Advanced imaging of the brain and spinal cord

Question 1

Computed Tomography (CT)

Answer 1

Produces ionizing radiation
Rotating photon source (x-ray tube)
Rotating detectors (measures transmitted radiation)

Question 2

CT vet applications of the bone

Answer 2

Fractures, elbow dysplasia, ear dz, spinal dz

Question 3

CT vet applications of the nasal cavity

Answer 3

Tumors, rhinitis

Question 4

CT vet applications of the lungs

Answer 4

Primary or metastatic tumors, diffuse lung dz (pneumonia), lung torsion

Question 5

CT vet applications for the abdomen

Answer 5

Masses, portosystemic shunt

Question 6

CT exam

Answer 6

Scout/ localizer image (image before real image- basic rad)
Acquired in transverse plane

Question 7

Hyperattenuating

Answer 7

White with highest HU value
Bone and metal

Question 8

Hypoattenuating

Answer 8

Black with lowest AU value
Air

Question 9

Hounsfield units (HU)

Answer 9

Air → fat → water (0)→ ST → bone

Question 10

CT contrast media

Answer 10

Iodinated contrast IV
Highlights BVs, enhances ST and identifies tumors leaky vasculature

Question 11

Advantages of CT

Answer 11

More detailed view of anatomy without superimposition
Faster and less expensive than MRI
Best for bone, lung and abdomen

Question 12

Disadvantages of CT

Answer 12

Radiation exposure
More expensive than rads
Poor ST contrast than compared to MRI

Question 13

MRI has better ______________ than CT

Answer 13

ST contrast (+ noninvasive)

Question 14

Disadvantages of MRI

Answer 14

Longer scan times
General anesthesia
Cost

Question 15

Vet MRI magnet

Answer 15

1.5 T to 3.0 T

Question 16

Basic principles of the MRI

Answer 16

Hydrogen atom has ideal magnetic properties (positively charged + spins on axis → creates its own magnetic field)
Protons in the magnetic filed are parallel to the field (Bo)
External radiofrequency pulse applies (disrupts alignment of protons)
Protons recover alignment releasing energy and creating a radiofrequency signal

Question 17

MRI contrast media

Answer 17

Gadolinium (Gd) given IV
Paramagnetic (alters magnetic filed causing nuclei to relax faster and tissues more hyperintense)

Question 18

What are MRIs used for?

Answer 18

Brain, spine and musculoskeletal (ST, tendons, ligs)
Scanned in @ least 3 fields: transverse, dorsal, sagittal

Question 19

MRI Terminology

Answer 19

Hyperintense: white
Hypointense: black

Question 20

Safety for CT and MRI

Answer 20

CT: ionizing radiation
MRI: Projectiles and metal implants

Question 21

When is the only time a magnet of MRI is off?

Answer 21

MRI quench: liquid cryogens that cool the magnet coils boil off rapidly → runaway immediately to avoid asphyxiation and cryoburns

Question 22

Brain CT

Answer 22

Good for identifying acute hemorrhage and skull fractures
Masses and ventricular enlargement

Question 23

T2 sequence (MRI)

Answer 23

Hyperintense: fluid, fat
Hypointense: bone, air and muscle
Best tissue contrast, good for pathology

Question 24

T1 sequence (MRI)

Answer 24

Hyperintense: fat, gadolinium
Hypointense: fluid
Great for anatomy

Question 25

Brain MRI

Answer 25

Masses (CHANG)
Multifocal lesions (encephalitis, metastasis, hemorrhage**)
Ventricular enlargement (hydrocephalus)
Meningeal thickening/ enhancement (meningitis, neoplasia)

Question 26

Spinal CT

Answer 26

Better for bony abnormalities
Spinal column: fractures or luxations
Mineralized disc extrusion

Question 27

Spinal CT contrast

Answer 27

Iodinated IV or subarachnoid admin (myelography for SC deviation)

Question 28

Spinal MRI

Answer 28

Modality of choice for SC and nerves
IV gadolinium