A time-scale sensitometric method for evaluating screen-film systems.

An x-ray sensitometer is used to measure the characteristic curve of radiographic films exposed with fluorescent intensifying screens. The series of relative exposures, necessary to cover the full density range of the film, can be obtained by either time-scale or intensity-scale sensitometric methods. We have developed a convenient method of exposing film-screen systems for time-scale sensitometry. In this method, during exposure the x-ray kilovoltage, tube current and x-ray intensity remain constant and a geometric series of exposures of the film is modulated by varying the exposure time. This time variation can be obtained when a lead disc with different sector openings is rotated in front of the film system by a stepping motor. The conditions normally used are 70 kVp x-rays, 3.5 mm Al total filtration at the tube, and 2.4 m focal spot-film distance. This exposure latitude gives a complete characteristic curve of film-screen systems.

A pulsatile flow model for in vitro quantitative evaluation of prosthetic valve regurgitation.

A pulsatile pressure-flow model was developed for in vitro quantitative color Doppler flow mapping studies of valvular regurgitation. The flow through the system was generated by a piston which was driven by stepper motors controlled by a computer. The piston was connected to acrylic chambers designed to simulate "ventricular" and "atrial" heart chambers. Inside the "ventricular" chamber, a prosthetic heart valve was placed at the inflow connection with the "atrial" chamber while another prosthetic valve was positioned at the outflow connection with flexible tubes, elastic balloons and a reservoir arranged to mimic the peripheral circulation. The flow model was filled with a 0.25% corn starch/water suspension to improve Doppler imaging. A continuous flow pump transferred the liquid from the peripheral reservoir to another one connected to the "atrial" chamber. The dimensions of the flow model were designed to permit adequate imaging by Doppler echocardiography. Acoustic windows allowed placement of transducers distal and perpendicular to the valves, so that the ultrasound beam could be positioned parallel to the valvular flow. Strain-gauge and electromagnetic transducers were used for measurements of pressure and flow in different segments of the system. The flow model was also designed to fit different sizes and types of prosthetic valves. This pulsatile flow model was able to generate pressure and flow in the physiological human range, with independent adjustment of pulse duration and rate as well as of stroke volume. This model mimics flow profiles observed in patients with regurgitant prosthetic valves.

Quality control of blood irradiation with a teletherapy unit: damage to stored red blood cells after cobalt-60 gamma irradiation.

BACKGROUND: Previous publications have documented the damage caused to red blood cells (RBCs) irradiated with X-rays produced by a linear accelerator and with gamma rays derived from a 137Cs source. The biologic effects on RBCs of gamma rays from a 60Co source, however, have not been characterized. STUDY DESIGN AND METHODS: This study investigated the effect of 3000 and 4000 cGy on the in vitro properties of RBCs preserved with preservative solution and irradiated with a cobalt teletherapy unit. A thermal device equipped with a data acquisition system was used to maintain and monitor the blood temperature during irradiation. The device was rotated at 2 r.p.m. in the irradiation beam by means of an automated system. The spatial distribution of the absorbed dose over the irradiated volume was obtained with phantom and thermoluminescent dosimeters (TLDs). Levels of Hb, K+, and Cl(-) were assessed by spectrophotometric techniques over a period of 45 days. The change in the topology of the RBC membrane was investigated by flow cytometry. RESULTS: Irradiation caused significant changes in the extracellular levels of K+ and Hb and in the organizational structure of the phospholipid bilayer of the RBC membrane. Blood temperature ranged from 2 to 4 degrees C during irradiation. Rotation at 2 r.p.m. distributed the dose homogeneously (92%-104%) and did not damage the RBCs. CONCLUSIONS: The method used to store the blood bags during irradiation guaranteed that all damage caused to the cells was exclusively due to the action of radiation at the doses applied. It was demonstrated that prolonged storage of 60Co-irradiated RBCs results in loss of membrane phospholipids asymmetry, exposing phosphatidylserine (PS) on the cells' surface with a time and dose dependence, which can reduce the in vivo recovery of these cells. A time- and dose-dependence effect on the extracellular K+ and plasma-free Hb levels was also observed. The magnitude of all these effects, however, seems not to be clinically important and can support the storage of irradiated RBC units for at last 28 days.

Quality control of blood irradiation: determination T cells radiosensitivity to cobalt-60 gamma rays.

BACKGROUND: To identify the most appropriate dose for the prevention of transfusion-associated graft-versus-host disease, the radiosensitivity of T cells has been determined in blood bags irradiated with X-rays produced by a linear accelerator and gamma rays derived from the cesium-137 source of a specific irradiator. In this study, the influence of doses ranging from 500 to 2500 cGy was investigated on T cells isolated from red blood cell (RBC) units preserved with ADSOL and irradiated with a cobalt teletherapy unit. STUDY DESIGN AND METHODS: A thermal device consisting of acrylic and foam was constructed to store the blood bags during irradiation. Blood temperature was monitored with an automated data acquisition system. Dose distribution in the blood bags was analyzed based on isodose curves obtained with a polystyrene phantom constructed for this purpose. The influence of cobalt-60 gamma radiation on T cells was determined by limiting-dilution analysis, which measures clonable T cells. T-cell content of the mononuclear cell population plated was assessed by flow cytometry with a monoclonal antibody specific for CD3. RESULTS: Blood temperature ranged from 2 to 4.5 degrees C during irradiation. Dosimetry performed on the phantom showed a homogenous dose distribution when the phantom was irradiated with a parallel-opposite field. A radiation dose of 1500 cGy led to the inactivation of T cells by 4 log, but T-cell growth was observed in all experiments. At 2500 cGy, no T-cell growth was detected in any of the experiments and a greater than 5 log reduction in functional T cells was noted. CONCLUSION: The results showed that a dose of 2500 cGy completely inactivates T cells in RBC units irradiated with cobalt-60 source.

