X-rays and ultrasound

X-rays are high frequency, short wavelength electromagnetic waves.They pass through healthy tissue but are absorbed by denser material such as bones and metal. They affect photographic film in the same way as light, they can be formed electronically using charge-coupled devices, these are silicon chips. Computerised axial tomography (CT) scan use x-rays to porduce high res images of soft and hard tissue. Xrays are fired from an xray tube and and are picked up by dectors on the opposite side. The xray tube and detectors are rotated during the scan, the signals are interpretated by a computer. They form an image of a 2D slice and they are put together to make a 3D image of inside the body.

X-rays cause cause ionisation so high doses will kill living cells, this means they can be used to treat cancers. They have to be carefully focused at just the right dose to kill cancer cells and not harm others. To treat cancer :The X-rays are focused on the tumour using a wide beam, the beam is rotated around the patient with the tumour at the centre. Radiographers take precautions to minimise radiation dose: they wear lead aprons, stand behind a lead screen or leave the room, they may also wear special badges that tell them the level of radition they have been exposed to.

Ultrasound is a higher frequency than humans can hear, electrical systems can produce electrical oscillations of any frequency. Human hearing ranges from 20 to 20000 Hz. When a wave passes from one medium into another some of the wave is reflected off the boudary between the two media, and some is transmitted(and refracted) this is partial reflection.If you point a pulse of ultrasound at an object the ultrasound will reflect at the boundary, it will take time for this to happen and this time can be measured to tell how far away the boundary is. S=vxt (S=distance in metres , v=speed m/s , t=time seconds). Ultrasound can be used in medicine to investigate blood flow in organs, breaking down kidney stones (breaks down the particles so they can be passed through the body) and pre-natal scanning of a fetus(the fluid in the womb and skin of the fetus is a boundary which ultrasound is reflected between, the timing and distrabustion of the echos make an image of the fetus.

• Safe?
• Ultasound uses non ionising waves, mainly safe
• X-rays are ionising
• CT scans use a high dose of x-ray radiation
• Quality?
• Ultrasound -fuzzy images
• X-rays are clear images but only of bones and metal
• CT scans produce high quality images