Unit 3: Week 2 Flashcards
What is Doppler shift?
The difference between transmitted and received frequency. As an object is moving towards you the distance decreases so wavelength decreases and frequency increases.
This reflected frequency is the Doppler shifted frequency
What is a Doppler flow meter used for?
Used to measure the flow of blood.
5.02 MHz is used as it has a reasonable chance of being reflected by RBC
Doppler shifter frequencies are usually in the audible range.
What is colour Doppler and how is it used?
Doppler sound is converted to colour overlays are added to images of blood vessels to depict speed and direction of blood flow. It is a diagnostic imaging technique.
What are some of the advantages of using US?
No radioisotope needed Portable bedside equipment Non invasive Generally better for soft tissue examination Can see function of organs Live image
What are some of the disadvantages of US?
Poor resolution
Can only see clearly up to certain depths
Can image hard/dense materials/structures
How are x rays produced? what are some inefficiencies of X-rays ?
- X rays are produced by electron build up on the cathode -ve end
- When there is a large enough potential difference (difference in voltage) then the electrons will move from the cathode to the anode tungsten target +ve end.
- Most of the energy will be lost as thermal energy- inefficient but some would be converted to characteristic/continuous x rays
Due to heat buildup oil needs to be circulated and the tungsten needs to be mounted onto a copper block. It spins do disapate more heat
Why is tungsten used?
High mp
Stable
Priced reliable de excitation in x ray range
What are characteristic x rays?
High energy electrons from the cathode allow electrons in the tungsten to transition excitation and deexcitation. The photon released would have a frequency in the x ray portion of the EMS
What are continuous x rays?
When an electron from the cathode travels near a nucleus and electromagnetically interacts with it. This causes the electron to slowdown and deflect giving off a photon with a frequency in the x ray portion of the EMS
What is a contrast dye and how are they used?
Contrast are radioopaque materials used to improve the visibility of soft tissue structures.
Since there is a difference in density soft tissue doesn’t show up well
Considered minimally invasive
What is a fluoroscopy and what is it used for?
They use continuous x rays to produced a series of scans to look at an organ moving in real time to study function.
Can be used to examine specific bone area, joints, muscle and organ functions such as heart kidney lungs or intestine.
What is a CT or CAT scan and how are they produced ?
Computer tomography or computer assisted tomography is a specialised xray that generally uses contrast dye injected into the blood to make structures more visible, attenuation- the reduction in strength between an initial and final xray- measured at different angles, and filtered back projection to produce an image/cross sectional images.
What are some uses of CT scans?
Good at detecting lymphoma-
Also can detect other cancers- overian, kidney, pancreatic, liver
Can also detect pulimanry embolisms
Simple x rays- bone absorbed X-rays so organs are not visible but CT measures attenuation and then uses filtered back projection to view soft tissue or images behind bone (head/ribs)
