10-18b Intro to Imaging: CT & MRI Flashcards Preview

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Flashcards in 10-18b Intro to Imaging: CT & MRI Deck (22):
1

How does Computed Topography Work? What is its unit?

Diff from radiograph x-rays b/c it is a three dimensional x-ray

images taken axially (transverse plane), info sent to computer, which reconstructs the image in any of the three planes

voxel: 3D pixel

higher density, more white (absorbed to a greater extent)

2

How does Computed Topography Work? What is its unit?

Diff from plain films b/c it is a three dimensional x-ray (can see tissue thickness)

images taken axially (transverse plane), info sent to computer, which reconstructs the image in any of the three planes

voxel: 3D pixel

higher density, more white (absorbed to a greater extent)

3

What is an advantage to CTs over plain filims?

one can distinguish b/w m. and fat due to 3D nature

most to least dense:
prosthesis
cortical bone
spongy bone
m.
blood
water
fat (negative)
soft tissues
lungs
air

4

What is one of the ways CTs are used? What is the advantage?

acute head trauma
quickly acquired and more routinely used
quickly ruling things in and out

thromboembolytic stroke: clot and can use clot buster

hemorrhagic stroke: no clot buster (white)

5

What is the second thing CTs are useful for?

complex fractures
needs more info for contrast quantification

6

What is the advantage of lung windowing?

sets the level to the HU of the observed tissue of interest

narrowing of the scale allows view of more details like tumors and other abnormalities

7

What is the advantage of lung windowing?

sets the level to the HU of the observed tissue of interest

narrowing of the scale allows view of more details like tumors and other abnormalities

8

What does bone windowing help with?

helps distinguish b/w cortical bone and spongy bone

9

What are the advantages to CT?

Acute intracranial bleeding differentiation

good for observing subtle/complex fractures/degenerative diseases in bone (spinal stenosis)

More available, less expensive, and quicker than MRI and more info than radiographs

can view heterotophic ossification: calcification in a place it shouldn't be

10

Disadvantages to CT?

not as good for soft tissue differentiation

larger exposure to radiation than radiographs

pretty short, but radiographs are shorter

11

What is the tech for MRIs?

Images are produced by the interaction of hydrogen containing molecules within tissues and a magnetic field produced by the magnet. (unique images are produced b/c each tissue has diff amt. of hydrogen and relax at different rates)

First, the hydrogen lines up with the field of the magnet

Second, a radio wave is delivered to the tissue which causes the hydrogen nuclei to absorb energy and change its alignment within the magnet (resonance).

The radio pulses are stopped, the absorbed energy is released and measured by the computer detector.

12

How do you read a T1 MRI?

subcutaneous fat is white due to enormous water content, then m., then bone is black

13

What are the two parameters for MRIs? What do these determine?

Repetition Time (TR): Time b/w two consecutive radio wave pulses

Echo Time (TE): is the time selected to wait after the start of the TR to receive the signal or “echo” from the patient.

The accentuation of different tissues

14

What causes diff quality images of same tissues?

length and sequence of the pulses

15

What will a shorter TE produce?

T1 weighted image

16

What will a longer TE produce?

T2 weighted image or STIR
suppresses fat and shows pathology

17

What are T1 images better for viewing? Greatest to smallest intensity?

anatomy

subQ fat, spongy bone, still fluid, cartilage, tumors, m., and fluid

18

What are T2 images better for viewing? Greatest to smallest intensity?

pathology since these images accentuate still fluid (inflammation)

inflammation, tumor, fluid, m., cartilage, spongy bone, subQ fat

19

Advantages of MRIs?

Superior soft tissue visualization (m., tendons, ligaments, nerves, articular cartilage, and menisci)

okay for spongy bone (high fat content)

no ionizing radiation

20

Disadvantages of MRI?

Thought to be very safe, however cannot use with patients who work with metal shavings, metal pacemakers, certain types of fixative devices (ferrous metals)

21

What is a MRI better for?

Spongy bone, Soft tissue (ligaments, tendons), Cartilage

22

What is a CT better for?

Cortical bone (subtle and complex fxs.)
Calcifications in any tissue
Acute intracranial bleeding