X-rays are the principal form of radiation used in radiodiagnosis. X-rays were discovered in 1895 by the German physicist Wilhelm Conrad Roentgen. The story goes that Roentgen was experimenting with Crookes’ tubes and discovered that a combination of low pressure of gas inside the tube and a high voltage across the tube caused mysterious rays to be emitted from the anode, or positive terminal of the tube. These rays which Roentgen called x-rays could blacken photographic film and pass through materials opaque to visible light such as paper, wood, or thin metal sheets. Roentgen also found that the rays would pass through his hand when he inserted it between the tube and a plate. The developed photograph indicated that the bones stood out clearly as dark shadows as compared with the flesh.
This means that the bones, more dense than the flesh, blocked the rays, whereas the rays could pass more easily through less dense materials, such as portions of the hand where there is no bone. As x-rays pass through the body, radiation is absorbed by denser parts and easily penetrates the less dense parts. The result is an image on the film placed on the other side of the body. The x-ray picture, called a radiograph, is a permanent picture of the internal body. It looks like a photo negative. Dark areas represent the least dense structures; white areas, the most dense structures. (See Figure 1 at end of unit.)
To produce usable roentgenographic images, it is necessary to produce and control roentgen rays of varying wavelengths and direct them to a recording instrument so that the image can be visualized. The source of roentgen rays is an x-ray tube; and images may be visualized on roentgenographic films, fluoroscopic screens, television or movie films.
Roentgen rays are forms of electromagnetic energy similar to visible light and radio and television signals, but with a shorter wavelength—the shorter the wavelength, the more energy the x-ray wave has. Therefore, the greater the energy, the better the wave will be able to penetrate matter. Longer wavelengths may be reflected from the surface of an object. There are different wavelengths to roentgen rays; in medical roentgenography, roentgen rays appear as a group, or spectrum, of energy levels or wavelengths. Roentgen rays travel at the speed of light and usually have a wavelength of 1/10,000 that of visible light.
To demonstrate waves—tie a 3-m length of clothes line to a doorknob of a closed door. Take the opposite end of the rope and stretch it across the room. Hold the rope loosely at the height of your waist. Flip the rope up and down several times. The rope makes a number of waves. The rope will form hills (crests) and valleys. The faster the rope flips, the more waves and the closer they are together. The distance from crest to crest is called wavelength. The number of crests that pass a given point in a second is called frequency. (See Figure 2 at the end of this unit.)
The x-ray tube is the source of the radiation. The tube is composed of an anode (+) and a cathode (-) enclosed in an evacuated glass container and surrounded by a lead housing. The cathode usually contains two different sizes of filaments and a focusing device which is a hollowed out metallic well into which the filaments are positioned.
To produce roentgen rays, electrons must be available. It is hard to explain where the x-ray comes from without going inside the atom. Inside the atom, the nucleus is the core with electrons in orbit around it. To make x-rays, the target is bombarded by electrons from the cathode. It takes alot of energy to disturb the electrons in the atoms of the target. The greatest amount of energy is needed to eject an electron from the inner shell which is close to the nucleus. The electrons cannot exist in this unbalanced state. An electron from a shell further away from the nucleus will replace the vacant space and give up energy during this shift in the form of x-radiation. Balance is regained when the atom picks up a free electron and all its orbits are filled. X-rays are the result of innershell disturbance. (See Figure 4 at end of unit). A more thorough discussion of this will be included in the unit by Zelda Kravitz.
The x-ray tube filament is composed of tightly wound tungsten wires and electrons form a cloud around the filament when electric current is passing through the wire. The electron cloud is focused to a small beam and is attracted to the anode of the x-ray tube by a voltage differential between the electrodes. The cathode of an x-ray tube can be compared to a floodlight. The reflector of the floodlight corresponds to the focusing cup of the x-ray tube.
