CT Hardware & System Operation Flashcards
What does the detectors convert the number of photons that pass through the patient into?
Tiny electrical signals that represents the attenuation information of the body
What is the operator’s console used for?
Viewing images Post-processing images Archiving images Filming images Patient registration
Where is the CT raw data storage device located?
Host computer
The patient table moves so that the anatomical region we want to scan always aligns with:
The beam of x-ray photons
In what ways can a gantry move?
By rotation and angling
Why would a gantry be angled?
To select oblique slices through the anatomy
What determines the number of electrons that flow from the cathode to the anode?
Temperature of the cathode filament
Why does the anode rotate?
Great amount of heat
Tube currents are generally selected in the range of:
Tens to hundreds of milliamperes (mA)
How does mA and photons correlate to one another?
The greater the mA, the more photons are produced
The energy level of the x-ray photons determines how:
Easily they will penetrate the patient’s body
Tube voltages are generally selected in the range of:
90 to 140 kilovolts (kV)
How does kV and photons correlate to one another?
The greater the kV, the more penetrating the photons will be.
The only opening in the tube housing that allows passage of the x-ray photons
Tube Window
What are collimators made of?
X-ray opaque material
Collimations restricts x-rays to only:
The selected cross-sectional region
What is the difference between pre-patient collimation on a single-row detector scanner versus a multi-row detector?
On a single-row detector scanner, the thickness of the cross-sectional slice is determined by the collimation
On a MDCT, the slice thickness is determined during image reconstruction
Which type of collimation acts to minimize scatter radiation as well as minimizing dose of ionizing radiation administered to the patient?
Pre-patient
Which type of collimation acts to minimize scatter radiation as well as provides better definition to the slice thickness?
Post-patient
Post-patient collimation is also referred to as:
Pre-detector Collimation
For an x-ray photon to generate a signal, it must:
Enter the detector
Collide with a detector atom
Produce a measurable event
What are the two basic categories of detectors?
Gas and solid state
What is the gas used in a gas detector?
Xenon
Having a large distance between xenon atoms could _____ the chance of x-ray production.
Decrease
Xenon gas is pressurized by up to __ times normal atmospheric pressure.
30
What happens when an incoming photon collides with a xenon atom?
That atom splits into a xenon ion and an electron
What is the charge of a xenon ion?
Positive
When charged particles migrate to the plate with the opposite polarity, what can this be measured as?
An electrical pulse
Xenon detectors have only been used in which generation scanners?
Third-generation due to the chamber aligning straight onto the CT x-ray tube at all times
Which detector is the most prevalent type of detector used on today’s CT scanners?
Solid state
A solid state detector is also referred to as:
Scintillation detector
What happens when a photon strikes with the solid state material of a detector?
It emits a flash of light converting into an electrical impulse by a photodiode
On MDCT scanners, how do you calculate the acquired slice thickness?
The thickness of the x-ray beam divided by the total number of slices acquired in a single rotation
What are the two different approaches for varying the acquired slice thickness?
Symmetric / Asymmetric detector arrays
How does DICOM and PACS relate to one another?
DICOM is neccessary for the transfer of data that occurs with PACS
Through which part of the CT x-ray tube do the electrons enter?
Cathode terminal
What control does the operator have over the x-rays in a CT exam?
Energy level and quantity of x-rays can be selected
What is the purpose of the tube window?
To allow x-rays to exit the tube
How is collimation accomplished?
By physically blocking x-rays
What affects the slice thickness on a single-row detector scanner?
Size of cathode filament
Size of focal spot (dependent on size of cathode filament)
Collimation thickness
The signals measured at the detectors must be digitized after they are amplified which is done by the:
Array processor
How do gas detectors create an electrical event?
By ionizing the detector material (an electrical event) when struck by a photon
How can an MDCT scanner obtain thicker slices?
The attenuation information from detectors in more than one detector array may be added together
