Advanced Modalities Review Flashcards
How do you explain a CT scan?
A process of creating cross-sectional images of any part of the body
***Who received the Nobel Prize in medicine and physiology for their work in CT?
- Godfey Hounsfield
- Allan Cormack
***Who developed the first whole body scanner in 1974?
Dr. Robert Ledley
How are CT scanners categorized and what is the difference between these categories?
- Generations
- Difference between generations related to number & arrangement of detectors
How many detectors did the 1st and 2nd generation CT scanners have and what type of beam resulted?
- 1st {1 to 3 detectors} pencil beam
- 2nd {30 detectors} fan shaped beam
What was unique about the 3rd & 4th generation scanners?
- 3rd generation – tube & detector array rotate simultaneously around patient
- **-4th generation – tube rotates but detectors remain stationary
A 5th generation CT scanner is classified as? What is a type of 5th generation scanner?
- High speed scanner
- Electron beam CT for cardiac studies
***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.
- Projections
- Scan profile
- Raw data
Define ray, view and profile:
- 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
What happens to the electrical signal in CT?
- 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
***What is a pixel and a voxel?
- Pixel – single square or picture element within matrix
- Voxel – volume element; slice thickness to pixel
An increase in the matrix will cause the pixel to be smaller and _________
allow small details to be seen in the image (better resolution but increase noise in image).
What is a Hounsfield unit?
Each pixel within image is assigned a number (CT number or Hounsfield unit) that is proportional to the degree of attenuation of that tissue
***What is the CT number of water?
0
CT numbers correspond to different shades of ____ in the image.
gray
What is window width?
- 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
What is window level?
- Determines the CT # that will be the center of the window width
- Midpoint of range of gray levels
What is an algorithm or kernel?
- Mathematical formula designed for computers to carry out complex calculations
- For enhancement of soft tissue, bone and edge resolution
What is a region of interest or ROI?
Measurement of CT numbers within a specified area for evaluation of average tissue density
***What are the names used for the preliminary image?
- Scanogram
- Scout
- topogram
***What is the barium concentration used for CT procedures?
2% - low concentration to prevent streak artifacts
What is dynamic scanning?
Rapid sequential scanning @ the same level to observe contrast filling or incremental scanning of rapid series scanning during bolus injection of contrast
***What is spiral or helical scanning? What special technology does it utilize?
- Gantry continuously rotates while table moves through aperture at all the same time
- Slip ring technology replaces high tension cables of earlier scanners
***What type of data set is acquired with spiral/helical scanning?
- Volume of data
- Forms a spiral path
- Scans volume rather than group of individual slices
***What is the central opening of the gantry?
aperture
***What is a solid state detector?
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
What does the CT collimator assembly consist of?
- Prepatient (@ x-ray tube)
- Postpatient (@ detector)
-Prepatient determines slice thickness
***What is another name for the CT table?
- Patient couch
- Designed to move in increments or indexing
What does the DAS consist of?
The data acquisition system consist of the method of scanning (conventional/helical) and image reconstruction (array processor)
What are the components on the operator console?
-Keyboard
-Graphic monitor
-Touch display screen
mouse
What is the scan field of view?
Includes entire cross section of body part or only a specified region within body part
***What is the display field of view?
- Refers to the anatomy that is displayed on the monitor
- Can be smaller than the scan field of view but not larger
***How do you define slice thickness?
- Number of millimeters intersecting thickness of x-ray beam
- Partially defined by size of focal spot
- Further refine the thickness by the collimators
What is spatial resolution?
A measure of the size of the smallest object that can be visualized in an image
***What is contrast resolution?
The ability to differentiate small differences in density on the image.
***What is noise?
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
***What is an artifact?
Beam hardening or streak artifacts
Metallic “spray” artifact
-dental fillings
-Pacemakers
-Prosthesis
-Bone-soft tissue interface (skull)***What is MPR?
- Reconstructing axial images into coronal, sagittal or oblique planes without the need for additional radiation
- Postprocesing technique
