Optimization of the exposure parameters in digital mammography for diverse glandularities using the contrast-detail metric.

PURPOSE: This investigation aims to study the optimization in digital mammography, considering a diverse percentage of breast glandularity using the contrast-detail metric. METHODS: The Figure of Merit (FOM), defined as the ratio of the square of the Inverted Image Quality Figure (IQFINV) by the Mean Glandular Dose (MGD), was used. A Monte Carlo simulation study was carried out to calculate the Normalized Glandular Dose (DgN). A contrast detail analysis employing the test object Contrast-Detail Mammography Phantom (CDMAM, type 3.4) was performed in the Hologic digital mammography system-model Selenia located in the Research Center in Radiation Sciences and Technologies (CPqCTR) facilities (Brazil). It employed the CIRS phantom with 20 %, 30 %, 50 % of glandularity, and 6.0 cm in thickness. RESULTS: It was obtained new acquisition parameters for all glandularities that achieved a decrease in the MGD up to âˆ¼ 50 %, maintaining the same image quality. The study was validated using the CIRS, TORMAM, and ACR phantoms through the contrast-to-noise ratio (CNR), the signal-to-noise ratio (SNR), and the MGD values obtained with the optimized parameters and the four AEC modes, which are the optimization proposed by the manufacturer. CONCLUSIONS: In this work, a new procedure was proposed that estimated the IQFINV value using the equivalence criterion between the CIRS phantom and the CDMAM test object with their respective PMMA plates. Based on the optimization carried out in this investigation, the AEC parameters, considering diverse glandularities, could be improved. This achievement permits the implementation of new protocols that optimize the ratio between the image's quality and the breast dose with 6.0 cm in thickness and 20 %, 30 %, and 50 % glandularity using contrast-detail metric.

Optimization of the exposure parameters in digital mammography using contrast-detail metrics.

PURPOSE: Optimization studies in digital mammography aid to assure the image quality and radiological protection of the patient. The aim of this work is to test effectiveness and applicability of a method based on a Figure of Merit (FOM=(IQFinv)2/AGD) to improve all the exposure parameters (Target/Filter combination, kVp and mAs) in order to improve the image acquisition technique that will provide the best compromise between image quality and the average glandular dose (AGD). METHODS: A contrast-detail analysis, employing the test object CDMAM, was carried out for the digital mammography unit manufactured by Lorad Hologic - model Selenia. We simulated two breast thicknesses using phantoms and a Figure of Merit as optimization tool, which includes an indicator of image quality, the IQFinv and the average glandular dose. Images of the ACR and TORMAM phantoms were obtained with both, automatic and optimized exposure parameters. In order to compare the image quality, the SNR (Signal to Noise Ratio) was measured in each image. RESULTS: In the two phantoms, for both 4.5 and 7.5cm thicknesses, the AGDs obtained with the optimized parameters show a reduction. In addition, the images obtained with the optimized exposure parameters, had the same or a better image quality when compared to the images obtained using the automatic mode. CONCLUSIONS: The proposed optimization methodology proved to be an effective tool to improve the digital mammography unit, due to the use of objective metrics for evaluation and validation of the results.

Direct measurement of clinical mammographic x-ray spectra using a CdTe spectrometer.

PURPOSE: To introduce and evaluate a method developed for the direct measurement of mammographic x-ray spectra using a CdTe spectrometer. The assembly of a positioning system and the design of a simple and customized alignment device for this application is described. METHODS: A positioning system was developed to easily and accurately locate the CdTe detector in the x-ray beam. Additionally, an alignment device to line up the detector with the central axis of the radiation beam was designed. Direct x-ray spectra measurements were performed in two different clinical mammography units and the measured x-ray spectra were compared with computer-generated spectra. In addition, the spectrometer misalignment effect was evaluated by comparing the measured spectra when this device is aligned relatively to when it is misaligned. RESULTS: The positioning and alignment of the spectrometer have allowed the measurements of direct mammographic x-ray spectra in agreement with computer-generated spectra. The most accurate x-ray spectral shape, related with the minimal HVL value, and high photon fluence for measured spectra was found with the spectrometer aligned according to the proposed method. The HVL values derived from both simulated and measured x-ray spectra differ at most 1.3 and 4.5% for two mammography devices evaluated in this study. CONCLUSION: The experimental method developed in this work allows simple positioning and alignment of a spectrometer for x-ray spectra measurements given the geometrical constraints and maintenance of the original configurations of mammography machines.

Optimization of Image Quality and Dose in Digital Mammography.

Nowadays, the optimization in digital mammography is one of the most important challenges in diagnostic radiology. The new digital technology has introduced additional elements to be considered in this scenario. A major goal of mammography is related to the detection of structures on the order of micrometers (µm) and the need to distinguish the different types of tissues, with very close density values. The diagnosis in mammography faces the difficulty that the breast tissues and pathological findings have very close linear attenuation coefficients within the energy range used in mammography. The aim of this study was to develop a methodology for optimizing exposure parameters of digital mammography based on a new Figure of Merit: FOM ≡ (IQFinv)2/AGD, considering the image quality and dose. The study was conducted using the digital mammography Senographe DS/GE, and CDMAM and TORMAM phantoms. The characterization of clinical practice, carried out in the mammography system under study, was performed considering different breast thicknesses, the technical parameters of exposure, and processing options of images used by the equipment's automatic exposure system. The results showed a difference between the values of the optimized parameters and those ones chosen by the automatic system of the mammography unit, specifically for small breast. The optimized exposure parameters showed better results than those obtained by the automatic system of the mammography, for the image quality parameters and its impact on detection of breast structures when analyzed by radiologists.

Dosimetria em exames endoscópicos / Dosimetry in endoscopic examinations

Em alguns endoscópicos específicos são realizadas radioescopias e radiografias com a equipe de médicos e enfermeiros próxima ao paciente. Através da simulação de exames e dosímetros termoluminescentes colocados em um fantoma antropomórfico foram determinadas as doses equivalentes em diferentes locais do corpo da pessoa que permanece na sala. Usando as normas nacionais e internacionais sobre os limites de dose recomendados foram calculados os números máximos de exames mensais e anuais recomendados às pessoas da equipe. Conclui-se que, com o uso de avental plumbífero, as altas doses equivalentes no cristalino (em média 1,67 mSv/exame) limitam o número de exames de que cada um pode participar.