The change of exposure conditions and its impact on patient\u27s dose with maintaining the same exposure index

Uvod: Zaradi diagnostične uporabnosti rentgenske slike, je potrebno tudi pri spremembi ekspozicijskih pogojev ohranjati enak ekspozicijski indeks. Pri spreminjanju ekspozicijskih pogojev, si lahko pomagamo s pravilom 15 %, ki opisuje razmerje med pospeševalno napetostjo - U (kV) in produktom toka in časa - It (mAs) ali z metodo, pri kateri za ohranitev enake jakosti snopa, mAs produkt spreminjamo s peto potenco razmerja med obema pospeševalnima napetostma (kV). Z uporabo pravila 15 % lahko vplivamo na znižanje dozne obremenitve preiskovanca ali na zmanjšanje sipanega sevanja in posledično boljšo kontrastno ločljivost slike. Namen: V okviru diplomskega dela smo ugotavljali, kako sprememba ekspozicijskih pogojev vpliva na dozno obremenitev pacientov ter poiskati optimalno jakost snopa, ki pade na slikovni sprejemnik. Metode dela: Merili smo produkt med dozo in površino ter ekspozicijski indeks pri različnih ekspozicijskih pogojih. Ekspozicijske pogoje smo nastavljali elektronsko z nastavitvijo tako pospeševalne napetosti (kV) kot električnega toka v določenem času ekspozicije (mAs). Rezultati in razprava: V raziskavi smo ugotovili, da pri izbranih napetostih v razponu od 45 kV do 81 kV, ne glede na debelino in absorpcijski koeficient objekta, pravilo 15 % načeloma drži, odstopanja so manjša, med 0 – 14 %, le pri povečanju napetosti iz 55 na 63 kV je odstopanje 21 %. Zaključek: Iz meritev opravljenih v tej raziskavi lahko zaključimo, da pravilo 15 % ni vedno točno, vendar je v vsakodnevni praksi dovolj zanesljivo, saj rentgenski aparat ponuja le določene vrednosti ekspozicijskih pogojev, zato ne moremo vedno nastaviti izračunanih oziroma optimalnih vrednosti. Bolj točno je, kadar osnovno pospeševalno napetost zmanjšamo za 15 % kot takrat, ko napetost povečamo za 15 %. Ob zniževanju pospeševalne napetosti dozo povečujemo in obratno. Z uporabo pravila v praksi lahko zmanjšamo dozno obremenitev pacienta in vplivamo na čas ekspozicije, s čimer optimiziramo radiološki poseg.Introduction: Due to the diagnostic applicability of an X-ray image, it is also necessary to maintain the same exposure index. When changing the exposure conditions, we can use the "15% rule", which describes the ratio between the acceleration voltage - U (kV) and the product of the current and time - It (mAs), or by a method in which, in order to maintain the same intensity of the beam, the mAs product is changed by the fifth exponent of the ratio between the two acceleration voltages (kV). By using the "15% rule" we can influence the reduction of the patient\u27s dose length or the reduction of the scattered radiation and consequently a better contrast resolution of the image. Purpose: We wanted to find out how the change of the exposure conditions affected the patient\u27s dose length and to find the optimal beam intensity that motions on the image receptor (IR). Methods: We measured the product between the dose and the surface, as well as the exposure index under different exposure conditions. The exposure conditions were set electronically by adjusting both the acceleration voltage (kV) and the electric current at a certain exposure time (mAs). Results: In the study, we found out that for the selected voltages in the range from 45 kV to 81 kV, regardless of the thickness and absorption coefficient of the object, the "15% rule" is in principle true, the deviations are between 0 – 14%, only when increasing voltage from 55 to 63 kV, is the deviation of 21%. Discussion and conclusion: From the measurements performed in this study, we can conclude that the "15% rule" is not always accurate, but it is reliable enough in everyday practice, because the X-ray apparatus only offers certain values of the exposure conditions, so this is why we can`t always set the calculated or optimal values. It is rather more accurate when the basic acceleration voltage is reduced by 15%, than when the voltage is increased by 15%. With the reduction of the acceleration voltage, the dose is increased and vice versa. By using the "15% rule" in practice we can influence the reduction of the patient\u27s dose length and reduction of the exposure time, with which we optimize the radiological procedure