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SSY186_Diagnostic Imaging > L3 Projection Radiography > Flashcards

L3 Projection Radiography Flashcards

1
Q

Describe the basic setup for Projection Radiography

A
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2
Q

A general overview of Projection Radiography

A

A general overview of Projection Radiography

  1. The most commonly used method of medical imaging utilizing X-ray.
  2. Projection of a 3D-volume onto a 2D surface (3D -> 2D).
  3. Represents the transmitted X-ray beam through the patient, weighted by the integrated loss of beam energy due to scattering and absorption in the body.
  4. Also known as Conventional Radiography
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3
Q

Another name for Conventional Radiography

A

Projection Radiography

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4
Q

Name some advantages with Projection Radiography

A

Advantages with Projection Radiography

  1. Short exposure time (0.1second)
  2. Production of large area image (14 x 17 inch)
  3. Low cost
  4. Low radiation exposure
  5. Excellent contrast and spatial resolution
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5
Q

Name a limitation with Projection Radiography

A

Limitation with Projection Radiography

Lack of depth resolution- superimpositions of shadows from overlying and underlying tissues sometimes “hide” important lesions, which limits contrast.

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6
Q

What would you check with a Chest X-ray?

A

Chest X-ray

  1. Airways
  2. Breast shadows
  3. Bones, e.g. rib fractures
  4. Cardiac enlargement
  5. Diaphragm (evidence of free air)
  6. Extrathoracic tissues (thorax)
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7
Q

What has higher X-ray attenuation - bone or soft tissue?

A

Bon has higher X-ray attenuation than soft tissue.

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8
Q

What do you observe with an abdominal X-ray?

A

Abdominal X-ray

  1. Covers liver, spleen, stomach, intestines, pancreas, kidneys and bladder
  2. Bowel obstructions (intestinal obstruction), volvulus and malrotations
  3. Renal, urethral and bladder stones
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9
Q

Explain Angiography

A

Vascular Imaging (Angiography)

  1. Inject Iodine-based contrast agent to study the compromised blood flow
  2. Mainly brain and heart
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10
Q

Explain Mammography.

A

Mammography

  1. Each breast is compressed horizontally (stable, avoid motion artifacts)
  2. X-ray is then illuminated and image is taken on the film plate.
  3. Around 10% of False Alarm rate.
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11
Q

Explain the principle of generating X-rays in the X-ray Tube

A

X-ray Tube

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12
Q

What kind of X-rays does the X-ray Tube generates?

A

X-ray Tube

Generates both Characteristic and Bremsstrahlung X-ray

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13
Q

What is the Energy efficiency of the X-ray Tube and how is this dealt with to avoid melt down?

A

Energy efficiency of the X-ray Tube

  1. 1% of energy is transferred to x-ray
  2. 99% of energy is dissipated as heat during the bombardment
  3. As a result, the anode is set into rotation to avoid melting the anode target (rotates 3200 - 3600rpm).
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14
Q

What is the purpose of Beam Hardening?

A

Purpose of Beam Hardening

Beam hardening = increasing the beam’s ”effective energy”

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15
Q

Explain Beam Hardening

A

Filtering - Beam Hardening

  • Undesirable for low-energy photons to enter the body (almost entirely absorbed within the body – high dose, no contribution to the image)
  • Filter low energy photons by
    • Anode absorbs LE photons
    • X-tube glass/oil housing
    • Extra aluminium filter
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16
Q

Explain Beam Restriction

A

Beam Restriction

  • X-rays that exit from the tube form a cone that is ordinarily much larger than the desired body region to be imaged.
  • The exiting beam must be further restricted
    • To avoid exposing body parts of the patient that need not to be imaged
    • To help reducing the effect of Compton scatter
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17
Q

Explain Diaphragms and Collimator

A

Beam Restriction - Diaphragms and Collimator

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18
Q

Name some different Compensation Filters

A

Compensation Filters

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19
Q

Explain Scatter Reduction

A

Scatter Reduction

  • X-ray that are not absorbed by the body will arrive at the detector from the line segment originate from the x-ray source
  • If the photon is scattered, it will still reach the detector, which will reduce the contrast of the image.
  • Three methods
    • Grid
    • Air gaps
    • Scanning Slits (in front of patient)
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20
Q

Name three methods for Scatter Reduction

A

Three methods for Scatter Reduction

  • Grid
  • Air gaps
  • Scanning Slits (in front of patient)
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21
Q

Explain Film Screen Detector and how this is dealt with in modern X-ray units

A

Film Screen Detector

  • X-ray exposes on today’s radiographic film.
  • Only 1 to 2% of X-ray are stopped by the film.
  • Inefficient!
  • As a result, modern x-ray units always have intensifying screens on both sides of the radiographic film.
22
Q

Explain the function of Intensifying Screen

A

Intensifying Screen

  • Stop most of the x-ray, converts them into light and then exposes the film.
23
Q

Name examples of Film-Screen → Digital systems

A

Film-Screen → Digital systems

  • Computed Radiography Systems
  • CCD Based Digital Radiography Systems (DRS)
  • Thin-Film-Transistor-Based DRS
  • CMOS-based DRS
  • Wireless and Rechargeable DR Detectors
24
Q

Explain Contrast Agents

A

Contrast Agents

  • Contrast agents are chemical compounds that are introduced into the body in order to increase x-ray absorption (attenuation) within the anatomical regions
  • With the agents, X-ray contrast is enhanced (compared with neighboring regions without such agents)
25
Q

Give examples of Contrast Agents and application areas

A

Contrast Agents

  • Iodine
    • Blood Vessels
    • Heart Chambers
    • Tumours
    • Kidneys
    • Bladder
  • Barium
    • Stomach
    • Lung (together with air)
26
Q

What is EB (Contrast Agents)

A

EB (Contrast Agents)

EB = K-shell electron binding energy

27
Q

Give an overview of the geometry of Projection Radiography

A

Geometry of Projection Radiography

28
Q

What is the Basic Imaging Equation?

