Preva Dental X-ray System User Manual, 00-02-1576, Revision ZA1
43
The X-ray tube output is defined as the quotient of the air kerma at a specified distance from the X-ray
tube focus by the tube current–exposure time product. The Preva X-ray tube output at 20 cm is shown in
the following table.
Table 1: Preva X-ray tube output at 20 cm from the X-ray tube focus
1.374 mGy·mA⁻¹·s⁻¹ 1.560 mGy·mA⁻¹·s⁻¹ 1.783 mGy·mA⁻¹·s⁻¹
The Preva X-ray tube output is not calibrated to the listed values and may change over the life of the
product. The presented data are based on statistical analysis of limited number of measurements made
on a limited number of Preva intraoral X-ray systems. The maximum deviation of the estimate does not
exceed 40% with confidence 99.9%. Calibrated measurement equipment must be used periodically,
and at least annually, to obtain precise values for the X-ray tube output and air kerma for each individual
machine at the technique factors of interest.
The incident air kerma is defined as the kerma to air from an incident X-ray beam measured on the
central beam axis at the position of the patient surface. Only the radiation incident on the patient or
phantom and not the backscattered radiation is included.
The incident air kerma for Preva at 20 cm from the X-ray tube focus is shown in the following table. The
values are calculated based on the X-ray tube output.
Table 2: Preva incident air kerma at 20 cm from the X-ray tube focus
Exposure
Time
60 kV 65 kV 70 kV
4 mA 5 mA 6 mA 7 mA 4 mA 5 mA 6 mA 7 mA 4 mA 5 mA 6 mA
0.020 s 0.110 mGy 0.137 mGy 0.165 mGy 0.192 mGy 0.125 mGy 0.156 mGy 0.187 mGy 0.218 mGy 0.143 mGy 0.178 mGy 0.214 mGy
0.025 s 0.137 mGy 0.172 mGy 0.206 mGy 0.240 mGy 0.156 mGy 0.195 mGy 0.234 mGy 0.273 mGy 0.178 mGy 0.223 mGy 0.267 mGy
0.032 s 0.176 mGy 0.220 mGy 0.264 mGy 0.308 mGy 0.200 mGy 0.250 mGy 0.300 mGy 0.349 mGy 0.228 mGy 0.285 mGy 0.342 mGy
0.040 s 0.220 mGy 0.275 mGy 0.330 mGy 0.385 mGy 0.250 mGy 0.312 mGy 0.374 mGy 0.437 mGy 0.285 mGy 0.357 mGy 0.428 mGy
0.050 s 0.275 mGy 0.344 mGy 0.412 mGy 0.481 mGy 0.312 mGy 0.390 mGy 0.468 mGy 0.546 mGy 0.357 mGy 0.446 mGy 0.535 mGy
0.064 s 0.352 mGy 0.440 mGy 0.528 mGy 0.616 mGy 0.399 mGy 0.499 mGy 0.599 mGy 0.699 mGy 0.456 mGy 0.571 mGy 0.685 mGy
0.080 s 0.440 mGy 0.550 mGy 0.660 mGy 0.769 mGy 0.499 mGy 0.624 mGy 0.749 mGy 0.874 mGy 0.571 mGy 0.713 mGy 0.856 mGy
0.100 s 0.550 mGy 0.687 mGy 0.824 mGy 0.962 mGy 0.624 mGy 0.780 mGy 0.936 mGy 1.092 mGy 0.713 mGy 0.892 mGy 1.070 mGy
0.125 s 0.687 mGy 0.859 mGy 1.031 mGy 1.202 mGy 0.780 mGy 0.975 mGy 1.170 mGy 1.365 mGy 0.892 mGy 1.114 mGy 1.337 mGy
0.160 s 0.879 mGy 1.099 mGy 1.319 mGy 1.539 mGy 0.998 mGy 1.248 mGy 1.498 mGy 1.747 mGy 1.141 mGy 1.426 mGy 1.712 mGy
0.200 s 1.099 mGy 1.374 mGy 1.649 mGy 1.924 mGy 1.248 mGy 1.560 mGy 1.872 mGy 2.184 mGy 1.426 mGy 1.783 mGy 2.140 mGy
0.250 s 1.374 mGy 1.718 mGy 2.061 mGy 2.405 mGy 1.560 mGy 1.950 mGy 2.340 mGy 2.730 mGy 1.783 mGy 2.229 mGy 2.675 mGy
0.320 s 1.759 mGy 2.198 mGy 2.638 mGy 3.078 mGy 1.997 mGy 2.496 mGy 2.995 mGy 3.494 mGy 2.282 mGy 2.853 mGy 3.423 mGy
0.400 s 2.198 mGy 2.748 mGy 3.298 mGy 3.847 mGy 2.496 mGy 3.120 mGy 3.744 mGy 4.368 mGy 2.853 mGy 3.566 mGy 4.279 mGy
0.500 s 2.748 mGy 3.435 mGy 4.122 mGy 4.809 mGy 3.120 mGy 3.900 mGy 4.680 mGy 5.460 mGy 3.566 mGy 4.458 mGy 5.349 mGy
0.640 s 3.517 mGy 4.397 mGy 5.276 mGy 6.156 mGy 3.994 mGy 4.992 mGy 5.990 mGy 6.989 mGy 4.564 mGy 5.706 mGy 6.847 mGy
0.800 s 4.397 mGy 5.496 mGy 6.595 mGy 7.694 mGy 4.992 mGy 6.240 mGy 7.488 mGy 8.736 mGy 5.706 mGy 7.132 mGy 8.558 mGy
1.000 s 5.496 mGy 6.870 mGy 8.244 mGy 9.618 mGy 6.240 mGy 7.800 mGy 9.360 mGy 10.920 mGy 7.132 mGy 8.915 mGy 10.698 mGy
1.250 s 6.870 mGy 8.588 mGy 10.305 mGy
12.023 mGy 7.800 mGy 9.750 mGy 11.700 mGy 13.650 mGy 8.915 mGy 11.144 mGy 13.373 mGy
1.600 s 8.794 mGy 10.992 mGy
13.190 mGy
15.389 mGy 9.984 mGy 12.480 mGy 14.976 mGy 17.472 mGy 11.411 mGy
14.264 mGy 17.117 mGy
2.000 s 10.992 mGy 13.740 mGy
16.488 mGy
19.236 mGy 12.480 mGy 15.600 mGy 18.720 mGy 21.840 mGy 14.264 mGy
17.830 mGy 21.396 mGy
Note: The röntgen (R), the legacy unit of quantity exposure, was used prior to the use of air kerma. Values of
exposure in röntgen can be converted to air kerma in gray using the conversion 0.876×10
–2
Gy/R. Similarly, air
kerma values in gray can be converted to exposure in röntgen using the conversion 114 R/Gy
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