Cone Beam CT: Part 1- The Basics

Question 1

What is image reconstruction?

Answer 1

Data is utilized by other software programs and produces different image presentations

Question 2

What are the digital image processing/modifications?

Answer 2

• Compression
• Imaging manipulations (Automated image analysis)
  —Qualitative – changes pixel’s digital value
  —Quantitative – counts the number of pixels
• Image Reconstruction

Question 3

What is computed tomography (CT)?

Answer 3

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.

Question 4

What are the two main forms of x-ray CT?

Answer 4

-CBCT (Cone Beam Computed Tomography)
–MDCT (Multi Detector Computed Tomography)

Question 5

Nearly all CBCT units are…

Answer 5

good quality high-end imaging equipment made for a very competitive marketplace

Question 6

CBCT machines become outdated due to competition from competitor brands and technical innovations such as…

Answer 6

• memory
• bit depth
• FOV options
• operating systems
• compatibility with software technologies

Question 7

The lifetime of a CBCT unit is ___ years

Answer 7

6-8

Question 8

CBCT has less radiation than other forms of CT (i.e. MDCT) for hard tissue imaging because of:

Answer 8

• less scanning of X-radiation
• lower radiation

Question 9

1 day of background radiation ____µSv

Answer 9

~8.5

Question 10

CBCT Dosimetry Study Values Vary
because Studies are not…

Answer 10

Directly Comparable

Question 11

What are the factors affecting dose for the CBCT?

Answer 11

• FOV
• Exposure
• Voxel
• Sensors

Question 12

What is a CBCT FOV flat panel detector?

Answer 12

Cylindrical shape and measurement characteristics
- Diameter (mm) x Height (mm)

Question 13

What is a CBCT FOV image intensifier detector?

Answer 13

Round spherical shape and measurement characteristics
- Diameter (mm) only

Question 14

CBCT units have capabilities for scanning a range of _______ sizes

Answer 14

FOV

Question 15

What is the range of kV for a CBCT?

Answer 15

ranges between various units
75 kV – 120 kV

Question 16

What is the range of mA for a CBCT?

Answer 16

7 mA – 20 mA

Question 17

How does the image production for CBCT work?

Answer 17

• 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.

Question 18

Multiple basis image projections form the…

Answer 18

projection data

Question 19

A _______________ is constructed by an imaging software program which then displays various image reconstructions.

Answer 19

volumetric data set

Question 20

What is the CBCT basis-image capture sequence?

Answer 20

Two basis-image capture sequences as the machine rotates counterclockwise from Position 1 to Position 2

Question 21

What is the range of images the CBCT basis-image captures?

Answer 21

scans routinely capture in the range of 100 to 600 basis images per rotational scan

Question 22

Number of basis images in a CBCT affects…

Answer 22

1. Image Quality
2. Dose

Question 23

What does the voxel size do?

Answer 23

increased voxel size…
- worse resolution

Question 24

small voxel yields _____ resolution

Answer 24

high

Question 25

What is the typical voxel size for a CBCT?

Answer 25

* 0.3mm3 = 300µm3 * 0.075mm3 = 75 µm3

Question 26

Small voxel yields LOWER signal to noise ratio, i.e., degraded image _________

Answer 26

quality

Question 27

Small voxel yields ________ radiation dose

Answer 27

high

Question 28

What is the threshold for a small versus large FOV when considering voxel size?

Answer 28

>0.200mm = 200µm – for larger FOVs <0.200mm = 200 µm – for smaller FOVs

Question 29

Small voxel yields high resolution but requires more __________________ to capture signal in the greater number of the smaller voxels

Answer 29

x-ray photons (higher exposure)

Question 30

Current scanners are not configured for the longer scan times and longer processing times for a _______ FOV with a ______ voxel size

Answer 30

large small

Question 31

Smaller voxels need more photon signal which yields a ______ radiation dose

Answer 31

higher

Question 32

What are the different types of CBCT image detectors?

Answer 32

- charge-coupled image intensifier detector - flat-panel detector

Question 33

Charge-coupled image intensifier detector has distortion of the image grid when moving __________ the center

Answer 33

away from

Question 34

Do flat panel decectors have distortion?

Answer 34

Even at more distant areas from the center of the grid, there is minimal to no distortion of the grid pattern.

Question 35

Flat panel image receptor area receiving the signal from the flat-panel detector’s __________ is flat.

Answer 35

scintillator

Question 36

Improved image quality and the higher signal-to noise ratio are noted in which type of detector?

Answer 36

flat-panel detector

Question 37

Lower radiation dose for which type of detector?

Answer 37

Charge-coupled device image intensifier