THE VIDEODENSITOMETRIC ANALYSIS OF THE RADIOGRAPHIC DENSITY AND CONTRAST

Videodensitometry법을 이용한 X선사진의 흑화도와 대조도에 관한 연구

Generally the patient's absorb dose and readability of radiograms are affected by the exposure time and kVp of which are related with the radiographic density and contrast The investigator carried studies to know the adequate level of exposure time and kVp to obtain the better readability of radiograms. In these studies dried human mandible with selfcuring acrylic resins attached with aluminum step wedge was used and readability of radiograms were compared with each other by videodensitometry among various combination sets of the exposure time, such as 5, 6, 8, 12, 15, 19, 24, 30, 38, 48 and 60, and varing level of kVp, such as 60, 65, 70, 80 and 90 respectively. The obtained results were as follows: 1. As exposure time and kVp were increased, radiographic density of radiograms was increased. 2. The subject contrast was increased where aluminum step wedge was thin and reduced in the reversed condition. At the thin aluminum step wedge, subject contrast was increased at the condition of lower kilovoltage than that of higher kilovoltage. 3. In the case of non-constant radiographic density, the radiographic contrast was reduced with the increment kilovoltage. The radiographic contrast was increased in the lower kilovoltage with the longer exposure time and the higher kilovoltage with the shorter exposure time. 4. At the condition of short exposure time, better readability of each reading item was obtained with the increment of the kilovoltage but at the opposite condition increasing exposure time worsened readability of radiograms. Since X-ray machine in the current dental clinics is fixed between the range of 60-70kVp and 10mA, good radiograms can be obtained by varied exposure time. But according to the conclusion of these studies, better radiograms can be obtained by using filtered high kVp and then the absorb dose to patient and exposure time can be reduced.