"Rectification & Circuits
OH MY!"
OH MY!"
X-Ray tubes operate on _______ current
DIRECT CURRENT
This is flow of electrons from cathode (-) to anode (+)
On the electromagnetic spectrum, x-rays have short ______ and high ______.
On the electromagnetic spectrum, x-rays have short __wavelength____ and high __frequency____.
The Charge coupled device stores charges in _______.
CAPACITORS
The CCD:
•Semiconducting device
•Converts light from the output phosphor to electrical charge
•Stores charge using capacitors
•Each capacitor represents a pixel in the image
All three types of rating charts for x-ray equipment plot these 3 things on a graph.
1. mA
2. kVp
3. Time
What determines which filament is heated?
The selected FOCAL SPOT.
We choose the Effective FS on control panel Selecting the FS determines which filament is heated.
**Module 5, Review: Tube Construction slide #11**
Dental imaging equipment uses ______ to operate the x-ray tube.
Self- Rectification
Only half of the wave is rectified with self-rectification. This form of rectification is no longer used in diagnostic x-ray due the risks of heat damaging the filament
The _____ is where x-rays are actually produced.
The _ANODE (ASSEMBLY)____ is where x-rays are actually produced.
This component of the image intensifier permits photoemission.
Photocathode
On tube rating charts, mA curves that are____ the intersection point are SAFE to use.
ABOVE
It's all about relationships:
_______ wavelength = _______frequency = _______ energy = _______penetration
DECREASED wavelength = INCREASED frequency = INCREASED energy = INCREASED penetration
**Module 5 Review: Quantity, Quality, Distance, Filtration.. Slide #3**
Diodes have 2 types of crystals. One type of crystal has loosely bound electrons. What type of crystal is this?
N-Type
N-type materials have loosely bound electrons resulting in a negative charge which causes electrons can move (away) from this side
Which TWO interactions occur at the target?
1. Bremsstrahlung
2. Characteristic
Write the formula for Minification gain.
Minification Gain = INPUT screen Diameter^2 ______________________
OUTPUT screen Diameter^2
The formula for calculating HU is:
Heat Units = kVp x mA x time x generator factor
The ______ in our eyes have poor visual acuity.
The __RODS__ in our eyes have poor visual acuity.
Rod vision:
•Responds to light at low brightness levels and darkness
•Very poor visual acuity
•20-30 min. dark adaptation to attain adequate sensitivity
•Rod vision is SCOTOPIC vision
**Module 6: Fluoroscopy Slide #4**
Which circuit of the Main X-ray circuit converts alternating current to direct current?
Secondary or High Voltage Circuit or HIGH Tension Circuit
Purpose:
•Increases voltage to high kilovoltage
•creates the POTENTIAL DIFFERENCE or Electrical pressure
•Converts A.C. to D.C.
Components:
•High voltage transformer
•STEP UP TRANSFORMER
•Bridge rectifier
kVp determines the predominant interaction. What kVp range causes scatter to be the predominant interaction?
70-90 kVp
•kVp determines what is the predominant interaction
1) High energy (90 kVp) – Transmission
2) Moderate energy (70-90 kVp) – Scatter
3) Low energy (35-70 kVp) - Absorption
Which converter allows us to see the image on the monitor?
The DAC
•An ADC converts the analog signal into a digital signal so the computer can understand and use it
• DAC converts the digital signal back to analog so we can see it.
The Generator factor for a:
1) Single phase generator is:
2) 3 phase or high frequency generator is:
The Generator factor for a:
1) Single phase generator is: 1
2) 3 phase or high frequency generator is: 1.4
Direct Capture flat panel detectors in fluoroscopy are made of:
AMA of amorphous selenium (a-Se) Thin-Film Transistors (TFT)
**Module 7 Fluoroscopy Viewing Systems.. Slide #17
The filament operates at ______ voltage, which permits _________ to occur.
The filament operates at LOW voltage and current.
The step-down transformer is used to decrease line voltage to 6-12 volts with 3-5 AMPS.
This permits THERMIONIC EMISSION to occur.
If the original input of x-rays was 100% and TWO HVL layers were used, _____ of the original intensity remains.
25% or 1/4
One HVL layer would reduce the intensity by 50%. Adding a 2nd HVL would drop the intensity by another half or 1/4 (25%) of the original intensity
Name the 5 parts of the Image intensifier (not including the glass envelope)
1) Input phosphor
2) Photocathode
3) Electrostatic focusing lenses
4) Accelerating Anode
5) Output phosphor
The _____ would reach its HU limit before the______ would reach its HU maximum limit.
The _ANODE____ would reach its HU limit before the__HOUSING____ would reach its HU maximum limit.
#1. A 3 phase 6 pulse generator has a _____ percent voltage ripple.
#2. A 3 phase 12 pulse generator has a _______ percent voltage ripple
#1. A 3 phase 6 pulse generator has a 14 percent voltage ripple.
#2. A 3 phase 12 pulse generator has a 4 percent voltage ripple
**Module 4 Circuits lecture Slide #27**