The x-ray machine is a delicate instrument that sends out x-rays in a controlled manner, so that a small carefully calculated amount of radiation is directed toward a specific part of the body. Some of the radiation emitted from the target (anode) is scattered in all directions. This form of radiation, which is not useful in the making of the x-ray, is called scattered radiation.
Because of its adverse effect of the image, it is necessary to minimize scattered radiation. There are several devices which can be attached to the x-ray to contain the x-radiation to the proper area being examined.
-
Marcella—Carolyn, talking about medical imaging in diagnostic radiography has been exciting.
-
Carolyn—Marcella, I know we did not cover all the possible areas, but I hope that we enlightened some teachers and students. It is very important for all of us to become aware of how x-rays affect our lives.
-
Marcella—Do you know that there is more background radiation introduced in the body than x-rays?
-
Carolyn—Yes, that means that background radiation is from a natural source and is in our environment. It is everywhere.
-
Marcella—If all of us are aware of the good that x-rays have done in the diagnosis of diseases, and the special care that is given to assure little or no risk in getting x-rayed, then we can spend more time in aiding doctors in making a good decision in diagnosing x-rays to help treat diseases.
-
Carolyn—I think you are right.
-
Marcella—Do you know that we did not talk about cost?
-
Carolyn—What about the cost?
-
Marcella—Most costs are covered by health insurance.
-
Carolyn—Diagnostic X-ray costs usually include hospital or lab charges for use of equipment, supplies, facilities, personnel and soforth. The radiologist charges for professional and consultation services.
-
Marcella—Costs are based on the procedures; however, earlier detection and more effective treatment may result in fewer procedures having to be done.
-
Carolyn—So what does this mean? Let’s summarize together.
-
Carolyn & Marcella—Diagnostic X-ray plays an important part in our total medical treatment process. It helps discover diseases and abnormal growths before they reach dangerous levels. It helps to diagnose specific problems in the functioning of body tissues and organs. It can help doctors provide the best treatment for you.
-
Remember: Be aware of what to expect and cooperate fully.
-
Marcella—Carolyn, I’ve learned so much about radiography. Conventional radiography certainly has and still is serving a vital function to mankind.
-
Carolyn—Gee Marcella, there is so much more that we did not discuss. Perhaps we can learn some more from other related units in medical imaging.
-
Marcella—Isn’t it great that we decided to do this unit?
-
Carolyn—Yes, I hope that the students and other teachers will have as much fun as we are having.
-
Marcella—Do you know that tomography has so much potential? I am amazed over what that modality does. It is God sent to the medical profession.
-
Carolyn—I am really excited about reading the unit on Computed Tomography developed by Glen Ann Hagemann and Joe Cummins. two more teachers from our Medical Imaging Team.
-
Marcella—Carolyn, Dr. Ablow, a physician that specialized in radiography, at Yale-New Haven Hospital is doing a fantastic job in preparing and motivating teachers to bring this information to students.
-
Carolyn—It is great that we can be a part of making students aware of the education and job opportunities that exist in this field.
-
Marcella—Many radiologists have saved lives of many people. They understand the seriousness of their jobs. They are trained to use very safe measures in administering radiation.
-
Carolyn—You are absolutely correct Marcella. Much research and concern has gone into this area.
-
Marcella—Well, then let’s talk about the biological effects. Carolyn, after researching the biological effects of radiography, I must tell you that my attitude has somewhat changed.
-
Carolyn—Why do you feel that your attitude has changed?
-
Marcella—Do you know that the benefits that we receive from radiography far outweigh the risks? So many people are being cured and so much more is known about cell activity. The amount of radiation received as background radiation is higher in dose than the amount you will receive in some radiological procedures. Background radiation is other kinds of natural radiation caused by energy from the sun or other natural sources. It is a part of our environment. Carolyn, this does not mean that we don’t have to be careful. It means that you should make sure there is a real need for the x-ray and that it is explained fully. It is a patient’s right to question the doctor about this.
-
Carolyn—Marcella, gee, now I am really eager to learn more.
-
Marcella—Great, then I will tell you a little more about the biological effects of radiography.
