P3 - X-rays and Ultraviolet
- Created by: Deepali Patel
- Created on: 04-03-13 18:23
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- P3 - X-rays and Ultraviolet
- X-rays in medicine - EM waves.
- X-ray images-used in hospitals for medical diagnosis-bone fractures & dental problems. High frequency, short wavelength EM waves.
- Affect photographic film same way as light, so they can be used to take photographs.
- Can be formed electronically, using CCDs. They're silicon chips divided up into a grid of identical pixels. They detect X-rays & produce electronic signals which are used to form HQ images.
- CT scans - Computerised axial tomography. Produce HQ images of soft and hard tissue.
- The x-ray tube and the detectors are rotated around during the scan.
- Detailed images, diagnose complicated illnesses.
- Can treat cancer. X-rays cause ionisation- high doses kill living cells. They have to be carefully focussed, and at the right dosage to kill the cancer cells, without damaging nomal cells
- Radiographers need to take precaution to minimise their x-ray dose. They wear lead aprons, stand behind a lead screen, or leave the room.
- X-ray - Clear images of bones and metal, but not a lot else.
- Ultrasound - sound higher than a frequency of 20,000 Hz.
- When a wave passes through media, some of the wave is reflected off the boundary, and some is transmitted (pass through) and refracted - partial reflection.
- You can point a pulse of ultrasound at an object, and wherever there are boundaries, some get reflected back.
- The time taken for the reflections to reach the detector, can be used to measure how far away the boundary is.
- You can use oscilloscope traces to find boundaries.
- S = V x T
- Used in medicine. Breaking down kidney stones and pre-natal scanning of a fetus.
- Non-ionising. Images are typically fuzzy - harder to diagnose.
- X-rays in medicine - EM waves.
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