image.
Ireland’s Dental magazine 45
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