Diagnostic Imaging in Neuro: MRI and CT

Who invented the CT?

Sir Godfrey Hounsfield

What are some of the advantages of CT over radiographs? (5)

Cross sectional images

Greater tissue contrast

Ability to manipulate the images to emphasize tissue contrast

Objective measurements of density (Hounsfield Unit/CT Number)

Can reconstruct images into different planes and 3D volume rendering

What are some skull indications for use of CT?

Lumps and bumps

Trauma

Nasal disease

Orbital masses/exopthalmos

Ear disease

Dental disease

What are some of the nasal diseases that can be indications for CT? (2)

Neoplasia

Fungal Infection - Aspergillosis

What are some of the spine indications for use of CT?

IVDD

Trauma

Aggressive osseous lesions

Congenital Abnormalities

Developmental Abnormalities

Degenerative Changes

What breed is seen to have IVVD commonly?

chondrodystrophic breeds

(dachshunds!!!)

What are some cons to CT use? (6)

Ionizing radiation

Improved soft tissue contrast over radiography but subtle differences in the neural soft tissues can be difficult to detect

Susceptible to motion artifact

Susceptible to metallic artifacts

Availability

Cost

How is the image created on a MRI?

manipulation of the body's protons by a strong magnetic field and radio frequency waves

Does MRI or CT have superior soft tissue contrast?

MRI

T/F MRI can determine tissue/lesion composition by signal intensities and different sequences

True

Does MRI or CT have a longer scan time thus requiring general anesthesia?

MRI

What is the gold standard for imaging of

most neurologic conditions?

MRI

What are TWO times when you should use MRI?

Intracranial neurolocalization

Spinal localization

T/F: MRI can diagnose parenchymal changes in the spinal cord that cannot or are difficult to diagnose with CT including FCE, intramedullary lesions (tumors, infectious/inflammatory), myelomalacia, ANNPE, IVDD in non chondrodystrophic breeds

True

What are some of the cons to MRI? (5)

More susceptible to motion artifact than CT due to

longer scan time - requires general anesthesia

Limitations for imaging osseous structures

Susceptible to metallic artifacts

Availability

Cost (>CT)

What does MRI use for imaging?

hydrogen nucleus

What lines up the small magnetic fields from the spinning proton of the hydrogen nucleus?

Main magnetic field strength

What disturbs the small magnetic

fields that are lined up?

Radiofrequency waves

T/F As protons return to their original orientation they release energy which is detected by the MRI machine

True

The higher the main magnet field strength usually the (worse/better) the images

better

What is the unit of magnetic field strength?

Tesla (T)

What is the range of Tesla that the MRI can have?

0.3 T- 3.0 T

What are the THREE planes for MRI and CT?

Transverse

Sagittal

Dorsal

T/F Different sequences can be produced to highlight or suppress different tissue types

True

What are MRI sequences determined by?

the timing of the radiofrequency

pulses applied from the machine and received from the tissues

What are the TWO parameter for MRI sequence?

TR (time of repetition)

TE (Time to echo)

What does MRI signal intensity depend on?

amount of protons in a tissue and

sequence selection

What are the bright areas and dark area of an MRI called?

hyperintense

hypointense

T/F fluid can be hypointense or

hyperintense depending on the sequence

True

What type of MRI weighted image is good for anatomy?

T1

what type of MRI weighted images is good for identifying pathology?

T2

Pathologic tissues such as tumors or areas of inflammation are "juicy" so _____

hyperintense

What is given IV for MRI contrast?

Gadolinium

What type of weighted images is used when doing an MRI contrast?

What do they differentiate?

T1

abnormal tissue from surrounding tissues

What type of T2 weighted image that suppresses signal from CSF?

FLAIR

What MRI image is used for hemorrhage/some

metals will cause a signal void?

T2* (T2 star)

What type of T2 weighted image is used that suppresses signal from Fat?

STIR

What MRI sequence identifies areas of

restricted fluid diffusion, good for ischemic strokes?

DWI/ADC