THE IMPORTANCE OF CALIBRATION IN RADIOLOGY
kVp
“The x-ray tube kVp is the most critical. A small error in this variable will have a greater
effect on the final radiographic or fluoroscopic image an equivalent variation in any
of the other parameters.....”
Basic Quality Control in Diagnostic Radiology, AAPM Report No. 4, 1977, pg 14
"A change of 1 kV can change the tube output, measured in mGy mAs. by about
measured between details in a rest object, and can also lead to a perceptible change in image quality.......”
Law, J., The measurement and routine checking of mammography x-ray tube kV.
Phys. Med. Biol. 1991; 36:1133-1139.
CALIBRATION AND MEASURING OF kVp INSTRUMENTS
Regular calibration of Diagnostic kVp meters and cassettes is imperative to ensure
reliable operation of your diagnostic x-ray machine. If the kVp of a diagnostic x-ray unit is in error by even a few kV, significant information may be lost in the image. In addition the patient may be exposed to excessive radiation. Having the ability to accurately measure
kVp, you can maximise contrast and resolution while minimising patient dose.
In order to accurately measure kv, your kVp meter must be in good working condition and have a valid calibration. Remember, your kVp meter is only as good as it's calibration. We strongly recommend that your kVp instruments be calibrated at least once every two
years in order to ensure continued accurate kVp measurements.
DIAGNOSTIC X-RAY EQUIPMENT COMPLIANCE TESTING PROTOCOLS
Studies in Australia and overseas of radiation doses from diagnostic x-ray procedures
have
identified poor equipment performance as a major contributor to unnecessary
patient
exposure.
To address this concern, quality assurance (QA) programs for medical radiology
equipment have been developing for a number of years in Australia. Theses programs
are
now mandatory in a number of jurisdictions.
The Radiological Council, a regulatory body established under the Radiation Safety Act
of
Western Australia, has decided that a program for the compulsory compliance testing
of
diagnostic x-ray equipment will commence on 1 January 1997.
The council is empowered under regulation 23 if the Radiation Safety Regulations to implement such a program. Initially, the specific requirements of the program will be imposed under section 36 of the Act as conditions on registrations and licences.
The council is mindful of the cost-benefit aspects of such a program, and will keep it’s
critical parameters under review.
The required tests are essentially concerned with the radiation safety of x-ray
equipment. As patient dose ultimately depends on the complete imaging process, it is
recommended
that these tests be supplemented with other radiographic, sensitometric and image quality
tests as part of a complete QA system.
The above mentioned Protocol contains information under the following subjects:-
- DOCUMENTATION, CERTIFICATION AND AUDITING OF COMPLIANCE TESTS
- REQUIREMENTS FOR QUALIFIED EXPERTS
- REQUIREMENTS FOR COMPLIANCE TESTERS
- REQUIRED EQUIPMENT COMPLIANCE TESTS
As well as the above information this protocol also provides the standard tests
approved by the Radiological Council for routine compliance testing of the following equipment:-
- MOBILE RADIOGRAPHIC EQUIPMENT
- MAMMOGRAPHIC UNITS
- MAJOR RADIOGRAPHIC UNITS
- FLUOROSCOPIC UNITS
- DENTAL RADIOGRAPHIC UNITS
- COMPUTED TOMOGRAPHIC UNITS
It is advised that all users of the above equipment utilise the protocol to assure a high
quality of performance.
These protocols are available through Gammasonics Institute for Research and Calibration
Pty Ltd upon request.
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