1 – Intro Flashcards

1
Q

What are some different medical imaging modalities?

A
  1. Radiography
  2. Fluoroscopy
  3. Sonography
  4. Cross-section imaging (CT, MRI)
  5. Nuclear medicine (scintigraphy, PET/CT)
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2
Q

What are x-rays?

A
  • Electromagnetic radiation
  • Different frequency and wavelength of waves OR energy level of the photos
  • *high energy UV light, X-ray, gamma-ray and many other subatomic particles are IONIZING RADIATIONS=can be detach electrons from atoms, rendering them unstable
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3
Q

X-ray machine

A
  • Cathode (negative charge) and an anode (positive charge, rotates as it works and rotates the heat) in a vacuum glass tube contained in an oil-containing (contain heat) lead casing
  • Electric current passed through the tungsten (very high melting point) filaments of the cathode, heating it up, and enables electrons to be released from filaments
  • Electrons attracted towards anode and hit tungsten target with a max energy determined by tube potential
  • X-ray photon (1%) and heat (99%) produced
    o Photons released in beam out of the window
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4
Q

What does the collimator control? (x-ray)

A
  • the size of X-ray beam and field of view
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5
Q

*X-ray smaller field of view leads to

A
  • Better image resolution
  • Less scatter radiation
  • *why you don’t just do the whole animal
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6
Q

Machine settings (x-ray)

A
  • mA: regulates electric current pathing through cathode filament
    o mAs: controls number of electrons released=X-ray photons produced
  • kVp (kilovoltage peak): regulates the voltage potential b/w cathode and anode (speed of electron bombardment=energy of the X-rays)
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7
Q

X-ray interaction with matter and image formation

A
  • depends on X-ray beam energy, tissue density and atomic number
  • can be transmitted, absorbed or scattered
  • Ex. higher density=attenuates more of beam=less reaches the plate=radiopaque
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8
Q

*radiopaque (white areas)

A
  • regions with complete absorption/attenuation
  • NO X-ray reaches the detector
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9
Q

*radiolucent (dark areas)

A
  • regions w/o absorption/attenuation
  • ALL X-rays reach the detector
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10
Q

Image storage and viewing (x-ray)

A
  • DICOM format (digital imaging and communications in medicine)
    o Can be manipulated (ex. brightness)
    o Patient info and time, etc.
    o Part of legal record
  • Can view on DICOM file-viewing software
  • PACS (picture archiving and communication system) is a large server for storage, organization, retrieving and sending studies
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11
Q

What are the 2 important factors of the X-ray work station?

A
  • Lightning: needs to be ambient
  • Monitor quality
    o Consumer grade LCD screens commonly used
    o Need minimal brightness of 350cd/m^2
    o Large monitors preferred
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12
Q

What is fluoroscopy?

A
  • Series of low dose X-rays which allows us to capture MOTION in real time (X-ray movie)
  • Provides info about structural function of organs
  • Many set ups, C-arms units most used in vet hospitals
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13
Q

What are some common indications for fluoroscopy?

A
  • Swallow study: dysphagia and regurgitation
  • Dynamic airway study: suspected airway collapse
  • Intra-operative orthopedic procedure
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14
Q

Ultrasound

A
  • Widely available
  • Relatively inexpensive
  • Portable
  • Non-invasive
  • No ionizing radiation
  • Real time imaging
  • Can be used to aid lesion sampling
  • BUT diagnostic value is highly operator-dependent
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15
Q

What are the basic ultrasound physics?

A
  • Like ordinary sound, but at a much higher frequency (ex. bats and dolphins)
  • Images produced by pulse-echo technique employed by transducers (probes)
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16
Q

What is the pulse-echo technique? (US)

A
  • Transducer generates pulse of US and send it to patient
  • Interacts with different tissues in different ways (reflection, refraction, transmission, attenuation)
  • Echoes are generated by tissues and returned to transducer where signal is detected and sent to computer
  • Timing and strength of returning echoes are important for image creation
17
Q

US echogenicity

A
  • Hyperechoic: lighter/white
  • Hypoechoic: darker
  • Anechoic=completely black (no echo=fluids)
  • Isoechoic: same echogenicity as the adjacent structures
18
Q

*US transducers

A
  • Lower frequency (5-8MHz)=better depth penetration, but reduced resolution
  • Higher frequency (15-18)=less depth penetration, but better resolution
  • Most are multifrequency probes
  • Curvilinear linear (not as crisp) or linear (crisp images)
19
Q

US machine knobs

A
  • Appropriate use is imperative in obtaining a diagnostic scan
  • *settings will need to be adjusted throughout the exam
20
Q

Gain control (US)

A
  • Controls overall brightness of image
21
Q

Time gain compensation (TCG) (US)

A
  • Control of gain at different depths
  • Helps to make a more uniform image
  • Automatically adjusted on higher end machines
22
Q

Depth and focus control (US)

A
  • Depth controls the field of view size (zoom)
    o Want it to be 2/3 of screen (ex. bladder)
  • Focus allows the image to be the clearest at the indicated level
23
Q

Patient preparation (US)

A
  • Prefer fast patients (gas and ingesta can attenuate US and obstruct view)
  • Sedat most patient at WCVM
    o Better image quality
    o Less scan time
    o Less stress on patient
    o Less strain on operator
  • Usually scan in dorsal recumbency
  • Wide clip field
24
Q

US-guided FNA

A
  • Selected acoustic window should be prepared aseptically
  • Generally use 22G, 1.5 inch needles
25
Q

What are the principles of cross-sectional imaging?

A
  • Computed tomography and magnetic resonance imaging
  • Advantages over radiographs
    o Tomographic nature: eliminates superimposition and reformatting abilities
    o Increased contrast resolution: easier to ID subtle variation in tissues
26
Q

Contrast agents for CT and MRI

A
  • Given IV
  • CT: iodine based
  • MRI: gadolinium based
  • *both have potential adverse effects
  • Make sure patient has adequate renal and liver function and is well-hydrated before contrast
27
Q

*CT: pros and cons

A
  • Great for osseous structures (can make 3D reconstruction)
  • Emits radiation (same as X-ray)
  • Can be done under sedation mostly
  • Scan time <1min
  • $$ ($800)
  • Artifacts from metallic devices: can be decreased with computer algorithms
28
Q

*MRI pros and cons

A
  • Excels in soft tissues (neural, MSK)
  • No ionizing radiation: use radiofrequency rather than EMR)
  • Requires general anesthesia
  • Scan time: 30+ min
  • $$$ ($2000)
  • Artifact from metallic devices, can’t be avoided unless remove device
  • Potential risks with metallic devices (migration, heat)
29
Q

Nuclear imaging

A
  • Administer substances that bind to a target molecule to IMAGE and MEASURE metabolic functions of organs to diagnose diseases
  • Want one with a shorter half life as the patient will be radioactive
30
Q

What do radiopharmaceuticals consist of? (nuclear imaging)

A
  • Radioactive isotope that creates image
  • Pharmaceutical that targets organ or disease of interest
31
Q

Nuclear scintigraphy

A
  • Use gammag camera
  • Major limitation is low spatial resolution (no clear anatomical reference)
  • Many tests lest commonly done, but still do
    o Bone scan: equine
    o Thyroid scan: cats
32
Q

PET/CT

A
  • Another functional imaging modality
  • Observes metabolic activities in the body to aid in detection of diseases
  • Combine with CT=functional info AND anatomy
  • *main use=oncology imaging
    o But also infectious diseases, orthopedics, diseases of unknown origin)
  • most common is glucose analog (18F-FDG)
  • *WCVM has the only vet PET/CT in Canada