Computed Tomography: Image
production in Computed Tomography
The general process of CT imaging may be divided into several steps which include: - correct answer
✔✔1. Image Acquisition
2. Data reconstruction
3. Multidimensional image display
4. Image Archival and Communication
What is image acquisition? - correct answer ✔✔Measurement of the attenuation that occurs along each
path through the patient from the x-ray tube to detector
What is Data Reconstruction? - correct answer ✔✔The computerized processing of the transmission
measurements into the CT image
What is multidimensional image display? - correct answer ✔✔Display of the reconstructed grayscale
image in two-dimensional (2-D) and/or three-dimensional (3-D) format; a representation of the
attenuation that occurred across the scanned volume of tissue
What is image archival and communication? - correct answer ✔✔Display as well as storage, both short-
term and long-term (archival), of images on computer workstations
What is scout image (localizer/scanogram) acquisition? - correct answer ✔✔Survey that can be obtained
by keeping the x-ray tube and detector array in a fixed position while the patient bed is translated
through the gantry
What is Azimuth? - correct answer ✔✔Angle of the tube and detectors in relationship tp the patient
position during scout acquisition
What does the CT gantry hold? - correct answer ✔✔Generator, x-ray tube, assorted collimators, data
acquisition system (DAS), slip-rings, and detectors
,What is the slip-ring technology? - correct answer ✔✔Eliminates the need for cables by utilizing a
system of contact brushes that supply electricity to power the system and enable the passage of
transmission data to the computer system
- allows for continuous helical acquisition that has become the standard in modern CT imaging
What are the technical elements of helical CT acquisition include: - correct answer ✔✔1. Continuous
rotation of the gantry components (slip-ring technology)
2. A powerful x-ray tube capable of long exposure output
3. Continuous movement of the patient bed
4. Mathematical reconstruction techniques
The development of multidetector CT (MDCT) helped advance? - correct answer ✔✔the helical
acquisition principle. Multidetector arrays enable CT sections of varying widths to be reconstructed at
any point along the acquired volume
What does the x-ray tube consists of? - correct answer ✔✔- Negative side (cathode)
- Positive side (anode)
How many focal spots are in a CT tube? - correct answer ✔✔Dual filaments allow for a choice of two
focal spot sizes ranging from .5 to 1.2mm in diameter.
What focal spot helps improve spatial resolution? - correct answer ✔✔- Smaller focal spot size
What is flying focal spot technology? - correct answer ✔✔Involves the electromagnetic steering of the
electron beam emitted from the cathode. The beam of electrons is directed toward two separate
locations on the rotating anode, resulting in two sources of x-radiation.
As the tube rotates around the patient, the number of data samples does what? - correct answer ✔✔-
Essentially doubles because of the electronic switching between the two focal spots. This oversampling
technology can be used to improve the system's temporal and spatial resolution
, The modern CT x-ray tube has specific characteristics that enable it to achieve the performance
demanded by state-of-the-art MDCT: - correct answer ✔✔1. High heat rating- must have the ability to
absorb tremendous heat, while dissipating it quickly
2. Small size, lightweight-must be capable of rotating within the CT gantry at a high rate of speed
3. Stable and long lasting- must be capable of withstanding huge centrifugal forces with an extended
useful life
Selection of mA setting depends on a number of factors including? - correct answer ✔✔- CT study
- Patient size/density
- Signal to noise ratio (SNR) for adequate examination quality
Automatic tube current modulation (ATCM) programs do what? - correct answer ✔✔Adjust the mA
throughout an acquisition to reduce patient radiation dose to a minimum. Automatically alters the
applied mA according to a predetermined noise index that is acceptable for appropriate image quality
Exposure time (last for 30 to 60 seconds) for a given CT acquisition varies and is determined by? - correct
answer ✔✔-Anatomic extent
- Detector configuration
- Table speed
mA*sec equals what? - correct answer ✔✔mAs
The mAs value directly controls what? - correct answer ✔✔Quantity of x-radiation, or photon fluence,
directed toward the patient
Photon flux definition - correct answer ✔✔Rate at which the photon fluence (quantity) passes through a
unit area over unit time
The mAs value for a given acquisition is directly proportional to what? - correct answer ✔✔- Patient
