Fluoro Review

Question 1

What mA ranges are produced by a fluoro tube?

Answer 1

0.5-5.0 mA

Question 2

Do fluoro tubes have a higher heat capacity than general radiography tubes?

Answer 2

Yes - FL = 500,000 HU vs. Gen Rad = 300,000

Question 3

What is the purpose of the image intensifier?

Answer 3

Receives remnant beam
Intensifies and converts the x-ray signal into a visible light image

Question 4

How is anode of an angiography FL unit different than a regular FL unit?

Answer 4

Larger diameter anode
Thicker anode (to tolerate high heat loads)
High power rating
C-arm is floor/ceiling mounted
Smaller focal spot (0.3mm)

Question 5

Which FL tube configuration results in greater dose to the operator?

Answer 5

Over-table tubes

Question 6

What part of the image intensifier converts x-rays into light?

Answer 6

Input phosphor

Question 7

What part of the image intensifier converts light into electrons?

Answer 7

Photocathode

Question 8

What part of the image intensifier focuses, converges, and directs the electrons towards the anode?

Answer 8

Electrostatic lenses

Question 9

What is the purpose of the anode in the image intensifier?

Answer 9

Positively charged to attract electrons towards the output phosphor

Question 10

What part of the image intensifier converts electrons to light? Where does the light signal go after that?

Answer 10

Output phosphor
Fiber optic bundle of the CCD (light is converted and stored as an electrical charge)

Question 11

What are some advantages of a flat-panel detector over image intensifiers?

Answer 11

More streamlined
Larger FOV
Multiple operational modes
Not affected by distortion
Mag mode doesn’t result in increased patient dose
Broader dynamic range
Better low contrast detectability

Question 12

What is the advantage of last image hold?

Answer 12

Dose reduction, as eliminates need for additional exposure (last image kept on screen even when not fluoroing)

Question 13

What is frame averaging?

Answer 13

Combining multiple frames to reduce noise (dose reduction because less mA required to minimize quantum mottle)

Question 14

In pulsed fluoroscopy, what is
a) interrogation time?
b) extinction time?

Answer 14

a) time required for tube to switch on and get to selected mA and kV
b) time required for x-ray tube to be switched off

Question 15

What are the advantages and disadvantages of pulsed FL?

Answer 15

Advantage - decreased dose
Disadvantages - increased QM, decreased image quality

Question 16

What are advantages and disadvantages of continuous FL?

Answer 16

Advantages - less QM, increased image quality
Disadvantages - increased patient dose; low mA but long time

Question 17

What type of DSA uses a mask image without contrast + image with contrast to subtract bone and tissues?

Answer 17

Temporal subtraction

Question 18

What type of DSA uses attenuation differences between tissues + contrast and different kV’s to create a subtracted image?

Answer 18

Dual Energy Subtraction

Question 19

What is road mapping?

Answer 19

Using DSA techniques to superimpose liver fluoro over previously subtracted image to help real-time catheter guidance through a blood vessel

Question 20

What DSA post-processing selects another mask image to help remove motion present after first mask image?

Answer 20

Remasking

Question 21

What DSA post-processing allows the user to move a mask image to correspond to patient movement/correct misregistration artifacts?

Answer 21

Pixel shifting

Question 22

What is a measurement of the total increase in image intensity achieved by an image intensifier?

Answer 22

Total brightness gain (= flux gain x minification gain)

Question 23

What is flux gain?

Answer 23

Ratio of the number of light photons at the output phosphor to number of x-ray photons at the input phosphor

Conversion efficiency of the output phosphor

Question 24

What describes the increase in intensity produced by an image intensifier due to the difference in diameters of the input and output phosphors?

Answer 24

Minification gain

Question 25

What can a technologist do to increase image brightness?

Answer 25

Increase technical factors

Question 26

What helps maintain the brightness of an image by adjusting mA, kV, or pulse width automatically?

Answer 26

ABC - automatic brightness control

Question 27

What appearance does lag have on a FL image?

Answer 27

Comet-tail

Question 28

How can geometric magnification be reduced? What other consequences does it have?

Answer 28

Decrease OID = decreased magnification This also decreases entrance skin dose to the patient (as SID will increase when OID is decreased)

Question 29

What occurs in the I.I. during electronic magnification?

Answer 29

Input screen diameter reduced Increased voltage to electrostatic lenses Electrons converge at a focal point closer to input screen Image is magnified + spatial resolution increased Increased dose to the patient to maintain image brightness

Question 30

What causes scatter in FL when using an I.I?

Answer 30

Scattered light and x-ray photons within the I.I. Veiling glare artifact = result

Question 31

How does spatial resolution in FL compare to general radiography?

Answer 31

Spatial resolution worse in FL (2-5 lp/mm) vs. general rad (10 lp/mm)

Question 32

What is the main element of a FL unit that controls spatial resolution?

Answer 32

Monitor resolution - large matrix and small pixels best

Question 33

What is pixel pitch? What happens when pixel pitch is large?

Answer 33

Pixel pitch = distance from center of a pixel to the center of adjacent pixel Large pixel pitch means there is lots of empty space between pixels = decreased pixel density = decreased spatial resolution

Question 34

Does increasing technical factors improve spatial resolution?

Answer 34

No - it actually decreases spatial resolution because of increased repulsion of electrons in the I.I. Increasing technical factors improves image brightness, but decreases spatial resolution

Question 35

What is vignetting?

Answer 35

Image is darker around the periphery and brighter in the center Distortion caused by greater exposure intensity at the center of an image compared to the periphery Occurs due tot he divergence of the beam + worse with large I.I's

Question 36

How can quantum mottle be decreased in FL?

Answer 36

Increase mA

Question 37

What part of the FL machine serves as the primary protective barrier?

Answer 37

Image receptor

Question 38

What lead equivalency must protective apparel have when using 150kV and over?

Answer 38

0.5 mm Pb/eq

Question 39

What is the largest contributor to occupational exposure in FL?

Answer 39

Scatter radiation

Question 40

Where should a technologist stand when using a FL machine to reduce their exposure?

Answer 40

Stand on image receptor size As far as possible

Question 41

What position/projection of the FL unit will produce the most dose?

Answer 41

Oblique

Question 42

What is the maximum exposure rate listed in SC35 for equipment equipped with ABC and high level irradiation?

Answer 42

150 mGy/min

Question 43

How can dose area product (DAP) be reduced?

Answer 43

Increase collimation

Question 44

After how much fluoro time will an audible alarm sound? Can it be reset to continue fluoroing?

Answer 44

5 min. Yes it can be reset

Question 45

What is the minimum source to skin distance (SSD) set by SC35 when using a) mobile equipment? b) stationary equipment?

Answer 45

a) 30 cm b) 38 cm

Question 46

What part of the mobile c-arm ensures that a minimum source to skin distance of 30 cm is maintained?

Answer 46

Collimator

Question 47

How large a hole can protective apparel have near the vicinity of the thyroid or reproductive organs according to SC35?

Answer 47

No larger than 5 mm

Question 48

What is the purpose of the low contrast QC test for FL?

Answer 48

Testing the ability to resolve objects that differ only slightly in attenuation from surrounding areas

Question 49

According to the inverse square law, how much dose will be decreased if we double our distance from the patient?

Answer 49

1/4 or 25%