Advanced imaging of the brain and spinal cord Flashcards
Computed Tomography (CT)
Produces ionizing radiation
Rotating photon source (x-ray tube)
Rotating detectors (measures transmitted radiation)
CT vet applications of the bone
Fractures, elbow dysplasia, ear dz, spinal dz
CT vet applications of the nasal cavity
Tumors, rhinitis
CT vet applications of the lungs
Primary or metastatic tumors, diffuse lung dz (pneumonia), lung torsion
CT vet applications for the abdomen
Masses, portosystemic shunt
CT exam
Scout/ localizer image (image before real image- basic rad)
Acquired in transverse plane
Hyperattenuating
White with highest HU value
Bone and metal
Hypoattenuating
Black with lowest AU value
Air
Hounsfield units (HU)
Air → fat → water (0)→ ST → bone
CT contrast media
Iodinated contrast IV
Highlights BVs, enhances ST and identifies tumors leaky vasculature
Advantages of CT
More detailed view of anatomy without superimposition
Faster and less expensive than MRI
Best for bone, lung and abdomen
Disadvantages of CT
Radiation exposure
More expensive than rads
Poor ST contrast than compared to MRI
MRI has better ______________ than CT
ST contrast (+ noninvasive)
Disadvantages of MRI
Longer scan times
General anesthesia
Cost
Vet MRI magnet
1.5 T to 3.0 T
Basic principles of the MRI
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
MRI contrast media
Gadolinium (Gd) given IV
Paramagnetic (alters magnetic filed causing nuclei to relax faster and tissues more hyperintense)
What are MRIs used for?
Brain, spine and musculoskeletal (ST, tendons, ligs)
Scanned in @ least 3 fields: transverse, dorsal, sagittal
MRI Terminology
Hyperintense: white
Hypointense: black
Safety for CT and MRI
CT: ionizing radiation
MRI: Projectiles and metal implants
When is the only time a magnet of MRI is off?
MRI quench: liquid cryogens that cool the magnet coils boil off rapidly → runaway immediately to avoid asphyxiation and cryoburns
Brain CT
Good for identifying acute hemorrhage and skull fractures
Masses and ventricular enlargement
T2 sequence (MRI)
Hyperintense: fluid, fat
Hypointense: bone, air and muscle
Best tissue contrast, good for pathology
T1 sequence (MRI)
Hyperintense: fat, gadolinium
Hypointense: fluid
Great for anatomy
Brain MRI
Masses (CHANG)
Multifocal lesions (encephalitis, metastasis, hemorrhage**)
Ventricular enlargement (hydrocephalus)
Meningeal thickening/ enhancement (meningitis, neoplasia)
Spinal CT
Better for bony abnormalities
Spinal column: fractures or luxations
Mineralized disc extrusion
Spinal CT contrast
Iodinated IV or subarachnoid admin (myelography for SC deviation)
Spinal MRI
Modality of choice for SC and nerves
IV gadolinium