radiation dose
production in Computed Tomography
The general process of CT imaging may be divided into several steps which include: - correct answer
✔✔1. Image Acquisition
2. Data reconstruction
3. Multidimensional image display
4. Image Archival and Communication
What is image acquisition? - correct answer ✔✔Measurement of the attenuation that occurs along each
path through the patient from the x-ray tube to detector
What is Data Reconstruction? - correct answer ✔✔The computerized processing of the transmission
measurements into the CT image
What is multidimensional image display? - correct answer ✔✔Display of the reconstructed grayscale
image in two-dimensional (2-D) and/or three-dimensional (3-D) format; a representation of the
attenuation that occurred across the scanned volume of tissue
What is image archival and communication? - correct answer ✔✔Display as well as storage, both short-
term and long-term (archival), of images on computer workstations
What is scout image (localizer/scanogram) acquisition? - correct answer ✔✔Survey that can be obtained
by keeping the x-ray tube and detector array in a fixed position while the patient bed is translated
through the gantry
What is Azimuth? - correct answer ✔✔Angle of the tube and detectors in relationship tp the patient
position during scout acquisition
What does the CT gantry hold? - correct answer ✔✔Generator, x-ray tube, assorted collimators, data
acquisition system (DAS), slip-rings, and detectors
,What is the slip-ring technology? - correct answer ✔✔Eliminates the need for cables by utilizing a
system of contact brushes that supply electricity to power the system and enable the passage of
transmission data to the computer system
- allows for continuous helical acquisition that has become the standard in modern CT imaging
What are the technical elements of helical CT acquisition include: - correct answer ✔✔1. Continuous
rotation of the gantry components (slip-ring technology)
2. A powerful x-ray tube capable of long exposure output
3. Continuous movement of the patient bed
4. Mathematical reconstruction techniques
The development of multidetector CT (MDCT) helped advance? - correct answer ✔✔the helical
acquisition principle. Multidetector arrays enable CT sections of varying widths to be reconstructed at
any point along the acquired volume
What does the x-ray tube consists of? - correct answer ✔✔- Negative side (cathode)
- Positive side (anode)
How many focal spots are in a CT tube? - correct answer ✔✔Dual filaments allow for a choice of two
focal spot sizes ranging from .5 to 1.2mm in diameter.
What focal spot helps improve spatial resolution? - correct answer ✔✔- Smaller focal spot size
What is flying focal spot technology? - correct answer ✔✔Involves the electromagnetic steering of the
electron beam emitted from the cathode. The beam of electrons is directed toward two separate
locations on the rotating anode, resulting in two sources of x-radiation.
As the tube rotates around the patient, the number of data samples does what? - correct answer ✔✔-
Essentially doubles because of the electronic switching between the two focal spots. This oversampling
technology can be used to improve the system's temporal and spatial resolution
, The modern CT x-ray tube has specific characteristics that enable it to achieve the performance
demanded by state-of-the-art MDCT: - correct answer ✔✔1. High heat rating- must have the ability to
absorb tremendous heat, while dissipating it quickly
2. Small size, lightweight-must be capable of rotating within the CT gantry at a high rate of speed
3. Stable and long lasting- must be capable of withstanding huge centrifugal forces with an extended
useful life
Selection of mA setting depends on a number of factors including? - correct answer ✔✔- CT study
- Patient size/density
- Signal to noise ratio (SNR) for adequate examination quality
Automatic tube current modulation (ATCM) programs do what? - correct answer ✔✔Adjust the mA
throughout an acquisition to reduce patient radiation dose to a minimum. Automatically alters the
applied mA according to a predetermined noise index that is acceptable for appropriate image quality
Exposure time (last for 30 to 60 seconds) for a given CT acquisition varies and is determined by? - correct
answer ✔✔-Anatomic extent
- Detector configuration
- Table speed
mA*sec equals what? - correct answer ✔✔mAs
The mAs value directly controls what? - correct answer ✔✔Quantity of x-radiation, or photon fluence,
directed toward the patient
Photon flux definition - correct answer ✔✔Rate at which the photon fluence (quantity) passes through a
unit area over unit time
The mAs value for a given acquisition is directly proportional to what? - correct answer ✔✔- Patient
radiation dose
