Lars Olsson1,2, Mats Nilsson1,3, Björn Svenson4, Kristina Hellén-Halme1. 1. 1 Department of Oral and Maxillofacial Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden. 2. 2 Department of Oral Radiology, Postgraduate Dental Education Center, Örebro, Sweden. 3. 3 Department of Radiation Physics, Skåne University Hospital, Malmö, Sweden. 4. 4 Postgraduate Dental Education Center, Faculty of Medicine and Health, School of Health and Medical Sciences, Örebro University, Örebro, Sweden.
Abstract
OBJECTIVES: Radiographic images suffer from varying amounts of noise. The most studied and discussed of these is random noise. However, recent research has shown that the projected anatomy contributes substantially to noise, especially when detecting low-contrast objects in the images. Our aim, therefore, was to evaluate the extent to which overprojected anatomical noise affects the detection of low-contrast objects in intra-oral images. METHODS: Our study used four common sensor models. With each sensor, we took four series of images, three series with and one series without an anatomical phantom present. In each series, we exposed a low-contrast phantom at 18 different exposure times using a standardized method. 4 observers evaluated all 288 images. RESULTS: The low-contrast characteristics differed substantially when imaging low contrast on a homogeneous background compared with imaging low contrast when an anatomical phantom was present. For three of the sensors, optimal exposure times for low-contrast imaging were found, while the fourth sensor displayed a completely different behaviour. CONCLUSIONS: Calibrating the low-contrast properties of an imaging system using low-contrast objects on a homogeneous background is not recommended. On an anatomical background, low-contrast properties are completely different, and these will mimic the clinical situation much more closely, directing the operator how to best use the system. There is a clear demand for further research on this subject.
OBJECTIVES: Radiographic images suffer from varying amounts of noise. The most studied and discussed of these is random noise. However, recent research has shown that the projected anatomy contributes substantially to noise, especially when detecting low-contrast objects in the images. Our aim, therefore, was to evaluate the extent to which overprojected anatomical noise affects the detection of low-contrast objects in intra-oral images. METHODS: Our study used four common sensor models. With each sensor, we took four series of images, three series with and one series without an anatomical phantom present. In each series, we exposed a low-contrast phantom at 18 different exposure times using a standardized method. 4 observers evaluated all 288 images. RESULTS: The low-contrast characteristics differed substantially when imaging low contrast on a homogeneous background compared with imaging low contrast when an anatomical phantom was present. For three of the sensors, optimal exposure times for low-contrast imaging were found, while the fourth sensor displayed a completely different behaviour. CONCLUSIONS: Calibrating the low-contrast properties of an imaging system using low-contrast objects on a homogeneous background is not recommended. On an anatomical background, low-contrast properties are completely different, and these will mimic the clinical situation much more closely, directing the operator how to best use the system. There is a clear demand for further research on this subject.
Authors: Markus Håkansson; Magnus Båth; Sara Börjesson; Susanne Kheddache; Anna Grahn; Mark Ruschin; Anders Tingberg; Sören Mattsson; Lars Gunnar Månsson Journal: Radiat Prot Dosimetry Date: 2005 Impact factor: 0.972