Radiography

“ Both CT and MRI produce 3D volumetric image data that are composed of individual volume elements (voxels) over which the local signal is averaged, an important distinction from imaging methods (e.g., X-ray and light photography) that simply produce 2D picture elements (pixels) . While voxel data are frequently viewed as 2D slices of pixels, it is important to understand that the information in a voxel is an averaged physical quantity that depends upon the particular acquisition method and the subsequent influence of the tissue on the signal. ”

“ With the very weak radiation that I have used for my experiments, corresponding to the ordinary radiographic and radioscopic work, it has been easy for me to obtain images of metallic objects and human bones placed on a sensitive plate 15 feet from the radiating source, although the rays pass directly through a slab of marble an inch thick, a sheet of lead one-tenth of an inch thick, and a flooring eight inches deep, built of oak boards and rough plaster. ”

“ The hand, for example, may be used as a negative for producing a photograph of the bones, as the rays do not pass equally well through flesh and bone.
Fig. 221.
[145]
Fig. 220 shows a Crookes tube fitted with a metal plate, so that the cathode rays coming from C will strike it. The X-rays are given out from P. These rays are invisible and are even given out where the cathode rays strike the glass. Some chemical compounds are made luminous by these rays; so screens are made and coated with them in order that the shadows produced by the X-rays can be seen by the eye. ”

“ Photography of microscopic objects as usually described, consists in passing a beam of light through the transparent object into the compound body of the microscope, and receiving it on its exit from the eyepiece upon a ground glass or sensitive plate. ”

“ The X rays may here be a great help. An attempt has been made by Rowland and Waggett. to skiagraph such foreign bodies, with encouraging results. Improvements in our methods will, I think, undoubtedly lead to a favorable use of the method in these instances. Beans, peas, wooden toys, and similar foreign bodies, being easily permeable to the rays, will not probably be discovered.
If our methods improve so that we can skiagraph through the entire body, it will be very possible to determine the presence and location of foreign bodies in the stomach and intestines. ”

“ But science is not rich, it does not dispose of important means, it does not generally meet recognition before the material usefulness of it has been proved. The factories produce many grams of radium every year, but the laboratories have very small quantities. It is the same for my laboratory and I am very grateful to the American women who wish me to have more of radium and give me the opportunity of doing more work with it.
The scientific history of radium is beautiful. The properties of the rays have been studied very closely. ”

“ So, a radiograph of even a part of a picture shows the layers of pigment that are hidden from the eye and the changes made during the composition of the work. One can easily distinguish the genuine from the spurious copies, for it is absolutely impossible for an imitator to make a copy that will stand the X-ray test. ”

“ I devised a very satisfactory method for determining the quantity of radium by the means of a radioactive gas produced by it and called "emanation." This method, frequently used in my laboratory, permits of the measurement of very small quantities of radium (less than a thousandth of a milligramme) , with a fair precision. More important quantities are often measured by their penetrating radiation, named Gamma-rays. For this we also possess in my laboratory a suitable equipment. It is easier and more satisfactory to measure the radium by the emitted rays, than to weigh it in a balance. ”

“ Radiographs.—The radiographic action of the new radio-active bodies is very marked. However, the method of operating should be very different with polonium and radium. Polonium acts only at very short distances, and its action is considerably weakened by solid screens; it is practically annihilated by means of a screen of slight thickness (1 m.m. of glass) . Radium acts at considerably greater distances. The radiographic action of radium rays may be observed at more than 2 m. distance in air, even when the active product is enclosed in a glass vessel. ”

“ A more practical method is to ensure that in all cases radiograms of any part of the body be absolutely comparable with one another by taking care to maintain the same relationship between the X-ray tube and the part under examination. ”

“ If one focuses an auxiliary microscope, carried in the inner tube, on the image situated in the back focal plane of the objective of a distant object, and then on the dust particles lying on a slide pressed against the end of the outer tube, the displacement of the auxiliary microscope gives the distance of the back focal plane of the objective from the end of the outer tube. To determine the position of the anterior focal plane of the eyepiece, the eyepiece is placed on the stage with the eye-lens downwards. ”

“ This is the method of the surveyor in measuring the mountain, if the principal vein descends inclined into the depths of the earth or the transverse vein is vertical. But if they are both inclined, the surveyor uses the same method, or he measures the slope of the mountain separately from the slope of the shaft. Next, if a transverse vein in which a tunnel is driven does not cut the principal vein in that spot where the shaft is sunk, then it is necessary for the starting point of the survey to be in the other shaft in which the transverse vein cuts the principal vein. ”

“ Microscopic agency, in thus assisting the medical man, contributes much to the alleviation of those multiplied “ills which flesh is heir to.” So fully impressed were the Council of the Royal College of Surgeons with the importance of the facts brought to light in a short space of time, that, in 1841, they determined to establish a Professorship of Histology, and to form a collection of preparations of the elementary tissues of both animals and vegetables, healthy and morbid, which should illustrate the value of microscopical investigations in physiology and medical science. ”

“ Like a child which hides behind a wooden door to shield itself from the bullets of a machine gun, our young radiologists believe they are safe when they have donned their gloves and examine their patients behind a sheet of lead glass. But, unfortunately, these enable them only to avoid those superficial skin affections caused by the most absorbable rays of the spectrum. ”

“ If the radius of the active surface is large compared with the distance of the plate A from it, the intensity of the radiation is approximately uniform over the opening in the plate A, and falls off with the distance x traversed according to an exponential law. ”

