The wide application of Computed Radiography and the recent development of Direct Digital Radiography(DDR) has brought a number of advantages to radiology departments. Digital radiology systems usually have a larger dynamic range than film screen systems and so can accept a wide range of exposures. Also, such systems should allow better dosage optimization for individual examinations. However, the wide exposure dynamic range of such systems may have the disadvantage that, if the x-ray generator Automatic Exposure Control (AEC) happens a fault or the output calibration drifts, the dosage increase/decrease may not be identified readily. At the same time, there is significant potential radiation for the initial set-up of such systems not to be optimized because of the wide exposure dynamic range.
The implementation of the following advises will help to minimize the above mentioned disadvantages:
1. The company supplying new digital equipment should supply information on the recommended receptor exposures, which give diagnostic images with the lowest possible patient dosage for each particular examination.
2. This figure for the patient dosage, should be proved with an in-beam phantom during hand-over; the manufacturer should also specify the phantom parameters. These dosage values could be adjusted at each local site, such as the practice applied to Image Intensifiers. It is important for departments to set up QA systems to routinely monitor factors, including clinical exposure constancy, imaging system sensitivity and  AEC performance.
3. Digital radiography systems may have different x-ray energy responses to film screen systems. Therefore,  the generator's Automatic Exposure Control compensation characteristics should be different from that.

For existing systems having been upgraded to use DDR or CR, the existing AEC compensation characteristics will need reprogramming. Medical x-ray machine manufacturers should be in a position to offer any necessary generator firmware, software or hardware upgrades.
Mobile X-ray machine should not be affected, as most do not normally use Automatic Exposure Control; however departmental exposure protocols should be adjusted to reflect the different characteristics of the digital image receptors.
4. Each image, whether produced on film or soft copy display, should ideally have an associated number to indicate the level of exposure to the detector. Currently all CR systems have a sensitivity index which is related to detector exposure, however, DR systems are generally not supplied with this feature.
5. According to new IPEM guidelines, Once CR and DR are in use, the constancy of applied exposure factors can be monitored on a regular basis when checked.

本文由廣州佳譽(yù)醫(yī)療器械有限公司編輯