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Science and Technology 1 > Introduction To Fluoroscopy > Flashcards

Introduction To Fluoroscopy Flashcards

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1
Q

What was the origin of fluoroscopy?

A

Wilhelm Roentegen discovered them

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2
Q

What was early fluoroscopy like?

A

A phosphor was backed up by lead glass to view the images directly. The radiologist was in line with the x-ray beam, but was protected by the lead glass (to a certain extent). However, the image would be very dim because the procedure was done in a dark room, and the image had very poor contrast

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3
Q

What is fluoroscopy?

A

An imaging technique that puts a patient in between an x-ray source and a fluorescent screen in order to get real time images of the internal structures of a patient

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4
Q

How does fluoroscopy work?
(3)

A

An x-ray image intensifier captures the time varying image

The images are displayed via a remote display (image captured via CCTV or CCD)

Computerised image processing is used to enhance presentation

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5
Q

What does CCD stand for?

A

Charge
Coupled
Device

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6
Q

How is the image intensifier constructed?
(5)

A

It’s an evacuated electron-optical device

The glass or ceramic envelope is surrounded by metal housing

It’s constructed from non-magnetic materials, as it can distort how it operates and prevents stray light from getting into the system

The large field has a typical input diameter of 35-40cm

It’s constructed to be robust in order to withstand the internal vacuum

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7
Q

What are the 3 main components of the image intensifier?

A

The input screen

The electron-optics

The output screen

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8
Q

What does the input screen of the image intensifier include?
(3)

A

The input window

The input phosphor

The photocathode

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9
Q

What does the input screen of the image intensifier do?

A

It’s the part where the x-rays will hit

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10
Q

What does the electron-optics of the image intensifier do?

A

It’s the main part

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11
Q

What does the output screen of the image intensifier do?

A

It’s coupled to the display device

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12
Q

What are the features of the input window of the image intensifier?
(3)

A

It’s robust to support the vacuum

It’s not so thick, so that a significant amount of x-ray photons can be absorbed or scattered

Too many interactions increase image noise, reduces contrast and increases patient dose

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13
Q

Which part of the image intensifier do the first interactions occur?

A

Input phosphor

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14
Q

What does the input phosphor look like?
(5)

A

A layer of fluorescent material is laid down on a thin metal layer

Modern ones use sodium activated caesium iodide

It has needle like crystals, which reduce scatter and reduce the diffusion of light photons

The sodium activated caesium iodide layer is 200-400 micrometers thick

The average diameter of a crystal needle is short, to reduce the spread of light photons

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15
Q

What happens when the x-ray photons reach the input phosphor?

A

Approximately 2/3 of the light photons reach the photocathode layer

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16
Q

What does the photocathode layer do?

A

It converts the pattern of light photons emitted by the input phosphor into electrons

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17
Q

Where is the photocathode layer of the image intensifier?

A

On the inside surface of the sodium activated caesium iodide layer

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18
Q

What is the photocathode made of?

A

A layer of caesium antimonide, which is well matched to the blue light emitted by the input phosphor

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19
Q

What happens at the electron-optics of the image intensifier?
(4)

A

Photo-electrons are released from the surface of the photocathode

The released electrons are fired at a high positive voltage

The voltage is applied to a cylindrical anode that’s attached to the output

The curve of the input means that all electrons have the same path length to the output window, and it means that the input x-ray intensity is lower on the edges

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20
Q

What are the features of the electron-optics of the image intensifier?
(2)

A

It has metal rings that the electrons are tracked to, to ensure that the electrons travel across in straight lines- the voltage must be set up correctly for this, or we won’t get a recognisable image

It acts as an electronic lens

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21
Q

What are the features of the output phosphor/window in the image intensifier?
(4)

A

It has a very small diameter that’s smaller than the input- this allows us to focus the electrons on a smaller area, so the number of electrons per area is higher, which makes the signal better

It amplifies the image brightness

The brightness is controlled by the Automatic Brightness Control (ABC)

It has a thin layer of aluminium over the output screen to prevent a scatter of light back into the input screen and release more electrons from the photocathode

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22
Q

What is the image intensifier conversion process?
(4)

A
  1. Input phosphor- x ray to light
  2. Photocathode- light to electrons
  3. Electrodes- accelerate electrons
  4. Output phosphor- electrons to light
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23
Q

Why is it important for the output phosphor to convert electrons to light?

A

It allows for more light to be created without increasing the dose, so the images can be seen (refer to early fluoroscopy)

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24
Q

What are the 2 types of image displays?

