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HEENOT 2 > Intro to Radiology > Flashcards

Intro to Radiology Flashcards

1
Q

Why is it important to limit use of radiology to necessity?

A

The amount of radiation for medical purposes is several times higher than environmental exposure

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2
Q

Risk of x-ray of fetus

A
  • increases probability of developing a malignancy in the first 10 yrs of life by about 40%
  • always ask, if unsure obtain urine beta-HCG
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3
Q

If a patient is pregnant is it possible to xray ?

A

Yes. Can xray areas away from abdomen w/ proper shielding

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4
Q

How are xrays produced?

A

-ionizing radiation:
Inside the xray machine, heat is applied to a cathode. The positively charged anode draws electrons from the cathode. This is a very high voltage difference so electrons are sent w/ high force, and w/ colliding atoms eventually energy is released in the form of an xray photon.

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5
Q

Charges of cathodes/anodes.

A

Cathode: -
Anode: +

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6
Q

What is the relationship between voltage and energy?

A

The degree of energy of the beam is proportional to voltage.
Higher voltage = more penetration.

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7
Q

Differential absorption of xrays

A
  • Gas (air) = black (blocked no xrays so will be the darkest)
  • Fat = slightly more dense than air
  • Soft tissues (muscle, solid viscera)
  • Calcified = white (blocked the most xrays)
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8
Q

What properties allow you to visualize things on xrays?

A
  • contrasting tissues

- between black and white, everything is gray. The human eye can recognize ~20 shades of gray.

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9
Q

Ways to enhance xrays

A
  • change kilavoltage: higher kV = more penetration = more black
  • use of grids (Bucky grid) to reduce scatter
  • Use of fluorescent screens to reduce exposure
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10
Q

How are plain films viewed?

A

as if the patient is facing you

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11
Q

If you want and xray to capture the heart and lungs, what view would you select?

A
  • PA

- beam penetrates posterior to anterior

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12
Q

If you want to capture the spine, what xray view would you select?

A

-AP

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13
Q

Explain why you always need at least 2 views in an xray

A

Sine the image is going from 3D to 2D, you need a view 90 degrees from the first view to be able to tell any depth of anything

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14
Q

Other options of xray views

A
  • PA
  • AP
  • lateral
  • oblique
  • L or R lat decubitus
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15
Q

What are other additions to plain films to give more information on the image?

A
  • R/L markers
  • bubbles w/ beads
  • arrow
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16
Q

Magnification on an xray

A
  • greater the distance from the film, the greater the magnification
  • this is why you want to be as close to film as possible
  • otherwise will get false widening
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17
Q

What point should be considered in horizontal films w/ an air:fluid interface?

A

If shot en face, the air:fluid interface is not visible.

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18
Q

What is significant about the lateral decubitis position in xrays?

A

This positioning allows for gravity to pool fluids, like in a pleural effusion

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19
Q

Silhouette sign

A

When 2 similar densities are side by side, their boundaries will be lost; ex: heart border could be obscured by pneumonia

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20
Q

air bronchogram

A

air-filled bronchus surrounded by greater density; pneumonia allows lung and bronchus to be ditinguished; so it is always pathologic

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21
Q

What points should be considered in the use of portable films?

A
  • can’t generate as high of energy level
  • Can’t get PA view
  • Can’t get down to 10th rib
  • Pt will be poorly inflated, improperly exposed, malpositioned and falsely magnified
22
Q

What can be used in xray for things that don’t normally show up?

A
  • contrast material: barium, iodine, etc.
  • swallowed, enema, or IV
  • not as common d/t use of CT and reactions
23
Q

How do structures show up on xray when contrast is used?

A
  • it will be a cast of the lumen of the structure
  • if a tumor is located w/i a muscle layer, it won’t be picked up
  • colon cancer would show up as a filling defect
  • a kidney stone would show up where contrast stopped
24
Q

When would you avoid using contrast?

