Tânia A. C. Furquim

Estimation of average depth of penetration of melanotropins in dimyristoylphosphatidylglycerol vesicles

The interaction of alpha-melanocyte stimulating hormone (alpha-MSH) and its analogs [Nle4,D-Phe7]-alpha-MSH (MSH-I) and [Nle4,Asp5,D-Phe7,Lys10]-alpha-MSH(4-10) (MSH-II) with vesicles of dimyristoylphosphatidylglycerol (DMPG) was studied by steady-state fluorescence spectroscopy. The association constants for the interaction were obtained from binding isotherms. Electrostatic effects on the interaction were taken into account through calculation of Gouy-Chapman potentials. The quenching of fluorescence of the peptides by acrylamide and nitroxide labeled lipids demonstrated that insertion of the peptides into the lipid phase of the vesicles causes the changes in the hormones fluorescence in the presence of DMPG. The parallax method was employed for the estimation of an average depth of penetration of the peptides in the DMPG vesicles. It was found that the Trp residue in alpha-MSH and in MSH-II is positioned around the carbons 6 and 8 of the aliphatic chain. The analog MSH-I goes deeper into the bilayer compared to the others peptides, and the Trp residue locates between carbons 10 and 11 of the acyl chain. The average depth of penetration shows correlation with the number of lipid molecules that interact with one molecule of peptide. There is no direct correlation between the association constants for the lipid-peptide interactions and the depth of penetration of the hormone.

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.

Riscos da Radiação X e a Importância da Proteção Radiológica na Cardiologia Intervencionista: Uma Revisão Sistemática

AbSTRACT Radiation Risks and the Importance of Radiological Protection in Interventional Cardiology: A Systematic Review We discuss some aspects related to the legal framework, international recommendations and training programs on radiological protection; image quality and equipment; the biological effects and risks of ionizing radiation; lesions in patients and operators; patient’s reference levels; occupational dose limit and preventive actions. The use of ionizing radiation involves risks that are justified in diagnostic and therapeutic procedures. The awareness and knowledge of these risks minimizes the damage, optimizing the quality of images and safe use of ionizing radiation. There is evidence of radiation-induced cataracts in individuals who work in catheterization laboratories. Several studies suggest there may be a significant risk of lens opacity, if radiological protection devices are not properly used. Additionally, these interventional procedures are performed in Latin America, usually by medical specialists in collaboration with nurses, technologists and technicians, who often do not have adequate training in radiological protection.

Radiation Risks and the Importance of Radiological Protection in Interventional Cardiology: A Systematic Review

ABSTRACT We discuss some aspects related to the legal framework, international recommendations and training programs on radiological protection; image quality and equipment; the biological effects and risks of ionizing radiation; lesions in patients and operators; patient’s reference levels; occupational dose limit and preventive actions. The use of ionizing radiation involves risks that are justified in diagnostic and therapeutic procedures. The awareness and knowledge of these risks minimizes the damage, optimizing the quality of images and safe use of ionizing radiation. There is evidence of radiation induced cataracts in individuals who work in catheterization laboratories. Several studies suggest there may be a significant risk of lens opacity, if radiological protection devices are not properly used. Additionally, these interventional procedures are performed in Latin America, usually by medical specialists in collaboration with nurses, technologists and technicians, who often do not have adequate training in radiological protection.

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.

Estimation of dose distributions in mammography into a tissue equivalent phan-tom

Mammography is considered the most suitable technique for the identification, tracking and staging of breast diseases, especially cancer. However, the use of ionizing radia-tion carries a risk of inducing cancer in this kind of breast imaging procedure. In this way, it is important to know the dose distribution in typical mammography techniques. The aim of this work was to estimate the dose distributions in dif-ferent positions parallel to the image plan and different depths of a tissue equivalent phantom using LiF thermoluminescent dosimeters (TLD). LiF TLDs pellets were positioned on the xy plan on a phantom BR12 at different depths. The set was irra-diated in a GE Senographe DS System for a maximum field size. The dosimeters were irradiated using a Mo/Mo an-ode/filter combination, 100 mAs, and different X-ray tube voltages (25, 28, 30 and 32 kVp). It was also used a fixed X-ray tube voltage (28 kVp), 100 mAs, and different anode/filter combinations (Mo/Mo, Mo/Rh and Rh/Rh). Dose variation in the y direction was more significant than in the x direction. It were observed variations up to 8% and 28.2% in x and y direc-tions respectively. For the tube voltage 28 kVp, the maximum dose in the phantom surface in the y-axis was 16(1) mGy for Mo/Mo, and 15.0 (9) mGy for Mo/Rh and 12.8(6) for Rh/Rh.

Espectrometria Compton aplicada à medição de doses em mamografia para combinações W/Mo e Mo/Mo

A dose glandular media (DGM) nao pode ser medida diretamente em equipamentos mamograficos. Metodos baseados na espectrometria Compton sao alternativas para avaliar distribuicoes de dose em um simulador de mamas, tornando possivel a estimativa da DGM. Neste trabalho, um detector de CdTe foi usado para as medicoes espectrometricas de feixes de raios X espalhados a aproximadamente 90o , por efeito Compton, por um cilindro de PMMA, inserido entre as placas de um simulador de mama. A reconstrucao do espectro dos feixes primarios, a partir dos medidos, foi feita utilizando a teoria de Klein-Nishina e o formalismo de Compton, seguida pela determinacao do kerma no ar incidente na superficie do simulador, da dose absorvida e, finalmente, da DGM. Os espectros dos feixes de raios X incidentes e as distribuicoes de dose em profundidade em um simulador de BR-12 foram determinados para a faixa de mamografia (28 a 35kV). Os resultados mostraram bom acordo com dados da literatura, obtidos com TLD.