Physics Applied to Radiology RADI R250 Fall 2003 CH 9
Description:
provide a specific current (mA) & voltage (kV) to the x-ray tube ... uses tube current (mA) to charge capacitor. time to charge capacitor = time of exposure ... – PowerPoint PPT presentation
operation selecting time varying resistance in rheostat to control time it takes to charge the capacitor activating exposure also begins storage of charge in the capacitor when a precise voltage is reached in capacitor, the switch opens terminates the exposure microprocessor computer chip technology shortest time 1 ms .001 s 1/1000 s rheostat switch 13 Functional Position 14 Timer Comparison
1Æ
mechanical shortest 1/4 s 250.0 ms
synchronous motor shortest 1/60 s 16.6 ms
impulse shortest 1/120 s 8.3 ms
3Æ
electronic shortest 1/1000 s 1.0 ms
15 Timer Circuit Types (3Æ)(cont.)
mAs timer
type of electronic timer
uses tube current (mA) to charge capacitor
time to charge capacitor time of exposure
on secondary side of HV transformer
16 Timer Circuit Types (3Æ)(cont.)
Automatic Exposure Control (AEC) timers
electronic timer
detects radiation that has passed through the patient
terminates exposure after set amount of radiation reaches sensing device
based on light emitted or ionization caused
17 Functional Position 18 Transformer Section
components
step-up transformer
mA meter
rectification circuit
step-down transformers
location
in box linked between control console x-ray tube
immersed in oil for insulation cooling
1. 2. 3. 4. 19 High Voltage Transformer
Fixed TR between 500 600
Primary Side (power from autotransformers secondary output)
PS-AT PP-HV
120V 10A 120V 10A
Secondary Side
V to kV
e.g. if TR 500 PP-HV 120 V 10 A
then VS-HV 500 x 120V 60 kV
and IS-HV 10A 500 .02 A
amplitude of V sine wave
see text Table 7.1, page 173
20 mA Meter
location
midpoint of secondary coil of HV transformer
face of meter may be on control console
grounded
safety
places 0V in center of coil
each wire out of HV transformer carries ½VT
operates only during an exposure
21 Rectification
purpose
convert HV AC to pulsed DC for x-ray tube
location
between HV secondary coil x-ray tube
types
full wave -- most common
half wave -- limited use
self -- rarely
22 Rectification
process of changing AC to pulsed DC
rectifier
device that allows I to flow in only one direction
PowerShow.com is a leading presentation sharing website. It has millions of presentations already uploaded and available with 1,000s more being uploaded by its users every day. Whatever your area of interest, here you’ll be able to find and view presentations you’ll love and possibly download. And, best of all, it is completely free and easy to use.
You might even have a presentation you’d like to share with others. If so, just upload it to PowerShow.com. We’ll convert it to an HTML5 slideshow that includes all the media types you’ve already added: audio, video, music, pictures, animations and transition effects. Then you can share it with your target audience as well as PowerShow.com’s millions of monthly visitors. And, again, it’s all free.
About the Developers
PowerShow.com is brought to you by CrystalGraphics, the award-winning developer and market-leading publisher of rich-media enhancement products for presentations. Our product offerings include millions of PowerPoint templates, diagrams, animated 3D characters and more.