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Applications Of Physics in the medical field
Strongly absorbed by bones Can penetrate soft tissues
Properties:
Hardness The penetration of the beam Depends on the Acceleration voltage
X Rays Tube High Voltage 50 200 KV DC Supply connected to 2 metal plates, a filament is heated to emit electrons (Thermionic emission) which are accelerated between the 2 plates a metal plate (target) is connected to the anode
X Rays are produced by bombarding a metal anode by accelerated electrons To produce more X Rays, increase the temperature of the filament, increasing the number of electrons emitted Methods of emitting X Rays Breaking Radiation (bremsstrahlung radiation) electrons lose all their energy in the form of X Rays
Electrons excite the electrons in the metal anode, emitting X Rays as they are de-excited, creating the Characteristic lines on the graph
X Rays that pass through the body are absorbed by a sensitive film to form an image.
Contrast The parts constituting the image represented by different degrees of blackness With Bones, contrast is very high A contrast medium is used to take images of soft tissues Sharpness Image with well determined edges
I ( x ) = I 0 e − μx
I 0 Original intensity before entering a medium, e.g. Bone I(x) Intensity after exiting the medium x Distance covered in the medium μ Attenuation Absorption) coefficient depends on: Typed of tissue Frequency of the X Rays
Medical Physics
X-Rays
Production of X-Rays
Properties of an X-Ray Image
Mathematics of X-Rays
x 12 → X half thickness :- x where the intensity is halfed
Soft X Rays Low energy X Rays that do not pass through the medium but are completely absorbed
an aluminum sheet can be placed in front of the X Ray tube to absorb Soft X Rays
X Rays are applied on a single plane from different directions to from a 2D image. This is repeated on the perpendicular axis several times and processed by a computer to form a 3D image Main Principles of CT scanning :
X-ray image of a cross section is taken from different angles Images are processed into a 2D image by a computer This is repeated for different cross-sections 3D image is formed
Sound is produced and received by a Pizoelectric Transducer , when the ultrasound waves reflect back and hit the silver plates, they induce a voltage, the sound waves have the same frequency as the transducer but a lower intensity
Pizoelectric Transducer Quartz crystal, with thin silver plates on either side acting as electrodes connected to an AC supply, this causes the Quartz crystal to vibrate at the frequency of the AC supply Main Principles behind the generation of ultrasound waves :
A Scan 1D image formed by sending ultrasound waves from one direction B Scan 2D image formed by sending multiple ultrasound waves from many directions which are processed by a computer
Main Principles of the use of ultrasound in imaging :
Pulse of ultrasound produced from a quartz crystal coupling medium (gel) is used to reduce reflection of sound waves at the surface of the skin sound waves are reflected off the boundaries between media reflected waves are detected by transmitter reflected waves are processed and displayed intensity of the wave gives information about the boundary time delay gives information about the depth of the boundary
Each medium has it's own specific acoustic impedance
Z = ρc
Z Specific acoustic impedance ρ Density of the medium c Speed of ultrasound in the medium
CT (Computing Tomography)
Ultrasound Imaging
Specific Acoustic Impedance (Resistance)
