Topic 5: fluoroscopy + Tomography Flashcards
1
Q
Fluoroscopy: How it works
A
2
Q
Fluoroscopy: Tubes
A
- Higher heat capacity than radiography only tubes (500,000 HU compared to 300,000 HU)
- Must be able capable of producing continuous and pulsed radiation
- Sometimes use specialized tubes such as MRC (maximum rotation ceramic) and grid controlled for pulsed radiation
- Must perform to the same standards as radiographic units (HVL, focal spot size, heat monitors)
3
Q
Fluoroscopy: Generators
A
- High frequency or 3 phase
- High output units - up to 100 KW rating
- Capable of producing continuous and pulsed radiation
- Must perform to the same standard as radiographic units (overload protection, kV accuracy, reproducibility, linearity, output waveform, AEC for spot imaging devices, grid alignment, etc.)
4
Q
Pulsed Exposures
A
5
Q
Fluoroscopic IRs
A
Image Intensifier
- older type
- cylindrical tube
- focused electrons
- x-rays in and light out
- Distortion artifacts caused by focusing electrons
- lower cost
- not really available for purchase new
Flat-panel detector (FPD)
- newer
- similar to DR detector
- x-rays in and electrons out
- lightweight, easier to move
- excellent image quality
- higher cost
6
Q
Fluoroscopy with II
A
- •Older technology but still widely used and available for purchase (used)
7
Q
Image intensifier: How it works?
A
8
Q
Image Intensifier: components
A
9
Q
Typically II Sizes
A
SFOV (in/cm)
- 4 (10)*
- 5 (13)*
- 6 (15)*
- 9 (23)
* Mini c-arms
LFOV (in/cm)
- 12 (30)
- 14 (36)
- 16 (40)
- 22 (56)
10
Q
Multifield Image Intensifiers
A
- Mag mode
- Operate by changing voltages on electrostatic lenses
- Tri-focus are most common
- Examples: 9/6, 23/15/10
- Numbers refer to the input phosphor diameters
- tri focus: normal (23) and 2 mag modes
11
Q
Mag Mode
A
•Most units have 1 or 2 Mag modes
•Minification gain is decreased when in Mag mode
12
Q
Normal vs Mag Mode
A
13
Q
Advantages of Mag Mode
A
- Only the central portion of input phosphor is used resulting in increased spatial resolution
- Patient radiation dose is higher as more x-rays per unit area are required resulting in less noise and increased contrast resolution
14
Q
Disadvantages of Mag Mode
A
-
Higher doses to compensate for decreased
minification gain - Dose is increased approximately equal to the ratios of the diameters of the input phosphor squared
e. x. 232/132 = 3.1 times higher
15
Q
TV camera (CCD)
A
- Changes light into electronic signal
- Electrons are released proportional to the intensity of the incident light – called video signal
- Charge-Coupled Device (CCD) – same technology used in some DR devices
- Video signal emitted in a raster scanning pattern
16
Q
A-D converter
A
18
Q
Interlaced scanning
A
- each frame divided into two fields
- used to eliminate flicker
- 2-2.5lp/mm