A

TV system

CCD cameras

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25
What happens with the TV system as an image display? (2)
Original TV systems used a lens system to focus the output screen onto the CCTV camera The CCTV camera is a vacuum device with a scanning electron beam that produces a voltage on a signal plate, which produces the image
26
What happens with the CCD cameras as an image display?
The TV camera produces an analogue signal, which is then converted to a digital signal. It’s easier to produce the image in a digital format
27
What was an issue with the early systems of CCD cameras?
Early systems suffered from lag and caused a ghosting effect on the image
28
What is gain? (2)
The extent to which the image intensifier has intensified the light output from the system It’s the ratio os the brightness of the output phosphor to that of the input phosphor
29
What is minification gain?
Intensification from reducing the image size at the output
30
When do image intensifiers naturally degrade? What does that cause us to do?
When there’s no more significant gain To increase the radiation dose
31
What does magnification do in fluoroscopy? (4)
The voltages of the focussing electrodes changes This results in a more limited area of the input being projected onto the output screen The TV system used to view the images usually limits spatial resolution, so magnification improves spatial resolution However, magnification reduces minimisation gain, so brightness and overall gain falls
32
How does that ABC compensate for the magnification reducing minimisation gain?
By increasing the exposure factors at the expense of increased patient dose
33
What does automatic gain control do?
It automatically adjusts the sensitivity of the TV system to maintain image brightness. However, this may be at the expense of high noise or high dose
34
What does automatic brightness control (ABC) do? (2)
It maintains a constant low dose rate at the input window, and therefore, constant displayed image brightness It takes a measurement of the light intensity of the output, or signal from the camera,and feeds back the changes required to the x-ray generator to maintain adequate light intensity
35
Which region of the image is usually used by the ABC?
Only the central region
36
What’s the impact of the ABC?
It can increase the kV and/or mA
37
What is used on modern fluoroscopy systems?
Flat panels
38
What are the 2 types of conversions?
Indirect conversion Direct conversion flat panels
39
What is used for direct conversion?
Phosphor coupled to a TFT
40
What is used for direct conversion flat panels?
A TFT array
41
What are the advantages of flat panel fluoroscopy? (2)
High quality dynamic and static image capture No distortions like the image intensifier
42
What is the disadvantage of flat panel fluoroscopy?
Not able to do genuine magnification
43
What are the advantages of flat panel fluoroscopy over image intensifiers? (3)
Larger size Less bulky profile Lack of distortion
44
What are the disadvantages of flat panel fluoroscopy over image intensifiers? (2)
It doesn’t have as good signal to noise ratio It has a slower response and lag compared to CCD
45
What are the variable systems in fluoroscopy? (5)
Bi-plane system General purpose Interventional (vascular/cardiac) Mobile “Mini” mobile
46
Why are pulse x-ray beams used in fluoroscopy?
To reduce patient dose
47
What is the continuous mode when using a pulse x-ray beam?
It’s often 25-30 pulses, so it’s not detectable to the eye
48
When do we use low pulse rates?
When there’s little or very slow movement, e.g. fracture fixation
49
When do we use higher pulse rates?
When there’s fast movement in order to avoid blurring or lag, e.g. the heart
50
What are the ways to reduce the dose in fluoroscopy? (3)
More filtration Higher kV Less pulses per second (but this will cause a lower contrast image)
51
What are the ways to get a high dose in fluoroscopy? (3)
Less filtration Low kV More pulses per second (this causes a higher contrast image)
52
How do modern fluoroscopy sets use filtration?
They use filters to harden the x-ray beam to reduce skin dose. This means that for the same input dose to the detector, less dose is given to the patient. Therefore, there’s a reduction in patient dose, at the expense of image quality. And there’s a reduced contrast as there’s a higher kV
53
Why is the live fluoro image rarely used for diagnosis? (2)
It’s difficult to analyse live images It has a relatively poor image quality
54
What is fluorography?
When digital systems store the signal from the detector when recording images
55
What is the simplest way to record images?
Last image hold
56
What is last image hold?
When the last frame acquired is left on the monitor after the x-ray beam is switched off for review.
57
What are the main ways to record images? (2)
Last image hold Digital spot images
58
What are digital spot images?
Single shot radiographs taken with high mA to give a low noise image
59
What is the job of the Digital Subtraction Angiography (DSA) (3)
To produce images of contrast filled vessels in isolation from other tissues. The images of the same region are taken in rapid succession, before and after an injection of a contrast medium. The movement of the patient is avoided between imaging sequences
60
When using DSA, when is the non-contrast image taken?
Before the contrast medium has reached the target area
61
How many image frames are taken when using DSA? Why?
2 One to stabilise exposure factors, second is the mask
62
When is the contrast image taken when using DSA?
When the vessels have filled with the contrast medium
63
How does DSA work? (4)
The contrast and non-contrast images are taken The 2 images are then subtracted, pixel by pixel The resulting subtraction image is stored as a 3rd image Recording can continue to provide a series of subtracted images (all the images can be viewed in real time)
64
Why will there be some misalignments when using DSA?
Due to movement, particularly around the high contrast edges
65
How can we minimise misalignments when using DSA?
By pixel-shifting. HOWEVER, it only corrects translational motion (side to side movement)
66
What is the side effect of using DSA?
It creates noise
67
How can we reduce noise in the final image when using DSA?
By obtaining and storing a sequence of such images and summing them pixel by pixel
68
What is used as an additional imaging tool for interventional, vascular, neuro procedures?
CBCT/Rotational
69
What does CBCT/Rotational do?
It obtains radiograph frame images at different projection angles
70
Which planes does CBCT/Rotational fluoroscopy use? (3)
Axial Saggital Coronal
71
What’s an advantage of CBCT/Rotational fluoroscopy?
It improves clinical interpretation over 2D projection
72
What are the systems to monitor radiation in fluoroscopy? (2)
Dose Area Product (DAP) Reference Air KERMA
73
What can DAP be used for? (3)
Clinical audits Optimisation Skin dose trigger levels
74
What is reference air KERMA used for?
Measuring radiation doses to the skin
75
Which is better- patient close to x-ray tube or receptor?
Close to receptor and far from x-ray tube
76
How far must the x-ray source be from the patient’s skin?
More than 30cm
77
Which is better- x-ray tube under or over the couch?
X-ray tube under the couch and receptor above the couch
78
Why is it better for the x-ray tube to be under the couch?
Because it allows the scatter to occur away from the vital organs and towards the feet, legs, etc, rather than lungs, thyroid gland, etc
79
Where is the clinician positioned for lateral projections?
On the side of the receptor- NOT the x-ray tube

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