30: Skull, CT, and MRI

Common indication for intraoral rads (where they may actually be useful)

Dental radiographs

Auricular structure that may be evaluated on radiographs

Tympanic bullae

Radiographic view done to evaluate nasal disease

Open mouth maxillary VD

Radiographic view done to evaluate the frontal sinus

Rostral → caudal skyline view

Radiographic view done to evaluate the TMJ

Double obliqued lateral view: rotate the head away from you and tip the nose

Common fracture of the scull

Depression fracture

How do radiographs estimate skull damage as compared to CT

Radiographs will underestimate skull fractures

Proliferative skull conditions we CAN evaluate on radiographs

• Calvarial hyperostosis

• Craniomandibular osteopathy

• Multilobular osteochondrosarcoma 

Calvarial hyperostosis

Increased deposition of new bone along the calvarium in puppies

Craniomandibular osteopathy

Increased deposition of new bone along the mandible in puppies

Multilobular osteochondrosarcoma

Slow-growing neoplasia in older dogs that looks like a popcorn ball

Imaging techniques that remove superimposition of the skull

CT and MRI

Other name for MRI

NMR

Energy used by CT

Still x-rays

Energy used by MRI

Magnetic and radiofrequencies

Tissue type better visualized on a CT

Bone

Tissue type better visualized on an MRI

Soft tissue

Which imaging modality (CT or MRI) is faster

CT

Which imaging modality (CT or MRI) is radiographically safer

MRI; no radiation!

How much more radiation does a CT give off than an X-ray

200x

Contrast used in CT

Iohexol

What indications are best for CT

Honestly most things

• Polytraumas

• Orthopedic disease

• Masses

• Vascular anomalies

• Head bones

• Exotics we don’t want to sedate

Basic physics of how MRI works

Strong superconducting magnet makes all the H atoms line up, then they are blasted with radiofrequency pulses to add energy, and the H atoms emit energy at different rates

Unit for measuring magnet strength

Tesla

Why do we have to be so careful about metal in MRI machines

The magnet can pull violently at things, and the radiofrequency can cause tissues and implants to heat up

How do we keep the MRI magnet cold

Liquid helium

Which imaging modality (CT or MRI) can evaluate different tissues in one take

CT; MRI you need to run different sequences to highlight different tissues

Contrast used for MRI

Gadolinium-based contrast

Tissue that does not take up gadolinium contrast well on MRI

Vasculature

Tissues that are best imaged by MRI

Brain, spinal cord, and distal ST in limbs