Unit 4: Fluoroscopy Flashcards
What is responsible in fluoroscopy for the converting of x-rays into visible light?
A phosphor screen
What is a spot film?
Digital images taken without the interruption of the dynamic examination that takes a still picture
What are the 2 main areas of angiography?
- Neuroradiology
- Vascular radiology
True or false?
Not all fluoroscopy treatments aloow digital images (spot films) to be obtianed.
False
What is the x-ray tube in fluoroscopy generally operated at in terms of mA?
Less than 5 mA
Does the 15% rule of thumb apply to fluoroscopy?
Yes
True or false?
ABC is always being used in fluoroscopy.
True
How does the fluoroscopy machine maintain ABC?
By varying kVp, mA or both as the x ray tube moves over body parts of differing thickness and attenuation
Why is an image intensifier necessary for the visualization of images in fluoroscopy?
W/o an image intensifier, we would only be using the rods in our eyes to visualize the images produced. An I.I. increases CR and SR.
What is the function of an I.I.?
Converts remnant x ray beams into a high intensity visible light image
What is responsible for converting the remnant x rays and its energy to light in fluoroscopy?
The input phosphor made of cesium iodide (CsI)
Why do we used CsI as the input phosphor in fluoroscopy?
- Has a high intrinic efficiancy which reduces patient dose
- It absorbs 2/3 of the incident beam
- Increase of SR
True or false?
CsI has a low atomic number.
False; high-it results in higher x ray absorption
Why does CsI increase SR?
1. Thinness: Reduces the amount of diverging photons since they dont have to go through as much material
2. Shape of crystals: They help direct light with little lateral dispersion and less blurring
What are the advantages of increasing the image phosphor thickness?
- There is a higher x ray absorption efficiency
- Patient dose is reduced
What are the disadvangaes of increasing the image phosphor thickness?
- Decreased spatial resolution
What is photoemission?
Occurs when the photocathode emits e- when light from the IP strikes it
What is the photocathode made of in fluoroscopy? What is it bonded to?
-Made of cesium and antimony compound
-Bonded directly to the input phosphor
True or false?
The number of e- emitted by the photocathode is indirectly proportional to the intensity of light that reaches it.
False; directly proportional
Why is the image phosphor curved?
To ensure that the e- emitted at the peripheral regions of the photocathode travel the same distance as those emitted from the central region to maintain resolution
How long is the image intensifier?
50 cm long
What is the anode plate in fluoroscopy?
A plate with a hole in the middle which allows e- to pass from the photocathode to the output phosphor attached to it
What is the potential difference in the accelerating anode across the tube between the PC and the anode?
25000-35000 V
What is the term that describes the engineering aspects required to maintain proper e- travel across the accelerating anode?
Electron optics