A medição da grandeza practical peak voltage na prática radiológica

Terini, Ricardo Andrade; Potiens, M.P.A.; Herdade, S.B.; Pereira, Marco Aurélio Guedes; Pires, J.; Videira, Heber Simões

doi:10.1590/s0100-39842009000600013

Cited by 10 publications

(4 citation statements)

References 6 publications

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“…Both meters were calibrated against a standard 30 cm 3 cylindrical PTW ionization chamber model 23361, calibrated at Instituto de Radioproteção e Dosimetria/Comissão Nacional de Energia Nuclear (IRD/CNEN), or a PTW TN 34014 transmission monitoring chamber, each one of them connected to a PTW UNIDOS electrometer, also utilizing a lead collimator as the reference aperture for P KA determination. Measurements have been made with standard beams of the RQR series (10) , in addition to others with fixed Al or Al + Cu filtration, similar to clinically utilized qualities (11) , utilizing tube voltages determined as per the practical peak voltage (PPV) parameter (12)(13)(14)(15) . 1The PDC meter is designed as a calibrator of clinical P KA meters.…”

Section: Equipment Utilizedmentioning

confidence: 99%

“…where: Û is the PPV value, U i represents the instantaneous values of the voltage applied to the tube acquired in N samplings comprising the waveform, and ω i (U i ) represents the values of polynomials defined in the references 11 e 12, weighting each U i value. In a previous issue of this journal, Terini et al (15) analyzed the measurement of PPV in the radiological practice.…”

Section: Measurement Of the Ppv Quantitymentioning

confidence: 99%

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Doses monitoring in radiology: calibration of air kerma-area product (PKA) meters

et al. 2013

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Materials and Methods: Different qualities of both incident and transmitted beams were utilized in conditions similar to a clinical setting, analyzing the influence from the reference dosimeter, from the distance between meters, from the filtration and from the average beam energy. Calibrations were performed directly against a standard 30 cm 3 cylindrical chamber or a parallel-plate monitor chamber, and indirectly against the PDC meter. Results: The lowest energy dependence was observed for transmitted beams. The cross calibration between the Diamentor E2 and the PDC meters, and the PDC presented the greatest propagation of uncertainties. Conclusion: The calibration coefficient of the PDC meter showed to be more stable with voltage, while the Diamentor E2 calibration coefficient was more variable. On the other hand, the PDC meter presented greater uncertainty in readings (5.0%) than with the use of the monitor chamber (3.5%) as a reference.

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Section: Equipment Utilizedmentioning

confidence: 99%

Section: Measurement Of the Ppv Quantitymentioning

confidence: 99%

Doses monitoring in radiology: calibration of air kerma-area product (PKA) meters

et al. 2013

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“…The results obtained using invasive and noninvasive X ray testers of two manufactures were compared in [30]. The noninvasive monitoring results were inconsistent with the standard [3].…”

Section: Reviewsmentioning

confidence: 99%

Methods and devices for anode voltage measurement in x-ray apparatuses

Muslimov

Lelyukhin

2011

Biomed Eng

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Anode voltage setting accuracy determines thera peutic efficacy and exposure of personnel in radiotherapy. Radiation safety requires periodic control of anode volt age setting. In medicine this control should be imple mented on the basis of X ray dosimetry without interven tion into the electrical circuitry of the X ray apparatus.The X ray tube power sources do not allow the anode potential to be measured using radiation methods. The following parameters are used to characterize anode volt age [1, 2]: -absolute peak voltage (kVp abs ) during exposure; -mean peak voltage (kVp mean ) during exposure; -effective peak voltage (kVp eff ) calculated as given constant voltage multiplied by an a priori factor of image contrast [2]; -actual peak voltage (PPV) providing image con trast equal to the given voltage shape [3,4].In case of constant anode potential, the values listed above are equal to each other. In the case of anode voltage pulsation, there is a trend toward an increase in these variables with increasing pulsation. This is due to varia tion of X ray radiation spectra with variable anode poten tial.X Ray apparatuses providing noninvasive detection of X ray tube anode voltage should meet the requirements of the Russian Federation (RF) standard [4] adopted in 2008. This standard determines PPV as the operating parameter of anode voltage of any shape. This standard allows calculation of the X ray spectrum using the follow ing equation:where P(U) is probability of voltage U distribution within voltage range U min U max and normalization condition w(U) is weight function derived theoretically in [6]; U max and U min are maximal and minimal anode voltage. The weight function determines PPV as constant potential providing the same contrast of air kerma as in case of con stant test voltage [4].It was demonstrated in [6] that invasive PPV of the X ray tube anode and contrast equivalent anode voltage (CEV) as determined for a given phantom were identical and independent of anode slope angle and anode voltage shape. It was demonstrated in [7] that PPV and CEV could be measured both invasively and noninvasively using air kerma contrast.Measurement of anode voltage of X ray apparatuses is discussed. Operational parameters are considered and standard requirements for devices for noninvasive control of anode voltage are analyzed. A comparative specifi cation table of modern X ray apparatuses is presented. The dual energy radiation method of measurement is described. Disadvantages of an indirect method of finding the practical peak voltage are shown. Reviews

