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Neuro Quiz 3 > Radiology Detailed_Jullet > Flashcards

Radiology Detailed_Jullet Flashcards

1
Q

CT: How does structures with HIGH hounsfield units (HU) look? Examples?

A

High HU = High attenutation; whiter Ex: bone

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2
Q

CT: How does structures with LOW hounsfield units (HU) look? Examples?

A

Low HU = low attenuation; darker. Ex: air/parenchyma

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3
Q

CT: What is the difference between BRAIN + BONE windows?

A

BRAIN: narrow range of density values (HU), which will result in better differentation of parehcymal structures, but bone will be less discrete. Bone: WIDE range of density HU values, improved visualization of bone but at the expense of brain parenchyma

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4
Q

CT: which one has higher attenutation - gray matter or white matter? How does this affect the image?

A

GM = lighter

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5
Q

CT: how does air look? CSF?

A

AIR: black becauase it does not attenuate beams. CSF: dark shades of gray

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6
Q

CT: Why is IV contrast used?

A

improve diagnostic capabilities. Structures that take up the dye will increase attenuation, thus making the tissue look whiter

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7
Q

CT: Why would you not use IV contrast for someone who has a hemorrhage? Why would you use it for someone who has a suspected tumor?

A

normal brain parenchyma does not enhance since the BBB is impermeable to the contrast dye. HEMORRHAGE: contrast will leak into the interstitial spaces, thus obscuring structures. TUMORS: new capilllary in tumors are abnormal and do not have the normal BBB, which is why most tumors will enhance.

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8
Q

CT: What is CT used to detect?

A

bone fractures, cerebral edema, epidural hematoma

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9
Q

MRI: What are the pros (3) and cons (3)?

A

PROS: 1) superior soft tissue contrast compared to CT. 2) multiple pulse sequences that can characterized lesions better than CT, 3) decrease need for biopsy
CONS: 1) Poor for bone imaging, since bone is devoid of water. 2) Expensive. 3) Long acquisition time (~3-5 minutes) per pulse sequence, and typically 4-6 pulse sequences are obtained for a complete brain MRI (not good for someone who has a hemorrhage or cerebral edema)

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10
Q

MRI: What is the basis for image acquisition??

A

Tissues will emit MR signals because they contain H2O, or molecules with an odd # of protons

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11
Q

MRI: What is an echo? How is it acquired

A

MR signal. Magnetic axes of tissue protons are randomly aligned, but will align along a magnetic field (MRI machine). A radiofrequency pulse is sent into the magnet, which is absorbed by the protons. This causes the protons to temporarily align against the field (high energy state). As, they relax, they emit the absorbed energy, which is recorded as the “MR signal” aka “Echo”.

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12
Q

MRI: What is a high signal intensity?

A

bright/white

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13
Q

MRI: What is a low signal intensity?

A

dark/black

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14
Q

MRI: What is a intermediate signal intensity?

A

gray

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15
Q

MRI: In a T1 weighted image, how does water and fat look?

A

WATER: low signal (dark), FAT: high signal (light)

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16
Q

MRI: In a T2 weighted image, how does water and fat look?

A

opposite to that of T1; WATER: high signal (light, think T2 = H2O), FAT: low signal (dark)

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17
Q

MRI: In a FLAIR weighted image, how does water look? What is it used for?

A

Optimal for showing fluid in abnormal locations (ie within parenchyma). FREE FLUID/CSF: dark like T1, PARENCHYMA FLUID: bright like T2

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18
Q

MRI: In a DIFFUSION weighted image, how does water look? What is it used for?

A

Areas where there is restricted diffusions (ie stroke, cytotoxic edema) are BRIGHT

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19
Q

MRI: What is the contrast used? How does it affect MRI imaging?

A

Gadolinium. Affects the proton relaxation times on T1 (but no significant effect on T2 images!!)

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20
Q

MRI: What is MRI used to diagnose?

A

fluid and swelling, blood, cortex and white matter abnormalities

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21
Q

How do you tell the difference between CT and MRI?

A

MRI: Bone is Black since it is devoid of water. CT: white unless bone window is used, then it is mid-gray

22
Q

Proton MR: What is this used for? What does it measure?

A

Performed in conjunction with a standard brain MRI to narrow in on potential pathological processes. Measures relative amounts of certain compounds in specific areas of the brain by detecting protons bound in different molecules, which will have different resonant frequencies

23
Q

Proton MR: What does increased choline signify?

A

cell proliferation or cell turnover (tumors/neoplasm)

24
Q

Proton MR: What does creatine signify?

A

internal control

25
Q

Proton MR: What does N-acetylaspartate (NAA) signify?

A

NAA is an amino acid that is abundant in neurons. Decreased levels indicate neuron destruction, decreased in tumors

26
Q

Proton MR: What does increased lactate signify?

A

Lactate is normally not present, but is present in ischemia; can be used to identify hypoxic ischemic insult in neonates

27
Q

fMRI: What is it used for? How is it acquired?

A

localize the region of cerebral cortex that controls a specific function. Images obtained BEFORE and DURING task and the images are compared to locate differences in signal intensity

28
Q

How can contrast dyes be harmful?

