Dynamic Imaging: Fluoroscopy Ch 10

Question 1

ADC

Answer 1

analog-to-digital converter

• Device that take the video (analog) signal and divides into a number of bits ( 1s and 0s) that the computer “understands.”
• number of bits into which the signal is divided determines the contrast resolution (number of shades of gray) of the system

**output of the ADC is then transferred to main memory and is manipulated so that a digital image in matrix form is stored

Question 2

ABC

Answer 2

automatic brightness control

automatically adjusts the kVp, mA (or both) to maintain overall appearance of the fluoroscopic image (contrast and density)

Tissue thickness

ABS = automatic brightness stabilizer

Question 3

brightness gain

Answer 3

A brighter image is the result of high-energy e- striking a small output phosphor = Image Intensification

an expression of the luminance at the output phosphor divided by the input exposure rate

Acceleration & focusing of the electron beam in an II

Example: 150 x-rays strike the input phosphor and 150,000 light photons exit the output phosphor…what is the brightness gain?

BG = 1,000

Question 4

camera tube

Answer 4

vacuum tube 6” in length that enclosed an electron gun and a photoconductive target assembly.

TV camera tube
Vidicon/Plumbicon
newer CCD

Question 5

CCD

Answer 5

charge-coupled device

• light sensitive semiconducting device that generates a electrical charge when stimulated with light and stores this charge in a CAPACITOR.

Question 6

continuous fluoroscopy

Answer 6

X-ray exposure continues without interruption while the exposure pedal/button is activated.

• 30 frames of fluoroscopy per second
• patient received a higher dose in continuous mode

Question 7

electrostatic focusing lenses

Answer 7

negatively charged plates found along the length of the image intensifier tube.

repel the e- stream and focus on the small output phosphor

Question 8

fluoroscopy

Answer 8

used to view the dynamic structures anatomy using x-rays.

Question 9

flux gain

Answer 9

accelerating e- increase the light intensities at the output phosphor

brightness gain = minification gain x flux gain

Question 10

image intensification

Answer 10

process in which the exit radiation from a patient interacts with the input phosphor for conversion to visible light – converted to e- by photocathode and e- are focused by lens – accelerated toward anode of the output phosphor and change to light to create a brighter image.

Question 11

input phosphor

Answer 11

Made of cesium iodide and bonded to curved surface of the tube

• cesium iodide absorbs exit radiation and emits light in response

Question 12

magnification mode

Answer 12

Improves spatial resolution

-increases patient dose

Question 13

photocathode

Answer 13

Made of cesium and antimony compounds, these metals emit e- in response to light
(process called photoemission).

Photocathode is bonded to input phosphor using a very thin adhesive layer

Layers are curved = so the light/e- all travel the same distance to the output phosphor

Question 14

output phosphor

Answer 14

coated with light-emitting crystals
- zine cadmium sulfide

light intensities from out phosphor are converted to an electrical video signal and sent to TV monitor to view.

Question 15

pulsed fluoroscopy

Answer 15

Fluoroscopy mode

• x-ray exposure is NOT continuous
• has gaps of NO exposure
• can choose 2 - 15 frames per second
• patient dose can be reduced

Question 16

spatial resolution

Answer 16

smallest structure that can be detected in an image
measured in lp/mm

• fluoroscopy has 4-6 lp/mm

Question 17

Digital Fluoroscopy

Answer 17

Early digital units employ CCD attached to II

Newer models have FPD instead of II & use mA similar to radiographic mode (100 - 1000 mA)

Indirect = cesium iodide amorphous silicon detector (current most common)

Direct = amorphous selenium direct capture detector

Capable of 60 frames per second

Question 18

Radiation Safety in Fluoroscopy

Table 10-1
Methods to Reducing Patient and Personnel Dose During Fluoroscopy

Answer 18

Key points:

• use lowest pulse mode/lower rate
• use last image hold
• keep fluoroscopy time to a minimum
• increase collimation
• remove grid
• minimize use of magnification mode
• document fluoroscopy time
• ABC units table exposure should not exceed 10R/min (5/R w/o ABC)
• SSD 15 “ for stationary fluoroscopy
• SSD 12” on mobile C-arm units
• Time - Distance - Shielding
• Bucky slot cover 0.25 mm of lead-eqiv
• Lead drape (curtain) 0.25 mm lead

Question 19

Radiation Safety in Fluoroscopy

Table 10-1
Methods to Reducing Patient and Personnel Dose During Fluoroscopy

Answer 19

Key points:

• use lowest pulse mode/lower rate
• use last image hold
• keep fluoroscopy time to a minimum
• increase collimation
• remove grid
• minimize use of magnification mode
• document fluoroscopy time
• ABC units table exposure should not exceed 10R/min (5/R w/o ABC)
• SSD 15 “ for stationary fluoroscopy
• SSD 12” on mobile C-arm units
• Time - Distance - Shielding
• Bucky slot cover 0.25 mm of lead-equid
• Lead drape (curtain) 0.25 mm lead
• Personnel aprons 0.5 mm lead equivalent (when kVp is 100 or higher)

Question 20

Conversion Factor

Answer 20

an expression of the luminance at the output phosphor divided by the input exposure rate, and its unit of measure is the candela per square meter per milliroentgen per second (cd/m2/mR/s)

Newer term used to express brightness
CF is approximately 1% of the brightness gain

Question 21

Magnification Mode

Answer 21

Trifocus Image Intensifiers 30/23/15

When operated in magnification mode, the voltage to the electrostatic focusing lenses is increased. This increase tightens the diameter of the electron stream, and the focal point is shifted farther from the output phosphor

Beam collimation is adjusted = more radiation dose to the patient due to the smaller collimated field

Increased spatial resolution - ability to visualize smaller structures

Example: MF = 30/15 = 2 x mag