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Dosimetry Physics 2 > CT Simulator > Flashcards

CT Simulator Flashcards

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1
Q

Which two researcher invested in CT?

A

Godfrey Hounsfield and Dr. Allan Cormack

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2
Q

When was the first CT of brain taken?

A

1971

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3
Q

What were some characteristics of the first CT scanners?

A

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

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4
Q

Describe the 1st generation CT Scanners?

A
  • Pencil Beam system
  • Parallel beam geometry
  • Excellent scatter rejection
  • Each Projection measured
  • 160 Parallel Rays
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5
Q

Describe 2nd Generation CT scanners.

A
  • Narrow Fan Beam (30 detectors)
  • Reduced # of exposure for acquisition
  • More scatter is detected than “Pencil” beam
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6
Q

Describe a 3rd Generation CT Scanner.

A
  • Rotate/Rotate (Translation eliminated)
  • Wider fan beam, enough to cover patient
  • Reconstruction takes seconds
  • More scatter detected than 2nd generation
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7
Q

Describe 4th generation CT Scanners.

A
  • Rotate/Stationary
  • Similar scatter to 3rd generation
  • Fixed array of detectors
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8
Q

What is helical scanning?

A
  • 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
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9
Q

What are hounsfield units?

A
  • CT Numbers that relate to linear attenuation coefficients

- Range from 3000 to -1000

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10
Q

What is Hounsfield equation?

A

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

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11
Q

Water has a hounsfield value of?

A

0

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12
Q

Bone has a Hounsfield value of ?

A

+1000

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13
Q

Air has a Hounsfield value of?

A

-1000

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14
Q

What is principle of Dual energy CT?

A

Materials exhibit different attenuation at different mean energies

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15
Q

What are the two interactions that photon have with matter?

A

Compton and Photoelectric effect

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16
Q

What happens to the atom to undergo photoelectric effect?

A

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

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17
Q

What is the K-Edge?

A

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

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18
Q

What is dual spiral?

A

Two spiral scans at low and high kV

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19
Q

What is slow Kv Switching?

A

Switch kV level typically once per gantry rotation

20
Q

What is fast kV switching?

A

Switch kV level every millisecond

21
Q

What is dual source?

A

Simultaneous scan with two tubes

22
Q

What is split filter?

A

Beam of one sources “sees” two different filters

23
Q

What type of detectors do dual energy CT use?

A

Sandwich type, two layers per channel

24
Q

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

A

Detection of lower energy quanta

25
Q

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

A

Detection of higher energy quanta

26
Q

What two examples of applying Dual Energy CT?

A

Metal Artifact Reduction, Certain structure exclusion with manipulating energy dependences

27
Q

What is required when working with metal artifact?

A

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

28
Q

What are the two used metal artifact reduction algorithms?

A

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

29
Q

What type of table top do CT Simulators utilize?

A

Flat patient to replicate the table on the linac

30
Q

What is the contiguous slice thickness and Increment?

A

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

31
Q

What is 50% overlap slice thickness and increment?

A

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

32
Q

What is a 100% gap slice thickness and increment?

A

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

33
Q

What is partial volume averaging?

A

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

34
Q

What is slice thickness for non-IMRT?

A

5mm

35
Q

What is slice thickness for IMRT/VMAT?

A

2-3mm

36
Q

What is the slice thickness for SBRT/SRS?

A

1-1.5mm

37
Q

As slice thickness increase, what happens to DRR Resolution?

A

Declines

38
Q

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

A

Often difficult to visualize certain structures, making PVA difficult

39
Q

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

A

Improves

40
Q

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

A

XYZ Coordination system

41
Q

The X plane utilizes which plane ?

A

Transverse plane (L or R)

42
Q

The y plane utilizes which plane ?

A

Longitudinal, extending from superior to inferior

43
Q

The z plane utilizes which plane ?

A

The Coronal, extending from superior to posters

44
Q

What is the purpose of the XYZ system?

A

To replicate the position relative to the linear accelerator

45
Q

What is localization?

A

Delineation of treatment target and placement of isocenter relative to target

Dosimetry Physics 2 (6 decks)

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