“ Diana Trenchant went on to explain that her manual was strictly concerned with basic radiology information; information that would prepare students for the more demanding courses in radiology therapy that they would encounter the next year. ”

“ The power of a telescope or a field glass can more accurately be measured by means of a dynameter, which is a microscope which can be fitted over the eyepiece end of the instrument, and which magnifies the image. ”

“ Gamma rays are absorbed in any material through which they pass, according to its density. A low radiation count at the detector indicates a high-density sediment: More radiation is absorbed and less is reflected back to the detector. Conversely, a high count indicates low density. Data are recorded on special cold-resistant film. A number of different sediment measurements can be made in several locations before the unit must be returned to the surface. ”

“ A nation that, in addition to what has been cited above, has likewise invented the telescope, the microscope, the thermometer, the method of measuring degrees of latitude and longitude, the pendulum clock, thereby putting before the world the beginning of anything which we can call accuracy in time, and discovered the capillary circulation of the blood, need not stop to split straws. ”

“ The process of photography of microscopic preparations he developed, by means of a new apparatus, to such an extent that all his results were satisfactory—results that would have been given to the world in a short time, if he had lived, in the form of a work on microscopic anatomy. ”

“ In my previous paper, read before the Royal Society on October 20, 1895, I described a method of determining the indices of refraction of various substances for electric radiation, the principle of which depends on the determination of the critical angle at which total reflection takes place. A semi-cylinder of the given substance was taken, and the angle of incidence gradually increased till the rays were totally reflected. ”

“ The maximum angle at which a radio wave may be emitted from an antenna, in respect to the plane of the earth, and still be returned to the earth by refraction or reflection by an ionospheric layer. 2. The angle at which radiation, about to pass from a medium of greater density into one of lesser density, is refracted along the surface of the denser medium. ”

“ For the accurate measurement of deviation, the effect produced by radiation on the receiver should undergo an abrupt variation. When the radiation passes from an optically denser to a lighter medium, then at a certain critical angle of incidence, the radiation is totally reflected. From the critical angle the index of refraction is easily determined. ”

“ For scientific measurements of temperature by the radiation method, the thermophile, or bolometer, or radio micrometer. previously calibrated by exposure to a black body at a known temperature, is directly exposed at a known distance to a known area of the source of radiation. The required result may then be deduced in terms of the area and the distance. The use of extraneous optical appliances is avoided as far as possible on account of selective absorption. ”

“ We of the school of science have cautioned you repeatedly to postpone the Day of Conquest until we should have mastered the secrets of sub-rays and of infra-rays. Unheeding, you of war have gone ahead with your plans, while we of science have continued to study. We know a little of the sub-rays, which we use every day, and practically nothing of the infra-rays. Some time ago I developed a detector for infra-rays, which come to us from outer space in small quantities and which are also liberated by our power-plants. ”

“ Owing to the differences in transparency of different materials to the rays, radiographs of different objects may be obtained, as in the case of Röntgen rays. Metals are, as a rule, opaque, with the exception of aluminium, which is very transparent. There is no noteworthy difference of transparency between flesh and bone. ”

“ Now, the special interest of radium is in the intensity of its rays which is several million times greater than the uranium rays. And the effects of the rays make the radium so important. If we take a practical point of view, then the most important property of the rays is the production of physiological effects on the cells of the human organism. These effects may be used for the cure of several diseases. Good results have been obtained in many cases. What is considered particularly important is the treatment of cancer. ”

“ Radial cells: the wing area between the radius and media; often divided: in the plural (Comst.) , are those cells anteriorly margined by the radius or its branches.
Radial cross vein: (Comst.) , is that which divides cell, radius 1.
Radial sector: in general, the lower of the two primary divisions of the radius (Comst.) : in Odonata, an indirect branch from the media, just below and parallel with media 2.
Radial vein: in Homoptera, the first important vein next the costa between it and ulnar: in Orthoptera, = radius (Comst.) : in Diptera, = 2d longitudinal vein (Meigen) , = radius 2 (Comst.) . ”

“ Where accurate readings are not required, as, for example, in testing for the presence or absence of a particular element, the position of the bands may be read to a sufficient degree of accuracy by means of a scale, the image of which is adjusted to coincide with the spectrum as seen through the eyepiece; but in mapping a spectrum accurately, more refined methods must of course be used. ”

“ The usual practice in securing radiograms is to place the subject in a position considered likely to give the best results, and then roughly, almost at random, to place the tube in some unknown relation to the part of the body under examination. The resulting shadow is often of no value because it is wanting in detail and depth. ”

“ The α rays from a thick layer of a simple radio-active substance consist of α particles of 178different velocities, which have ranges in air lying between 0 and the maximum range. The ionization of the particles per unit path is greatest near the end of its range, and decreases somewhat as we approach the radiant source. A complex source of rays like radium gives out four types of rays, each of which has a different but distinct range. ”

“ XII. fig. 4, parallel rays will be reflected to a focus a, nearer the mirror than the centre of its curvature b, and this focus is called the principal focus; while diverging rays are brought to a focus nearer the centre of curvature; and converging rays form a focus further from the centre of curvature.
Lenses.—In most instances, as far as the microscope is concerned, the surfaces of the glass through which the rays of light are transmitted are not plane or flat, but curved-being either convex or concave, and belonging to convex or concave lenses. ”