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39 Cards in this Set
- Front
- Back
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What is data acquisition?
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Data acquisition refers to the method by which the patient is scanned to obtain enough data for image reconstruction.
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What is scanning?
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The beam geometry, which characterizes the particular CT system and also plays a central role in spatial resolution and artifact production.
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What is beam geometry?
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The size, shape, and motion of the beam and its path.
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What is a ray?
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Part of the beam that falls from the x-ray tube to the detector.
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What is a view?
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A collection of rays for one translation across the object constitutes a view.
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What were first generation scanners based on?
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They were based on the parallel beam geometry (pencil beam) and translate-rotate scanning motion.
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What were second generation scanners based on?
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They were based on fan beam geometry and translate-rotate motion.
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What were third generation scanners based on?
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Fan beam geometry and complete rotation of the x-ray tube and detectors.
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What were fourth-generation scanners based on?
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Fan beam geometry and complete rotation of the x-ray tube around a stationary ring of detectors.
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What were fifth-generation scanners based on?
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They were developed primarily for high-speed CT scanning. These were based on special configurations intended to facilitate very fast scanning.
Electron Beam CT |
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What were sixth-generation scanners based on?
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They have multiple x-ray tubes and detectors. These scanners are to image moving structures like the heart.
Dual-Source CT |
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What were seventh-generation scanners based on?
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They use flat-panel digital area detectors similar to the one used in digital radiography.
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What did the first EMI scanner scan?
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the brain
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What did the second-generation scanners have that the first ones didn't?
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linear row of detectors (about 30 detectors)
multiple pencil beams |
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What were 3rd-generation scanners based on?
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fan beam geometry
slip ring |
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The fourth-generation scanners feature 2 types of beam geometries. What are they?
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rotating fan beam within a stationary ring of detectors
nutating fan beam in which the apex of the fan (x-ray tube) is outside a nutating ring of detectors. |
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What does nutating mean?
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the tilting action of the detector ring during data collection.
Nutate-rotate systems are not currently manufactured. |
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Why are fifth-generation scanners considered high-speed ct scanners?
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because they can acquire scan data in milliseconds.
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What is the overall goal of the EBCT scanner?
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To produce high-resolution images of moving organs that are free of artifacts caused by motion.
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What was the DSCT designed for?
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cardiac CT imaging because it provides the temporal resolution needed to image moving structures such as the heart.
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Flat-panel detectors produce excellent spatial resolution but lack good what?
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contrast resolution
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Spiral-helical CT is made possible through the use of what?
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slip ring technology
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What is a slip ring?
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an electromechanical device consisting of circular electrical conductive rings and brushes that transmit electrical energy across rotating brushes.
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What are the 2 slip ring designs?
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disk and cylinder
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What are the 2 common brush designs?
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wire brush
composite brush |
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What are the advantages of slip rings?
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1) Faster scan times and min. interscan delays
2) Capacity for cont. acquisition protocols 3) Elimination of the start-stop process characteristic of conventional CT's 4) Removal of the cable wraparound process |
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What type of beam is used in today's x-ray tube in CT's?
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heterogeneous beam
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CT scanners now use what type of generator?
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high-frequency generators
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What are some advantages of the high-frequency generator?
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small
compact more efficient than conventional generators |
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Where are the high-frequency generators located?
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inside the gantry
in some scanners, it is mounted on the rotating frame with the x-ray tube. in other scanners, it is located in a corner of the gantry and does not rotate with the tube. |
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What is the voltage ripple of a high-frequency generator?
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less than 1%
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The radiation source requirement in CT depends on two factors. What are they?
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radiation attenuation
quantity of radiation required for transmission |
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First and second-generation scanners used what type of x-ray tube?
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fixed-anode
oil-cooled |
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Do modern CT x-ray tubes use a fixed and rotating anode?
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rotating
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What is the target for CT anodes made of?
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It is made of a graphite body with a tungsten-rhenium layer deposited on the focal track by a chemical vapor process.
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What is the target angle?
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12 degrees
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What is the rotation speed of today's CT x-ray tubes?
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3600 to 10,000 (high-speed rotation) rpms
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What is the working life of a modern CT x-ray tube?
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10,000 to 40,000 hours
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What is the fundamental problem with conventional x-ray tube?
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heat dissipation
slow cooling rates |
