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Clinical > MRI > Flashcards

MRI Flashcards

1
Q

How to evaluate hydrocephalous… measurement

A

callosal height - range of 3.7mm to 7.3 mm though abnormal range overlaps

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2
Q

What radiographic diagnosis is happening in this images where the white arrows are pointing?

A

Transtentorial herniation and foramen magnum herniation

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3
Q

What type substances will strengthen the magnetic field of an MR machine?

What type of substances will weaken it?

A

Strengthen: paramagnetic and ferromagnetic

Weaknen: Diamagnetic

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4
Q

Magnetic susceptibility artifact is when?

A

There is local alteration of the magnetic field reulting in spatial misregistration and image distortion

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5
Q

What common surgical material can cause suspetibility artifact?

A

Suture and can remain for years

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6
Q

Susceptibility artifact is proportional to what?

A

The strength of the magnet… the bigger the magnet the more susceptibility artifcat you see.

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7
Q

What sequences exhibit more susceptibility artifacts?

A

Long echo time (TE) or T2W images

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8
Q

Besides ferro and paramagnetic objects, where can you see susceptibility artifact?

A

air-tissue or air-bone interface

Ex. Frontal sinus, nasal cavity, mouth and neck

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9
Q

What type of sequences improves visibility of areas effected by susceptibility artifact

A

Spin-echo rather than gradient echo.

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10
Q

What other actions can be taken while planning an MRI to reduce suspectibility artifact?

A

Decrease voxel size (most useful: done by decreasing FOV and/or slice thickness)

Increase reciver bandwidth

Changing the frequency encoding direction.

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11
Q

CSF signal loss occurs due to?

A

High velocity or turbulent CSF flow

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12
Q

Where does CSF signal void usually occur?

A

In areas of narrowing

Ex: Mesencephalic aqueduct, lateraly ventrical, fourth ventrical and syrinxes

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13
Q

Explain why CSF Signal void happens?

A

A spin-echo is performed by admitting an intial 90 degree RF pulse and then followed by a 180 degree refocusing RF pulse.

In CSF signal void, the protons that have received the 90 degree RF pulse have moved on before being exposed to the 180 degree refocusing FR pulse.

Therefore the protons that enter that area have received no excitation pulse and therefore do not admit a signal

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14
Q

What affects the CSF signal?

A

Turbulence

obstruction

Cardiac motion

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15
Q

How does cardiac motion affect CSF signal?

A

During systole the blood enters the choroid plexus and parenchymal vasculature causing CSF to flow faster in an antegrade direction (systolic pseudogating) - leads to decrease in signal

Opposite during diastole (diastolic pseudogating) - leads to increase in signal

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16
Q

What are some ddx for CSF signal void?

A

COMS

Intra and extraaxial masses

Intraventricular tumors

Hydrocephalous

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17
Q

CSF signal void occurs in what weighting?

A

T2W

18
Q

Ghosting is what in MR?

A

Macroscopic motion causes structures to be in different positions duringt the phase-coding process

19
Q

Aliasing is AKA?

A

Wraparound artifact

20
Q

Aliasing occurs when?

A

When parts of the anatomic structures being imaged are outside the FOV.

The structures are then superimposed on the opposite side of the image/FOV

21
Q

You can correct aliasing in MR by?

A

Increasing FOV

Using oversampling technique

Apply a saturation pulse

22
Q

FLAIR images null out what type of fluid?

A

Low-protein fluid (CSF or water)

23
Q

Incomplete suppression of FLAIR can indicate?

A

Artifact (propofol, increased O2, motion, inhomogeneity of the magnetic field)

Hemorrhage

meningitis

neoplasia (leptomeningeal mets)

24
Q

Post-contrast T1W MRI pseudolesions?

A

Trigeminal Nerve enahncement (CNIII)

Choroid Plexus enhancement

25
Q

Branches of the trigeminal nerve

A

ophthalmic

maxillary

mandibular

26
Q

Why does CN3 and choroid plexus contrast enhance in face of no pathology?

A

Incomplete blood nerve barrier

27
Q

Where is the choroid plexus locacted?

A

Ventral portion of the lateral ventricles

dorsal aspect of the 3rd ventricle

Caudal dorsal aspect of the 4th ventricle

28
Q

Hyperintensity of the neurohypohysis is commonly seen in what species?

A

Dogs—-NOT cats

29
Q

Reasoning behind T1W hyperintensity of the neurohypophysis as an artifact?

A

Storage of arginine vasopressin (in humans but is correlated to dogs as well)

30
Q

Decrease is neurohypophysis signal on T1W could indicate?

A

Diabetes mellitus

Diabetes insipidus

Hypersecreation of Arginine vasopressin

31
Q

What is external hydrocephalus?

A

CSF in the subarachnoid space around the brain

32
Q

Bilaterally symetrical brain lesions think what type of ddx?

A

Metabolic

Toxin

Storage

33
Q

T1 hyperintensity pre-contrast material?

A

My Very Best Friend is Cool

Melnan, Magnesium, Mucin

Vasopressin

Blood

Ferrous objects, fat

Cu, Ca+2

Hepatic encephalopathy is hyperintensities

34
Q

Thamine definency is seen where?

A

Thalamus and Brainstem

35
Q

Size of pituitary gland in a Cat? Dog?

A

Cat: ~5mm in height and 3.5mm in width

Dog: 4.5mm in height and 6mm in width

36
Q

Big findings for a AHNCNPE

Acute hydrated non-compressive nucleus pulposus extrusion

A

Focal T2 hyperintensity

Non-compressed cord

Changes in the cord or epidural fat

37
Q

Suggested cut off for length of L2 single shot fluid signal attenuation with developing or not developing myelomalacia?

A

>7.4 of L2 is high risk for developing

38
Q

What percentage of BCS dogs do not have a septum lucidum?

A

80% - Free flowing lateral ventricles

39
Q

What are the clinical questions that need answered when looking at meningitis?

A
  1. Distribution: Cerebellum vs cerebrum vs brainstem… this will help the clinician know the clinical signs to watch out for
  2. Necrotizing areas - prognosis
  3. Amount of edema or area - prognosis
  4. Mass effect/herniation - manitol treatment
40
Q

An annular tear is when what happens?

A

The annulus tears with no extrusion of disc material. This can be painful as the outer 1/3 of the disc annular ring is highly innervated with pain fibers

Clinical (12 decks)

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