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Uncertainty evaluation of non-invasive multi-parameter detector measurements in quality assurance of diagnostic
M Senthilkumar1, C Senthil Kumar1, R U Parmar2
1Southern Regional Regulatory Centre, Atomic Energy Regulatory Board, Chennai, Tamil Nadu, India.
Objective:
To optimize the patient dose and image quality through quality assurance (QA) of diagnostic x-ray equipment and to ensure compliance with international and national standards in x-ray specification parameters, the use of contactless and quick non-invasive instruments has gained importance. Considering the importance of equipment qualification and the intervention level for equipment management, it is vital to account for uncertainties in the measurement of parameters in diagnostic radiology. However, the limits and measurement uncertainties associated with the parameter measurement are not well established and many technical and scientific literature provide different tolerance values, either as absolute or in terms of percentage.
Methods And Materials:
In this paper, the authors analyze non-invasive multi-parameter detector measurements with the aim to (i) improve the accuracy in measurement of x-ray parameters (kilovoltage, dose, and exposure time); (ii) estimate the uncertainty associated with such measurements; (iii) analyze the tolerance values prescribed by various professional and regulatory bodies and propose an improvised method of reporting the parameters. The approach adopted in this paper takes into account the uncertainties associated with traditional instruments and the subjectivity in the measurements.
Results:
Estimated uncertainty for kV measurements in the range between 1.45 kV at 40 kV measurements and 4.88 kV at 150 kV measurements. The MU associated with the dose measurement is estimated to be 6.2% at 110 kVp, 100 mA, and 500 msec. Maximum MU estimated at 10 msec exposure time is 4.5% and with MU of 5% deviation added to 9.5%.
Conclusions:
The current practice of reporting the measured mean values deviation without considering the inherent measurement uncertainty may not be a correct quantification procedure in QA. This is evident from the case study that 3% addition to the measured kV, 6.2% addition in the measured dose, and 4.5% to the measured time accounts for measurement uncertainty.
