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At least 433 records · Page 24Linked to original sources
PubMed1994

Sub-kilohertz flash X-ray generator utilising a glass-enclosed cold-cathode triode.

The construction and fundamental studies are described for a sub-kilohertz X-ray generator for producing low-dose rate flash X-rays. The X-ray tube was a glass-enclosed cold-cathode triode, composed of a tungsten plate target, a rod-shaped graphite cathode, a mesh-type trigger electrode made of tungsten wires, and a glass tube body. The coaxial condenser was charged up to 60 kV by a power supply, and the electric charges in the condenser were discharged to the X-ray tube repetitively when a negative high-voltage pulse was applied to the trigger electrode. The maximum tube voltage before the discharging was equivalent to the initial charged voltage of the condenser, and the maximum tube current was about 0.3 kA with a charged voltage of 60 kV. The X-ray durations were about 1 microsecond, and the X-ray intensity was about 0.47 microC kg-1 at 0.5 m per pulse with a charged voltage of 60 kV. The maximum repetition rate of the X-rays was about 0.4 kHz, and high-speed radiography was performed.

Animals↗
PubMed1995

The early history of x-ray diagnosis with emphasis on the contributions of physics 1895-1915.

The contribution of physics to the development of x-ray diagnosis was vital in the early years of this century following Röntgen's discovery of x-rays in November 1895. This review records some of the highlights during the period 1895-1915. Much of the information presented has been buried in libraries for more than 50 years and the selection of illustrations and text will be largely unknown to today's readership of Physics in Medicine and Biology. It is also a celebration of what could be achieved in physics before the occurrence of the technological revolution involving not only computer applications but also the disappearance of the small independent x-ray companies into today's multinational companies. Research and development is nowadays just too expensive for much independent practical high-technology contributions without financial backing. Hence this review takes us to those bygone years of experimental physics in home laboratories, poorly equipped university physics laboratories and of the lecture-demonstrations of the period. The sections are presented in a logical order beginning with the discovery of x-rays, followed by x-ray tube technology to the advent of the hot cathode Coolidge tube, with the third and final section covering diagnostic radiology physics. It has been compiled from personal research over 35 years in libraries worldwide, drawing on textbooks, journals, popular magazines, newspapers, x-ray company catalogues and museum exhibits. I have included a certain amount of anecdotal information, because after all, much of the early commentaries were indeed anecdotal--and make very interesting reading. Finally it is commented that although this review is devoted to x-ray diagnosis, x-ray therapy should not be forgotten, and readers are referred to another review by the author on early therapeutic advances.

Biophysics↗
PubMed2001

Comparison of image quality indicators among mammography facilities in Ontario.

OBJECTIVE: To compare the technical aspects of image quality of mammography machines in facilities across Ontario. METHODS: Eight mammographic physics consultants took measurements and calculated accreditation phantom scores, mean glandular dose, entrance exposure, average optical density, half value layer and the limiting resolution of the imaging chain for 100 mammography machines across Ontario. RESULTS: Of the 100 machines, 39 were affiliated with the Ontario Breast Screening Program (OBSP), and the remaining 61 were applying to become OBSP affiliates. All of the OBSP facilities and 32 of the applicants were accredited with the Mammography Accreditation Program (MAP) of the Canadian Association of Radiologists (CAR). All OBSP facilities had passing phantom scores, and 84% of the applicants with CAR accreditation and 79% of those without had passing phantom scores. The mean glandular dose was 1.5 (range 1.0-1.9, standard deviation [SD] 0.22) mGy for OBSP facilities, 1.3 (0.8-1.8, SD 0.29) mGy for CAR accredited and 1.4 (0.9-1.9, SD 0.24) mGy for nonaccredited applicants. Mean entrance exposures were 798 (540-1280, SD 135) mR, 717 (430-980, SD 153) mR and 770 (520-930, SD 116) mR for the OBSP, accredited and nonaccredited facilities respectively. There were no appreciable differences in the mean optical densities (approx. 1.62 OD), mean half-value layers (approx. 0.34 mm Al) or mean resolutions measured with the large focal spot (nominal size of 0.3 mm) either parallel (approx. 16 line pairs/mm) or perpendicular (approx. 14 line pairs/mm) to the cathode-anode axis of the x-ray tube, among the 3 types of facilities. CONCLUSION: Image quality is increased and variability is decreased in facilities participating in a province-wide screening program.

