Cone Beam CT: Part 1- The Basics Flashcards
What is image reconstruction?
Data is utilized by other software programs and produces different image presentations
What are the digital image processing/modifications?
- Compression
- Imaging manipulations (Automated image analysis)
—Qualitative – changes pixel’s digital value
—Quantitative – counts the number of pixels - Image Reconstruction
What is computed tomography (CT)?
Use of computers to generate multiple images of an object from digitized density information obtained from various signals; x radiation (MDCT, CBCT), magnetic fields (MRI), sonar radiation (ultrasound), etc.
What are the two main forms of x-ray CT?
-CBCT (Cone Beam Computed Tomography)
–MDCT (Multi Detector Computed Tomography)
Nearly all CBCT units are…
good quality high-end imaging equipment made for a very competitive marketplace
CBCT machines become outdated due to competition from competitor brands and technical innovations such as…
- memory
- bit depth
- FOV options
- operating systems
- compatibility with software technologies
The lifetime of a CBCT unit is ___ years
6-8
CBCT has less radiation than other forms of CT (i.e. MDCT) for hard tissue imaging because of:
- less scanning of X-radiation
- lower radiation
1 day of background radiation ____µSv
~8.5
CBCT Dosimetry Study Values Vary
because Studies are not…
Directly Comparable
What are the factors affecting dose for the CBCT?
- FOV
- Exposure
- Voxel
- Sensors
What is a CBCT FOV flat panel detector?
Cylindrical shape and measurement characteristics
- Diameter (mm) x Height (mm)
What is a CBCT FOV image intensifier detector?
Round spherical shape and measurement characteristics
- Diameter (mm) only
CBCT units have capabilities for scanning a range of _______ sizes
FOV
What is the range of kV for a CBCT?
ranges between various units
75 kV – 120 kV
What is the range of mA for a CBCT?
7 mA – 20 mA
How does the image production for CBCT work?
- X-ray beam projection scheme shows “cone” beam (left) imaging geometry with the resultant image production.
- Multiple basis image projections form the projection data.
- A volumetric data set is then constructed by an imaging software program which then displays various image reconstructions.
Multiple basis image projections form the…
projection data
A _______________ is constructed by an imaging software program which then displays various image reconstructions.
volumetric data set
What is the CBCT basis-image capture sequence?
Two basis-image capture sequences as the machine rotates counterclockwise from Position 1 to Position 2
What is the range of images the CBCT basis-image captures?
scans routinely capture in the range of 100 to 600 basis images per rotational scan
Number of basis images in a CBCT affects…
- Image Quality
- Dose
What does the voxel size do?
increased voxel size…
- worse resolution
small voxel yields _____ resolution
high
What is the typical voxel size for a CBCT?
- 0.3mm3 = 300µm3
- 0.075mm3 = 75 µm3
Small voxel yields LOWER signal to noise ratio, i.e., degraded image _________
quality
Small voxel yields ________ radiation dose
high
What is the threshold for a small versus large FOV when considering voxel size?
> 0.200mm = 200µm – for larger FOVs
<0.200mm = 200 µm – for smaller FOVs
Small voxel yields high resolution but requires more __________________ to capture signal in the greater number of the smaller voxels
x-ray photons (higher exposure)
Current scanners are not configured for the longer scan times and longer processing times for a _______ FOV with a ______ voxel size
large
small
Smaller voxels need more photon signal which yields a ______ radiation dose
higher
What are the different types of CBCT image detectors?
- charge-coupled image intensifier detector
- flat-panel detector
Charge-coupled image intensifier detector has distortion of the image grid when moving __________ the center
away from
Do flat panel decectors have distortion?
Even at more distant areas from the center of the grid, there is minimal to no distortion of the grid pattern.
Flat panel image receptor area receiving the signal from the
flat-panel detector’s __________ is flat.
scintillator
Improved image quality and the higher signal-to noise ratio are noted in which type of detector?
flat-panel detector
Lower radiation dose for which type of detector?
Charge-coupled device image intensifier