A

if they have the possibility of stroke or an area that the contrast could leak out

25
Q

Renal calculi on xray

A
  • 75% calcium oxalate/phosphate will show up on plain xray
  • ~10% triple phosphate stones
  • ~15% uric acid stones
  • ~1% cystine stones (radiolucent)

All show up on CT

26
Q

Gallsones on xray

A
  • 75% are cholesterol (radiolucent)
  • 25% pigmented w/ calcium (radio-opaque)
  • since only 25% chance of seeing them on xray, send to get other modality
27
Q

Computerized Axial Tomography aka CAT, CT

A
  • instead of film uses gas or crystals
  • increases gray scale to ~2,000 shades of grey
  • this improves gradation w/i soft tissues
28
Q

The measurement window used in CT

A
  • hounsfield units (HU)
  • 1000 HU (air) is black and +1000 (bone) is white
  • wide window = increased gray
  • narrow window = increased contrast (b/c anything less than window will be black and anything higher will be white)
29
Q

What is the ideal window of HU in CT?

A

You want to narrow the window to no more than 400 HU to get the ideal amount of contrast in CT

30
Q

How are CTs viewed?

A

as if you’re standing at the patients feet looking up towards their head

31
Q

CT is good for what?

A

bones, head, neck, chest, abd, pelvis

32
Q

CT is not detailed enough for what?

A
  • fine image of brain, soft tissues of joints or spine (MRI better)
  • not good for same densities
33
Q

How can you enhance CT?

A
  • w/ IV contrast (same in MRI)

- only used if need to distinguish it from another area and it will pick it up

34
Q

Magnetic Resonance Imaging (MRI)

A
  • Does not utilize ionizing radiation

* Exploits the magnetic properties of elements and for medical purposes, i.e. hydrogen in water and lipids

35
Q

What does the quality of image in MRI depend on?

A

-amount of water/lipid in tissues

36
Q

MRIs are good for what?

A
  • soft tissues
  • brain
  • SC
37
Q

MRIs are contraindicated in who?

A
  • people w/ aneurysm clips
  • pacemakers (not always)
  • foreign body in eye, etc
  • however, nothing these days that’s implanted is magnetic
38
Q

What is the principle mechanism of MRI?

A
  • random nature of water molecules under magnetic field align positive H nuclei toward negative pole
  • a radiofrequency pulse is applied perpendicular to the alignment, causing tilt
  • when the rf is turned off, the H rearranges, releasing radio wave
  • the wave is picked up, amplified, digitized and projected
39
Q

“T” weights

A

T1: pure fluid is black (CSF, blood)
T2: pure fluid is white

40
Q

if you want to capture the vertebra what modality would you choose?

A

CT

41
Q

if you want to capture the spine what modality would you choose?

A

MRI

-but know that insurance can’t go to an MRI first

42
Q

MRA

A

combination of MRI and angiography

43
Q

Ultrasound

A 
• Very high frequency, converted to digital
signal 
• Air does not provide a medium for
transmission, bone blocks transmission 
• No fixed projections 
• No harm to fetus at energy level used
44
Q

Ultrasound is best for what?

A
  • best on soft tissues and soft tissue interfaces
  • e.g: fluid filled cyst
  • never use contrast
45
Q

Ultrasound is useful in what areas?

A
  • OB/GYN
  • cardiology
  • GI
  • GU
46
Q

Doppler Ultrasonography

A

• Moving structures produce a shift in
frequency which corresponds to speed of movement
• US converted to color-enhanced visual
signal and/or audible signal – doppler shift

47
Q

Doppler Ultrasonography is useful for what?

A
  • fetal heart sounds
  • DVT
  • atherosclerosis
48
Q

Radionuclide imaging

A

• Takes advantage that certain chemicals concentrate in
certain structures, i.e., iodine in thyroid, phosphates for bone, etc.
• Tag the organ-specific chemical with a radioactive compound

49
Q

What is the most common radioactive compound used in radionuclide imaging

A

Technetium (99mTc)

-other examples: thallium scan for heart and xenon or vent/perf scan

50
Q

Why is there poor spatial resolution in radionuclide imaging?

A
  • Gamma rays = decay of nucleus = gamma counter

- Short half life; hours to days

HEENOT 2 (7 decks)

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