Introduction to Radiology

Question 1

Who discovered X-rays?

Answer 1

Wilhelm ROentgen 1895

Question 2

Describe the general theory behind x-rays?

Answer 2

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

Question 3

Why are x-rays capable to harming biological tissue?

Answer 3

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

Question 4

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

Answer 4

CT

Question 5

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

Answer 5

48%

Question 6

What are some deterministic effects of radiation?

Answer 6

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)

Question 7

What are some stochastic effects of radiation?

Answer 7

cancer like leukemia

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

Question 8

WHat is ALARA?

Answer 8

the practice of keeping exposure levels as low as reasonably achievable

Question 9

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

Answer 9

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

Question 10

What is the scientific unit of measurment for radiation?

Answer 10

millisieverts (mSv)

Question 11

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

WHere is the radiation coming from?

Answer 11

about 3 mSv

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

Question 12

Where does our evidence of cancer from radiation come from?

Answer 12

• 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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

the linear no-threshold dose response curve

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

bones and gas will show up well

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

Question 19

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

Answer 19

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

Question 20

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

In an extremity film?

Answer 20

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

AP, Lateral and Oblique

Question 21

How does ultrasound work?

Answer 21

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

Question 22

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

Answer 22

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

Question 23

How does computed tomography (CT) work?

Answer 23

it uses electromagnetic energy

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

Question 24

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

Answer 24

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

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

Why and when is oral contrast given?

Answer 28

oral contrast is used to opacify the bowel in abdominal studies

IV contrast can opacify the vessels

Question 29

What are the risks of IV contrast?

Answer 29

allergic reaction - most mild, but some severe

contrast-induced nephropathy

Question 30

How can we avoid contrast induced nephropathy?

Answer 30

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)

Question 31

How does MRI work?

Answer 31

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

Question 32

FOr what two body systems is MRI most useful?

Answer 32

brain and musculoskeletal system - especially the spine

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

Question 33

What are some pros and cons of MRI?

Answer 33

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

Question 34

How does nuclear medicine work?

Answer 34

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

Question 35

How does a barium examination work?

Answer 35

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

Question 36

How does PET work?

Answer 36

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

Question 37

What are some downfalls of PET?

Answer 37

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)