CT Image Production

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Interpolation

Estimating an unknown value when surrounding values are known

If rotation time is decreased what other parameter should be changed to maintain image quality?

Increase mA

What is the primary reason for decreasing the detector thickness for CTA

Increase spatial resolution

Shifting the center of a Sagittarius image changes the coordinates to which two data sets?

Y-axis & Z-axis

What process prevents star-like artifact from appearing of CT images

Back-projection filter

Blood HU

+39 hu

A single "view" acquired during a scan is also called a:

Projection

Fat

-52 hu

What is the main difference between image production of CT vs Xray?

Projections are compiled into a 3D volume of data

During axial scanning, what two variables determine the total amount of anatomical coverage per tube rotation

# of activated detector rows Thickness of activated detector rows

What axis position changes while moving through the axial set of data (superior to inferior)

Z-axis (longitudinal)

What is the pitch of the scan Acquisition thickness: 20 Detector rows: 20 Rotation time: 0.8s Tube current: 250 mA Table movement: 10 mm

1 Beam width=detector rows x acquisition thickness Pitch=table movement / beam width

What is a common kVp setting used in CT?

120 kVp

Calculate the total beam width of a scan using 32 detector rows, 0.5 mm detectors, 100 mA, 140 kVp

16 mm (32 rows X 0.5mm/row)

"8-slice scanner" refers to a system that has

8 detector rows

Compared to general radiography, CT X-ray tubes require

A larger heat capacity

The signal produced by a CT detector is an

Analog electrical signal (detector capture remnant X-ray photons & produce an electrical signal proportional to the number of photons they received)

What portions of a patient receive radiation exposure during CT

Any portion within the gantry

The specific process that accelerates electrons in an X-ray tube

Application of voltage (kVp)

What is the relationship between acquisition thickness and spatial resolution?

As acquisition thickness increases, spatial resolution decreases

What acquisition mode collects a series of adjacent axial sections

Axial Scanning

Describe the flow of electrons through an X-ray tube

Cathode To anode (The cathode is the same as the filament, the source of electrons -. The anode is the target +.)

The width of the xray beam is controlled by

Collimation

Where is raw data stored

Computer system

Which component of the CT imaging system is responsible for creating reconstructed image data?

Computer system (Last step in the data transformation process)

What is the result of the change: 0.625mm X 16 rows to 1.25mm X 8 rows

Decreased pt dose

Compare protocols using a pitch of 0.73 vs 0.87. The pitch of 0.87 will result in what two differences

Decreased scan time Decreased pt dose

Helical scanning is preferred over axial for what three reasons?

Decreased scan time Improved IV contrast timing Improved post-processing

X-ray tubes in CT are most similar to which other modality

Diagnostic radiography

Slice interval

Distance from the start of one slice to the start of the next slice

If mA is decreased by a factor of 2, how is the pt radiation dose changed if all other factors remain the same

Dose is decreased by 2

What is the orientation of the X-axis

Extends horizontally across the scanner Represents data coordinates from Lt to Rt

During helical scanning if the table moves a greater distance than the beam width, the pitch will be

Greater than 1

The principal advantage of thin detector rows is

Higher spatial resolution

How is data from the SFOV used during image production?

Image reconstruction

An increase of which exposure factors would increase the total # of xray photons exposing the detectors? (Three)

Increased mA (total # of photons produced) Increased kVp (penetration ability) Increased Rotation Time (longer exposure)

Which of the following effects can occur when mA is increased? (Three)

Increased pt dose Increased beam intensity Increased exposure of detector elements

The inner rows of a non-uniform detector array have the advantage of

Increased spatial resolution

Increasing the mA & kVp will usually result in: (two)

Increases pt dose Decreased image noise

What technical change is expected to increase penetrating ability of an X-ray beam

Increasing kVp

A pitch of 0.79 will result in

Overlap in scan data

The process of assigning a specific level of edge enhancement is controlled by: (3)

Reconstruction algorithms Reconstruction filters Reconstruction kernels

Iterative Reconstruction

Reduces pt dose Increases image quality

What two algorithms are most useful for viewing soft tissue changes around the cranium

Smoothing algorithm Standard algorithm

Production of X-rays in CT requires (three)

Source of electrons Mean of rapidly accelerating electrons Means of rapidly deceleration of electrons

Convolution

The mathematical filtration of CT data to enhance the appearance of specific tissue types

Under what two circumstances would it be impossible to retro missing anatomy

The original SCAN data has been deleted from the computer system The missing anatomy was outside the original SFOV

Pitch

The ratio of the table movement to beam width

The sequential acquisition mode is described as

The table only moves between exposures

Acquisition thickness refers to:

The thickness of active detector rows

Physical components located inside the CT Gary typically include (two)

X-ray tube High voltage generator


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