Accreditation↗
PubMedDate not supplied

Using the anode heel effect for extremity radiography.

The profession's literature contains numerous references to the variations in x-ray intensity along the cathode-anode axis of the x-ray tube. The significance of this gradient in intensity when x-raying extremities is neither recognized nor routinely used by radiographers. This study documents the significance of the anode heel effect for balancing densities of distal and proximal joints during long bone extremity radiography.

Arm↗
PubMedDate not supplied

Grid controlled x-ray tube switching time: implications for rapid exposure control.

The transient response properties of a conventional grid controlled x-ray source and the implications for rapid exposure control are studied. The use of a cathode cable with a length of only 1 m to connect the x-ray tube and the grid control electronics results in a switching time of 19 microseconds. The phototiming artifacts from the delayed radiation delivered during this transition time can be severe for short pulses. An analog correction technique that anticipates the magnitude of the delayed radiation is used to overcome this limitation and allows accurate phototiming over a wide range of pulse widths ranging down to 20 microseconds.

Humans↗
PubMed1986

The Columbian exchange: American physiologists and neuroscience techniques.

Neurophysiological techniques, far from being mere manual or instrumental procedures, are intimately bound up with the concepts and social processes of experimental physiology. This proposition is argued by examining the prepublication history of four important technical innovations in 20th-century neurophysiology, and their associated innovators: the vacuum-tube amplifier (Lucas, Williams, and Forbes, 1912-1922); the cathode-ray oscillograph (Gasser, Newcomer, and Erlanger, 1919-1923); single-fiber recording (Adrian, Zotterman, Forbes, Davis, and Gasser, 1912-1926); and the intracellular microelectrode (Graham, Gerard, Ling, Hodgkin, and Nastuk, 1940-1950). From these episodes I conclude that: each technique has its own set of conceptual presuppositions, limitations, and biases--in a word, techniques are idea-laden; techniques have an inertia of use that is overcome often only in unusual circumstances of crisis or opportunity; techniques, in their origin, evaluation, demonstration, and diffusion, are embedded in a network of social contacts among researchers; and 4) techniques evolve with favorite biological materials that, by fitting the apparatus and the questions asked, also impose limits on the concepts educed from that preparation.

Amplifiers, Electronic↗
PubMed1985

Dosimetry comparison and characterisation of an Al K ultrasoft x-ray beam from an MRC cold-cathode source.

Ultrasoft x-rays of 0.3-5 keV have provided a unique tool for the investigation of intracellular mechanisms of radiation action in biological organisms, including mammalian cells. However, their use presents unique practical problems in dosimetry and experimental design. Detailed interpretation of the biological results requires reliable dosimetry and well characterised monoenergetic beams. This paper presents a comparison between two fundamentally different dosimetric techniques, namely the ionisation current in an extrapolation chamber and photon counts in a proportional counter. Agreement within 7% was obtained when these two methods were applied to an Al K x-ray beam (1.5 keV) from an MRC cold-cathode transmission target discharge tube as previously used in many biological experiments. Photographic film was calibrated as a relative dosimetric technique and used for investigation of the intensity uniformity of the radiation field. These techniques provide a comprehensive characterisation of the beam in the position of the biological cells, including photon flux (or absorbed dose rate), spectral purity (showing much less than 1% bremsstrahlung relative to characteristic Al x-rays) and uniformity over the irradiation area (within about 5% for mammalian cell irradiations).

Cell Survival↗
PubMed1987

An arrangement for irradiating cultured mammalian cells with aluminium characteristic ultrasoft x-rays.

Ultrasoft x-rays are useful for testing the validity of mechanistic models of biological damage caused by radiation. Described here is the construction and operation of a cold-cathode transmission-target discharge tube for irradiating mammalian cells in vitro with aluminium characteristic x-rays (1.487 keV). Particular attention is given to the problems of sample preparation and dosimetry for this shallowly penetrating radiation. The proportion of contaminating bremsstrahlung radiation is measured to establish the optimum operating conditions. Preliminary data from experiments using V79 Chinese hamster cells show that aluminium characteristic x-rays are about twice as effective at inactivating the cells as 250 kVp x-rays.

Aluminum↗
PubMed2003

The use of CVD diamond to produce carbon K ultrasoft x-rays.

