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AAA Companion Animal VMS4005 > Advanced Imaging for Small Animals > Flashcards

Advanced Imaging for Small Animals Flashcards

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1
Q

MRI

A
  • Nuclei (neutrons/protons) +/ve charge
  • 1H and 31P spin around axis
  • External magnet aligns nucleus in parallel or perpendicular to magnetic field - spin in sync, same speed + direction
  • Second radiofrequency magnetic field applied in short microsecond pulses alters spin -> in proton energy (resonance)
  • Energy absorbed (and released) induces a voltage
  • Emitted voltages detected using coils and allows for creation of images
  • Requires supercooled magnets, always on
  • 0.5 - 1.5 Tesla, size of magnet, 1.5 standard, smaller = hazier image
  • Liquid helium
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2
Q

T1-weighted images

A
  • T1 = time taken to return to 63% equilibirum following radiofrequency pulese
  • When switch pulse off -> releases energy - diff tissues emit diff energy
  • As protons drop from high to low energy they emit energy, picked up by coil = longitudinal/time one relaxation/T1
  • Longitudinal relaxation
  • High to low energy
  • Short repetition time (T1)
  • Bone = black, solid
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3
Q

T1 - water

A
  • Black - long T1, contains a lot of protons
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4
Q

T1 - fat

A
  • White, bright - short T1
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5
Q

T1 - brain

A
  • Grey
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6
Q

T1 - CSF

A
  • Dark, long T1 values
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7
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A
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8
Q

T2-weighted images

A
  • Transverse relaxation
  • Time to spin out of sync
  • Long TE (time echo)
  • Water = long T2 (white)
  • Fat = shorter T2 (light grey)
  • i.e. CSF/fluid is white and brain
    is shades of grey
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9
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A
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10
Q

MRI - adv

A
  • 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
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11
Q

MRI - disadv

A
  • 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 - poor at looking at air, lungs move + MRI slower
  • Magnet is always on - must avoid anything that might interfere/interact with magnetic field e.g. jewellery, watches, credit cards, zips, hairpins, dental work, pens
  • Not good for bone lesions (no signal, black) unless ST metastasises within
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12
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13
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14
Q
A

-

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15
Q
A

Meningioma

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16
Q

CT

A
  • Essentially an x-ray procedure - 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
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17
Q

Difference between CT + radiography

A
  • X-ray tube continuously revolves 360 degrees round the patient
  • Patient bed moves either continuously through the bore of the CT tube (helical scan) or in a series of small increments (axial scan) -> progressive imaging
  • Controlled by computer
  • Images are viewed at the time and remotely on other workstation
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18
Q

CT scan procedure

A
  • Type of examination required is chosen by computer - usually preset
  • Choose the length / area of scan required
  • Choose the thickness of the slices required
  • 1). Scout Scan - scan patient in low reso -> to choose area of interest
  • 2). Scan (displayed in 2 - 3 window settings)
  • 3). May repeat having given intravenous contrast (non-ionic iodine based agents only)
  • May use programs which look at arterial and venous phases
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19
Q
A
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20
Q

Interpreting CT image - viewing image

A
  • Usually produced in one plane (transverse (axial))
  • Reconstructed in different planes which are usually sagittal, dorsal and oblique
  • Reconstructions are often useful for surgeons but do not add anything to the information already there
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21
Q

