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Flashcards in Introduction to Radiology Deck (38)
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1
Q

Who discovered X-rays?

A

Wilhelm ROentgen 1895

2
Q

Describe the general theory behind x-rays?

A

x-rays are waves of ionizing energy that will pass through the patient and strike a cassett which contains a screen of fluorescent phosphors that will expose the film

the x-rays will pass thorugh material differently depending on density

they will not pass through bone, so bone swill appear white.

They will pass through air, so lungs appear black

they will pass through water and gas to a lesser extent = gray

3
Q

Why are x-rays capable to harming biological tissue?

A

it is short wave length, high energy rays that can displace electrons from their energy level or shell around the nucleus

the displaced electron can harm the tissue, as can the resultant free radical

4
Q

What form of medical imaging is responsible for the majority of excess radiation exposure?

A

CT

5
Q

What percentage of our radiation exposure is due to medical imaging?

A

48%

6
Q

What are some deterministic effects of radiation?

A

these are actual cell death:

skin erythema, epilation, radiation burns, or cataracts

these are easier to document and predict because there is an exposure threshold (.5-2 Gy dose to les leads to risk of cataracts)

7
Q

What are some stochastic effects of radiation?

A

cancer like leukemia

these are more difficult to predict - we don’t know the threshold level

8
Q

WHat is ALARA?

A

the practice of keeping exposure levels as low as reasonably achievable

9
Q

What are three reasons why children are at greater risk for stochastic effects?

A

They live longer, so there is more time for the cancer to develop after exposure

they have a higher proportion of rapidly dividing cells

they are smaller, so it’s more difficult to shield them effectively

10
Q

What is the scientific unit of measurment for radiation?

A

millisieverts (mSv)

11
Q

What is the yearly background radiation we’re exposed to on average?

WHere is the radiation coming from?

A

about 3 mSv

from radon gas from the earth, natural radioactivity from rocks, cosmic rays, smoke detectors, TVs, etc.

12
Q

Where does our evidence of cancer from radiation come from?

A
  • people treated for thymic disorders can develop tumors in those areas
  • people with TB or scoliosis have multiple chest studies and have higher risk for breast cancer
  • atomic bomb survivors
13
Q

What amount of radiation dose is needed for a significant increase in cancer risk?

A

studies vary, some say 5-125 mSv, others say 50-120 mSv

14
Q

What is the most widely accepted risk model estimating the lifetime risk of radiation-induced cancer>

A

the linear no-threshold dose response curve

15
Q

What does the lienar no-threhold dose response curve model say is the cancer risk to radiation?

A

1/1000 patients exposed to 10 mSv effective doses of radiation will develop a radiation-induced cancer

16
Q

What are some technical things we can do to reduce radiation dose?

A
  1. decrease tube current or voltage (but this will increase image noise)
  2. Choose wider collimation or change the speed at which the table moves
17
Q

At what point during pregnancy is x-ray imaging advised against?

A

Try to avoid exposure during first trimester because that’s the time of organ formation (especially in first two weeks)

18
Q

In an abdomen film, what shows up well and what will not be seen?

A

bones and gas will show up well

abdominal orgens like the liver, spleen and kidneys are not well seen

19
Q

Why is it necessary to always get more than one view when taking x-rays

A

x-rays are two dimensional pictures of three dimensional objects, so you need at least two to be able to figure out what you’re dealing with and where it is in the body

20
Q

What are the different views you can take in a CXR?

In an extremity film?

A

PA, AP, Lateral, Lateral decubitus view (laying down

AP, Lateral and Oblique

21
Q

How does ultrasound work?

A

it uses high frequency sound waves that leave a probe, travel through the body, and are reflected back to the machine to be analyzed

the location of the structure is based on the amount of time required for the sound waves to return to the prove

the intensity of the echnoes on the image is dependent on the composition of the structures

22
Q

What are some of the things we almost always use ultrasound for?

A

evaluating pregnancy

evaluating the gallbladder (this is the absolute best way for this)

asses abdominal or pelvic pain in a woman (really good at evaluating the uterus and ovaries)

evaluate abdominal pain in children and thin females (they don’t have fat to act as a contrast for CT anyway)

evaluating veins for DVT

23
Q

How does computed tomography (CT) work?

A

it uses electromagnetic energy

the patient moves through a gantry and it makes scans form many angles and generates a 3D image

24
Q

In terms of the brain, what is CT best for?

A

it’s the best test for screening the brain for acute hemorrhage

also the best to look for mass effect or herniation

NOT as god as MRI for seizure foci, MS, acute or non-hemorrhagic infarction

25
Q
A
26
Q

In terms of the chest, what is CT best for?

A

it’s the best for almost all imaging of the chest, including PE, tumor, and interstittila lung disease

27
Q

In terms of the abdomen, what is CT best for?

A

This is the best test for almost all abdominal screening, including tumor, inflammation, obstruction, or urinary tract disease, including stones

28
Q

Why and when is oral contrast given?

A

oral contrast is used to opacify the bowel in abdominal studies

IV contrast can opacify the vessels

29
Q

What are the risks of IV contrast?

A

allergic reaction - most mild, but some severe

contrast-induced nephropathy

30
Q

How can we avoid contrast induced nephropathy?

A
  1. screen patient’s renal function
  2. only use contrast when indicated
  3. keep the patient well hydrated
  4. give mucosmist to diabetics on metformin (an antioxidant)
31
Q

How does MRI work?

A

It uses a high field strength magnet to align hydrogen ions

a radio frequency pulse specific to hydrogen ions causes them to spin

over time, the hydrogen atoms will return to alignment with the magnetic field

different tissues will return to alignment in different amounts of time

32
Q

FOr what two body systems is MRI most useful?

A

brain and musculoskeletal system - especially the spine

it’s typically only a problem solving technique in the chest abdomen and pelvis

33
Q

What are some pros and cons of MRI?

A

It does not use ionizing radiation, so no risk of cancer

but….it takes a long time and it’s expensive

plus, people have to hold still for a long time in a really some gantry

metal causes lot so f artifacts and there are contraindications: pacemakers, aneurysm clips, other surfical devices

34
Q

How does nuclear medicine work?

A

radiotracers are injected into the body and then the patient is imaged with a special scanner to visualize the tracers within the body

this allows the test to be more functional, but you get less detailed anatomic information

35
Q

How does a barium examination work?

A

it utilizes x-rays

the barium contrast material is placed into the GI tract - either a barium swallow or a barium enema, depending

less common now - we use endoscopy and CT more

36
Q

How does PET work?

A

it uses fluorine 18 fluorodeoxyglucose or FDG
, which is an analog of glucose

it’s good for loking at tumors because tumors take up glucose at higher rates

37
Q

What are some downfalls of PET?

A

images often lack anatomic landmarks for precise morphologic orientation - that’s why they are oten overlayed with CT scans

the sites of pathologic uptake could be confused with normal physiologica uptake or vice versa (i.s. the brain, bladder, and left ventricle take up more glucose naturally, but that doesn’t mean a tumor can’t grow there as well)

38
Q
A