The Attenuation Of The X Ray Beam Biology Essay

The intent of this experiment is to show how kVp and rarefying thickness affect the fading and transmittal of an x-ray beam. A quantitative experiment was designed, exposing assorted thicknesses of rarefying stuff to a scope of kVp values. An automatic exposure control ( AEC ) was used to find the ma produced by the exposure and an norm of the consequences was calculated. The consequences corresponded with the hypothesis, demoing that an addition in kVp reduced the ma, and an addition in thickness increased the ma.

During exposure, the x-ray photons in the primary beam are reduced because they are capable to interactions happening between the photons and affair. This procedure is known as fading. The photons are reduced by a fractional sum per increase of affair they pass through, therefore the relationship is exponential ( Bushong, 2008 ) . The per centum of the X raies attenuated per unit of thickness is known as the linier fading coefficient ( NDT, 2010 ) .

Within the diagnostic scopes of skiagraphy, there are two possible interactions that result in the fading of the x-ray beam: the photoelectric consequence and Compton sprinkling ( Fauber, 2009 ) . The photoelectric consequence consequences in soaking up of the x-ray photons. During this interaction the photon is absorbed by an inner shell electron giving it adequate energy to be ejected from its adhering shell: a procedure known as ionization. The vacancy left on the inner shell is occupied by an outer shell negatron, returning the atom to its natural province ( Bushong, 2008 ) . During a photoelectric interaction a secondary photon is produced because the outer shell negatron looses energy as it moves to the inner shell. The secondary photon does non impact the image quality since it is absorbed by next tissues ( Bushong, 2008 ) .Compton spread, occurs when the photon interacts with an outer shell negatron. The incident photon does non reassign all of its energy to the negatron and is deflected, go oning in a different way with less energy ( Farr, 1998 ) . Scattered radiation may interact with the image receptor but contributes no diagnostic information to the image. Scattered radiation does affect image quality because it consequences in a decrease of image contrast. Photons that are neither captive nor capable to Compton dispersing are transmitted through the affair and make the image receptor.

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Increasing the kilovoltage applied to the x-ray beam increases the energy of the photons and their penetratability ( Shepherd, 2003 ) . Increasing the kilovolt above the appropriate degree for an scrutiny consequences in over-penetration and produces a low contrast image. Excessive denseness will besides be evident on the attendant image ( Bushong, 2008 ) . On the other manus, increasing the kVp allows for a decrease of ma and the exposure clip, cut downing the patient ‘s exposure to radiation ( Fauber, 2009 ) . The radiographer should take to bring forth images with optimum denseness and contrast, but at the same clip, exposure to the patient should be kept to a lower limit ( IR ( ME ) R, 2000 ) .

Automatic exposure controls ( AEC ) , measure the familial X raies during an scrutiny. X-ray photons interact with the air or gas contained within an ionization chamber, bring forthing an electrical charge ( Fauber, 2009 ) . The AEC is programmed to let a specific electromotive force to be met harmonizing to the scrutiny being completed. When the desired electromotive force for the scrutiny has been received the exposure is terminated ( Shepherd, 2003 ) . The exposure clip is determined by the figure of photons interacting with the AEC. When used right, the attendant image should show an optimum degree of denseness ( Fauber, 2009 ) .


Ha‚? Increasing the rarefying thickness will ensue in increased ma. The ma will be reduced if the kVp is increased.

Ha‚ˆ Changing the rarefying thickness and the kVp will hold no consequence on the ma produced.


A quality control trial was completed before the experiment began ( Appendix A ) . The consequences of the trial ( Table 1 ) showed that, when compared with old QC consequences ( Appendix B ) , the AEC performed systematically, hence, any alterations to the ma during the experiment occurred because of alterations made to the kVp value or rarefying thicknesses.




Post ma



( & A ; uuml ; / & A ; ucirc ; )




& A ; uuml ;

Group 2

Centre merely



& A ; uuml ;

Group 2

( Table 1 – Consequences of QC proving )

The experiment was completed in the same forenoon during a one hr timescale. The equipment was set up as shown in exposure 1. In add-on, a cassette mensurating 35cm ten 43cm and a tabular array to enter the informations were used during the experiment.

( Photograph 1 – X-Ray room 1 set up and equipment )

The Centre of the rarefying stuff was centered to the cassette to guarantee that the X raies penetrated the rarefying stuff efficaciously. The collimation was adjusted, go forthing a infinite of 1cm at each border of the rarefying stuff, curtailing the utile x-ray beam to the country above the ionization Chamberss.

