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Radiographic Absorptiometry (Photodensitometry)
Published in Stanton H. Cohn, Non-Invasive Measurements of Bone Mass and Their Clinical Application, 2020
Charles Colbert, Richard S. Bachtell
Originally, the microdensitometer plotted a simple graphic record of the densities in the scan path. The scanner was modified so that: (1) a computer controls film table motion, (2) the film table continuously reports its position relative to the fixed light beam, and (3) the optical density readings are digitized and read into the computer. The microdensitometer, a double beam comparator, splits an intense light source into pencil beams, one of which passes through a pixel on the radiograph while the other passes through a pixel on an optical density wedge of tinted glass which ranges from minimum density at one end to maximum density at the other end. The wedge is mounted on a wheeled carriage mechanically positioned on a track by a servo motor. Through the use of a rotating motorized disk “chopper”, the attenuated beams alternately illuminate the photocathode of a photomultiplier, producing an error signal. The servo motor drives the carriage across the light beam until the error signal is extinguished and the wedge grey level matches the radiograph grey level. Thus the track position of the carriage, corresponding to the pixel grey level of the radiograph, is converted to a digital signal by a shaft-angle encoder.
Tissue Preparation For Autoradiography the Autoradiographic Process
Published in Lelio G. Colombetti, Principles of Radiopharmacology, 2019
Alicia S. Ugarte, Lelio G. Colombetti, Dieudonne J. Mewissen
More recently, microdensitometers such as the Joyce-Loebl have been used to measure the transmitted light, but instruments of this type do not solve all the problems associated with the true measuring of the number and density of silver grains present in the specimen after development. Problems such as the color and stabilization of the light source could give rise to great variations in readings. Rogers suggested the use of three standards to calibrate the microdensitometer: a completely transparent emulsion layer, an emulsion fully blackened, and an intermediate density slide.41 Other instruments can also be used such as the Leitz Classimat® which has computer circuitry making it much easier to measure the intensity of the silver grains deposited in the specimen. Today, we can use a computer program to analyze the data obtained from the Classimat and to convert these figures into disintegrations per second.
3D Dosimetry in Synchrotron Radiation Therapy Techniques
Published in Ben Mijnheer, Clinical 3D Dosimetry in Modern Radiation Therapy, 2017
For beam sizes between 25 and 100 μm FWHM, the use of a 3CS Microdensitometer (Joyce-Loebl [JL] Automation) or a modified Zeiss Axio Vert.A1 microscope (www.zeiss.fr) with EC Plan-Neofluar objective lenses, are currently good options, both meeting the requirements in terms of spatial resolution (Figure 25.2). The old technology of a microdensitometer unfortunately is lacking sufficient stability of the instrument in time and requires several attempts to identify stable conditions for reliable data for dose measurements.
Solanaceae glycoalkaloids: α-solanine and α-chaconine modify the cardioinhibitory activity of verapamil
Published in Pharmaceutical Biology, 2022
Szymon Chowański, Magdalena Winkiel, Monika Szymczak-Cendlak, Paweł Marciniak, Dominika Mańczak, Karolina Walkowiak-Nowicka, Marta Spochacz, Sabino A. Bufo, Laura Scrano, Zbigniew Adamski
A semi-isolated heart placed in an incubation chamber of the microdensitometer was able to work uninterruptedly for a minimum of 5–6 h with saline perfusion. During the registration of its control action, for 22 min, the heart contraction frequency did not change by more than ± 3% (Figure 2(A)). When saline was replaced with verapamil solutions, a decrease in heart frequency was observed, and the changes depended on the concentration. The highest concentration of verapamil tested (5 × 10−5 M) caused an arrest of myocardial activity in almost all preparations after a mean time of 1.70 ± 0.77 min, and the calculated t50 was 1.04 ± 0.62 min, while the lowest concentration (9 × 10−6 M) caused a decrease of only an average of −15.9 ± 3.39% with a t50 equal to 1.32 ± 0.26 min. All observed changes were reversible, and heart rate returned to the baseline value with an RT50 time of 2.65 ± 0.93 min for verapamil at a concentration of 5 × 10−5 M. The determined IC50 value was equal to 1.685 × 10−5 M (Figure 2(B)). The a coefficient values also showed that the dynamics of the decrease in heart contraction frequency and recovery to the control range differed between concentrations. Interestingly, after finishing the perfusion of the heart with verapamil at the highest tested concentration, restoration of the basic frequency of heart contraction occurred with the highest dynamic (Table 1).
Elke Bräuer-Krisch: dedication, creativity and generosity: May 17, 1961–September 10, 2018
Published in International Journal of Radiation Biology, 2022
A large part of the thesis focuses on experimental dosimetry, particularly on how to measure the high dose rate in a homogenous field, and on how to convert those data to absolute dose measurements. Highly resolved dose measurements of the spatially fractionated beam, obtained by use of several types of detectors, were presented and analyzed. For instance, Gafchromic film dosimetry in combination with a microdensitometry showed slightly higher (∼10–15%) valley dose than Monte Carlo calculated values. Elke also presented and discussed the great potential of her concept based on interlaced microbeams. Such extensive, sophisticated microdosimetric and treatment planning strategies perfected the patient safety systems at the ID17 beamline of the ESRF. Elke presented theoretical and practical advances at many meetings. Expert audiences received them well and extensively discussed them (Doran et al. 2013; Bartzsch et al. 2014; Cornelius et al. 2014; Bräuer-Krisch et al. 2015).