Carbon K ultrasoft x-rays (278 eV) interact with biological material producing random, isolated tracks of single electrons with a range < 7 nm (cf width of DNA helix approximately2 nm). The electron tracks produced by these ultrasoft x-rays are similar to the numerous secondary electrons and 'track ends' produced by essentially all ionizing radiations. They therefore provide a unique tool in the study of mechanisms of radiation action in the cell. Conventional carbon targets used with the Medical Research Councils cold-cathode discharge tubes have a limited lifetime of 40-50 min. We have investigated the use of thin, freestanding diamond films produced using chemical vapour deposition techniques as a new transmission target for a cold-cathode tube. We present here a novel use of diamond to produce CK ultrasoft x-rays for irradiation purposes. The system described produces an entrance absorbed dose rate to attached cells of approximately 0.2 Gy min(-1) which due to the long target lifetime is usable for low dose-rate CK x-ray studies.

Diamond↗
PubMed1995

AAEM minimonograph #45: the early development of electromyography.

The use of electricity for therapeutic purposes began in the first century and became more refined as the properties of electricity became more understood. The works of Franklin, Galvani, Volta, and others contributed to this body of knowledge. Development of the string galvanometer, the advent of the vacuum tube, the introduction of concentric needle electrodes, and the development of the cathode-ray oscilloscope occurred during the first half of the 20th century. The science of electromyography and electrodiagnosis grew in its sophistication, leading to the formation of the American Association of Electromyography and Electrodiagnosis (now the American Association of Electrodiagnostic Medicine) with James Golseth, MD, as its first president in 1953.

Electromyography↗
PubMed1976

Wide-field X-ray tube comparisons.

X-ray tubes having similar resolution capabilities along the central ray were compared for their wide-field characteristics. It has been suggested that focal spot size, and therefore resolution capability, along the cathode-anode axis may vary in a manner which is dependent upon the tube target angle. The authors show that differences beyond the effects of target angle occur, the extent of those differences varying from tube to tube. Although 2 different-sized focal spots may be adjusted to have equivalent central beam resolution capabilities, they can exhibit different imaging capabilities at wide-angle (off central axis) position. More than one parameter (equivalent focal spot size) is needed to characterize the behavior of a focal spot.

Mathematics↗
PubMed1979

A calibration system for X-ray generators and tube factors.

An apparatus (Machlett's Dynalyzer II system) is described that makes real-time dynamic tests on the output and performance of the X-ray tube and generator so that a single exposure gives information on mA and mAs; exposure time (ms); kVp anode to earth; kVp cathode to earth; kVp cathode to anode; tube filament current; line voltage and radiation output of the tube (mR). The method of use is described together with the results of comparisons made with other test equipment. Some novel design features are of particular interest. The results show that by using this apparatus present design characteristics of X-ray generator-control-tube systems are such that the accuracy of calibration can be improved by at least an order of magnitude.

Calibration↗
PubMed2005

Robust x-ray tubes for use within magnetic fields of MR scanners.

A hybrid system that combines an x-ray fluoroscopic system and a magnetic resonance (MR) system can provide physicians with the synergy of exquisite soft tissue contrast (from MR) and high temporal and spatial resolutions (from x ray), which may significantly benefit a number of image-guided interventional procedures. However, the system configuration may require the x-ray tube to be placed in a magnetic field, which can hinder the proper functioning of the x-ray tube by deflecting its electron beam. From knowledge of how the magnetic field affects the electron trajectories, we propose creating another magnetic field along the cathode-anode axis using either solenoids or permanent magnets to reduce the deflection of the electron beam for two cases: a strong and slightly misaligned field or a weak field that is arbitrary in direction. Theoretical analysis is presented and the electron beam is simulated in various external magnetic fields with a finite element modeling program. Results show that both correction schemes enhance the robustness of the x-ray tube operation in an externally applied magnetic field.

Computer-Aided Design↗
PubMed1995

[100 years roentgen rays--a discovery conquers the medical world].

In the second half of the nineteenth century the prerequisites for research on the discharge of electricity in gases and the related phenomena were fulfilled. The first gas discharge tubes are associated with names like GeiBler, Hittorf, Crookes, Goldstein, Lenard and Hertz. These researchers studied the electrons escaping from the cathode, magnetic and electrical influence, chemical results, loss of energy and heating up of the anode. Lenard and Jackson were the first to describe phenomena outside the tube, but related the effects to electrons. It was W.C. Roentgen who discovered the ¿unknown rays¿; he systematically measured their penetrating properties and described them a short time thereafter. The scientific world was ready for this discovery, and the new of Roentgen's findings spread across the world in a matter of days, followed by intensive development of this innovation. The first and most important 35 years of development of the different types of X-rays tubes are described.

