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Investigations > Ophthalmic radiology > Flashcards

Ophthalmic radiology Flashcards

1
Q

What is a situation when plan xrays are useful in ophthalmology?

A

to exclude a radio-opaque foreign body (and therefore may preclude an MRI)

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2
Q

What is the role of plan xrays for orbital fractures?

A

they may be identifiable on plain xray but generally require furher characterisation by CT/MRI

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3
Q

What are 3 commonly used views for plan film xrays in ophthalmology?

A
  1. occipitomental (Water’s view)
  2. overtilted occipitomental
  3. lateral
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4
Q

If IOFB is suspected when doing plain xrays what may help to demonstrate it?

A

upgaze and downgaze view may show a change in position

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5
Q

Is dacryocystography (DCG) still commonly performed?

A

no

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6
Q

What does dacryocystography involve?

A

requires the injection of radio-opaque contrast medium (oil-based) into the lacrimal drainage system + xrays performed to look for contrast to identify level of obstruction if present + distinguish masses, stenosis or fistulae

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7
Q

What is the xray irradiation from DCG comparable to?

A

6-12 months of natural atmospheric radiation

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8
Q

What are 4 sites where contrast is seen in DCG if the bilateral lacrimal drainage systems are patent?

A
  1. fornices
  2. canaliculi
  3. common canaliculi
  4. nasolacrimal ducts
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9
Q

Is reflux of contrast in DCG pathological?

A

yes - nearly always

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10
Q

What does dacryoscintigraphy (DSG) involve?

A

more useful as physiological test of tear flow through the lacrimal system (more physiological than DCG)

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11
Q

What can DSG be useful for diagnosing (2 things)?

A
  1. functional epiphora
  2. proximal obstruction - may be masked in DCG by overvigorous injection of dye into the lacrimal system
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12
Q

What is the xray radiation provided by a CT head comparable to?

A

10 months of background radiation

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13
Q

How does CT compare with MRI?

A

quick, reliable, reproducible, cheap, appropriate in the setting of trauma

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14
Q

What are 7 indications for CT in ophthalmology?

A
  1. Orbital cellulitis
  2. orbital lesions
  3. orbital trauma
  4. intracranial lesions
  5. detection of a foreign body
  6. cerebrovascular accidents (CVA)
  7. contraindication to MRI
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15
Q

What does CT involve?

A
  • rotation of highly collimated xray beam and detector around the patient
  • from data gained in different projectinos, an image of a single plane (‘slice’) is reconstructed
  • series of slices is recorded through the area of interest; can therefore reconstruct 3D images
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16
Q

What type of lesions can be visualised well with CT?

A

lesions of bony orbit and lesions with calcification - orbit and globe

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17
Q

What type of lesions can be visualised well with CT?

A

lesions of bony orbit and lesions with calcification - orbit and globe

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18
Q

What are 7 groups of patients who are at increased risk of adverse reactinos or nephrotoxicity from CT with iodinated contrast media?

A
  1. history of previous reaction
  2. asthma
  3. multiple allergies/severe allergy requiring treatment
  4. renal disease, DM, conditions assoc w/ renal impairment
  5. age >75y
  6. heart failure
  7. renal transplant
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19
Q

What eGFR indicates a) severe and b) moderate renal impairment?

A
  • a) <30
  • b) 30-59
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20
Q

What consideration should be made regarding metformin after performing contrast-enhanced CT?

A

if impaired renal function prescan, make decision to stop metformin for 48h post-scan with referring clinician/diabetologist

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21
Q

What are 3 indications for CTA?

A
  1. Intracranail aneurysms
  2. vascular lesions
  3. neurosurgical planning
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22
Q

How is CTA performed?

A

high-resolution, thin-cut CT scan, combined with IV contrast media injection - provides excellent vasculature anatomy in 3D with adjacent bony structure

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23
Q

What is the benefit of CTA for assessment of aneurysms?

A

helps delineate borders of aneurysms and neck size to aid endovascular treatment planning

24
Q

What type of aneurysms is CTA particularly useful for assessing?

A

small aneurysms of the circle of Willis

25
Q

What type of aneurysms is CTA particularly useful for assessing?

A

small aneurysms of the circle of Willis

26
Q

How does the imaging of different tissue types compare between CT and MRI?

A
  • CT -excellent bony detail while MRI is inferior
  • Soft tissue contrast is excellent with MRI but inferior in CT
27
Q

What are 3 disadvantages of MRI compared with CT?

