Quality control is very essential for a department specially when we are working in a hospital where chances of infection is very high. A small mistake can lead a big disaster. Broadly, quality control have following three most important aims:
1. For the better performance of equipment,
2. For the protection of staff and patients from radiation, and
3. Ultimately for the better performance of the department.
In Fluoroscopy, examinations can result in the high patient radiation dose, the Entrance Skin Dose (ESD) for a adult is around 30-50 mGyt/min. (i.e. 3-5 R/min.); this can easily results in a skin dose of 100 mGyt (10rad) for many Fluoroscopy examinations. So, overall quality assurance is very essential for a Fluoroscopy unit. Following are the three main areas of Fluoroscopy Quality Control measurements:-
1. Exposure Rate.
2. Spot-film Exposure.
3. Automatic Exposure System.
Exposure Rate
Measurements are made with a calibrated radiation dosimeter to ensure that these levels are not exceeded. Lucite, aluminium, copper and lead filters are used to determine the adequacy of any Automatic Brightness Stabilization system (ABS system).
Most state statutes require that under normal operation, the ESD rate shall not exceed 100mGyt/min. For international radiology procedures, the fluoroscope may be equipped with a high-level control, which allows an ESD upto 200 mGyt/min. Unlimited exposure rates are permitted for recorded Fluoroscopy, such as cine-radiography.
Spot -film Exposure
Spot-film devices are used to evaluated the radiation exposure and proper collimation. During testing, proper exposure of the cassette spot film depends on the kVp, mAs and sensitivity characteristics of the screen-film combination, make sure all parameters are correct.
Note that the use of grid during photofluorospot imaging approximately double the ESD.
Automatic Exposure Stabilization System
It it abbreviated as ABS system, equipped in all Fluoroscopy units. This system functions in the manner of the photo timer of a radiographic imaging system, producing constant image brightness on the television or flat panel monitor, regardless of the thickness or composition of the anatomy. These systems tend to deteriorate or fail with use and can lead high radiation dose.
Performance monitoring of an ABS is conducted by determining that the radiation exposure to the input phospher of image-intensifier tube is constant, regardless of patient thickness. With a test object, the image brightness on the video monitor should not change perceptibly when various thickness of patient simulating material are inserted into the beam. The input exposure rate to the image-intensifier tube is measured and should be in range of 0.1-0.4 microGyt/second. This assesses spatial resolution, contrast resolution and noise.
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