Advanced Imaging for Small Animals Flashcards
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
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
3
Q
T1 - water
A
- Black - long T1, contains a lot of protons
4
Q
T1 - fat
A
- White, bright - short T1
5
Q
T1 - brain
A
- Grey
6
Q
T1 - CSF
A
- Dark, long T1 values
7
Q
A
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
9
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A
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
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
12
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A
13
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A
14
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A
-
15
Q
A
Meningioma
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
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
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
19
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A
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
21
Q
CT reconstruction
A
- Axial transverse
22
Q
CT reconstruction
A
- Sagittal
23
Q
CT reconstruction
A
- Coronal dorsal
24
Q
CT - adv
A
- Speed
- Reduced anaesthetic time
- Cost “Whole body” scanning
- Angiography
- Cheaper instal than MRI
- Intuitive - can alter contrast during
25
Q
CT - disadv
A
- Radiation dose
- Need for GA/heavy sedation - Not as good as MRI for the brain and spinal cord
- Still relatively expensive
26
Q
CT - patient prep
A
- 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
27
Q
Contrast CT
A
- IV contrast
- Omnipaque - 2 mL/kg BW
29
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A
31
Q
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- Arterial (hepatocellular carcinoma)
32
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- Venous phase same site
34
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35
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36
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37
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Sx resection possible - not approaching brain, only in frontal sinus
38
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39
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42
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Scintigraphy - thyroids, zygomatic/molar
43
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Scintigraphy - thyroids - 20 min post injection, bilateral
44
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- Scintigraphy - 20 mins post injection, right thyroid plus ectopic hyperfunctional mediastinal tissue
45
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A
- Scintigraphy - thyroids
- Parotid
46
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- Scintigraphy - thyroid carcinoma
47
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- Scintigraphy (99mTcO4-) Incidental - salivary glands
50
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- Bone scintigraphy - kidneys, bladder
51
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- Bone scintigraphy - kidneys, bladder
53
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Scintigraphy - costochondral junctions, incidental finding
54
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- Scintigraphy - OA incidental finding
55
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Scintigraphy - rib metastasis - osteosarcoma
56
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57
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59
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- Indium-111 labelled B-12
61
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62
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Stent placed using fluorscopy
63
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64
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65
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66
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67
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