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MS Week 1 > Imaging > Flashcards

Imaging Flashcards

1
Q

Does an X-ray have more or less energy than light? Long or short wavelength? Why does this matter?

A

More and shorter wave length.

Because they have more energy, they are able to pass through some substances that light cannot.

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2
Q

What is the basis of X-rays?

A
  • X rays pass through/are blocked to varying degrees by different substances.
  • Depends on the density and thickness of substance
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3
Q

What are the methods of obtaining an x-ray image?

A
  1. Films with fluorescent phosphorous
  2. Computed Radiology (CR) where x-rays strike a sensitized plate which is read and digitalized into a computer image.
  3. Digital Radiography (DR) where x-rays strike a plate of sensors producing the computer image directly
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4
Q

Are x-rays a form of ionizing radiation? Why is ionizing radiation bad?

A

Yes. This is a hot topic, especially with regard to pediatric patients. The goal is to reduce radiation exposure.

Ionizing radiation can displace electrons creating “free radicals” that harm biologic tissue via cell death.

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5
Q

What imaging study is responsible for most ionizing radiation in the US? How is radiation measured?

A

The CT scan (especially a pelvis and A/P = 15 mSv)! Radiation is measured in millisieverts (mSv)

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6
Q

What are the deterministic effect of radiation? Can we predict and document these?

A

Deterministic effects result from cell death.
Examples include skin erythema, epilation, radiation burns and cataracts. These are easily predicted/documented because there is an EXPOSURE THRESHOLD.

Effective dose is estimate of radiation effect to POPULATION, not a specific patient

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7
Q

What are the stochastic effects of radiation? Can we predict and document these? What is ALARA?

A

The stochastic effects of radiation are cancer or leukemia. These are hard to predict because there is NO THRESHOLD. May/may not occur, after a long delay (think pediatric patients!), at a very low rate. Just the possibility of these effects lead to exposure levels being kept as low as reasonably achievable (ALARA).

Effective dose is estimate of radiation effect to POPULATION, not a specific patient

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8
Q

Why are pediatric patients more at risk for stochastic radiation?

A
  • Stochastic effects generally occur many years after radiation exposure- a child has many more years of life than an elderly patient.
  • They have a higher proportion of rapidly dividing cells aka radiosensitive cells
  • Harder to shield due to small size
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9
Q

What shape of curve is the lifetime risk of radiation-induced cancer?

A

A linear, no threshold dose response curve.
Average lifetime attributable risk of 1/1,000 patients receiving a 10mSv effective dose. Approximately half expected to be fatal.

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10
Q

Do medical x-rays pose a threat to a developing fetus?

A

No, but all females are screened and take a pregnancy test if necessary.

  • x-rays are highest risk during the 1st trimester because the fetus is in very early development.
  • Risk decreases with fetal age, so must balance risk to mother with risk to fetus. Would still do an x-ray if you suspect a PE or appendicitis.
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11
Q

What is the first line of imaging for evaluation of the lung, heart and skeleton? Why?

A

X-ray, due to its availability, speed and low cost.

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12
Q

Examples of x-ray images. Are they 2D or 3D?

A

2D–> ALWAYS get more than one view

  • Chest x-ray (CXR)
  • Spine films
  • Skeletal films
  • Abdomen films
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13
Q

How do x-rays pass through bones, metals, air and fat respectively?

A
  • Bones and metals ABSORB x-rays, making them look WHITE.

- Air or fat PASS THROUGH x-rays, making them look black.

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14
Q

What is the basis of ultrasound? Does it involve ionizing radiation?

A

High frequency sound waves leave probe, travel into body and are differentially reflected back to the machine for analysis. Location of structures is based on time to return, composition of structure is based on intensity of echoes.
- Fluid is black, reflections are white (fat/gallstones)

NO.

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15
Q

How to differentiate a gallstone from tumor in gallbladder? What imaging?

A

Use ultrasound- the fluid is black while stones are white. if a gallstone, they should be MOTILE and move as your reposition the patient.

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16
Q

What is ultrasound used for?

A

Evaluating pregnancy and gallbladder!

  • Best way to assess abdominal or pelvic pain in women, very good at evaluating the uterus and ovaries
  • Good option for children because NO radiation
  • Deep vein thrombosis leading to pulmonary emboli
17
Q

What is the basis for CT?

A

Electromagnetic energy (ionizing radiation) moves around the patient in a tube (the GANTRY moves) scanning from many angles to generate a 3D image.

18
Q

What is CT used for? What is it NOT suited for?

A
  • Best test for screening the brain for acute hemorrhage, and looking for mass effect or herniation in the brain.
  • Best test for almost all imaging of the chest (PE), tumor and interstitial lung disease.
  • Best test for almost all abdominal screening (tumor, inflammation, obstruction, urinary tract disease/stones). Can actually see the KUB (vs KUB x-ray, see none of that)

Not suited for GB disease or abdominal pain in young women (US is best).

