Image quality is a concept to represent information content in the image. Therefore, medical images must have sufficient information needed for the correct diagnosis. Basic knowledge about diagnostic image quality is essential to perform imaging diagnosis at high level. Physical image quality consists of three components; (spatial) resolution, contrast (resolution), and noise. Resolution and contrast make signals needed for detection task, while noise is the factor that disturbs signal detection. Some measures, such as signal-to-noise ratio or contrast-to-noise ratio are used to represent integrated physical image quality. Observer performance changes according to the physical image quality. High observer performance can be expected by using high physical quality images to some extent. However, there is a limit where observer performance reaches maximum even if the physical image quality further increases. Receiver Operating Characteristic (ROC) curves are used to evaluate final diagnostic outcome from the images. The diagnostic image quality must be assessed using ROC analysis. Observer performance using some phantoms is highly correlated with the diagnostic image quality obtained from ROC curves. Therefore, physical image quality, observer performance, diagnostic image quality are closely associated with each other. The key factor in evaluating diagnostic image quality using ROC analysis is appropriate selection of the samples and the observers for the given task.
There are many kinds of diseases in oral and maxillofacial regions, whose anatomy is very complex. Even experienced dentists cannot have appropriately decided to select the imaging modalities for the diseases in oral and maxillofacial regions. Therefore, in the present review, clinical applications in imaging modalities for many kinds of lesions in oral and maxillofacial regions are considered based on our routine examinations. In concrete, we review that the appropriate imaging modalities should be selected according to both of the regions and the suspected pathological diagnosis of diseases. At the same time, we explain that the medical interviews, visual examinations, palpations, and laboratory examinations are very important to select the appropriate imaging modalities. In particular, we precisely interpret the methods to select the appropriate modalities for the diseases in soft tissues because many dentists may be relative poor for it. In the present review, we are delight to that our methods are useful to select the appropriate imaging modalities as one of criteria for readers.
Objectives: To develop a new psychophysical method for evaluating image quality using just noticeable differences (JND) and to clarify its usefulness. Methods: An aluminum phantom composed of 12 steps, with seven holes in each step, was radiographed using three intraoral radiographic systems. In the analytical method, detection thresholds were calculated based on the JND and standard deviation values for the background gray level. The number of undetectable holes in each image was assessed using the software ImageJ. In the observer performance test, eight observers evaluated the number of imperceptible holes on each image. We compared the number of undetectable holes according to the analytical method with the values obtained by the observers. Results: The numbers of undetectable holes according to the analytical method exhibited predictable relationships with the values obtained by the observers for all three intraoral radiographic systems. The standard deviation values produced by the analytical method were smaller than those obtained by the observers. Conclusions: Our JND-based psychophysical method can be used to predict observer performance. This method can be used to evaluate the image quality of radiographic imaging systems without observers.
Purpose: Application of small field of view (FOV) is effective to reduce radiation exposure indental cone-beam CT (CBCT). However, it is not easy to depict objective teeth in aFOV of 40-50mm in diameter. Therefore an automated FOV adjustment system basedon the panoramic radiography 3D mapping technique was developed. We evaluated thereproducibility of the FOV in objects with various head position. Materials and method: A head phantom especially designed for panoramic radiography was used as an objectto be imaged. A hybrid x-ray imaging system combining digital panoramic radiographywith CBCT (QR-master H/Revo) was used. This system equiped a FOV adjustmentsystem. In the FOV adjustment system, at first a panoramic radiography was taken as ascout image. In the panoramic image, when a dentist chooses a position to be imaged, athree-dimentional position of a FOV with 50mm in diameter and 45mm in height wasdefined automatically. Panoramic radiograph and CBCT were obtained in various headposition. The reproducibility of the FOV adjustment system was evaluated in themaxillary anterior region. Results and conclusion: The depiction of objective teeth in CBCT was stable when the position of head phantomshifted toward bilaterally. Objective teeth were protruded from FOV when the positionof phantom shifted anteroposterior direction widely. Widely vertical tilting of head alsoaffected the reproducibility of FOV. It was suggested that the FOV adjustment systemrevealed high reproducibility as far as the position of patient’s head was setappropriately.