Fluoro Lecture 1 Flashcards
Most of the newer II (image intensifiers) are of the _____-______ type. (dual, tri and quad focus)
Multi- Field
What crosses at the focal point?
Electrons coming from the photocathode heading toward the output phosphor
Multi- field image intensifiers provide for greater ________ for all fluoroscopic exams.
Flexibility
What is the largest number you look at on the image intensifier
The normal size, which is the actual size of the input phosphor
What are the other numbers you see (smaller numbers) on the image intensifier other than the largest number for?
The size of the input phosphor you will be using to get the magnified image
What are some routine sizes of the image intensifier?
12”, 9”, 6”, 4.5”
16” & 20”
In the normal size (largest number), the ________ ________ of the IP is used to produce the image on the OP.
Entire Surface
In the normal size, how much of the electrons being produced on the photo cathode will be striking the output phosphor to produce an image?
All of them
What happens when you shift to a smaller size (number or FOV)?
The voltage of the electrostatic lens inside the image intensifier is increased
Increase the negative value of the voltage
When you increase the negative value of voltage inside the image intensifier, what are you doing?
Forcing the electron beam closer and closer together, forcing the focal point to occur sooner than it did earlier
Because the electrons focus closer to the input phosphor, what does this result in?
Less of the e- beam will strike the OP, which will cause the image to appear larger
When the electrons focus closer to the IP what does the OP (output phosphor) think it’s seeing?
The OP in the normal mode thinks it’s seeing the electrons coming from the entire surface, so it will show a normal sized image
When the electrons focus closer to the input phosphor, the electron beam diverges sooner. What happens to the electron beam
Some of the beam goes through the hole in the anode and some of it strikes the anode becoming part of the current
What happens when you shift the number on the electrostatic focusing cup to a higher value?
- The electrons focus sooner
- Focal point is now closer to the IP
- Electrons diverge out
- Less electrons hit the OP (divergence of beam)
- Thinks it’s getting electrons from entire surface
- Image looks larger/ magnified
If we magnify the image, what is the relationship between the number of electrons hitting the output phosphor in normal and the number of electrons hitting the output phosphor in a magnified view?
The normal view will have higher number of electrons
Magnified view will not be getting all the electrons
Will you have more or less electrons hitting the output phosphor in a magnified mode?
Less
What happens to the brightness level if you have less electrons hitting the output phosphor?
- It’s less bright and the image on the monitor dims.
- ABC will adjust technique (increasing mA)
How does the magnified view affect patient dose?
It increases it (because of ABC)
What are the 12, 9, 6 & 4.5 numbers on the control panel?
The different sized magnification.
Where 12 is the normal size, you use the entire surface of the input phosphor
What are the sequence of events when you shift to a magnified mode?
- Less e- striking the OP
- Dimmer image from the OP
- Sensed by the ABC circuit
- Sends feedback signal to the x-ray tube
- Increases current to the x-ray tube filament
- Increases mA
- Increases # of x-rays produced
- Increases # of light photons produced at the IP
- Increases # of e- produced at the PC
- Increases the brightness of the image at the OP
- All result in an increase in Pt dose
What is the Mirror Optical System?
A system of Mirrors and Lenses in Image Monitoring
The Mirror Optical System magnifies the image from the OP onto a ________ glass.
Viewing (was really another mirror)
What were some disadvantages of the Mirror Optical System?
- Screen too small
- Only allowed one viewer at a time
- Increased pt. dose
- Significant amount of light loss from OP
- Can increase light from OP, but it requires increasing technique (resulting in increased Pt dose)
In the T.V Monitoring System, a T.V camera tube converts _____ ______ from the OP to an ________ signal and conveys it to the monitor
Light Image
Electrical
What are the (2) most commonly used T.V cameras?
Vidicon
Plumbicon
What were Advantages to the T.V Monitoring System?
- Brightness and Contrast adjust electronically (ABC)
- Several observers at one time
- Monitors can be placed outside the area for others to view
T.V monitoring allows for what?
Storage of the image on Discs or tapes for future playback
What is Vignetting?
- Decrease in the light intensity or brightness at the periphery (edge) of an image
- Unfocused
Magnification mode results in?
- Better spatial resolution
- Better contrast resolution
- Higher patient dose
What is a significant advantage of television monitoring?
Brightness levels and contrast can be controlled electronically
What does the television camera tube do?
Converts light signal from the OP to an electric signal
