Master in Medical Physics 2015 to 2016

Quality control in Conventional X-Ray

Francisco J.Hernández Flores∗

International Centre for Theoretical Physics

franciscohernandez_f2010@hotmail.com

August 7, 2015

Abstract

This task it is about the quality control in Conventional X-Ray, The aim ofthe present Quality Control (QC) testing is to detect changes that may resultin a clinically significant degradation in image quality or a significant increasein radiation exposure. of conventional x-ray such as reproducibility of tubevoltage, dose out put, time, and x-ray tube efficiency, Accuracy of kVp, mA, time.Examinations of these factors are studied using adequate instrumentation formeasure different parameter in the hospital Majore of Trieste Italy.

I. Introduction

The principle goal of quality con-trol of x-ray machine is obtain accu-rate and timely diagnosis. The sec-ondary goals are minimization of radi-ation exposure and obtain high imagequality. This can be assess by perfor-mance the x-ray machine by optimumoperating parameters such as repro-ducibility of tube voltage, dose out

put, time , x-ray tube efficiency, Accu-racy of kVp, mA, time, focal spot sizeand half value layer.

During this practical we make onlymeasure about kVp mA and outputfactor, we know about the instrumen-tation used in quality control in radiodiagnostic and which parameter affectthe quality of the imaging.

II. Theory

I. KV Effect

The relationship between x-ray pro-duction efficiency and KV has a spe-cific effect on the practical use of x-ray equipment. As we will see in a

later chapter, x-ray tubes have a def-inite limit on the amount of electri-cal energy they can dissipate becauseof the heat produced. This, in prin-ciple, places a limit on the amountof x-radiation that can be produced

∗Physics of diagnostic X ray 2

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Master in Medical Physics 2015 to 2016

by an x-ray tube. By increasing KV,however, the quantity of radiation pro-duced per unit of heat is significantlyincreased. [2]

II. EFFICACY (OUTPUT)

The x-ray efficacy of the x-ray tube isdefined as the amount of exposure, inmilli Grays, delivered to a point in thecenter of the useful x-ray beam at adistance of 1 m (see fig. 1) from the fo-cal spot for 1 mAs of electrons passingthrough the tube. [2]

The efficacy value expresses the

ability of a tube to convert electronicenergy into x-ray exposure. Knowl-edge of the efficacy value for a giventube permits the determination ofboth patient and image receptor ex-posures by methods discussed in laterchapters. Like x-ray energy output,the efficacy of a tube depends on anumber of factors including KV, volt-age waveform, anode material, filtra-tion, tube age, and anode surface dam-age. The illustration below gives typi-cal efficacy values for tungsten anodetubes with normal filtration. [2]

Figure 1: Detector in air at 100 cm from focus [Estimation of output (Ka/mAs) as function ofkV] [1]

III. Material and Methods

For quality control they were usedthe following measuring instruments.meter, ionization chamber parallel

plane, kVp, Electrometer.The chamber of ionization was po-sitioned at 100 cm of distance at fo-

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Master in Medical Physics 2015 to 2016

cal spot, connected at the electrome-ter for evaluated the Ka. then mea-surements began varying the kV withthe same mAs at same distance fo-cal spot surface this result is showsin the graph 2. The Quality Control(QC) in radiography is a central partof QA programme, which deals withequipment maintenance and monitor-

ing. QA in diagnostic radiology isa mean of maintaining standards inimaging and working towards min-imizing patient and staff doses. Toaccomplish these objectives, a numberof physical parameters that affect theperformance of X-ray imaging systemare to be measured.

IV. Results and discussion

The kV is very useful in controlling the radiation output of an x-ray tube.The figure below shows a linear relationship, tube output dependence on kV2,the values obtained i the graph they were measure in the practice, with theirrespective error bar

4,000 6,000 8,000 10,0001.00

2.00

3.00

4.00

kVp2

Out

putµ

Gy/

mA

s

y= 0.0004332 ∗ x − 0.3699

Figure 2: Output (Ka/mAs) as function of kV

V. Conclusion

• In our few experience as stu-dent, was useful know QC pro-gram has positive effect on X-rayequipment performance.

• The graph obtained from thedata measured during practicemeets theory linearity of the out-put factor when compared tosquare kV.

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Master in Medical Physics 2015 to 2016

References

[1] Paola Bregant , Lecture Physics of Diagnostic with x-ray 2, ICTP Trieste Italy,2015.

[2] Perry Sprawls, Ph.D. , The Physical Principles of Medical Imaging, 2nd edition,May 1995.

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