Benefit and lessons of acceptance tests

 
Acceptance testing, performed by NRIRR, includes all diagnostic radiology equipment, except intraoral dental and bone densitometry. Bedside (mobile) radiographic, (mobile) surgical image intensifiers and conventional tomography equipment belong to group of radiographic and fluoroscopic equipment. Moreover, acceptance tests are performed for mammographic, digital subtraction angiography (DSA), computed tomography (CT) and panoramic (recently also 3D) dental equipment.
According to generally accepted definitions, the main aim of acceptance testing is checking the compliance of the equipment with the contract and/or manufacturer’s specifications (and local regulations, if applicable). It is the first benefit of the user. In the – very unlikely but in principle possible – case of non-compliance the user can successfully complain at the installing firm, using the test report, in case of need a further expert opinion of NRIRR. As this always is in the warranty period, these repairs and/or adjustments are free of charge for the user. It must be emphasized that testing activity of NRIRR is independent from manufacturers; it is run within the frame of an accredited testing laboratory, using calibrated measuring instruments, performed by highly qualified personnel and based on valid international standards (which are identical with European and also with Hungarian standards). The other benefit for the user is the measuring of the so-called base levels for further QA, i.e. initiating of a QA programme assuring long, safe and optimum performance of equipment.
Determination of initial values of the quality parameters to be tested, which is the main aim of testing, was successful almost in every case. Modern new X-ray generators – apart from some rare exceptions – have considerably better characteristics, relating to accuracy, linearity and reproducibility of the parameters than required by valid standards. Naturally, it may not be a reason for omitting these tests as the aim is just detecting exceptions. Almost in every third case some errors or values outside tolerances which need servicing or adjustment were detected. The most frequent problems are the improper adjustment of beam limiting devices and automatic exposure control, other errors are very rare. These are recorded not only in the test reports but also in the official letters written to the competent leaders of the health institutions. As it always happens in the warranty period, these servicing or adjustments are free of charge for the hospitals. It has to be mentioned that with appropriate measuring instruments differences between specified and actual filtration of the X-ray tube assembly or between displayed and actual X-ray tube current could be detected. QC tests are always non-invasive, i.e. takes place by measurement of the radiation only.
Modern X-ray equipment have the general characteristics that the possibility of operator errors is minimized by their construction. These equipment are called user-friendly. In contrary of it, they are not “measurement-friendly”. Taking into account the non-invasive character of the tests, it is not possible to go into a so-called “service mode” if no authorized service personnel is present. This property makes testing difficult in some cases.
Some examples for the difficulties arisen from it: one has to remove and take back cassette or enter “patient data” before every exposure. In some cases there is impossible to measure tabletop attenuation, as without the presence of a radiographic cassette an exposition is not possible. Moreover, many times only the current time product can be selected, the tube current is not independent. For digital equipment, it is not possible to determine constancy of film density (in automatic exposure control AEC mode) but constancy of dose only. Measurements on DSA equipment are performed always with the aid of a service engineer of the manufacturer, while in case of CT testing presence of an experienced CT-operator is absolutely necessary. Further, mostly organizational problems occur in testing surgical image intensifiers in operating theatres.
Careful use of the equipment is a mutual interest. Testers insist on the presence of the representative of the customer, mainly from the point of view of avoiding later legal disputes: testing laboratory does not “use” their equipment.
In general, knowledge of radiographers is very uneven, so improving education and training of radiographers as well as training them on QA is a very urgent and necessary task. It is extremely important also from radiation protection point of view.

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