19
Q

When is MRI more advantageous than CT?

A
  • MRI is preferred for seizure foci or MS.

- MRI is preferred for acute, non-hemorrhagic infarction (stroke). CT could miss this initially.

20
Q

How does CT administered? When is it used?

A

CT Contrast is an iodine based dye
Oral: opacify the bowel (esophagus, stomach, small bowel)
IV: opacify vessels, demonstrate lesions in organs, identify lymph nodes from their adjacent vessels

21
Q

What are the risks of CT Contrast? What screening test do we use?

A
  • Allergies:
    1. usually mild, rash/hives
    2. rarely, severe hypotension, bronchospasm and death
  • Nephropathy: VERY common source of acute renal failure. MUST TEST FOR RENAL FUNCTION. Risks: preexisting poor renal function, type 2 diabetes, nephrotoxic drugs and reduced IV volume.
22
Q

How can we prevent CT contrast neuropathy?

A

RENAL SCREENING

  • hydration
  • mucomist- antioxidant given to people on some hypoglycemia agents (metformin)
  • Try different contrast medias
23
Q

What is the basis for MRI? How is an image generated?

A
  • Tissues are mostly water with 2 hydrogen atoms/protons.
  • In the magnet, dipoles of protons line up with direction of magnetic field
  • A radiofrequency pulse is applied to flip the spins
  • Protons then relax as electromagnetic field is turned off
  • Receiver coils read the radio frequency signal generated by tissues

Image generated by length of TIME for protons to relax, resulting in different signals sent to coils.

24
Q

Is an MRI safe? When is it contraindicated?

A

YES! Especially compared to CT- it has no ionizing radiation.

  • Risky with patients with pacemakers or implants like aneurysm coils, surgical devices.
  • Image may have artifacts due to other metals (like braces or rods in bones etc.)
25
Q

What are the limitations of MRI?

A
  • MRI is slow (motion artifacts) and expensive!
  • Viewed previously as a problem solving technique in the chest, abdomen and pelvis.
  • CANNOT generate sagital view with MRI data (can with CT). You MUST have images taken with the patient in the tube.
26
Q

When is MRI used?

A
  • Best imaging of anatomic images of brain, spine and musculoskeletal system
  • Important for imaging patients with inflammatory bowel disease (can see active inflammation and complications of prior inflammation)
  • Important for evaluating liver for hepatocellular carcinoma in patients with liver cirrhosis. May use contrast to differentiate between cancer and benign liver lesions.

Good because lack of ionizing radiation!

27
Q

How does MRI contrast work? When is it used?

A

MRI contrast is a gadolinium metal bound to organic chelate, causes changes in T1 relaxation times
- Used for CNS and abdominal imaging and arthrograms

28
Q

What are the risks of MRI contrast?

A

Mild hives, nausea, bad taste
NOT nephrotoxic BUT can lead to NSF (renal function check first!)
Anaphylactoid reactions are rare

29
Q

What is nephrogenic systemic fibrosis? How is it prevented?

A
  • NSF is a rare condition caused by gadolinium based contrast (MRI contrast) that leads to multisystem fibrosis.
  • Risk factors include chronic renal insufficiency, hemodialysis and multiple exposures to contrast

Prevented by screening for renal function before MRI contrast!

30
Q

What is the basis for nuclear medicine? When is it used?

A

Radiotracers are injected into the body, giving less anatomic information but more functional data. White areas are more metabolically active and take up more tracer!
- Often used for liver/biliary disease, GB disease (autoimmune attack of brain) or bone scans

31
Q

What is the basis of a barium study?

A

Barium studies use contrast placed into GI tract and visualized by x-ray.
- Antegrade for upper GI and retrograde for colon.

32
Q

When is a barium study used? What technology is now more effective?

A

Previously used to evaluate the bowel.

  • Now we can use endoscopy to visualize the bowel and take direct biopsy if necessary.
  • CT has also replaced barium in diagnosing diverticulitis and small bowel obstructions
  • Could also swallow camera
33
Q

What is the basis for a positron emission tomography (PET) scan?

A

Uses fluorine 18 flurodeoxyglucose (FDG) to demonstrate abnormal metabolism in organs that appear morphologically normal. Glucose and FDG are similar enough that they are taken up by the same mechanism, so high FDG is indicative of metabolism.
- A functional imaging modality!

34
Q

When is a PET scan used? What are its limitations?

A

Cancer. Basis: tumors take up more glucose (and FDG) than surrounding cells because they have increased metabolic activity.
- Infection/inflammation may also have increased metabolism due to healing processes and thus could be mistaken for a tumor!

35
Q

Why are PET/CT done together? When is it used?

A

PET scans lack anatomical landmark- by using it and a CT you can see metabolic uptake with accurate localization of anatomy.

  • Improves sensitivity and specificity of information!
  • Used for oncologic imaging!

MS Week 1 (11 decks)

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