Essay on Ultrasounds and X-Rays and the Physics Involved

Essay on Ultrasounds and X-rays and the Physics Involved

In this essay I will explain about ultrasound and x-rays and talk about how they are put to use in the medical profession. I will not only talk about the physics involved when putting these technologies to work but also the dangers they may impose if not used correctly.


An ultrasound is a medical imaging technique that basically uses sound waves (which are of a high frequency) and records its echoes. Just like what submarines use to located other ships or submarines (sonar) as well as what bats use to see in the dark. Ultrasound works in the medical profession by the ultrasound machine transmitting high frequency sound pulse though the body using a probe. The frequency of the sound is about (1 to 5 megahertz). The sound then travels though the body until it hits a tissue boundary for example between fluid and a soft tissue.
Some of these sound waves are reflected back to the probe as other care on going deeper into the body until they also reach another boundary and are reflected back. These are then picked up by the probe, which relays the signal back to the machine. The machine then calculates the distance from the probe to the tissue or organ boundary using the speed of sound in standard tissue, which is about 1,540 m/s, and the time it takes for each echo to return. The machine then displays the distances and intensities of the echoes on the screen, forming a two dimensional image.

The parts of a standard ultrasound machine are the transducer probe, which sends out the sound waves and receives the sound waves.
Then there’s the CPU or central processing unit, this is basically where all the calculations are done. The transducer pulse controls, this changes the amplitude, frequency and duration of the pulses emitted from the transducer probe. The display displays the image of the processed ultrasound data. The keyboard/cursor allows you to input data and take measurement of the display and a printer for printing out the displayed images.

Different types of ultrasound

There are three sorts of ultrasound that is widely used in the medical profession. One which presents a two dimensional image. This is a slice of an organ or of a fetus. The other types of ultrasound are 3D ultrasound imaging and Doppler ultrasound.

3D ultrasound imaging

These are ultrasound machines that are capable of three-dimensional imaging. In these machines, several two dimensional images are acquired by moving the probes across the body surface. The two dimensional scans are then combined by specialised computerised software to form a 3D image. This form of ultrasound is used for many different tasks like in the early detection of cancers and benign tumours to blockages in the in the colon and rectum.

Doppler ultrasound

The Doppler ultrasound is based on the Doppler effect. When the object reflecting the ultrasound is moving, it changes the frequency of the echoes. Creating a higher frequency when the object is moving towards the probe and a lower frequency when an object is moving away from the probe. How much the frequency changes depend on how fast the object is moving. Doppler ultrasound is used mostly to measure the rate of flow the heart and major arteries.

The dangers of ultrasound

The dangers of ultrasound is that because the sound waves have energy they heat up the water molecules in the body and the temperature of the water is risen locally.
Also when the solutions in the body are heated the dissolved gases come out of the solution and form bubbles a similar thing to what drivers get when they surface too quickly. These affects can be dangerous to an unborn child so it is recommended that only a certain amount of scans should be done per pregnancy.

The future of ultrasound

Ultrasound technology will become faster and smaller in the future, there is research on a very small version allowing use of ultrasound in the field for example for paramedics.

X rays

A German physicist called Wilhelm roentgen discovered x rays in 1895 while he was experimenting with electron beams in a gas exchange tube.
The radiation, which was given off, penetrated the screen, which surrounded the tube and made another nearby screen glow. When he put his hand in front of the florescent screen he was an outline of his bones.
This is when he discovered x-rays.

What are x-rays?

X-rays are wave like forms of electromagnetic energy just like visible light. The difference is that x-rays has a higher energy level so the wavelength is much shorter. This is also the reason why we cannot see ex-rays.

How are x-rays created?

Visible light photons and x-ray photons are both produced by the movement of electrons in atoms. Electrons occupy different energy levels or orbital, around the atoms nucleus. When an electron drops to a lower orbital, it needs to release some energy it releases the energy in the form of a photon (electromagnetic energy).
The energy level of the photon depends on how far the electron drops between orbitals.

Only large atoms can absorb the x-ray photons so because your body is made of mainly small atoms your body does not absorb them very well. This means that the x-rays are able to pass though the body with ease.
However the calcium atoms that make up the bone structure of the body are much larger atoms and they do absorb the x- rays.

The x-ray machine

The high impact collisions involved in the creation of X rays generates a lot of heat. A thick lead shield (to prevent the x-rays from escaping out in all directions) surrounds the x-ray machine. A small window in the shield allows the r-ray to escape in a narrow beam. This beam passes through a series of filters before it goes out to the patent.

A camera on the other side of the patent records the pattern of x-ray light as it passes though the patents body. The film used is ordinary photographic film but generally the doctors look at the film in negative as it shows the bones as whit and is thereby easier to see.

The dangers of x-rays

X-rays can be harmful to the body because it is an ionising radiation. This means that when the x-rays hit an atom, it can knock electrons off the atom to create an ion. Free electrons then collide with other atoms to create more ions.
An ions electrical charge can lead to unnatural chemical reactions inside cells as well as breaking the bonds of the DNA strands in the cell either killing it or causing a mutation.