Lecture 2

Question 1

what are the two types of radiation damage ? give examples of each kind of damage

Answer 1

deterministic: dose dependent, there are “safe” thresholds, effects include erythema, hair loss, sterility, cataracts, lethality, radiation burns, etc

stochastic effects: no dose associated, singular exposure can cause cellular mutation and cancer, consequences do not change per dose BUT risk does increase with dose, more of a cummulative effect

Question 2

the average public exposure per year is

Answer 2

2-4mSv

Question 3

tissues with particular sensitivity to radiation include:

Answer 3

testes/ovaries, lymphoid tissue, bone marrow, intestine

Question 4

canadian limits on exposure
- what is the annumal limiation and the 5 year limitation?

Answer 4

annual: 50mSv
5 year: 100mSv, if pregnant, 4mSv

Question 5

list 3 ways you can decrease radiation exposure

Answer 5

reduce time (retakes, mAs)
increase distance (think of inverse square law)
increase shielding

Question 6

true or false: protective gear for radiographs are to protect you from the primary X ray beam

Answer 6

FALSE it is to protect you from scatter radiation DUH

Question 7

what is the difference between diagnostic and theraputic ultrasound?

Answer 7

diagnostic US is at a higher frequency and works at a depth of up to 20cm and there is no clinical effect on the tissues

theraputic works at a low frequency and works at depts of 1-3cm, and has an impact in many aspects of inflammation to promote healing

Question 8

explain briefly what an ultrasound is

Answer 8

an oscillating sound pressure wave outside the frequency of human hearing (above 20,000 Hz), contains traits like amplitude and frequency

Question 9

how is an ultrasound image produced?

Answer 9

crystals vibrate and send out a sound wave to the tissues, and then the crystals detect whatever is reflected back

Question 10

in regards to ultrasound, what is attenuation?

Answer 10

the loss of the signal intensity during it’spath through the tissue

Question 11

list some examples of factors that affect an ultrasound image

Answer 11

tissue density, frequency of probe, depth of tissue, focus, gain, etc

Question 12

which is better at penetrating deeper tissues, high or low freq?

Answer 12

low–>think of whales talking to each other in a really low freq really far distances

Question 13

describe what gain is in regards to an ultrasound

Answer 13

it is essentially how long you listen for sounds to return or how long you’re waiting for more echos to come back. when you increase gain, you allow the machine to “listen” for more sound waves

Question 14

what does being “off beam” mean in regards to an ultrasound?

Answer 14

if the waves dont hit the tissues exactly perpendicular to the tissue, they are defelcted and lost, which is why you rock the probe back and forth to get the sound waves to line up perpendicular to the tissue so the machine can then detect the waves as they are reflected back

Question 15

briefly explain what a CT scan is and how it works

Answer 15

it is a radiograph on steroids, it uses ionizing radiation but there is a rotating gantry with both a generator and a detector. the detector spins around in a circle so you’re getting a 3D radiograph. Produces a “volume of voxels” which is essentially a bunch of transverse sections put together to make a 3D image. The computer can reconstruct these sections into any plane you want. This eliminates superimposition

Question 16

list some pros and cons of CT scans?

Answer 16

pros: superior contrast resolution, eliminate superimposition, multiplanar reconstruction

cons: require anesthesia, greater exposure to radiation, expensive, lots of data

Question 17

briefly explain how MRIs work and what they are

Answer 17

expose patient/tissue to magnet, which aligns all of the electrons in a certain plane, then you use a second magnet to disrupt the alignment, when the second magnet is taken away, the rate at which the electrons return to alignment is detected (depends on the hydrogen in each tissue type)

Question 18

list some pros and cons of MRIs

Answer 18

pros: superior contrast resolution, eliminate superimposition, multiplanar reconstruction, no radiation, better than CT for soft tissue like brain and spinal cord, can see bone edema

cons: requires anesthesia, takes time, subject to artifacts, expensive, lots of data, CT is better for bone marigins and lytic lesions

Question 19

briefly explain nuclear scintigraphy. pros and cons?

Answer 19

you inject the patient with technetium 99 and it goes to places of inflammation. it is also radioactive (releases gamma rays) and this can be detected by a gamma camera

pros: very sensitive (notspeific)

cons: nonspecific, not anatomically specific, poor spatial resolution, labor intensive (requires isolation), acquisition time is long (you have a radioactive animal)