CT Simulator

Question 1

Which two researcher invested in CT?

Answer 1

Godfrey Hounsfield and Dr. Allan Cormack

Question 2

When was the first CT of brain taken?

Answer 2

1971

Question 3

What were some characteristics of the first CT scanners?

Answer 3

Low Resolution, Long acquisition times and Long data to image conversion times

Question 4

Describe the 1st generation CT Scanners?

Answer 4

• Pencil Beam system
• Parallel beam geometry
• Excellent scatter rejection
• Each Projection measured
• 160 Parallel Rays

Question 5

Describe 2nd Generation CT scanners.

Answer 5

• Narrow Fan Beam (30 detectors)
• Reduced # of exposure for acquisition
• More scatter is detected than “Pencil” beam

Question 6

Describe a 3rd Generation CT Scanner.

Answer 6

• Rotate/Rotate (Translation eliminated)
• Wider fan beam, enough to cover patient
• Reconstruction takes seconds
• More scatter detected than 2nd generation

Question 7

Describe 4th generation CT Scanners.

Answer 7

• Rotate/Stationary
• Similar scatter to 3rd generation
• Fixed array of detectors

Question 8

What is helical scanning?

Answer 8

• 3rd and 4th generation with continuous motion of source
• Slip rings provide electrical connection to x-ray tube (and detectors in 3rd generation)
• Table continuously move with source and detectors rotating

Question 9

What are hounsfield units?

Answer 9

• CT Numbers that relate to linear attenuation coefficients

- Range from 3000 to -1000

Question 10

What is Hounsfield equation?

Answer 10

HU= (Ux-Uwater)/ (Uwater-Uair) x 1000

Question 11

Water has a hounsfield value of?

Answer 11

0

Question 12

Bone has a Hounsfield value of ?

Answer 12

+1000

Question 13

Air has a Hounsfield value of?

Answer 13

-1000

Question 14

What is principle of Dual energy CT?

Answer 14

Materials exhibit different attenuation at different mean energies

Question 15

What are the two interactions that photon have with matter?

Answer 15

Compton and Photoelectric effect

Question 16

What happens to the atom to undergo photoelectric effect?

Answer 16

photon has sufficient energy to overcome the binding energy of the K-shell

Question 17

What is the K-Edge?

Answer 17

The K-shell threshold of a substance, that is unique to every substance

Question 18

What is dual spiral?

Answer 18

Two spiral scans at low and high kV

Question 19

What is slow Kv Switching?

Answer 19

Switch kV level typically once per gantry rotation

Question 20

What is fast kV switching?

Answer 20

Switch kV level every millisecond

Question 21

What is dual source?

Answer 21

Simultaneous scan with two tubes

Question 22

What is split filter?

Answer 22

Beam of one sources “sees” two different filters

Question 23

What type of detectors do dual energy CT use?

Answer 23

Sandwich type, two layers per channel

Question 24

What is the purpose of the top layer of the detector?

Answer 24

Detection of lower energy quanta

Question 25

What is the purpose of the bottom layer of the detector?

Answer 25

Detection of higher energy quanta

Question 26

What two examples of applying Dual Energy CT?

Answer 26

Metal Artifact Reduction, Certain structure exclusion with manipulating energy dependences

Question 27

What is required when working with metal artifact?

Answer 27

The artifact must be contours and assigned a proper density for accurate dose distrubtion

Question 28

What are the two used metal artifact reduction algorithms?

Answer 28

Normalized Metal Artifact Reduction (NMAR) AND Empirical Beam Hardening and Scatter Correction (EBHSC)

Question 29

What type of table top do CT Simulators utilize?

Answer 29

Flat patient to replicate the table on the linac

Question 30

What is the contiguous slice thickness and Increment?

Answer 30

2mm & 2mm, which exhibits acceptable quality and acceptable dose

Question 31

What is 50% overlap slice thickness and increment?

Answer 31

2mm slice & 1mm increment, best quality and highest dose

Question 32

What is a 100% gap slice thickness and increment?

Answer 32

2mm slice and 4mm increment, worst quality and lowest dose

Question 33

What is partial volume averaging?

Answer 33

When object is partially out of the scan plane or smaller than the spatial resolution. The visible portions can be averages to estimate a hounsfield

Question 34

What is slice thickness for non-IMRT?

Answer 34

5mm

Question 35

What is slice thickness for IMRT/VMAT?

Answer 35

2-3mm

Question 36

What is the slice thickness for SBRT/SRS?

Answer 36

1-1.5mm

Question 37

As slice thickness increase, what happens to DRR Resolution?

Answer 37

Declines

Question 38

As slice thickness increases, what happen to partial volume averaging?

Answer 38

Often difficult to visualize certain structures, making PVA difficult

Question 39

As slice thickness increase, what happens to signal to noise ratio ?

Answer 39

Improves

Question 40

What is the name of the system used for patient positioning.

Answer 40

XYZ Coordination system

Question 41

The X plane utilizes which plane ?

Answer 41

Transverse plane (L or R)

Question 42

The y plane utilizes which plane ?

Answer 42

Longitudinal, extending from superior to inferior

Question 43

The z plane utilizes which plane ?

Answer 43

The Coronal, extending from superior to posters

Question 44

What is the purpose of the XYZ system?

Answer 44

To replicate the position relative to the linear accelerator

Question 45

What is localization?

Answer 45

Delineation of treatment target and placement of isocenter relative to target