Fluoroscopy (Erin)

Question 1

The entrance surface dose should not exceed ??? mGy/min for any given field of view

Answer 1

100mGy/min

Question 2

An anti-isowatt curve for automatic brightness control causes the kV and mA to…

Answer 2

increase in proportion with one another to maintain image brightness

Question 3

What is the equation for brightness gain

Answer 3

Minification gain x flux gain

Question 4

What is the equation for minification gain

Answer 4

(D input / D output)2 (where D is diameter of input and output screen respectively)

Question 5

What is the typical number value for flux gain

Answer 5

50

Question 6

What is the typical value number for minification gain

Answer 6

100

Question 7

What is the input phosphor made of?

Answer 7

Sodium activated caesium iodide (CsI:Na)

Question 8

What is the X-ray absorption efficiency of the input phosphor (%)

Answer 8

70-90%

Question 9

What colour light photons does the input phosphor convert X-rays to?

Answer 9

Blue spectrum light photons

Question 10

What is the photocathode made of (material)?

Answer 10

Antimony caesium (SbCs3)

Question 11

What is the role of the photocathode?

Answer 11

Absorption of fluorescent light photons (from inout phosphor) and conversion to electrons

Question 12

Is the input screen maintained at a positive or negative voltage with respect to the anode (output screen)

Answer 12

Negative voltage

Question 13

What is the potential different (in kV) across the image intensifier

Answer 13

25kV

Question 14

What is the role of focusing electrodes in the image intensifier

Answer 14

Metal rings held within the tube that are held at positive voltages with respect to the photocathode. Contains the electrons in the tube to travel along paths that lead them directly to the output screen

Question 15

What is the output screen made from?

Answer 15

Silver activated zinc cadmium sulphide (ZnCdS:Ag)

Question 16

What is the typical diameter of the output screen?

Answer 16

25-35mm
Around 2.5cm

Question 17

Skin doses to patients may be reduced by… (3)

Answer 17

1. Increasing the patient to detector distance
2. Reduced Minification/magnification
3. Lower/less exposures
4. Smaller field of view

Question 18

What are the 3 layers of the input screen in an image intensifier and how do they work?

Answer 18

1. Input window (Aluminium)
2. Phosphor layer of caesium iodide that converts X-rays to light and channels them
3. Photocathode layer of antimony caesium to convert light into electrons

Question 19

In fluoroscopy at the output stage what happens

Answer 19

The output layer is Zinc cadmium sulphide silver and it converts electrons back into light

Question 20

Magnification improves image…? But because of this, minification gain …? And therefore dose must…?

Answer 20

Image quality
Decreases
Increase

Question 21

Fluoroscopy artefact: describe Veiling glare

Answer 21

Spreading of signal across the field of view where it shouldn’t be, due to scattering of light within the image intensifier

Question 22

DSA: what kind of subtraction is required from the pre contrast compared to post contrast image

Answer 22

Logarithmic subtraction

Question 23

DSA: the subtraction process has what effect on noise?

Answer 23

Increase image noise but perception of vessels is increased

Question 24

DSA: uses what kind of tube voltages?

Answer 24

Usually at least 70kVP to maximise attentuation in iodine based contrast

Question 25

What is the typical diameter of the input screen?

Answer 25

25cm

Question 26

Magnification equation involving distances?

Answer 26

Magnification = Focus-film distance / (Focus-film distance - Object-film distance)

Question 27

Increasing the focus-film distance will increase/reduce magnification?

Answer 27

Reduce

Question 28

Reducing the object to film distance will increase or reduce magnification?

Answer 28

Reduce

Question 29

What is the effect of a thicker input screen crystal on efficiency and spatial resolution?

Answer 29

Thicker crystal will be more efficient at converting X-rays to light photons however the spatial resolution is reduced with thicker crystals

Question 30

How thick are the input screen CSI crystals?

Answer 30

5 micrometers

Question 31

What is the k edge of caesium iodide doped with sodium in the input screen

Answer 31

33 and 36 keV

Question 32

What colour of light photons are produced at the output screen

Answer 32

Green (530nm wavelength)

Question 33

How is the image between the input screen and output screen changed (in terms of orientation)?

Answer 33

Inverted And Flipped left to right

Question 34

Digital fluoroscopy: what happens to light photons after leaving the output screen?

Answer 34

They enter a CCD which converts the light into electrons for readout and digital conversion

Question 35

Digital fluoroscopy: read out at the CCD happens at what frame rate?

Answer 35

About 30 fps

Question 36

What is the function of the aluminium backing at the output screen?

Answer 36

Acts as a anode Prevent light photons from leaking back into the image intensifier

Question 37

What is flux gain?

Answer 37

When a single electron has enough energy from acceleration to create many light photon in the output phosphor

Question 38

Dual energy subtraction images: how is this done?

Answer 38

Separate images taken with one being low kv and one being high kv

Question 39

What is the purpose of dual energy subtraction images?

Answer 39

To bring out bony detail usually. Can be used the other way round too for chest imaging (remove rib detail)

Question 40

ABC is achieved by using signal from what part of the image?

Answer 40

Centre

Question 41

What is the purpose of ABC?

Answer 41

To guide adjustment of kvP and mas to maintain image brightness with different body parts

Question 42

During angiographic procedure, to maintain brightness which parameter should be increased preferentially?

Answer 42

mAs Kv should be held at about 60 to take advantage of k edge of iodine

Question 43

A digital spot image is equivalent to how many seconds of continuous screening?

Answer 43

2 seconds

Question 44

A low dose high kv curve is useful for which group of imaging?

Answer 44

Paediatric imaging

Question 45

In a low dose high kv curve, the dose is preserved at the expense of…?

Answer 45

Image quality

Question 46

Spatial resolution in Fluoro is most limited by…

Answer 46

Light spread in output phosphor

Question 47

Spatial resolution in fluoroscopy is about…?

Answer 47

5 lp/mm

Question 48

Fluoroscopy usually uses a focal spot of size…?

Answer 48

0.6mm

Question 49

DSA: what image is subtracted from what?

Answer 49

The pre contrast mask image is subtracted from subsequent contrast runs

Question 50

What is pixel shifting?

Answer 50

A technique to reduce motion artefact in Fluoro

Question 51

The CCD array of a. Fluoroscopy unit has matrix size of…?

Answer 51

1024x1024 pixels

Question 52

Standard tube current in fluoroscopy is…?

Answer 52

2-6mA

Question 53

IN fluoroscopy, patient ESD usually increases with image intensifier field size. T/F?

Answer 53

False

Question 54

T/F- The entrance surface dose rate should ideally be less than 50mGy/min

Answer 54

True