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Karan - MBBS Year 1: Principles Week 1 > Principles of Imaging > Flashcards

Principles of Imaging Flashcards

1
Q

Define radiology

A
  • Medical specialty concerned with radiation, for the diagnosis and treatment of disease
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2
Q

What is the basis of radiology?

A

EM Spectrum
- UV and gamma rays are ionising raditon and can be a health hazard so only used when needed

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3
Q

What sections of the EM Spectrum are the modalities of radiology based on?

A

IONISING
- X-RAYS/FLUOROSCOPY AND CT - X-Rays
- Nuclear imaging - Gamma rays
NON-IONISING
- MRI - Magnetic fields and radio waves
- Ultrasound - Sound waves

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3
Q

What is the difference between a radiographer and radiologist?

A
  • RADIOGRAPHER - take pictures for scanning
  • RADIOLOGIST - interpret images taken by radiographers/interventional radiology
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4
Q

How are X-Rays produced? PART 1

A
  • X-Ray tube contains a cathode and anode
  • Low voltage supply heats up a filament at the cathode.
  • Filament emits electrons by thermionic emission.
  • Current is passed in-between cathode and anode.
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4
Q

How are X-Rays produced? PART 2

A
  • Electrons are accelerated towards anode.
  • When electrons collide with anode, decelerate
  • X-rays are produced, passed through human body, attenuated according to body part density and image produced on screen.
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5
Q

What are PA X-rays?

A
  • X-rays pass from posterior to anterior sided of body before forming image
  • EXAMPLE: Chest X-rays
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6
Q

How does density affect the X-ray image colour? PART 1

A
  • Bones are very dense so X-rays become completely attenuated as they pass through - image is white
  • Soft tissue has less density than bones so image is light gray
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7
Q

How does density affect the X-ray image colour? PART 2

A
  • Density of fat is even lower - more X-rays pass through - less are attenuated - appear dark grey
  • Air is the least dense - more X-rays pass through - appears black
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8
Q

Define fluoroscopy.

A
  • Radiological technique - gives ‘real time video’ image of X-rays on a TV screen
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9
Q

How do fluoroscopic units work and when can they be used?

A
  • X-Rays pass through human body
  • Connected to an image intensifier (caesium iodide screen) which is connected to a TV screen
  • Barium studies and angiographies
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10
Q

How do CT scanners work?

A
  • Patient placed on table in CT scanner gantry
  • Gantry rotates around moving patient table
  • Thin axial slices of image acquired
  • Images can be reformatted e.g VR and MIP rendered
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11
Q

How do MRI scanners work? PART 1

A
  • Patient placed in static magnetic field
  • Body hydrogen atoms aligned in long axis of direction of external magnetic field
  • Radio frequency pulses switched on
  • Produces EM field
  • Alters axis of alignment of protons
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12
Q

How do MRI scanners work? PART 2

A
  • Radio frequency pulses switched off
  • Protons realign with axis of eternal magnetic field
  • Protons emit radiofrequency signal
  • Position of signal detected and image formed
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13
Q

How does ultrasound imaging work?

A
  • Ultrasound scanner converts electrical energy to mechanical energy and then to ultrasound waves
  • Ultrasound waves penetrate body
  • Reflected back to transducer and reconverted to electrical energy
  • Image formed
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14
Q

Describe the phenomenon that ultrasound scanning is based on.

A

PIEZOELECTRIC PHENOMENON
- When piezoelectric crystal subjected to mechanical pressure, electrical voltage generated
- Crystal becomes electrically pulsed so vibrates and produces sound wave that propagates through tissue and reflects back to transducer.

15
Q

Define nuclear medicine with an example

A
  • Uses small amounts of radiotracer with an affinity for a particular body part
  • Tracer injected into bloodstream and emits gamma radiation
  • Patient scanned with gamma camera and emission pattern allows image to form
  • EXAMPLE: SPECT Scanning
15
Q

What is PET CT scanning?

A
  • PET scanning (a type of nuclear scanner) used in fusion with CT scanning
  • Commonly used in cancer imaging
16
Q

How does PET scanning work in cancer imaging?

A
  • Cyclotron produces radiotracer e.g FDG
  • Cancer grows at a faster rate than healthy tissue so absorbs FDG
  • Detected and depicted in image (colour coded to distinguish between normal and cancerous tissues)
17
Q

Describe SPECT scanning.

A
  • Soecial type of nuclear scanner - two gamma cameras
  • Can do cross section imaging and produce multiplanar and 3D images
  • Can be combined with CT and MRI scans
18
Q

Describe the physics behind PET scan image formation. PART 1

A
  • Patient injected with FDG which accumulates in cancer cells
  • Patient placed in PET scanner gantry
  • FDG decays and emits positron
19
Q

Describe the physics behind PET scan image formation. PART 2

A
  • Positron collides with electron. Positron-electron annihilation
  • Two equal gamma radiations move in opposite directions
  • PET scanner localises radiation and produces image

Karan - MBBS Year 1: Principles Week 1 (14 decks)

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