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Radiation Physics And Safety > Midterm 2 - CT, MRI, Scintigraphy, Ultrasonography > Flashcards

Midterm 2 - CT, MRI, Scintigraphy, Ultrasonography Flashcards

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1
Q

CT was invented by who (2) in what year?

A

Hounsfield and McLeod

1973

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2
Q

Modern scanners have multiple detector arrays that are stationary around what degree of the patient?

A

360 degrees: tube rotates around patient

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3
Q

The CT tube rotates around patient in the ___ plane

A

Axial

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4
Q

Helical CT scanners create a ______ acquisition of data

A

Spiral

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5
Q

Multi-slice scanners create data in thin slices, referred to as

A

Volumetric acquisition

This means 1) there are no gaps in acquisition of data and 2) when data is reformatted, the quality is as good as axial data.

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6
Q

What are small squares of CT data that make up the image we see on axial orientation scans?

A

Pixels — picture elements

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7
Q

What are comprised of pixel element PLUS depth of box?

A

Voxels — volume elements

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8
Q

What kind of scanner can produce isotopic voxel?

A

Helical CT

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9
Q

What is a voxel that has the same depth, width and height?

A

Isotopic voxel

In other words, the resolution of the data is the same no matter which plane you choose to see — the voxel and pixel elements have the same dimensions.

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10
Q

Reformatting allows views of data from:

A

Sagittal, coronal or 3-D

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11
Q

What are used to describe the shade of grey that a tissue presents on the scale on CT?

A

Hounsfield units (HU)

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12
Q

HU scale ranges from

A

-1000 to 3072 HU

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13
Q

Only ___ (#) HU can be assigned per pixel/voxel

A

1

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14
Q

HU translate to grey scale. +1000 is going to be [lighter/darker] -1000 [lighter/darker]

A 
\+1000 = lighter e.g. bone
-1000 = darker e.g. air
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15
Q

What is the process of emphasizing certain ranges in the HU scale? E.g. if we want to see more bone e.g. higher value end of the HU scale OR if we want to see more soft tissue

A

Windowing

Soft tissue windows allow better viewing of the low HU end of the scale: soft tissues.

Bone windows emphasize the higher value end of HU scale: cortical and medullary bone.

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16
Q

What is -1000 HU?

A

Air

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17
Q

What is 0 HU?

A

Water

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18
Q

What is +400 HU?

A

Cancellous bone

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19
Q

What is +700 to +2000 HU

A

Cortical bone

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20
Q

What is +2500 to +3000 HU

A

Metal

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21
Q

When the CT detector cannot distinguish between different tissues because they are in the same pixel, its called

A

Partial Volume Effect

Machine has to decide if it will make the Pixel black or white.

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22
Q

What technology uses a magnetic field?

A

MRI

23
Q

In MRI, echo time (TE) and repetition time (TR) allow what?

A

Creation of sequences known as T1 and T2

24
Q

In MRI, what is brightest for T1-weighted image? What is not bright?

A

Brightest: Fat
Not brightest: Water and fluid

Note: opposite is true for T2

25
Q

In MRI, what the high signals/low signals in T2-weighted images

A

Bright = water & fluid
Not bright = fat

Basically, the less free protons, the lower signals
Compact tendon = low signal

26
Q

A T-2 weighted sequence can be converted to a _____ sequence

A

FLAIR, Fluid Attenuated Inversion Recovery

27
Q

What kind of image suppresses fat signal in MRI to make it appear black so that you can see tissue and fluid better?

A

STIR (short tau inversion recovery)

28
Q

Overall, T1 vs T2 vs fluid sensitive studies (FLAIR, STIR) (what are they good for)

A

T1 = evaluate anatomy
T2 = find pathology
FLAIR, STIR good for pathology and edematous/watery tissues

29
Q

Batteries e.g. cardiac pacemakers, insulin or infusion pumps; metals e.g. shrapnel from accidents or some high metallic tattoos; patients who can’t stay still because of seizures… these are contraindications for what procedure?

A

MRI

30
Q

Looking at an MRI, the fat is bright. What weight of MRI is it?

A

T1

31
Q

Looking at an MRI, water is bright. What weight of MRI is it?

A

T2 weighted

32
Q

Between CT and MRI which one has less risk as far as radiation exposure?

A

MRI

33
Q

How do CT and MRI refer to the tissue?

A

CT - density

MRI - signal intensity

34
Q

CT is good at ___ while MRI is good at ___

A

CT - detail

MRI - tissue differentiation

35
Q

what is faster: CT or MRI

A

CT

36
Q

What procedure can be done on patients with metal or batteries: CT or MRI

A

CT

37
Q

Is CT or MRI better for clinically unstable patients/

A

CT

38
Q

Which one requires no reformatting: CT or MRI

A

MRI because it directly acquires multiplanar images

39
Q

What type of imaging uses radioisotopes chelates to substances that are inert but processed by various tissues of the body?

A

Radionuclide Imaging AKA Scintigraphy

Technetium 99m is most common and used in bone scans

40
Q

What does scintigraphy identify in organs and bones?

A

Physiological activity

41
Q

Scintigraphy characterizes areas by

A

High or low metabolic activity

42
Q

3 levels of scintigraphy scan comprehensiveness include:

A

Whole body = bony problems
Limited/pin-hole = fractures
3-phase = flow, blood pool, delayed images used for infections

43
Q

Hot spot is an area of increased

A

Physiological activity

44
Q

Cold spot is an area lacking

A

Vascular supply

45
Q

20 m of Technetium-99m has an effective dose of 3 mSv in the whole body. What is the half life WITH body’s help in excretion by urinary system?

A

4.8 hour effective

Includes isotope decay + help from body

46
Q

20 m of Technetium-99m has an effective dose of 3 mSv in the whole body. What is the half life WITHOUT body’s help in excretion by urinary system?

A

6 hour

Raw rate of decay, no help from body

47
Q

20 m of Technetium-99m has an effective dose of 3 mSv in the whole body. What is the biological half-life??

A

24-hour

48
Q

What imaging modality uses sound waves to create images?

A

Ultrasonography

49
Q

When the sound waves bounce off internal structures, they create sound waves that bounce back which are called

A

Echoes

They come back to the source and are converted into images

50
Q

How are images created in an ultrasonography scan?

A

Changes in tissue density cause sound waves to “bounce back” to the ultrasound transducer at differing rates which creates different images

51
Q

What is the wand device called in ultrasonography?

A

Transducer

52
Q

Ultrasound wave frequencies range

A

2-20 million Hz

53
Q

What poisons ultrasound image?

A

Air

Metal

54
Q

Strengths of Ultrasonography:

A 
Internal organ evaluation
Obstetrics
Arteries, veins
Joints
MSK
Cyst vs solid
Cost effective

Radiation Physics And Safety (8 decks)

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