3: Intro to Neuroradiology II

Question 1

(OBJ) Compare and contrast the techniques, benefits and limitations of CT angiography (CTA) and MR angiography (MRA) in evaluating the carotid arteries and intracranial vasculature.

Answer 1

CTA:

• -Requires IV contrast
• -CT scan ~20 seconds after contrast given (longer for veins)
• -Can display as 2D maximum intensity projection or 3D volume rendering techniques (with brain parenchyma subtracted out)
• -BENEFITS: FAST scanning of LARGE area, shows SMALL peripheral vessels well, demonstrates lumen diameter and WALL CHARACTERISTICS (diseases of intima, media, and surrounding tissues)
• -LIMITATIONS: need contrast, radiation exposure

MRA:
–Without contrast: good for circle of willis (COW), not other places because they are too large
–With contrast: good for aortic arch, carotid/vertebral, COW
–Same timing as CT
STRENGTHS: no radiation, bones not imaged -> less artifact at skull base, no contrast needed for COW
LIMITATIONS: long acquisition time, must use contrast for carotid arteries, don’t see small peripheral vessels or wall characteristics

Question 2

(OBJ) Discuss the risks and benefits of conventional cerebral angiography and list what information it provides which cannot be obtained with CTA or MRA.

Answer 2

RISKS:

• -Expensive!
• -Transient deficit, stroke, puncture site complications
• -Only lumen visualized: no information on wall, plaque morphology, tissues around vessel, etc

BENEFITS:

• -Gold standard for intracranial vascular diseases
• -Great for small arteries
• -Can see flow dynamics
• -More sensitive than CTA/MRA for small aneurysms
• -Good for cerebral ischemia (more sensitive), known subarachnoid hemorrhage (good for small aneurysms), and congenital A-V malformations

Question 3

(OBJ) Explain why CT is preferred over MRI for evaluating the osseous structures of the spine.

Answer 3

CT is better for bone (bone is black on MRI)

Question 4

(OBJ) Discuss circumstances where a patient with a known vertebral fracture (diagnosed on CT scan or radiographs) may still require an MRI of the spine.

Answer 4

MRI can tell acute from chronic by seeing edema in bone marrow (brighter than normal)
–Also, MRI better for imaging contents of spinal column

Question 5

(OBJ) Describe an alternative imaging technique that can be used to image the spinal cord & nerve roots in patients who cannot have an MRI.

Answer 5

MYELOGRAPHY: fill subarachnoid space with contrast (x-ray dye), then take radiographs or CT images
–Allows evaluation of cord morphology, nerve roots, and disc abnormalities

Question 6

(OBJ) Explain how functional MRI differs from conventional MRI in technique and in the information it provides.

Answer 6

fMRI: using MRI to localize the region of cerebral cortex that controls a specific function
–Active areas of cortex = higher blood flow = higher oxygen = enhancement/brighter image

TECHNIQUE:
Two sets of images: baseline (at rest) and while task is being performed -> compare signal intensity

USE:

• -Preoperative localization of cortical function
• -Research

Question 7

(OBJ) Describe how images of the brain are obtained using nuclear medicine techniques.

Answer 7

Nuclear medicine: give patient radioactive substance and then detect radioactivity emitted by patient using a camera

Question 8

(OBJ) Describe the benefits and limitations of nuclear medicine studies of the brain as compared with CT or MRI.

Answer 8

BENEFITS
–Evaluates FUNCTION rather than structure (PET measures metabolic activity)

LIMITATIONS:
–Not high resolution