ABSTRACT
OBJECTIVES: To investigate the effect of tube current-exposure time (mAs) reduction on clinical and technical image quality for different CBCT scanners, and to determine preliminary minimally acceptable values for the mAs and contrast-to-noise ratio (CNR) in CBCT. METHODS: A polymethyl methacrylate (PMMA) phantom and an anthropomorphic skull phantom, containing a human skeleton embedded in polyurethane, were scanned using four CBCT devices, including seven exposure protocols. For all protocols, the mAs was varied within the selectable range. Using the PMMA phantom, the CNRAIR was measured and corrected for voxel size. Eight axial slices and one coronal slice showing various anatomical landmarks were selected for each CBCT scan of the skull phantom. The slices were presented to six dentomaxillofacial radiologists, providing scores for various anatomical and diagnostic parameters. RESULTS: A hyperbolic relationship was seen between CNRAIR and mAs. Similarly, a gradual reduction in clinical image quality was seen at lower mAs values; however, for several protocols, image quality remained acceptable for a moderate or large mAs reduction compared with the standard exposure setting, depending on the clinical application. The relationship between mAs, CNRAIR and observer scores was different for each CBCT device. Minimally acceptable values for mAs were between 9 and 70, depending on the criterion and clinical application. CONCLUSIONS: Although noise increased at a lower mAs, clinical image quality often remained acceptable at exposure levels below the manufacturer's recommended setting, for certain patient groups. Currently, it is not possible to determine minimally acceptable values for image quality that are applicable to multiple CBCT models.
Subject(s)
Cone-Beam Computed Tomography/methods , Radiographic Image Enhancement/methods , Radiography, Dental, Digital/methods , Adult , Anatomic Landmarks/diagnostic imaging , Artifacts , Cone-Beam Computed Tomography/instrumentation , Humans , Male , Mandible/diagnostic imaging , Maxilla/diagnostic imaging , Phantoms, Imaging , Polymethyl Methacrylate/chemistry , Radiation Dosage , Radiography, Dental, Digital/instrumentation , Skull/diagnostic imaging , Time FactorsABSTRACT
Silastic intubation was performed for Canaliculus communis obstruction in 32 cases. Two eyes showed additional impatent nasolacrimal duct and were not treated. The silastic intubation was performed by aid of a long, hollow blunt injection needle which allows us to check the patency of the lacrimal system once the stenosis of common canaliculus is perforated. The success rate for isolated silastic intubation was 70%, which is similar to the results of other often more invasive surgical techniques for Canaliculus communis stenosis.
Subject(s)
Dacryocystorhinostomy , Intubation/instrumentation , Intubation/methods , Adult , Aged , Aged, 80 and over , Female , Humans , Lacrimal Duct Obstruction/diagnosis , Male , Middle Aged , Needles , Silicone ElastomersABSTRACT
Recession of levator aponeurosis and Muller muscle by hot cautery is a simple and reliable method in case of thyroid disease. The operation is performed under local infiltration anesthesia. The advantage is less bleeding and immediate control of the height of the eyelid.
