Neuroradiology

Question 1

What is CT (general characteristics, image quality, use of contrast)? What is it most useful for?

Answer 1

Computed Tomography (CT) is a rapid, inexpensive radiologic procedure that uses a linear x-ray that rotates around the head. IV contrast enhances CT in depicting vasculature and hypervascular tumors- contrast contains iodine which is denser than brain and will appear hyperdense in areas of increased vasularity or breakdown of the blood–brain barrier. Often, images are obtained with and without contrast for comparison. It uses a small amount of ionizing radiation. Use: CT distinguishes very different tissue compositions (e.g., blood vs. brain vs. bone) which helps identify hemorrhage, skull fracture, and mass effect.

Question 2

Four facts about the single-slice CT

Answer 2

1) the scanner is shaped like a large ring; 2) the patient lies on the table & moves through the ring in small steps; 3) at each stop, X–rays are scanned through the patient and picked up by detectors on the opposite side of the ring; 4) the amount of energy absorbed depends on the density of the tissues traversed

Question 3

Why are axial slices in CT scans sometimes adjusted a few degrees off of the true axial plane? (2)

Answer 3

1) Enables the whole brain to be covered using fewer slices. 2) This procedure reduces radiation exposure to the eyes.

Question 4

What is MRI? What is it most useful for?

Answer 4

Magnetic Resonance Imaging (MRI) uses a strong magnetic field causing protons to align their intrinsic spins in parallel with the magnetic field. It does not use ionizing radiation & is generally safe but restricted to persons who can be exposed to high field magnets; not safe with implanted devices or residual metal from accidents. Images have greater resolution and tissue differentiation for identifying white matter conditions and differential diagnoses.

Question 5

T1 vs. T2 MRI: What is the benefit of using either T1–weighted versus T2–weighted MRI?

Answer 5

T1 scans demonstrate greater anatomic detail but less tissue contrast; it’s better for identifying anatomy because of higher resolution. T2 scans have enhanced contrast and looks like a film negative; it has greater clinical benefit in differentiating various types of brain tissue and neuropathologies. Intact white matter appears gray, while axonal injury will appear much brighter. CSF appears brighter.

Question 6

MRI axial slices are true horizontal slices: True or False

Answer 6

True

Question 7

What is FLAIR MRI?

Answer 7

Fluid-attenuated inversion recovery (FLAIR) uses IV-injected paramagnetic contrast media (gadolinium) to detect blood-brain barrier perturbations, cerebral blood flow, infection, or inflammation.

Question 8

What is diffusion-weighted MRI?

Answer 8

Variant of MRI used to evaluate stroke- discriminates cytotoxic edema from vasogenic edema. Useful in identifying acute brain ischemia after stroke and acute vs. remote infarcts.

Question 9

What is perfusion-weighted MRI?

Answer 9

Measures relative cerebral blood flow through the use of injected contrast medium or endogenous blood flow markers. Allows for identification of cerebral blood flow abnormalities and can demonstrate reperfusion of brain regions following pharmacologic/other interventions.

Question 10

What is fMRI?

Answer 10

Measures local blood flow indicating . Blood oxygen level dependent (BOLD) fMRI response results with increased neural activity in a brain region, leading to increased local blood flow.

Question 11

What is MRS?

Answer 11

Magnetic Resonance Spectroscopy (MRS) is an MRI-based procedure characterizes distinct magnetic profiles of endogenous biological markers such as creatinine (Cre), glutamate (Glu), choline variants (Cho), and n-acetyl aspartate (NAA); represented as a waveform series that can be differentially localized and quantified in space.

Question 12

What is DTI?

Answer 12

Diffuse Tensor Imaging (DTI) identifies white matter integrity and white matter tracts. DTI yields a primary dependent variable index referred to as fractional anisotrophy (FA), which is higher in highly organized and densely myelinated regions. Areas that are less organized, less myelinated, or in a state of edema/injury have lower FA values.

Question 13

What is MRA?

Answer 13

Magnetic Resonance Angiography (MRA) is a noninvasive alternative to conventional arteriography, used to visualize carotid arteries and proximal aspects of intracranial circulation. It has poorer spatial resolution and less sensitivity to slow blood flow compared to conventional angiography, but has no risks comparatively.

Question 14

What is PET?

Answer 14

Positron Emission Tomography (PET) uses IV tracers (e.g., 18F-flurodeoxyglucose) for characterization of resting regional brain metabolism, specific biochemical processes, and cerebral blood flow. As a radioisotope-based technique, tracers have been developed to target dopaminergic, serotonergic, and other receptor systems, but requires an on-site cyclotron for most tracers. It’s particularly useful in evaluating brain tumors- high grade neoplasms demonstrate increased metabolism while low grade neoplasms demonstrate decreased activity.

Question 15

What is SPECT?

Answer 15

Single-Photon Emission Computed Tomography (SPECT) detects regional accumulations of radioisotopes that represent regional changes in brain activity or chemistry. Most are of cerebral blood flow - increased neural activity in a region of the brain increases blood flow.

Question 16

CT scans differ in what two ways from conventional X–rays?

