1 – Intro Flashcards
1
Q
What are some different medical imaging modalities?
A
- Radiography
- Fluoroscopy
- Sonography
- Cross-section imaging (CT, MRI)
- Nuclear medicine (scintigraphy, PET/CT)
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
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
4
Q
What does the collimator control? (x-ray)
A
- the size of X-ray beam and field of view
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
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)
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
8
Q
*radiopaque (white areas)
A
- regions with complete absorption/attenuation
- NO X-ray reaches the detector
9
Q
*radiolucent (dark areas)
A
- regions w/o absorption/attenuation
- ALL X-rays reach the detector
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
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
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
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
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
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)
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
What are the principles of cross-sectional imaging?
- 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
Contrast agents for CT and MRI
- 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
*CT: pros and cons
- Great for osseous structures (can make 3D reconstruction)
- Emits radiation (same as X-ray)
- Can be done under sedation mostly
- Scan time <1min
- $$ ($800)
- Artifacts from metallic devices: can be decreased with computer algorithms
28
*MRI pros and cons
- Excels in soft tissues (neural, MSK)
- No ionizing radiation: use radiofrequency rather than EMR)
- Requires general anesthesia
- Scan time: 30+ min
- $$$ ($2000)
- Artifact from metallic devices, can’t be avoided unless remove device
- Potential risks with metallic devices (migration, heat)
29
Nuclear imaging
- 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
What do radiopharmaceuticals consist of? (nuclear imaging)
- Radioactive isotope that creates image
- Pharmaceutical that targets organ or disease of interest
31
Nuclear scintigraphy
- 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
PET/CT
- 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