A

CT: iodine dye can cause acute tubular necrosis, leading to renal failure. MRI: Galodium doesn’t harm the kidneys, but it can build up in the kidneys of patients with pre-exisitng renal failure and can cause nephrogenic systemic fibrosis (NSF)

29
Q

What are invasive ways to measure intercranial vasculature? Noninvasive ways?

A

NON-INVASIVE: CT angiography (CTA) and MR angiography (MRA). INVASIVE: conventional (catheter) angiography

30
Q

CTA: How is it acquired?

A

Contrast is injected through the peripheral vein and ~20 seconds is allowed to pass before the scanning begins. This allows the contrast to travel through the arteries but not the veins. Blood vessels have a high attenuation and are easily distinguished from relatively the brain parenchyma, which has relatively low attenuation. Brain parenchyma is manually subtracted out of hte image such that only the blood vessels are displayed

31
Q

CTA: Pros? Cons?

A

PROS: shows lumen diameter + characteristics (plaques, intramural hemorrhage, vessel dissection) CONS: cannot be performed without IV contrast and radiation exposure

32
Q

MRA: How is it acquired?

A

technique capitalizes on inherent properties of flowing blood to create the image; thus flow velocity can be attained by comparing both hemispheres to see how fast the dyes travels. Images can be contrasted vs non-contrast enhanced

33
Q

MRA: Pros? Cons?

A

PROS: no radiation, can view circle of willis, no artifact or interference from the skull or brain, can obtain flow velocity. CONS: long acquisition time, only large vessels are adequately visualized

34
Q

Conventional Angiography: how is it acquired?

A

Fluoroscopic guidance of a wire through a large artery using continuous XRAYs. Once the wire reaches the ICA or vertebral artery, contrast is injected into the artery while rapid sequetnial images are taken

35
Q

Conventional Angiography: Why would you want to inject the contrast into the ICA as opposed to the CCA?

A

dye will also flow into the external carotid artery, which will obscure portions of the intracranial vessels.

36
Q

Conventional Angiography: Pros? Cons?

A

PROS: measure flow dynamics, better resolution of small vessels/arteries than CT/MRA. CONS: cost, risk, only lumen is visualized - does not provide any information about wall, plaque character, intramural blood

37
Q

Conventional Angiography: What is the purpose of digital subtraction angiography? How is it acquired?

A

Reducing background (ie this method prevents small vessels from being obscured by the bone structures). ACQUISITION: An initial xray image is taken prior to injecting the contrast, and this is subtracted from dye-images to remove bone structures

38
Q

Conventional Angiography: When would you use this?

A

1) identify aneurysms (which can rupture and cause catastrophic hemorrhage), 2) cerebral ischemia - to identify occluded or narrowed intracranial arteries, particularly small vessels, 3) Arterio-venous malformations - to identify congenital abnormal connections between arteries and veins

39
Q

What imaging technique is better to visualize bone?

A

CT because it has better spatial resolution

40
Q

How do you differentiate between acute vs chronic spine fracture?

A

Although MRI is not sensitive for evaluation of bone, certain MRI sequences can suppress the signal from marrow fat and augment the signal from fluid to determine if spinal fractures are acute or chronic (old), by demonstrating bone marrow edema

41
Q

What imaging technique would you use to visualize CSF, dura and nerve roots?

A

MRI - used to evaulate all soft-tissue structures of the spinal canal, since these are not seen on CT (very low resolution)

42
Q

What is an alternative imaging techqniue if a patient can’t have an MRI done?

A

Myelography - contrast study of the subarachnoid space.

43
Q

Myelography: how it acquired?

A

sterile contrast is injected into the subarachnoid space, and the spinal cord and nerve roots are “filling defects”

44
Q

Myelography: cons?

A

PROS: excellent resolution of the subarachnoid space. CONS: invasive procedure, risks of bleeding, post procedure headache, infection

45
Q

Nuclear medicine: What is it used for? What are the different types of nuclear medicine imaging? (3)

A

Evaluates function, rather than structure (like CT, MRI, Angiography). TYPES: 1) PET scan, 2) cerebral perfusion, 3) neuronal uptake

46
Q

Nuclear medicine: How is it acquired?

A

FDG (radioactive glucose) is injected into a patient via IV and is taken up and concentrated by tissues/cells with high glucose metabolism. Result: very low anatomic resolution image, but HIGH METABOLIC resolution

47
Q

Nuclear medicine: What is a PET scan used for?

A

detect tumors or characterize dementia (different types of dementia demonstrate different patterns of reduced cerebral glucose metabolism!)

48
Q

Nuclear medicine: What is a cerebral perfusion scan used for?

A

areas of high regional perfusion will appear “HOT” (ex: seizures – results in increased local blood flow)

49
Q

Nuclear medicine: What is a PET scan used for?

A

used to determine areas with reduced/absent neuronal uptake (brain death); will appear “COLD”

50
Q

Nuclear medicine: What are some examples of radiopharmaceuticals?

A

FDG and lipophilic agents

51
Q

How is a CT different than a nuclear imaging?

A

CT: source of radiation is external and radiation source penetrates through the patient; any radiation that is not attenuated by the patient is absorbed by the detector
NUCLEAR MEDICINE: radiation is emitted from the patient, which is detected by a gamma camera

Neuro Quiz 3 (7 decks)

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