At the hospital we were taken round many departments in which physics could be seen clearly at work, I have chosen to look specifically at X-rays and Ultrasound.
Ultrasound is used mainly in three areas of medicine; Obstetrics, Cardiology and Urology. Ultrasound is most widely known for its uses in Obstetrics which is the branch of medicine which deals with women through pregnancy and child birth.
During pregnancy Ultrasound can be used to check the size of the foetus to estimate the due date, the sex of the baby, the position of the foetus, to detect an ectopic pregnancy or even to monitor the baby during specialist procedures such as amniocentesis. This is just a brief outline of how ultrasound is used in Obstetrics.
Ultrasound is used in Cardiology to identify abnormal structures of the heart and to measure blood flow through the heart and major blood vessel. In Urology it is used to detect prostrate cancer early, to find kidney stones and to measure blood flow through the kidney.
An ultrasound wave is a high energy longitudinal wave, it operates at a frequency higher than the human ear can detect.
Ultrasound is used in medicine in the following way. A special gel is applied to the part of the body which is to be scanned this acts as a coupling agent so that the waves pass right into the body without having to pass through air first.
The machine then emits ultrasound waves through special pads into the gel and then to the body. The wave is absorbed by some tissue but passes through others and is reflected by still more. The reflected waves travel back up through the body into a sensor which is linked to the ultrasound machine.
It then generates a moving image based on the data it receives from the sensor which is also located in the pad. Knowing which tissues reflect ultrasound and which do not the operator can identify from the images different parts of a persons anatomy and also find things that shouldn’t be there.
Ultrasound is a very safe and cheap way of getting a look inside the human body, one test can be carried out and a diagnosis made very quickly. Some scientists have suggested that when pregnant women are scanned repeatedly the heat given off when the waves are absorbed can affect the baby’s development but this is still unproved.
Ultrasound can also be used in other fields such as in deep sea fishing, ultrasound is sent down to detect where shoals of fish are this saves large amounts of time, also it can be used in metal work to quickly check that joints are secure.
X-Rays are used widely throughout medicine in various ways and forms. They are most widely known for their usefulness in detecting fractures or breakages in bone, they are used in many other ways. They can be used to detect cavities, swallowed objects and look at softer tissue like lungs or blood vessels or even to find tumours.
X-Rays were first discovered in 1895 by Wilhelm Roentgen a German physicist. He named them X-radiation because of their mysterious nature at the time. He found that they could pass through many objects that reflected visible light and could dislodge electrons from atoms.
X-rays are a form of Electromagnetic energy like visible light they carry energy in particles known as photons. X-rays have a higher energy level and shorter wavelength than visible light. Our eyes can’t detect the high wavelength of X-rays so they appear invisible to the naked eye.
An x-ray can be created in one of two ways. The first is illustrated in figure 1; first a moving particle collides with the atom and transfers some extra energy to it. This causes some of the electrons to move up into higher orbits (more energy), when they sink back they emit this extra energy in the form of electromagnetic energy, the energy released in the collision will determine what kind of electromagnetic radiation is released.
The second way is this, if an electron passes near an atom and it is attracted to the nucleus like a comet to the sun, it slows down as it goes round it, which means it must emit a photon to get rid of the excess energy. If the electron was travelling at a great speed to begin with it would have had more energy and so the difference would have been greater and the energy level of the photon would be higher (x-ray).
The human body is good at absorbing visible light because the energy level of the photon is enough to jump the “forbidden gap” accelerate electrons into the valance band. Most radio waves pass right through us because their photons have far too low energy levels, x-rays mostly through us because they have high energy levels, but they can be absorbed by atoms.
An x-ray or any high energy photon can knock an electron right out of the orbit of a nucleus, the first part of the energy is given to jump out of the orbit of the atom and the rest accelerates it through space. The body’s soft tissue doesn’t absorb x-rays very well
Medical x-ray machines use this characteristic to take pictures of things inside a person’s body. The x-rays pass through the soft tissue of the human body and are mostly absorbed by the bones and harder tissues.
Under the part which is being x-rayed there is a slide of x-ray film as the x-rays hit it they darken it, the higher energy level the wave has when it hits the darker the film goes. The x-rays that pass through bone and harder tissue have less energy as it has been absorbed into the body. Once the film is processed in an automated machine a film is produced so that a radiographer can analyse the film and send a report to the doctor.
One of the major new advances in x-ray technology is digital scanning which is already being used in some hospitals. This innovation will enable radiographers to render a computer image of the x-ray this means that it can be analysed much more quickly and will cut costs greatly.