Advanced Imaging Flashcards
What advanced imaging modalities are there?
MRI
CT
Nuclear Scintigraphy
Fluroscopy
What do we base Imaging choice on?
- Animal -> type of dx, ease of exam, clinical condition, exotics
- Owner Based-> Emotions, expectations, finances
describe MRI
- Nuclei +/ve charge 1H & 31P spin aroudn axis
- External magnet aligns nucleus in parallel or perpendicular to magnetic field
- 2nd radiofrequency magnetic field applied in short microsecond pulses alters spin
- Energy absorbed induces a voltage
MRI how it works pt2?
Emitted voltages detected using coils and allows
for creation of images
Requires supercooled magnets, always on
0.5-1.5 Tesla
Liquid helium to cool down
What is a T1?
time taken to return to 63% equilibrium following RF pulse
Long vs short T1?
Long T1 - dark - water & CSF
Short T1 - bright
Advantages of MRI?
Does not involve ionising radiation or radioactivity
Frequencies in normal radio frequency range so no adverse
health effects
Detailed images of soft tissues e.g. muscle, brain, tendons,
ligaments, joints
Contrast agents less likely to produce allergic reaction cp
iodine based substance
Disadvantages of MRI?
Expensive (2500-3000 inc anaesthesia)
Cannot distinguish benign from malignant often
Slow……….
Risks of magnetic implants
Requires anaesthesia
Cannot easily image lungs (moving) so poor for metastatic
screening test
What is a CT?
Essentially an x-ray procedure
A narrow x-ray beam passes through the patient
Picked up by a series of detectors
Signals from the detector pass to the computer
Images are generated
How is CT different from radiography,
The x-ray tube continuously revolves 360 degrees round
the patient.
The patient bed moves either continuously through the
bore of the CT tube (helical scan) or in a series of small
increments (axial scan)
Controlled by computer
Images are viewed at the time and remotely on other
workstations
What size nodules does CT detec t? Xray?
CT: 1-2mm
Xray: 4-5 mm
Describe the CT procedure?
- Start with a scout scan (helps us program where we want to take it
- DO pre-contrast scan
- Give IV contrast (iodine-based)
- May used programs which look at arterial and venous phases
Different windows we might do?
how broad we want tp look in tissue
Wide: wide range of attenuation in air or bone structures
Narrow: narrow range of attenuation in abdo, brain etc
Advantages of CT?
- Excellent low contrast resolution
- WW/WL
- Spinal CT
- Image manipulation
CT views?
Advantages of CT?
Speed
Reduced Anaesthetic Time
Cost
“Whole body” scanning
Angiography
Disadvantages of CT?
Radiation Dose
Need for GA/heavy sedation
Not as good as MRI for the brain & spinal cord
Still relatively expensive
Patient prep for CT?
– Starved for 8-12 hours in the main
– Recent pre GA bloods esp. urea, creatinine, liver
parameters etc
– Recent urea and creatinine are mandatory pre
contrast
What do we use for contrast in CT.
IV Contrast
– Omnipaque @2mls/kg bodyweight
Protocol for Contrast CT?
- GA - Preferred
- Large Bore Cannula – Pink Dogs, Blue Cats
- T-Connector
- 2mls/kg Bodyweight
- Survey Scan
- Hand Injection
- Scan Triggered 1-3 minutes Post Injection
Dual phase CT?
- Pressure Injector
- Survey Scan
- Dual Phase
– ROI
– Scan and View Position
– Trigger Scan and Injection
– Manual / Automatic Trigger for Scan
– Arterial Phase within 10 Seconds
– Venous Phase Triggered after 15-25 seconds (HR)
Indications for CT?
Trauma Patients
Thoracic
Skull
Orthopaedics
Tissues
Abdomen
Spine
Scintigraphy needs radioactive material license ?
yes
describe thyroid radionuclide scan?
Technetium 99m pertechnetate (99mTcO4-)
Pertechnetate imitates the halogens, similar to iodine
Is actively trapped and concentrated in thyroid gland, not
incorporated into thyroid hormone
Can image at 20 minutes
Short half-life 6.01hrs
Main use of doing thyroid scintigraphy?
Finding areas of hyperthyroidism like ectopic thyroid tissues etc.
describe bone scitingraphy
- Very sensitive, detects changes in bone metabolism
- skeletal disease, injury, arthropathy, osteomyelitis,
neoplasia
detects increases in bony remodelling that develops before
actual morphological changes are seen on radiographs
Timing of bone scintigraphy?
- Immediate - vascular phase
- 5-20 mins - soft tissue phase
- 2-3 hours - bone phase
- Acquired over 60s period using gamma camera and collimator
What is fluroscopy use for?
- Swallowing disorders (barium meal)
- Collapsing airways
- PSS
- Urinary dx
REAL TIME
