16th Computed Maxillofacial Imaging Congress

Abstract

Keywords Kinetic image Á Flat-panel ditector Á Noise power spectrum Á Modulation transfer function Á Lag images Purpose Recently, diagnoses of dentistry are performed by panoramic radiography, dental X-ray or CT etc. Especially, for the functional diagnosis of temporomandibular joint or swallowing, the kinetic image is necessary. The kinetic image is got by the X-ray fluoroscopic examination. Until now, the detector of fluoroscopic device was image intensifier (I.I.). But in these days, flat-panel detector (FPD) is used for digital fluoroscopy.Alphard 3030 is corn-beam CT equipped with FPD created by ASAHI RENTGEN. This device is usually used as corn-beam CT with rotation of the arm. Otherwise, when the arm is locked, it can be used as a fluoroscopic device. If the kinetic image is possible by the device usually used in dentistry it is useful for the functional analysis on the oral and maxillofacial region, and a diagnosis of temporomandibular joint or swallowing will develop. So we measured the image quality of Alphard 3030 and examined its utility. Methods Measurement of patient exposureTo measure the patient exposure, we put the chamber at the position of patient and exposed with changing the tube voltage, tube current and exposed time. Then we measured the exposure. The exposure was converted to the skin surface dose and compared it to them of other systems. Evaluation of image quality We evaluated the granularity and sharpness by measuring the noise power spectrum (NPS) and modulation transfer function (MTF).For the measurement of NPS, we attached a 5-mm thick Aluminium filter at the X-ray tube side. We changed the tube current 1, 2 and 4mA and then exposed. We got the kinetic images and divided it into the static images at every 0.03 second. (Because Alphard 3030 provides dynamic radiographs at a rate of 30 frames/ sec.) By using these images, we calculated the spatial and the temporal NPSs.For evaluation of MTF, we used the edge method. A tungsten edge was placed at the surface of the FPD and exposed to get the kinetic image. The kinetic image was divided to 10 static images at every 0.03 second, then these 10 static images were averaged to got one image. We calculated the presampled MTF with the averaged image. MTF was calculated at the spatial domain only. Analysis of lag images We measured the lag images with an iron ball (11mm in diameter) that was moved like the pendulum. We got the kinetic image of this iron ball and divided it to static images, then measured the movement of the iron ball that was affected in one image. Exposure of phantomThe phantom is a life size oral-pharyngeal plaster model for CT image data. We poured barium into the phantom and got the kinetic image. Alphard 3030 and conventional video fluoroscopic device were used. Both images were observed and compared. Results Measurement of patient exposurePatient exposure of the kinetic image was not so high compared to those of other systems. So, patient exposure is enough good to use the system in the clinical site. Evaluation of image q...