Germany↗
PubMed1992

Radiographic detail and variation of the nominal focal spot size: the "focal effect".

It is not generally appreciated that there is a gradation of the focal spot size from the anode to cathode end of an x-ray field that can dramatically affect radiographic detail from one end of a radiograph to the other. The authors name this gradation the "focal effect." Gradations in radiation intensity and focal spot size were measured from anode end to cathode end of a 14 x 17-inch field and were visually demonstrated with lymphangiograms and line-pair patterns. The degradation in spatial resolution along the anode-cathode axis was found to be as much as 75%, depending on the orientation of the patient with respect to the x-ray tube. Radiographic detail is, therefore, significantly improved (even when the large focal spot is used) by exploiting the focal effect and placing the body part requiring the best radiographic detail at the anode end of the table.

Contrast Media↗
PubMed2006

Effect of rare-earth component of the RE/Ni catalyst on the formation and nanostructure of single-walled carbon nanotubes.

A systematic experimental study has been carried out on the efficiency of bimetallic catalysts based on Ni and the rare-earth elements Y, La, Ce, Nd, Gd, Tb, Dy, Ho, Er, and Lu (group A) and Eu, Sm, Yb, and Tm (group B) in the synthesis of single-walled carbon nanotubes (SWNTs). The two groups give quite different results when analyzed by a combination of SEM/TEM and Raman and UV-NIR spectroscopies. The elements in group A have an obvious catalytic effect and increase the yield of SWNTs dramatically, whereas those in group B are not efficient catalysts. The diameter distribution of the synthesized SWNTs was also affected by the rare-earth element used. For group A metals, there is a tendency that the fraction of small-diameter tubes decreases with decreasing ionic radius of the rare-earth element used. EDX and X-ray analyses indicate that group A metals deposit on the cathode deposits and form rare-earth carbides, whereas no group B metals are found in cathode deposits, except for a small amount of Tm present in the form of thulium carbide. Further analysis indicates that there is a very strong correlation between the ability to form rare-earth carbides and the catalytic efficiency for the formation of SWNTs.

Journal Article↗
PubMed2006

Compatibility of interventional x-ray and magnetic resonance imaging: feasibility of a closed bore XMR (CBXMR) system.

A next-generation interventional guidance system is proposed that will enable intraprocedural access to both x-ray and magnetic resonance imaging (MRI) modalities. This closed bore XMR (CBXMR) system is comprised of a conventional radiographic rotating anode x-ray tube and a direct conversion flat panel detector on a rotating gantry positioned adjacent to the bore of a 1.5 T MRI. To assess the feasibility of such a system, we have investigated the degree of compatibility between the x-ray components and the MRI. For /-->B(ext)/ < 200 G the effect on the radiographic tube motor was negligible regardless of the orientation of -->B(ext) with respect to the motor axis of rotation--the frequency of anode rotation remained within 6% of the 3400 rpm frequency measured at 0 G. For /-->B(ext)/ >2400 G the anode slowed down to below 2400 rpm at all orientations. At intermediate B(ext), the frequency of rotation varied between 2400 and 3200 rpm, showing a strong dependence on orientation, with -->B(ext) perpendicular to the tube axis having a much stronger effect on the rotation frequency than -->B(ext) parallel to the tube axis. In contrast to the effect of -->B(ext) on the induction motor, parallel -->B(ext) had a stronger detrimental effect on the cathode-anode electron beam, whose path was at 16 degrees to the tube axis, than the perpendicular -->B(ext). Parallel -->B(ext) of several hundred Gauss had a defocusing effect on the x-ray focal spot. -->B(ext) perpendicular to the electron beam shifted the beam without significant defocusing. We have determined that the direct conversion flat panel detector (FPD) technology is not intrinsically sensitive to -->B(ext), and that the modifications required to make the proposed FPDs MRI compatible are minimal. The homogeneity of the MRI signal in the normal field of view was not significantly degraded by the presence of these x-ray components in the vicinity of the MRI bore entrance.

Equipment Design↗