A

Basic Imaging Equation

Intensity at the detector

29
Q

Name some Geometric Effects

A

Geometric Effects

  • Inverse Square Law
  • Obliquity
  • Beam Divergence and Flat Detector
  • Path Length
  • Depth-dependent Magnification
30
Q

What is Inverse Square Law

A

Inverse Square Law

It states that the net flux of photons (i.e. photons per unit area) decreases as 1/r2 , where r is the distance from x-ray origin.

31
Q

Explain Inverse Square Law and what the consequence may be if this is not compensated for

A

Inverse Square Law

  • Intensity at arbitrary point r(x,y) on the detector plane is given as seen in the picture.
  • Without compensation, this effect could falsely be interpreted as object attenuation in a circular pattern around the detector origin.
32
Q

Explain Obliquity

A

Obliquity

Reduction in beam intensity due to obliquity

33
Q

Explain the geometrical depiction of Path Length

A

Geometrical Depiction of Path Length

34
Q

Explain Path Length

A

Path Length

  • Consider imaging a slab of material with constant linear attenuation and thickness L.
  • If not compensated, it will be interpreted as different attenuation within the object or different object thickness.
  • Ambiguous situation
  • Radiologist are trained to study radiographic locally
  • Not a desirable situation for computer-based image analysis.
35
Q

Explain Anode Heel Effect

A

Anode Heel Effect

  • Generation of x-rays within the anode is isotropic at the atomic level, but the geometry of the anode makes that the x-rays beam’s intensity is not uniform.
  • X-rays travelling in the directions having more anode material to go through will be attenuated -> non uniform beam intensity
  • This effect can outweight the effects of obliquity and inv. sq. law -> should be compensated by filters
36
Q

Explain Depth-dependent magnification and the consequences

A

Depth-dependent magnification

  • Consider the object with the height w.
  • Object’s height wz on the detector is given by:
    wz=w*d/z
  • The magnification M(z) is defined as:
    M(z)=d/z

Consequence:

  • Two objects within the body of the same size may appear to have different sizes on the radiograph.
  • Comparison of the radiograph of the same patient taken over months or years can only be made if the same radiographic conditions and patient position is used.
37
Q

Explain Imaging Equation with Geometric Effects

A

Imaging Equation with Geometric Effects

  • Instead of attenuation, consider the object tz(x,y) as a transmittivity rather than attenuation.
  • If the object is located at the detector plane, there is no magnification:
    Iz(x,y)=I0cos3(theta)td(x,y), where cos(theta)=d/sqrt(d2+x2+y2)
38
Q

Imaging Equation with Magnification

A

Imaging Equation with Magnification

39
Q

Imaging Equation with Geometric Effects - Overall Expression

A

Imaging Equation with Geometric Effects - Overall Expression

40
Q

Why can we can neglect x-ray refraction in medical imaging?

A

We can neglect x-ray refraction in medical imaging because:

41
Q

Explain local SNR at each detector (Noise)

A

Local SNR at each detector (Noise)

42
Q

Explain what happens if we consider the effect of Compton Scattering on SNR

A

Effect of Compton Scattering on SNR

43
Q

Explain two different scenarios of Noise

A

Noise

  • Low X-ray Energy (keV)
    • Contrast is high as the difference between the attenuation of different tissue increases as energy decreases
    • Less transparent to the body (absorbed, high dose)
    • As a result, Nb is low
  • High X-ray Energy
    • Low Contrast – attenuation to different tissue is similar
    • Nb is high
  • Extreme high or low energy results low SNR (Tradeoff)
44
Q

Explaing Quantum Efficiency

A

Quantum Efficiency

  • In order to be detected, an incident photon needs to interact with the detector.
  • However, not all the photons will interact with the detector.
  • Quantum Efficiency is the probability that a single photon incident upon the detector will be detected.
  • A basic property of the detector.
45
Q

Explain Detective Quantum Efficiency

A

Detective Quantum Efficiency

  • To better characterize detector performance, detective quantum efficient (DQE) considers the transformation of SNR from a detector’s input to its output.
46
Q

Explain Narrow Beam - Monoenergetic

A

Narrow Beam - Monoenergetic

  • Monoenergetic - All photons have the same energy level
  • Assume the slab is homogenous, the measured intensity at the detector becomes I=I0e-µ(delta)x
47
Q

Describe the Fundamental Attenuation Law

A

Fundamental Attenuation Law

48
Q

How is the Fundamental Attenuation Law altered for a narrow, monoenergetic beam if the slab is not homogenous?

A

Narrow Beam - Monoenergetic beam - Heterogen Slab

49
Q

Explain the Basic Measurement of a CT Scanner

A

Basic Measurement of a CT Scanner

  • The basic measurement of a CT scanner is a line integral of the linear attenuation coefficient
50
Q

Explain Hounsfield units (HU)

A

Hounsfield units (HU)

  • Linear attenuation coefficients are transformed into Hounsfield units (HU).
51
Q
A

SSY186_Diagnostic Imaging (3 decks)

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