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Hannah RAD III > Advanced Modalities Review > Flashcards

Advanced Modalities Review 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
  • Godfey Hounsfield

- Allan Cormack

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3
Q

***Who developed the first 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 & 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 & 4th generation scanners?

A
  • 3rd generation – tube & 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 of 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 increase in the matrix will cause the pixel to be smaller and _________

A

allow small details to be seen in the image (better resolution but increase noise in image).

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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 numbers 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
  • Determines 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
  • topogram
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 @ the same level to observe contrast filling 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 then to a digital signal

27
Q

What does the CT collimator assembly consist of?

A
  • Prepatient (@ x-ray tube)
  • Postpatient (@ detector)

-Prepatient determines slice thickness

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 or 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 (skull)
38
Q

***What is MPR?

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

Hannah RAD III (25 decks)

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