Film og digitale intraorale røntgenreceptorer
Tandlæger arbejder i dag med tre typer af receptorer til intraorale røntgenundersøgelser: den konventio- nelle dentalfilm, et fosforpladesystem eller en sensor med eller uden ledning. Artiklen beskriver fysisk- tekniske forhold for disse receptorer, fejl under bil- leddannelsen, problemer i forbindelse med patientun- dersøgelsen, herunder ubehagsfølelse for patienten, omtagningsfrekvens og dosis. Desuden beskrives forhold, der bør lægges vægt på ved betragtningen af det digitale billede på en monitor samt nyere dia- gnostiske undersøgelser, hvor digitale receptorer har været anvendt, eventuelt sammenlignet med film, til diagnostik af carieslæsioner, marginal og apikal knog- le og rodfrakturer, i forbindelse med endodontisk be- handling og til at skelne mellem dentalmaterialer. Bil- ledbehandling efter optagelsen er et vigtigt element i digital billeddannelse, og udbyttet diskuteres, ligesom der peges på fremtidens mulighed for diagnosespeci- fik billedbehandling. Desuden diskuteres, hvilke hen- syn der bør iagttages i forbindelse med lagring af det digitale billede og ved forsendelse over internettet
Film and digital radiographic receptors: X-ray film emulsion consists mainly of silver halide grains, which after exposure are reduced to metallic silver in the basic – or more recently ascorbic acid-based – developmental process. Ascorbic acid-based chemicals are less toxic and do not smell and should be preferred in dental practice. The dentists can choose between the film and three well established digital receptors for intraoral radiography, the CCD- based (»charge-coupled device«) sensor, the CMOS-based (»complementary metal oxide silicon«) sensor and the photostimulable phosphor plate (PSP). The spatial resolution (line pairs/mm) in images from intraoral examination is lower in many digital systems than in the dental film and varies between approximately 6 and 20 lp/mm. The contrast resolution or bit depth (number of possible shades of grey available) in digital intraoral images is between 8 (256 grey shades) and 16 (65,536 grey shades), and the image file (size of the image) increases in proportion to the resolution. For caries diagnosis no studies have found differences between intraoral digital images with various resolutions; for endodontic file measurements 12-bit images had higher accuracy than 8-bit images. PSP systems have a larger dynamic range than CCD and CMOS sensors, i.e. PSPs tolerate more variation in exposure settings.
