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Rad III > Advanced Modalities > Flashcards

Advanced Modalities Flashcards

1
Q

How do you explain a CT scan?

A

A process of creating cross-sectional images of any part of the body

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2
Q

Who received the Nobel Prize in medicine and physiology for their work in CT?

A

Godfry Hounsfield and Allan Cormack

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3
Q

Who developed the fist whole body scanner in 1974?

A

Dr. Robert Ledley

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4
Q

How are CT scanners categorized and what is the difference between these categories?

A
  • Generations

- Difference between generations related to number and arrangement of detectors

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5
Q

How many detectors did the 1st and 2nd generation CT scanners have and what type of beam resulted?

A
  • 1st (1 to 3 detectors) pencil beam

- 2nd (30 detectors) fan shaped beam

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6
Q

What was unique about the 3rd and 4th generation scanner?

A
  • 3rd gen - tube and detector array rotate simultaneously around patient
  • 4th generation - tube rotates but detectors remain stationary
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7
Q

A 5th generation CT scanner is classified as? What is a type or 5th generation scanner?

A

High speed scanner

Electron beam CT for cardiac studies

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8
Q

The tube rotates around the patient and for every position of the tube, the detectors measure the transmitted x-ray values (known as….) and converts them into an electrical signal

A

Projections, scan profile, raw data

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9
Q

Define ray, view and profile:

A

Ray - part of x-ray beam that falls onto one detector
View - a collection of rays for one translation across object
Profile - a view generates a profile

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10
Q

What happens to the electrical signal in CT?

A
  • It is sent to the computer to be digitized where a number is assigned that is directly proportional to signal strength
  • Those numbers are arranged in a grid (rows/columns) = Matrix
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11
Q

What is a pixel and a voxel?

A

Pixel - single square or picture element within matrix

Voxel - volume element; slice thickness to pixel

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12
Q

An _____ in the matrix will cause the pixel to be smaller and allow ___ detail to be seen in the image (better resolution but increase noise in image)

A

Increase; small

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13
Q

What is a Hounsfield unit?

A

Each pixel within image is assigned a number (CT number or Hounsfield unit) that is proportional to the degree of attenuation of that tissue

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14
Q

What is the CT number of water?

A

0

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15
Q

CT number correspond to different shades of ____ in the image

A

Gray

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16
Q

What is window width?

A
  • The range of CT #s that are displayed as shades of gray

- A wide window width has more shades of gray and a narrow window width has fewer shades of gray

17
Q

What is window level?

A
  • Determine the CT # that will be the center of the window width
  • Midpoint of range of gray levels
18
Q

What is an algorithm or kernel?

A
  • Mathematical formula designed for computers to carry out complex calculations
  • For enhancement of soft tissue, bone and edge resolution
19
Q

What is a region of interest or ROI?

A

Measurement of CT numbers within a specified area for evaluation of average tissue density

20
Q

What are the names used for the preliminary image?

A

Scanogram, scout, tapogram

21
Q

What is the barium concentration used for CT procedures?

A

2% - low concentration to prevent streak artifacts

22
Q

What is dynamic scanning?

A

Rapid sequential scanning at the same level to observe contrast filing or incremental scanning of rapid series scanning during bolus injection of contrast

23
Q

What is spiral or helical scanning? What special technology does it utilize?

A
  • Gantry continuously rotates while table moves through aperture at all the same time
  • Slip ring technology replaces high tension cables of earlier scanners
24
Q

What type of data set is acquired with spiral/helical scanning?

A
  • Volume of data
  • Forms a spiral path
  • Scans volume rather than group of individual slices
25
Q

What is the central opening of the gantry?

A

Aperture

26
Q

What is a solid state detector?

A

Composed of photodiodes coupled with scintillation crystal material that converts transmitted x-ray energy into light which is then converted into electrical energy and the into a digital signal

27
Q

What does the CT collimator assembly consist of?

A
  • Prepatient (at x-ray tube); determines slice thickness

- Postpatient (at detector)

28
Q

What is another name for the CT table?

A
  • Patient couch

- Designed to move in increments or indexing

29
Q

What does the DAS consist of?

A

The data acquisition system consist of the method of scanning (conventional/helical) and image reconstruction (array processor)

30
Q

What are the components on the operator console?

A

Keyboard, graphic monitor, touch display screen, mouse

31
Q

What is the scan field of view?

A

Includes entire cross section of body part of only a specified region within body part

32
Q

What is the display field of view?

A
  • Refers to the anatomy that is displayed on the monitor

- Can be smaller than the scan field of view but not larger

33
Q

How do you define slice thickness?

A
  • Number of millimeters intersecting thickness of x-ray beam
  • Partially defined by size of focal spot
  • Further refine the thickness by the collimators
34
Q

What is spatial resolution?

A

A measure of the size of the smallest object that can be visualized in an image

35
Q

What is contrast resolution?

A

The ability to differentiate small differences in density on the image

36
Q

What is noise?

A
  • A fluctuation in the CT number within a uniform material making the image appear grainy or speckled
  • Difficult to see subtle contrast differences or fine details
37
Q

What is an artifact?

A
  • Beam hardening or streak artifacts

- Metallic “spray” artifact (dental fillings, pacemakers, prosthesis, bone-soft tissue interface)

38
Q

What is MPR?

A
  • Reconstructing axial images into coronal, sagittal or oblique planes without the need for additional radiation
  • Postprocessing technique

Rad III (5 decks)

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