NB2-1 - Practical Clinical Neuroimaging DLAs

Question 1

Describe how a cerebral angiography is done, the risks associated with it, and the typical indications for performing it.

Answer 1

A cerebral angiography involves taking an X-ray of the head after a contrast medium (usually containing iodide) is injected into the blood supply. Risks associated with this procedure include allergic reaction and/or arterial spasm which can lead to a cerebral infarction. This procedure is usually performed to locate vascular malformations and obstructions.

Question 2

Answer 2

1. Internal Carotid artery
2. Carotid Siphon
3. Anterior Cerebral Artery
4. Medial Cerebral Artery
5. Posterior Cerebral Artery

Question 3

Answer 3

1. Internal Carotid Artery
2. Carotid Siphon
3. Anterior Cerebral Artery
4. Medial Cerebral Artery
5. Posterior Cerebral Artery

Question 4

What is the arrow pointing to?

Answer 4

A vascular tumor on the middle cerebral artery

Question 5

Name what type of imaging modality is used in each picture, describe the differences between them, and when you’d use one over the other.

Answer 5

Left - Conventional angiography; Right - Digital subtraction angiogaphy

With digital subtraction angiography, an X-ray without contrast is taken as well. A computer then subtracts the structures the images have in common. These removes any structure that does not have contrast in it from the image. This allows you to see vessels that would otherwise be obscured.

Question 6

Name and describe the imaging modality used here. What is the arrow pointing to?

Answer 6

The imaging modality is myelography which involves injecting contrast into the subarachnoid space, via a lumbar puncture, and taking an X-ray.

The arrow is pointing to a pathologic narrowing of the subarachnoid space

Question 7

What structures can a head CT diffentiate well? What structures can it not?

Answer 7

• A head CT can differentiate bone, white matter, gray matter, and fresh blood (hemorrhage)
• A head CT suboptimally represents brainstem structures due to interference from the skull

Question 8

What is the pathology present in this patient? What usually causes this pathology?

Answer 8

An epidural hemorrhage which is usually caused by a skull fracture damaging the dural vessels

Question 9

What pathology is present in this patient?

Answer 9

A subarachnoid hemorrhage

Question 10

What pathology is present in this patient? What typically causes this pathology?

Answer 10

A subdural hemorrhage which are often causes by trauma-induced tearing of the dura

Question 11

On a CT, how can you tell the difference between an epidural and subdural hemorrhage?

Answer 11

An epidural hemorrhage has a biconcave shape (look more like a circle) while a subdural hemorrhage often has a crescent shape

Question 12

How does an MRI generate an image?

Answer 12

The MRI machine applies a strong magnetic field to the body that aligns the magnetic moments of hydrogen protons. It then pulses a radio wave that disrupts this alignment. When the protons realign, this yields a signal that the machine uses to generate an image.

Question 13

Describe the differences between T1 and T2 MRI and the applications for both of them.

Answer 13

T1 signals are most strongly emitted from fatty tissue, making fat appear brighter. Because much of the nervous system is composed of fat, T1 is useful for imaging the structure of the nervous system.

T2 signals are most strongly emitted from water tissue, making CSF, blood, urine, etc appear brighter. This is useful for finding pathologies such as edemas.

Question 14

What type of imaging modality is used here? How can you tell?

Answer 14

This is a T1 MRI. The bones are not bright, ruling out CT or X-ray. The ventricles (filled with CSF) are dark, ruling out T2 MRI. Also the fat in the face is bright, which indicates T1.

Question 15

Which MRI imaging modality is most useful for differentiating gray and white matter? Why?

Answer 15

T1

The biggest difference between grey and white matter is the presences of myelin, which is full of fat.

Question 16

Describe the advantages and disadvantages of using T1, T1 with contrast, and T2 when scanning for a brain tumor.

Answer 16

T1 - easiest method, may still see the tumor but it wont be well defined

T1 with contrast - if tumor disrupts the BBB then the contrast will define these disruptions very nicely. May cause allergic reactions or vascular spasms, may not help locate tumor.

T2 - easiest method, will see edema from the tumor very well which may outline the tumor, it also may obscure the tumor.

Question 17

Say what the imaging modality is

Answer 17

Question 18

What is the contrast agent typically used with MRI Angiography?

Answer 18

Gadolinium

Question 19

What does PET stand for? How does a PET scan produce an image? What is this useful for?

Answer 19

PET stands for Positron Emission Tomography. An unstable (short half-life) radioisotope of a physiologic molecule (usually glucose) is introduced into the blood stream. In the case of glucose, it can be taken up by neurons but not metabolized. A proton in the isotope decays into a neutron and a positron. When the positron collides with an electron, two gamma-rays (photons) are emitted in perfectly opposite directions. Detectors encircling the body record this emission and can estimate its source. This is useful for observing physiological processes.

Question 20

What does SPECT stand for? How does a SPECT scan generate and image and what is this modality usually used for?

Answer 20

SPECT stands for Single Photon Emission Computerized Tomography. This technique uses a radiotracer that emits a single gamma ray (photon) instead of two (like PET). It cannot provide an image as detailed as PET and is therefore most often used to determine cerebral blood flow.