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“…Such channels have different spectral sensitivities. A method for PPV calculation from recovery of absolute peak voltage was reported in [2,3]. This method caused a measuring error that cannot be normalized, which is inconsistent with standard requirements.…”

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Determination of Actual Peak Voltage from Recovered Spectral Distribution of Bremsstrahlung

2011

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A new standard for X ray dosimeters is based on noninvasive monitoring of X ray tube voltage with detec tion of practical peak voltage (PPV) [1].The standard requires that PPV is measured using discrete probability distribution of voltage within a given range or PPV calculation using a given algorithm. The contrast PPV voltage is determined within a wide range of X ray tube anode voltages.In practice, X ray tube anode voltage is measured using two or more detection channels. Such channels have different spectral sensitivities. A method for PPV calculation from recovery of absolute peak voltage was reported in [2,3]. This method caused a measuring error that cannot be normalized, which is inconsistent with standard requirements. Therefore, the search for new methods of PPV determination is rather urgent.The method of PPV determination suggested in this work is based on the following principles:-bremsstrahlung signal decay is detected using a linear detector;-the signal is minimized for signal spectrum and X ray phantom contrast depending on X ray tube anode voltage;-bremsstrahlung contrast equivalent voltage (PPV) is calculated from a calibration curve.Absorption curves are detected using a linear GaAs detector located along the X ray beam to provide radia tion filtration [4].The X ray spectrum is recovered in this case using spatial localization of detectors as a line. This gives rise to a set of linear algebraic equations S⋅Ewhere S is nor malized quantum detection efficiency (sensitivity) n of the microdetectors within spectral line m (width ΔE); E _ = (E 1 , E 2 , ..., E m ) T is quantum energy vector in the linear microdetectors; I _ = (I 1 , I 2 , ..., I n ) T is signal vector in the n microdetectors. This set of linear algebraic equations is stochastic. It can be solved using a method of directed minimization [5]. This method is based on comparison between two states of the system: μ 1 and μ 2 . The states are determined by vectors P _ apost. = (P 1 , P 2 , ..., P n ) and P _ apr. = (S 11 , S 12 , ..., S nm )·q j , which determine a posteriori probabil ity of quantum absorption P i = N i /N eff of each photode tector and a priori probability S ij = P j ·Q ij of effective absorption of quantum beam q j in each microdetector. The following notation was used: N i is number of absorbed quanta in microdetector i; N eff. is number of absorbed quanta in all microdetectors; P j is probability of quantum absorption at energy E j in the individual detection chan nel; Q ij is probability of absorption of a quantum with energy E j in detector i; q j is probability of generation of a quantum with energy E j in the bremsstrahlung spectrum.Kulback compared macrostates μ 1 and μ 2 and demonstrated that, according to the mean information criterion, μ 1 had advantages over μ 2 [6]:(1) Substitution of probability gives:(2)A procedure for determination of actual peak voltage from recovered spectral distribution of bremsstrahlung is described. The bremsstrahlung spectrum is restored from absorption curves detected using a linea...

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A medição da grandeza practical peak voltage na prática radiológica

Cited by 10 publications

References 6 publications

Doses monitoring in radiology: calibration of air kerma-area product (PKA) meters

Doses monitoring in radiology: calibration of air kerma-area product (PKA) meters

Methods and devices for anode voltage measurement in x-ray apparatuses

Determination of Actual Peak Voltage from Recovered Spectral Distribution of Bremsstrahlung

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