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Diagnostics > MRI, CT, Ultrasound and X-ray > Flashcards

MRI, CT, Ultrasound and X-ray Flashcards

1
Q

What element in the body does MRI use?

A

Hydrogen

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2
Q

What combination is needed for MRI?

A

Magnetic field, radiography waves & a computer

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3
Q

What precautions need to be taken when using MRI?

A
  • Patients with metal implants
  • Operators with pace makers, implants or are pregnant
  • Credit/debit cards will be wiped if taken into the scanner field
  • Ear protection for high field unit use as very noisy
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4
Q

Compare high field and low field in MRI

A

High Field:

  • > 1 Tesla
  • Uses liquid helium to enable superconducting
  • Very sensitive (even to breathing)
  • More expensive
  • Artefacts increased around metal objects

Low Field:

  • 0.27 Tesla
  • Temperature controlled by environment
  • Less sensitive than high field but tolerates more
  • Cheaper to install & maintain
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5
Q

What mechanism interrupts the magnetic field during MRI?

A

Radiofrequency waves

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6
Q

What is a ferrous metal?

A

Metal that can cause interruption of magnets in MRI

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7
Q

What is the purpose of the Gauss line?

A

Boundary to prevent interruption of magnetic field

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8
Q

What is the purpose of the kV and mAs in X-ray?

A

kV (killovoltage) controls penetrating power of quality of x-ray beam
mAs (millamperage seconds) controls quantity of x-ray photons that emerge from primary beam, known as the intesity

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9
Q

Explain how an X-ray machine produces photons and radiation

A
  1. Electric passes from mains but is too strong so must be stepped down by filament transformer before entering CATHODE
  2. Electrical current passes through cathode and heats up, releasing a cloud of electrons known as thermionic emission
  3. To travel across the anode there must be high electrical potential difference between the cathode (-ve) and anode (+ve)
    - Process takes up more electricity than mains voltage can supply and must be stepped up by high tension transformer (measured in kV)
  4. Cloud of electrons (-ve) is repelled by cathode and attracted to anode
  5. Electrons hit target anode at speed and produce X-ray photons via release of their energy
  6. X-ray photons form primary beam and exit tube head via tube window
  7. Heat is a by-product of the process so both the cathode and anode are made from Tungsten Alloy. 99% of energy released from electrons when they hit the target is lost as heat
  8. Excess heat is absorbed by a copper block by conductions and travels via copper stem to be cooled in oil bath
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10
Q

When and why may CT be used over MRI?

A
  • Faster than MRI
  • Cheaper
  • General detail of an area including bone structures and soft tissue
  • Patients with metal implants
  • Review of tumour development
  • Patient size
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11
Q

What are the properties of CT scanning?

A
  • Utilises same basic principles of X-rays
  • Can be used to create 2D or 3D images
  • Cross section images of the body structure calculated
  • 360 rotating beam of X-ray directly opposite a moving detector that collects information
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12
Q

How does a CT scanner function?

A
  • Thin beam of X-ray is streamed through the cross-section of the tube while rotated around the circumference of inner gantry
  • Patients anatomy of interest is passed through the gantry slowly while detail is gained
  • Detector opposite radiation source obtains this information
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13
Q

What are the 2 common types of methods of CT scanning and their properties?

A
  1. Regular CT scanning
    - Allows operator to search for tumours, nodules and lesions that they do not know the location of
    - Use volume averages to detail tissue composition into each slice
  2. High resolution CT scanning
    - Much better quality of image
    - Images produced are representations of the exact location the slice originated from
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14
Q

What are the diagnostic applications of CT scanning?

A
  • Relatively quick process creating quality images
  • Although uses radiography, detailed images of bone, soft tissue and organs may be gained
  • Moderate movement artefacts are tolerated
  • Can be used in conjunction with contrasts to accentuate structures
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15
Q

What areas is CT scanning preferable?

A
  • Musculoskeletal injuries
  • Internal bleeding and RTA patients
  • Bone remodelling and arthritis
  • Foreign bodies
  • Unknown mass dimensions
  • CT guided biopsies
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16
Q

How does a CT scanner unit need to be managed?

A
  • CT produces large amounts of heat, so ambient temperatures should be consistently controlled
  • Unit room should be encased by lead lined walls
  • Before use machine should be warmed up gradually
  • Annually serviced
  • RPA needs to be informed of new instalment and planning permission required
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17
Q

Explain how an ultrasound is produced

A

Uses a combination of electrical signals and oscillating Piezoelectric crystals to create real-time images of internal structures

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18
Q

Explain the following meanings:

  1. Echogenic
  2. Anechoic
  3. Hypoechoic
  4. Hyperechoic
A
  1. Amount of sound waves and density of structure
  2. ‘No echo’ - darkness/no image produced/found
  3. Limited echo (darker)
  4. Increased echo (brighter)
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19
Q

Explain how different frequencies effect the images produced with ultrasounds

A

Higher frequency = shallow waves BUT high resolution

Lower frequency = Deeper waves BUT lower resolution (used in the abdomen and to navigate around)

20
Q

What are some applications for MRI?

A
  • Produces cross-sectional images in 3 planes
  • Soft tissue information greater than CT
  • Orthopaedics (including articular cartilage, joint fluid, etc)
  • Brain and spinal cord conditions
  • Used in conjunction with contrast media
21
Q

What are the clinical applications of MRI?