Answer 16

1) Rather than taking only one view, the CT X–ray beam is rotated around the patient and takes many different views 2) The CT X–ray data are reconstructed by a computer to obtain a detailed image of all the structures in the slice (e.g., liquid, air, bone, soft tissue)

Question 17

On a CT scan, what does white represent?

Answer 17

dense structures, like bone

Question 18

On a CT scan, what does black represent?

Answer 18

less dense materials, like air

Question 19

On a CT scan, what color is white matter?

Answer 19

Slightly darker than celluar gray matter due to its high myelin content (gray matter is slighly lighter than white matter due to its high water content)

Question 20

On a CT scan, what shade is CSF?

Answer 20

Dark gray

Question 21

On a CT scan, what color is fat tissue just outside the skull (subcutaneous)?

Answer 21

nearly black

Question 22

On a CT scan, what does hyperdense refer to?

Answer 22

bright areas

Question 23

On a CT scan, what does hypodense refer to?

Answer 23

dark areas

Question 24

On a CT scan, what does isodense refer to?

Answer 24

intermediate density materials similar to brain tissue

Question 25

What do hemorrhages look like on a CT scan?

Answer 25

It depends on how old the hemorrhage is: Fresh intracranial hemorrhage shows up as a hyperdense area relative to brain tissue. One-week old hemorrhage looks isodense. Older hemorrhage (2-3 weeks) looks hypodense.

Question 26

Are acute cerebral infarcts readily detectable on CT scans?

Answer 26

No, acute infarcts (the first 6–12 hours) are often not seen on CT scans. After 12 hours, cell death and edema lead to an area of hypodensity seen in the distribution of the occluded artery.

Question 27

Intracranial hemorrhage on MRI: What is the characteristic course?

Answer 27

Acute hemorrhage is hard to see b/c it is gray and looks like CSF.Subacute hemorrhage looks white.Chronic hemorrhage looks dark. They also usually have a bright center with a dark rim.

Question 28

What is cerebral arteriographcy (angiography)?

Answer 28

The study of the central nervous blood vessels and related vasculature using radiographs during injection of a IV contrast (iodine-based) into cerebrovasculature via catheter in the femoral or brachial artery and threaded up to aortic arch. It is the gold standard for evaluating vasular diseases in the head, neck, and spine.

Question 29

What are the current uses of angiography?

Answer 29

1) characterization of lesions of blood vessels, AVM, aneurysms, cerebral venous sinus thromboses
2) differential diagnosis of tumors that produce “stain” or blush as the results of fine neovascularization- assess the tumor’s vascular anatomy when planning neurosurgery
3) visualization during interventions such as embolization

Question 30

What factors make angiography an invasive procedure?

Answer 30

It requires local anesthesia and catheter insertion, typically in the femoral artery

Question 31

What are less-invasive techniques for visualizing blood vessels? (3)

Answer 31

1) Doppler ultrasound
2) Magnetic Resonance Angiography (MRA)
3) CT Angiography (CTA)

These techniques are not as sensitive or specific

Question 32

What is EEG and its use? What are waveforms?

Answer 32

Electroencephalography (EEG) The original method for measuring brain activity, measuring electrical activity along the scalp (voltage fluctuations within neurons of the brain closest to the skull). Activity represents summed synchronous activity of thousands-millions of neurons with similar spatial orientation, measured in waveforms. Waveforms are classified according to frequency, amplitude, and shape. It’s useful in evaluating seizure activity and detecting widespread abnormality in brain function.

Question 33

What is evoked potential?

Answer 33

It is similar to an EEG. The brain’s electrical activity is recorded in response to specific stimuli; involves noninvasive stimulation of afferent pathways.

Question 34

Waveform frequencies: Alpha

Answer 34

8-12 Hz Observed in all ages but more common in adults; occur rhythmically and bilaterally but slightly higher in amplitude on the nondominant side; they predominate in posterior brain regions; are prominent when persons are relaxed with eyes closed and disappear when eyes are open or person is actively attending to info

Question 35

Waveform frequencies: Beta

Answer 35

12-30 Hz Observed in all ages; small amplitude, symmetric, represented in more anterior brain regions; sedative-hypnotic medications tend to increase

Question 36

Waveform frequencies: Theta

Answer 36

4-7 Hz Observed in all ages during sleep; in awake adults, excessive appearance is abnormal

Question 37

Waveform frequencies: Delta

Answer 37

up to 4 Hz Observed across the lifespan during sleep; abnormal if occurring in awake adults

Question 38

What is Wada testing?

Answer 38

Intracarotid Sodium Amobarbital Procedure, named for John Wada, uses barbiturate injection to cerebrovasculature via angiographically guided catheter, briefly anesthetizing each hemisphere allowing testing of function (cognitive, speech, motor) in the awake hemisphere

Question 39

What is a lumbar puncture used for?

Answer 39

Diagnose infective or inflammatory disorders, subarachnoid hemorrhage, and abnormalities or intracranial pressure that affect CSF. Puncture is made in the L3-4 or L4-5 intervertebral space below the spinal cord.