Basics of Imaging Flashcards

1
Q

What type of studies are mammograms and fluroscopic?

A

X-ray based

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2
Q

How is a standard X-ray generated?

A

Via heating of Tungsten to fire off photons. More dense areas will by light because fewer photons got thru. Many photons = black

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3
Q

What color does air appear on CT? Fat? Water?

A

Air = completely black
Fat = slightly more black than water (less dense)
Water = neutral
Muscle / tissue = slightly more white than water

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4
Q

Why are X-rays dangerous?

A

They break molecular bonds, and specifically water bonds to produce H and OH free radicals

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5
Q

What percentage of photons emitted from a Tungsten filament are actually used for imaging?

A

15%

85% are emitted away

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6
Q

How many equivalents of background radiation are used for a thorax CT?

A

About 6 months of background radiation

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7
Q

How much equivalent radiation does a flight from USA to China give?

A

One single view chest X-ray

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8
Q

What is the most common cancer linked to radiation and when does it occur?

A

Leukemia - usually 15 years after exposure longterm. Exposure effects are cumulative

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9
Q

What are the two most radiosensitive organs?

A
  1. Thyroid

2. Reproductive organs

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10
Q

What is MRI measuring?

A

Protons in water will align to the lowest energy state in a magnetic field. When a radiofrequency pulse is applied, MRI measures the time it takes for a proton to return to resting state, and the energy that was released to do this

Measures the energy as it relates to surrounding tissue (absorbed via fat, soft tissue, or other fluid)

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11
Q

What is MRI best for? How does the strength of the magnet change this?

A

Best for evaluating soft tissues, since energy released is very much based on surrounding soft tissues.

Higher magnet strength = greater resolution

3T magnet is the standard today

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12
Q

How does fluid appear in T1 weighted sequences and what are they used for?

A

Fluid appears black. Used for studying anatomy + when we are using a contrast (which will appear a different color)

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13
Q

How does fluid appear in T2 weight sequences and what is it used for?

A

Fluid is white

Sensitive to pathological processes like vascular abnormalities.
Eyes will be white in this scan (filled with water)

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14
Q

What is a gradient echo and what is it used for?

A

A type of T2-weight image

CSF will appear white, but its parameters are turned up so high than black dots are seen in blood due to iron (FE)

Used for detection of microhemorrhages

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15
Q

What type of image is Diffusion Weighted Imaging and why is the CSF black?

A

It’s a T2 weighted image

CSF is black because it is diffusing freely. The parameters are turned up so only fluid trapped in cellular swelling in stroke can be seen (osmolytes build up in brain cells)

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16
Q

What is DWI used for?

A

Most important sequence in MRI -> used for detection of stroke in brain, with non-moving fluid. Will appear white. Free-moving liquids will appear black

17
Q

What is contrast used for?

A

Determining blood flow in organs and tumors -> does the tumor have primarily arterial flow, how good is the venous drainage, etc

18
Q

What are the contrasts used for CT / MRI? Are these substances safe in pregnancy?

A

CT - iodine, substance safe in pregnancy

MRI - gadolinium, unsafe in pregnancy

19
Q

What is the biggest side effect of MRI?

A

Noise / claustrophobia

20
Q

Can CT be done during pregnancy?

A

Nope, too much radiation. Only MRI without contrast can be done with pregnant women