Quality control system for blood irradiation using a teletherapy unit.

BACKGROUND AND OBJECTIVES: Irradiation of whole blood and blood components before transfusion is currently the only accepted methodology to prevent transfusion-associated graft-vs.-host disease. In the present work, we developed an automated system for blood bag storage during irradiation, using a teletherapy unit. MATERIALS AND METHODS: A device with two thermal compartments was constructed in acrylic and foam, for the storage of blood bags during irradiation. An automatic acquisition system, coupled with an amplifier and a thermal-sensitive probe, were developed to check blood temperature during irradiation. A polystyrene phantom was constructed to simulate the volume of blood routinely irradiated. The dose distribution was measured in the phantom using thermoluminescent dosimeters and represented in terms of isodose curves. RESULTS: The thermal device kept the blood temperature below 6 degrees C for more than 2 h. Our system allowed the simultaneous irradiation of two different blood components while maintaining a constant temperature. The temperature monitoring system remained invariant (0.2 degrees C) over the whole irradiation interval. Phantom dosimetric results showed a homogeneous dose distribution when the phantom was irradiated, using rotational fields with a 2 r.p.m. frequency. CONCLUSIONS: The methodology developed in the present work provides appropriate storage conditions during irradiation of both red blood cells and platelet blood components using a teletherapy unit.

A pulsatile flow model for in vitro quantitative evaluation of prosthetic valve regurgitation

A pulsatile pressure-flow model was developed for in vitro quantitative color Doppler flow mapping studies of valvular regurgitation. The flow through the system was generated by a piston which was driven by stepper motors controlled by a computer. The piston was connected to acrylic chambers designed to simulate "ventricular" and "atrial" heart chambers. Inside the "ventricular" chamber, a prosthetic heart valve was placed at the inflow connection with the "atrial" chamber while another prosthetic valve was positioned at the outflow connection with flexible tubes, elastic balloons and a reservoir arranged to mimic the peripheral circulation. The flow model was filled with a 0.25 per cent corn starch/water suspension to improve Doppler imaging. A continuous flow pump transferred the liquid from the peripheral reservoir to another one connected to the "atrial" chamber. The dimensions of the flow model were designed to permit adequate imaging by Doppler echocardiography. Acoustic windows allowed placement of transducers distal and perpendicular to the valves, so that the ultrasound beam could be positioned parallel to the valvular flow. Strain-gauge and electromagnetic transducers were used for measurements of pressure and flow in different segments of the system. The flow model was also designed to fit different sizes and types of prosthetic valves. This pulsatile flow model was able to generate pressure and flow in the physiological human range, with independent adjustment of pulse duration and rate as well as of stroke volume. This model mimics flow profiles observed in patients with regurgitant prosthetic valves.

Consideraçöes sobre a produçäo de campos ultra-sônicos / Considerations about an ultrasonic field productions

O ultra-som é uma das principais ferramentas para diagnósticos na área médica. Através da interação dos campos ultra-sônicos pode-se obter várias características dos tecidos biológicos, portanto é importante conhecer sua distribuição de pressão no meio de propagação. Neste trabalho é estudado o campo ultra-sônico produzido por um transdutor piezoelétrico anular. Os resultados experimentais mostram que o campo ultra-sônico depende do material empregado na construção do transdutor.

The ultrasound is a important tool for diagnostics on medical area. Throught of ultrasonic fiel d interaction we can obtain some characteristics of the biologycal tissues, thus it is important to know the pressure distribuition in the propagation medium. ln this paper is studied the ultrasonic field generated by a ring piezoelectric transducer. The experimental results show the ultrasonic field depends of the material employed in the transducer construction.

Câmara de ionizaçäo com ar comprimido e parede de alumínio para dosimetria em leventamento radiométrico / Pressurized air ionization chamber and aluminium walls for dosimetry in radiometric survey

Uma câmara de ionização de 23 cm3 com ar comprimido e parede de alumínio foi construída e apresenta sensibilidade uma ordem de grandeza maior quando comparada a câmaras de mesmo volume à pressão ambiente. A utilização de ar a uma pressão 2500 KPa minimiza sua dependência energética que se mantém menor que 5 por cento para energias de fótons na faixa de 40 KeV a 1.250 KeV. Esta câmara apresenta melhor desempenho do que as câmaras convencionais em medidas de baixas taxas de exposição.

Anais do 3§ Congresso Brasileiro de Físicos em Medicina / Annals of the III Brazilian Congress of the Physics in Medicine

A idéia de se utilizar eletreto em detecçäo e dosimetria das radiaçöes ionizantes foi patenteada em 1954. Devido a baixa sensibilidade a radiaçäo dos eletretos existentes, näo houve uma utilizaçäo prática até os trabalhos de Fabel e Henisch, que usaram folhas de TEFLON e PVDF, encontrando sensibilidades muito mais altas que os dosimetros termoluminescentes. Os trabalhos desenvovlidos e publicados desde entäo trouxeram um progresso considerável na área de detecçäo e dosimetria com eletretos. Dentre os quais destacamos os trabalhos de Bauser, Gross, Gross, Ikeya, Kotrappa, Mascarenhas, Zimmerman, Cameron, Pretsch, Pelá e outros. Mais recentemente, uma câmara de ionizaçäo cilíndrica co m uma camada de boro depositada em sua parede interna, que permite detectar e fazer dosimetria de neutrons térmicos foi desenvolvido. Esta última referência apresenta uma completa revisäo até o presente da detecçäo e dosimetria utilizando eletretos. O objetivo deste trabalho é apresentar uma análise numérica com relaçäo a resposta da câmara de ionizaçäo de eletretos para detecçäo de neutrons térmicos