Medical Physics

Endoscopy
1. Flexible tube, allows us to look into the body
2. Non-invasive / key-hole surgery
3. Optical fibre / TIR
4. Angle of incidence in glass exceeds the critical angle
5. Light can be directed into body cavities
6. Two bundles of optical fibres
  1. Illumination Bundle = Carries light to object
  2. Image Bundle = Carries back reflected light
7. Fibres are coherent bundles
  1. Parallel to each other
8. Image viewed or photographed through a magnifying glass
9. Endoscope allows range of minor surgical treatments ( Forceps, Electrodes, Extractors)
Ultrasound
1. Range of human hearing = 20Hz - 20KHz
2. Ultrasound frequency > 20KHz
3. Longitudinal pressure waves
4. Diagnostic frequencies = 1MHz - 15MHz
5. Low intensity waves pass through tissue causing no harm
6. Waves reflected at boundaries between biological structures
7. Ultrasound transducer generates and receives sound waves
  1. Piezoelectric Effect
8. When alternating voltage is applied to certain crystals, they expand and contract (vibrate)
9. These vibrations produce sound waves
10. Incoming waves distort crystals structure which generates small electrical signals
11. Waves emitted for 5µs then gap of 100µs
  Annotations:
  - µ = Micro = \[10^-6\]
  1. µ = Micro = 10^-6
12. Reflected waves are associated with pressure changes which change shape of PZT
13. Electrical voltage produced, then detected and processed by a computer
A Scan
1. Amplitude
2. Horizontal Axis = Time
3. Vertical Axis = Aplitude
4. This method is used to measure diameter of foetal head
5. Diameter = Indicator of development of baby
B Scan
1. Brightness
2. Produces an image that is easily interpreted
3. Scanned across the body in a series of ines
4. Strength and position of reflected ultra-sound stored electronically
5. Stored data used to produce an image on the screen
6. Strength of signal determines brightness
7. Can also identify tumors in organs
8. Waves strongly reflected at air-skin boundary
9. Water based cellulose gel smeared on skin as coupling agent
MRI Scans
1. Magnetic Resonance Imaging
2. Basis = NMR Nuclear Magnetic Resonance
3. Nucleus of some atoms spin creating a magnetic field
  1. No magnetic field = randomly orientated Magnetic field = line up with field
4. Some aligned in same direction = low energy state
5. Some aligned in opposite direction and in high energy state
6. Precession = Thermal motion that causes a wobble about the X-Axis
7. Larmour Frequency = Frequency at which nuclei wobble
8. If electromagnetic radio frequency is applied at Larmour frequency , nuclei absorb energy and low energy nuclei jump to opposite direction
9. When radio waves stopped, nuclei return to low energy state and re-emit the absorbed radio waves
10. Re-emitted waves are detected and processed to give image
11. Magnetic field = 0.1T - 4T
12. No adverse effects
13. Magnetic field produced by superconducting alloys
14. Can identify tumors, MS, ligament damage, examine anatomy of brain
X-Rays
1. Heated filament emits electrons by thermionic emmission
2. They are accelerated through a vacuum by a high P.D
3. They then collide with a target, usually made of Tungsten, with a large atomic mass
4. The electrons are then slowed and the energy lost is emitted as X-Rays
5. The target spins so as not to concentrate all the heat on one area alone and damage it
CT Scan
1. Computed Tomograpghy Scan Computed Axial Tomography Scan
2. Ability to image soft tissue, bone, blood vessels
3. Rotating X-Ray device
4. Creates cross-sectional images
5. Preferred method for diagnosing lung, liver, and pancreas cancer
6. Can detect internal bleeding for trauma patients, tumors, blood clots, blood vessel defects
7. Patient lies on bed with specified part inside the round tunnel
8. Bed moves forward and backwards and X-Ray tube is rotated round patient
9. Computer constructs image from detector signal
10. More expensive and higher dose (of radiation) than normal X-Ray

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	Created by Tim Davidson over 10 years ago