A
  • Predominately soft tissue
  • Inflammatory process in bones
  • Sensitive to bone density changes and remodelling
  • Pre-fractural planes
  • Single lobe damage to tendon and ligament tissue
22
Q

What is the use of the gradient coil in MRI?

A

To focus the magnetic field down to one point, similar to focusing cup on X-ray machines

23
Q

What is T1 and T2 relaxation in MRI?

A

T1 = measures how long to get back to alignment with magnet (happens last)

T2 = measures how long takes to stop spinning to just precess and stop going around magnet (happens first)

24
Q

What do T1W and T2W measure?

A 
T1W = fat
T2W = water
25
Q

What are the 3 main rules of radiation protection?

A
  1. Radiation should only be done with clinical justification
  2. Time, distance, shielding (minimal exposure)
  3. No dose limit should be exceeded
26
Q

Identify 4 types of radiation

A
  1. Alpha
  2. Beta
  3. Gamma
  4. X-ray
27
Q

How may the smell of a urine sample indicate a result?

A
  • Strong smell = concentrated, therefore dehydrated
  • Ammonia/stale smell = Stale sample or bacteria
  • Sweet smell (pear drops) = Presence of ketone bodies in urine, diabetes mellitus
28
Q

What 3 things may happen to X-ray photons when directed at matter?

A
  1. Photons pass through patient, shown on cassette black
  2. Absorbed into bone, shown as white
  3. Bounced off into the environment as scatter
29
Q

How will Gas show up on an X-ray?

A

Black

30
Q

How will Fat show up on an X-ray?

A

Dark grey

31
Q

How will soft tissue and fluid show up on an X-ray?

A

Light grey

32
Q

How will bone show up on an X-ray?

A

Almost white

33
Q

How will metal show up on an X-ray?

A

Bright white

34
Q

How can radiation exposure effect the body?

A
  • It can interrupt the normal respiration of cells and disturb chemical bond
  • High radiation exposure can destroy the nucleus of the cell
  • Can cause radiation poisoning (cumulative effect of damage on human body post large amount of radiation exposure)
35
Q

Identify what must be recorded with each X-ray (6 marks)

A
  1. Patient ID/Name
  2. Date
  3. Exposure factors
  4. Position
  5. Restraint of animal (if required)
  6. Quality of image
36
Q

Define carcinogenic radiation damage

A

Indication of cancer in tissues that have been exposed to radiation

37
Q

Define genetic radiation damage

A

Specific mutations within the ovaries and testes if radiated

38
Q

Identify how to minimise radiation risk

A
  • Wear PPE
  • Monitor dosing
  • Stay away from primary beam
  • Only use when necessary
  • Refine exposure settings
  • Collimate
  • Regular maintenance of equipment
39
Q

What are some considerations to be made when X-raying exotics?

A
  • Low stress
  • Minimal restraint
  • Try to keep still
  • Consider images needed
  • If gassing down think of own safety
  • Bone density in birds much lower so need lower settings
40
Q

What are 4 dangerous properties of radiation?

A
  1. Latent effect
  2. Cumulative
  3. Invisible
  4. Painless
41
Q

How is an MRI produced?

A
  1. Magnetic field is applied to the structure of interest
  2. Spinning protons rotate to align with the magnet
  3. Series of radio-frequency waves are applied
  4. This forces the proton AWAY from the magnet to 90-180 degrees
  5. Transmission of radio-frequency waves ceased, the protons return to their original position with the magnet
  6. The movement and energy this causes is detected by sensors (radio-frequency coil) within system
  7. These signals are then converted from analogue to digital images
42
Q

What considerations need to be made and why when X-raying neonates?

A
  1. Bone density:
    - Have open growth plates
    - Less bone density so settings need to be reduced
  2. Restraint:
    - DON’T use ties (except foals)
    - Careful with restraint
  3. Developmental stage:
    - Altered interpretation
    - If GA be mindful of hypothermia
  4. Species
43
Q

Identify the 3 types of radiation damage

A
  1. Somatic
  2. Carcinogenic
  3. Genetic
44
Q

How can somatic effects be broken down (with examples)

A
  1. Acute effects:
    - ARS (Acute Radiation Syndrome)
    - Sterility
    - Skin erythema
  2. Late effects:
    - Cancer
    - Cataract
    - Leukaemia
45
Q

What are some clinical signs of somatic radiation effects?

A
  • Fatigue
  • Vomiting / diarrhoea
  • Severe skin burn
46
Q

Explain the production of an ultrasound when used on a patient

A
  1. Electrical current from socket output transferred into the transducer of the ultrasound machine
  2. Piezoelectric crystals become electrically charged
  3. The piezoelectric crystals oscillate in the probe head, creating ultrasonic sound waves
  4. Via a contact medium, these sound waves are emitted into the tissues
  5. Some waves will lose energy or continue through the body, some waves will hit dense structures and be reflected
  6. Positioning and echogenicity will dictate the degree of reflection of sound waves back to the probe head
  7. The transducer calculates the time passed since a pulse was transmitted and received then converts this into electrical signals
  8. The computer interprets electrical signals to produce a real-time image on the monitor

Diagnostics (3 decks)

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