A
  1. higher cost
  2. more time consuming
  3. metal/implants contraindicated
28
Q

Which imaging types can be used in which parts of pregnancy?

A
  1. CT - not recommended during pregnancy
  2. MRI - not recommended during first trimester of pregnancy
29
Q

What are 7 contraindications to MRI?

A
  1. metallic orbital FB
  2. cochlear implants
  3. neural stimulators
  4. pacemakers
  5. some aneurysm clips
  6. recent surgical metalic implant (within 8 weeks)
  7. claustrophobia
30
Q

What are 3 stages to how MRIs work?

A
  1. tissue exposed to short electromagnetic pulse undergoes rearrangement of hydrogen nucleii
  2. when pulse subsides, nuclei return to normal resting state but re-radiate some energy they absorbed
  3. sensitive receivers pick up the electromagnetic echo
31
Q

What are 3 things that T1 and T2 times depend on?

A
  1. proton density
  2. tissue components
  3. magnetic properties of tissue components
32
Q

What are 7 indications for MRI?

A
  1. orbital masses or tumours
  2. optic nerve tumours (glioma, meningioma)
  3. intracranial extension of orbital tumours
  4. suspected compressive optic neuropathy
  5. detecting white matter plaques in retrobulbar neuritis
  6. suspected lesions of chiasm e.g. pituitary tumours
  7. intracranial aneurysms
33
Q

Why is MRI useful n retrobulbar neuritis to asess for the present of multiple white matter plaques?

A

predictive of the development of clinical multiple sclerosis

34
Q

What are the conventional MRI sequences?

A

T1- and T2-weighted

35
Q

What determines the protool for MRI imaging?

A

determined by the examining radiologist and the clinical situation

36
Q

What additional technique is required in MRI for orbital imaging?

A

specialised fat suppression techniques - useful for optic nerve visualisation (otherwise masked by high signals from orbital fat)

37
Q

What are diffusion-weighted (diffusino tensor) MRI sequences useful for?

A

Brownian motion wihin tissues - intially useful in acute strokes, also for intracranial abscesses and distinguishing epidermoid from arachnoid cyst

38
Q

What substance is used as ‘contrast’ for MRI?

A

IV paramagnetic gadolinium

39
Q

What are 3 indications for gadolinium-enhanced scans?

A
  1. detection of blood-brain barrier abnormalities
  2. inflammatory changes
  3. increased vascularity
40
Q

What is the safety of gadolinium based contrast agents for MRI?

A

they are safe with a low adverse event rate

41
Q

What is the safety of gadolinium based contrast agents for MRI?

A

they are safe with a low adverse event rate

42
Q

What has been seen in the use of gadolinium based contrast agents for MRI in severe renal impairment?

A

nephrogenic systemic fibrosis

43
Q

When should renal function be checked for MRI?

A

for those at risk of renal impairment, particularly if aged >65y and with co-existing diabetes

44
Q

What is a situation in which CT and MRI imaging are often complementary?

A

tumour staging around the skull base and orbits

45
Q

Label the following on the MRI:
* 3rd ventricle
* 4th ventricle
* corpus callosum (splenium)
* cerebellum
* optic chiasm
* pituitary sella
* midbrain
* pons
* medulla

A
46
Q

What is MRA?

A

non-invasive method to image intra- and extracranial carotid and vertebrobasilar circulations

47
Q

Which circulations are visualised with MRA?

A

intra- and extracranial carotid and vertebrobasilar circulations

48
Q

What is the principle of computerised image reconstruction for MRA based on?

A

haemodynamic properties of flowing blood, rather than vessel anatomy

49
Q

What are 4 examples of abnormalities that can be detected by MRA?

A
  1. stenosis
  2. occlusion
  3. AVMs
  4. aneurysms
50
Q

What are 2 types of MRA and what are they used for?

A
  • static MRA
  • time-resolved MRA - highlights separate arterial and venous supplies to intracranial AVM
51
Q

What are 3 disadvantages of MRA?

A
  1. cannot detect aneurysms <5mm in diameter
  2. long acquisition time
  3. suboptimal detection fo intravascular calcifications
52
Q

What are 3 disadvantages of MRA?

A
  1. cannot detect aneurysms <5mm in diameter
  2. long acquisition time
  3. suboptimal detection fo intravascular calcifications
53
Q

How does MRV differ from MRA?

A

the imaging is ‘gated’ to the speed of venous flow

54
Q

What is MRV useful for detecting?

A

cerebral venous sinus thrombosis

55
Q

What is MRV a commonly performed investigation for?

A

papilloedema

Investigations (29 decks)

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