Medical Physics Flashcards
How do CAT Scans Work?
-An X-ray tube rotates around the patient
-A thin fan shaped beam of X-Rays is sent towards the patient
- Images of the patients cross section are taken as the X-ray tube spirals along the body
The transmitted rays are received by the detector and a computer produces the 3d image
How are X-Rays produced (X-ray tube) ?
-A filament is heated at the cathode allowing the emission of electrons by thermionic emission.
A high voltage allows the electrons to be accelerated towards the anode where there is a target metal.
- Electrons hit this target metal and this sudden decrease in kinetic energy creates a continuous spectrum of X-rays (German word)
How do PET scans work?
-The body is surrounded by a ring of gamma detectors.
-A tracer that emits positrons through beta decay is injected into the body and the positron annihilates with an electron in the body.
-This produces 2 gamma-ray photons that travel in opposite directions.
-The delay time between receiving these gamma photons allows a doctor to determine the location of the annihilation.
How can we determine the speed of blood flow.
The ultrasound transducer is placed at an angle to the artery.
Blood moving away from the transducer is reflected at a lower frequency than blood moving towards the transducer.
This change in frequency allows us to find the speed of blood flow by using Δf=2vfcos(
How can we determine the speed of blood flow?
-The ultrasound transducer is placed at an angle to the artery.
-Blood moving away from the transducer is reflected at a lower frequency than blood moving towards the transducer.
-This change in frequency allows us to find the speed of blood flow by using Δf=2vfcos(o)/c
Simple Scattering X-ray Absorption Mechanism)
-An X-ray incident on an atom interacts with an electron and is scattered at a different angle with no loss in energy.
Compton Scattering
-A high-energy X-ray interacts with an electron. The electron is removed from the atom and a low energy photon is scattered.
Photoelectric effect
-An X-ray is absorbed by an electron. This causes an electron with some kinetic energy to be emitted.
Pair-Production
-Incoming X-ray with high energy has enough energy to interact with a nucleus. This creates a electron-positron pair that annihilate and create a pair of low energy photons.
How does an A-scan work?
A single transducer is placed on the skin emits a single, short pulse. Echoes return from boundaries between different body tissues. The output is displayed as a graph on an oscilloscope, showing how the echo amplitude changes with time.
How does a B-scan work?
-Using pulsed ultrasound waves in different positions to produce several measurements of time intervals between generating and receiving pulses.