CT reconstruction

A
  • Axial transverse
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22
Q

CT reconstruction

A
  • Sagittal
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23
Q

CT reconstruction

A
  • Coronal dorsal
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24
Q

CT - adv

A
  • Speed
  • Reduced anaesthetic time
  • Cost “Whole body” scanning
  • Angiography
  • Cheaper instal than MRI
  • Intuitive - can alter contrast during
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25
CT - disadv
- Radiation dose - Need for GA/heavy sedation - Not as good as MRI for the brain and spinal cord - Still relatively expensive
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CT - patient prep
- Starved for 8-12 hours in the - Recent pre GA bloods esp. urea, creatinine, liver parameters etc - Recent urea and creatinine are mandatory pre-contrast - IV iodine-based contrast agents can cause acute kidney injury (AKI), rapid renal vasodilatation followed by long vasoconstriction that results in a rise of intra-renal vascular resistance, with a decrease in renal blood flow (RBF) and a fall in filtration fraction
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Contrast CT
- IV contrast - Omnipaque - 2 mL/kg BW
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Contrast CT protocol
- GA - preferred - Large bore cannula – pink dogs, blue cats - T-Connector - 2 mL/kg BW - Survey scan - Hand injection - Scan triggered 1 - 3 minutes post-injection - waiting for aorta to fill w/ contrast = change in density = bolus tracker
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CT - dual phase
- Pressure injector - Survey scan - Dual phase - Region of interest - Scan + view position - Trigger scan + injection - Manual/automatic trigger forscan - Arterial phase within 10 s - Venous phased triggered after 15 - 25 s (HR)
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- Arterial (hepatocellular carcinoma)
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- Venous phase same site
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Indications for CT
- Trauma patients - Thoracic - Skull - Orthopaedics - Tissues - Abdomen - Spine
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Sx resection possible - not approaching brain, only in frontal sinus
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Scintigraphy health + safety
- Radioactive materials license - Training in nuclear medicine - Training in radiation safety - Annual audit by granting agency
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Thyroid radionuclide scan
- Technetium 99m pertechnetate (99mTcO4-) - v similar to iodine take up into thyroid + salivary glands - 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
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Scintigraphy - thyroids, zygomatic/molar
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Scintigraphy - thyroids - 20 min post injection, bilateral
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- Scintigraphy - 20 mins post injection, right thyroid plus ectopic hyperfunctional mediastinal tissue
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- Scintigraphy - thyroids - Parotid
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- Scintigraphy - thyroid carcinoma
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- Scintigraphy (99mTcO4-) Incidental - salivary glands
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Bone scintigraphy
- Very sensitive, detects changes in bone metabolism - predicts bone change, inc bone turnover hotspots - Skeletal disease, injury, arthropathy, osteomyelitis, neoplasia - IV bolus 99m technetium hydroxymethylene diphosphonate (99mTc- HDP) - 99mTc-HDP (technetium) binds to inorganic component of bone (hydroxyapatite); is adsorbed onto exposed surface of crystal in areas of active bone resorption - Detects increases in bony remodelling that develops before actual morphological changes are seen on radiographs
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Bone scintigraphy - image, procedure, patient prep
- 48.1 MBq/4.5kg bodyweight Imaged - Immediate - vascular phase - 5 - 20 mins - soft tissue phase - 2 - 3 hours - bone phase - Acquired over 60s period using gamma camera and collimator - Increased radiopharmaceutical uptake (hotspot) = inc bone hotspot - Mild/moderate; focal/generalised - Lesion orientated radiographs to follow - Dogs kept in isolation for upto 24h until surface exposure rate below 1 mR/h
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- Bone scintigraphy - kidneys, bladder
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- Bone scintigraphy - kidneys, bladder
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Non-skeletal scintigraphy
- Bladder (normal excretion) - Injection site (minimal residual concentration at the catheter port) - Thyroid (small impurities in the labelling process)
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Scintigraphy - costochondral junctions, incidental finding
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- Scintigraphy - OA incidental finding
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Scintigraphy - rib metastasis - osteosarcoma
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Indium-111 labelled B-12
- Lymphoma requires increased levels of vitamin B12 to survive - Indium-111 isotope attached to B12 - Taken up by lymphoblasts - LNs take up B12 allowing delivery of therapeutic radiation dose to the tumour
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- Indium-111 labelled B-12
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Fluroscopy
- Continuous series of very low dose x-ray images - Real-time images of tissues - Swallowing disorders - barium in food - Collapsing airways - air = negative contrast, will appear white - Portosystemic shunting (vascular maps) - Digital fluoroscopy - apid acquisition of x-ray based images - Some radiation exposure unavoidable - Protective equipment required
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Stent placed using fluorscopy
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AAA Companion Animal VMS4005 (17 decks)

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