Biophysics Flashcards
Uses for ultrasound
Determine the nature of a tissue
Assess the movement of a tissue
Measure blood flow
Measure structures
How does ultrasound work
Uses a piezoelectric crystal in a transducer that changes electrical energy to mechanical, and visa versa. It uses sound waves (mechanical energy) to disrupt a medium
What are the 3 principal interactions with tissue seen in ultrasound
Reflection - at the interface between tissues with different characteristics. Determined by the acoustic impedance, which is related to the tissue density and ultrasound velocity. The higher the difference in acoustic impedance, the greater the degree of reflection
Scatter - when USS interacts with structure with dimensions equal to or less than the wavelength of the USS
Absorption - conversion of mechanical energy into heart or internal molecular energy, which increases with increasing frequency
What is the doppler frequency shift and its use in clinical medicine
Difference between the frequency of returning echo and the transmitted ultrasound wave
Used to measure blood flow
What is a sievert unit
The standard international’s unit of measurement for radiation, measures the amount of energy going to the body by gamma radiation
How does x-ray work
Produced by accelerating electrons which are then made to collide with a metal target
In the X-ray tube, they suddenly decelerate upon collision with the metal target, which can knock out an electron from the inner shell of the metal atom
Electrons from higher energy levels then fill up the vacancy and x-ray photons are emitted as a result
How does a CT scan work
Uses x-rays and the principle of x-ray formation, detection and contrast
Emitted x-rays form a beam which passes through the biological material toward a detector on the other side.
The detector measures the number of protons and the altered protons in voxels, which are computed divisions of the body organs and tissues into small volumes. Each voxel is given a number, or an attenuation coefficient. Attenuation values of the x-ray beam are recorded and data is used to build a 3D representation of the scanned object or tissue
How does MRI work
The patient is placed in a static magnetic field, which is created to align the H+ ions present in tissue water molecules. These protons possess an intrinsic magnetisation called spin.
Then a radio frequency pulse is emitted from the scanner, which is used to disrupt the alignment of the protons with the main magnetic fields
Following the pulse, protons drift back into alignment with the magnetic field, emitting a detectable radio frequency signal as they do so, which is captured to form your MRI image