The beginning to image receptor distance ( SID ) , focal topographic point size, ma choice, and chamber choice remained changeless throughout the experiment. The SID was set at 110cm to account for the inbuilt tabular array bucky grid, and prevented grid cut-off of the x-ray beam. A wide focal topographic point choice reduced the hazard of possible harm to the x-ray tubing. 100mA produced a sufficient figure of photons and remained unchanged throughout the experiment to guarantee that any alterations to the ma occurred as a consequence of alterations made to the variable factors. For the same ground, the centre chamber choice remained changeless throughout the experiment.

Before the experiment, a pilot trial was completed utilizing 6cm of rarefying stuff. An exposure was made utilizing 60kVp and 100mA. The pilot indicated that 60kVp produced X raies with sufficient energy to perforate 6cm of rarefying stuff.

To get down the experiment, 6cm of rarefying stuff were exposed to 100mA at 60kVp. The ma produced was recorded on the tabular array ( Appendix C ) , by two people to cut down the hazard of mistake, and the process was repeated twice more: enabling the mean ma to be calculated. The process was repeated at 80kVp, 100kVp, and 120kVp, and so at each increase of rarefying thickness, taking 1cm of rarefying stuff at a clip, until the process had been completed at 0 rarefying thickness.


Table 2 displays the mean ma calculated from the informations collected during the experiment. The full information collected ( Appendix C ) demonstrated small or no divergence and has hence non been acknowledged in the consequences displayed. The graph below shows a comparing of the mean ma recorded for each rarefying thickness at changing kVp factors.

Rarefying stuff ( centimeter )

kVp Choice








































( Table 2 – Average ma calculated from informations collected during experiment )


The information obtained during the experiment clearly demonstrates that when the kVp value increased, the ma reduced. The graph shows that a comparing can be made, for illustration, to the consequences obtained at 60kVp and those obtained at 120kVp. At 60Kvp, the ma produced is significantly higher than at 120kVp. The consequences indicate that at 120kVp the energy of the x-ray beam was greater, leting the photons to perforate through the attenuating stuff and bring forth the charge required to end the exposure quicker than at 60kVp. The figure of photons in the beam remained changeless during the experiment, therefore the exposure was terminated because fewer interactions occurred at a higher kVp value and transmittal of the photons increased.

The consequences besides show that changing the rarefying thickness of the stuff had an consequence on the ma produced during the experiment. As the thickness of the stuff increased, the ma increased. An illustration of this is clearly shown on the graph at 60kVp. When 0 rarefying thickness was exposed to 60kVp 0.7mAs was produced. In contrast, when 6cm of rarefying stuff was exposed to 60kVp the exposure produced 2.6mAs. The consequences indicate that fading of the x-ray beam increased when the thickness of the rarefying stuff increased. The addition in mAs tantrums an exponential trendline illustrating that the x-ray beam is being attenuated by a fractional sum as it interacts with the rarefying stuff.

In clinical pattern this information is relevant because the thickness of the patient and the choice of exposure factors must be considered in order to bring forth diagnostic images when utilizing an AEC. The x-ray beam must hold adequate energy to perforate the anatomical country of involvement in order for a sufficient charge to be generated to end the exposure. If the exposure is non terminated suitably the patient may be exposed to an unneeded sum of radiation during an scrutiny. Increasing the energy of the x-ray beam besides allows for a lower ma choice, cut downing the patient ‘s exposure to radiation. On the other manus, increasing the kVp over the appropriate bounds for the scrutiny consequences in a decrease of image quality as discussed in the literature reappraisal.

The consequences show that the cogency of the experiment was sufficient as small or no divergence of the ma produced was noted. The AEC gave consistent consequences throughout the experiment. The truth of the experiment was capable to human interaction. The place and change of the rarefying stuff was done by manus and non measured on each juncture. A marker was placed to guarantee that the Perspex remained in about the same place ; nevertheless this could hold been measured more accurately if the clip of the experiment had non been limited. The consequences obtained during this experiment prove that the hypothesis was right.


In decision, the experiment undertaken set out to show that changing the kVp, and/or rarefying thickness had a direct consequence on the ma produced during an exposure. The experiment proved that the hypothesis was right. When the kVp increased, a decrease in ma was recorded. In add-on, when the rarefying stuff increased, an addition in ma was seen.

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