QA for MSCT - beyond IPEM 91 CTUG Nov 06 IPEM 91 IPEM Report 91 - - PowerPoint PPT Presentation

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QA for MSCT - beyond IPEM 91 CTUG Nov 06 IPEM 91 IPEM Report 91 - - PowerPoint PPT Presentation

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QA for MSCT - beyond IPEM 91 CTUG Nov 06 IPEM 91 IPEM Report 91 (2005) Recommended Standards for Routine Performance Testing of Diagnostic X-Ray Systems Chapter 12 CT Image quality CT number calibration Radiation

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SLIDE 1

CTUG Nov 06

QA for MSCT - beyond IPEM 91

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SLIDE 2

CTUG Nov 06

IPEM 91

  • IPEM Report 91 (2005)

– Recommended Standards for Routine Performance Testing of Diagnostic X-Ray Systems

  • Chapter 12 CT

– Image quality – CT number calibration – Radiation dose – Mechanical tests – Axial, helical images – Inner and outer detector rows

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SLIDE 3

CTUG Nov 06

Beyond IPEM 91

  • All the slices?
  • MPRs
  • AEC
  • Cone beam artefacts
  • Other issues ?
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SLIDE 4

CTUG Nov 06

  • Four slice, outer slices noise ~ 5% high

All or some of the slices ?

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 1 2 3 4 Detector Bank Image Noise (%)

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SLIDE 5

CTUG Nov 06

  • Noise 16 slice – not so predictable

All or some of the slices ?

0.80 1.20 1.60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Slice # noise %

Std Head StdBody

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SLIDE 6

CTUG Nov 06

  • Z-sensitivity (slice thickness) 16 slice
  • QC is about change – does this graph matter ?
  • Test some or all ?

All or some of the slices ?

0.48 0.5 0.52 0.54 0.56 0.58 0.6 0.62

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Slice number fwhm (mm)

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SLIDE 7

CTUG Nov 06

Volume Imaging

  • Volume imaging

– MPRs, 3-D

  • Should it be tested?

– directly ? – indirectly?

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SLIDE 8

CTUG Nov 06

MPR Direct Testing

  • Noise
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SLIDE 9

CTUG Nov 06

MPR Direct Testing

  • Resolution

– bead or wire orientated appropriately (PSF -> MTF) – Visual repeating pattern

10 20 30 40 50 60 70 80 90 100 2 4 6 8 10 Frequency (lp/cm) MTF (%)

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SLIDE 10

CTUG Nov 06

MPR Direct Testing

  • Advantage

– What you see is what you get – Takes into account any special reconstruction or interpolation algorithms

  • Disadvantage

– MTF analysis, but fwhm PSF or visual can be fine

10 20 30 40 50 60 70 80 90 100 2 4 6 8 10 Frequency (lp/cm) MTF (%)

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SLIDE 11

CTUG Nov 06

MPR Indirect Testing

  • Noise from helical slice

Recon position 1

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SLIDE 12

CTUG Nov 06

MPR Indirect Testing

  • 3-D resolution

– z-axis (helical z-sensitivity)

50 100 150 200

  • 10
  • 8
  • 6
  • 4
  • 2

2 4 6 8 10

mm C T N um bers

2.5mm 5mm

FWTM FWHM

perspex rod

Helical Z-Sensitivity tool

0.05 mm tungsten thin disk

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SLIDE 13

CTUG Nov 06

MPR Indirect Testing

  • 3-D resolution

– x-y (scan plane)

10 20 30 40 50 60 70 80 90 100 2 4 6 8 10 Frequency (lp/cm) MTF (%)

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SLIDE 14

CTUG Nov 06

MPR Indirect Testing

  • Advantage

– Doing these tests anyway

  • Disadvantage

– Is it ok ? Recon is from raw data not from slices – But looking for change… – Doesn’t take into account special interpolation algorithms in the 3-D

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SLIDE 15

CTUG Nov 06

MPR Testing

  • Should it be tested ?

– Directly or indirectly ?

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SLIDE 16

CTUG Nov 06

  • Tube current modulation

– Patient size, z-axis, rotational – Axial and helical modes

Testing the AEC

From patient to patient Along patient length Around the patient

mA angle

  • 180

+180

Low mA High mA mA

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SLIDE 17

CTUG Nov 06

  • Test object to vary in z-axis and rotationally

– eg Perspex phantom, conical with elliptical cross section

Testing the AEC

End view Side view

CT scanner couch Catphan carrying case

  • Based on ‘Apollo’ phantom developed by

Muramatsu, National Cancer Centre, Tokyo

  • Nick Keat – now at GSK
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SLIDE 18

CTUG Nov 06

  • Image along length of phantom – AEC off, on

– Monitor image noise, mA, CTDIvol,

AEC off, Constant mA

Testing the AEC

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SLIDE 19

CTUG Nov 06

  • Circular, elliptical phantoms of various sizes

– Scan short lengths over each section – Monitor image noise, mA, CTDIvol,

Testing the AEC

  • E. Castallano – RMH, London
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SLIDE 20

CTUG Nov 06

Testing the AEC

GE LightSpeed16

4 8 12 16 20 24 28

  • 150
  • 100
  • 50

50 100 150 Z-position (mm) Noise (%) automA off Noise Index 12

Increased mA Decreased mA

www.impactscan.org/bluecover.htm

Increased mA Decreased mA

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SLIDE 21

CTUG Nov 06

Coronal view Sagittal view z-axis AEC off z-axis AEC on

Noise increases Constant noise

Testing the AEC – Viewing with MPR

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SLIDE 22

CTUG Nov 06

Testing the AEC

  • Should this be a described test ?
  • In a specified phantom ?
  • How often?
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SLIDE 23

CTUG Nov 06

Cone beam artefact

  • Teflon (PTFE) rod in water, to simulate rib at an

angle to scan plane

David Platten – now at Kings

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SLIDE 24

CTUG Nov 06

Standard reconstruction AMPR

AMPR Algorithm

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SLIDE 25

CTUG Nov 06

Windmill artefact in consecutive images

  • Teflon (PTFE) rod in water, to simulate rib at an

angle to scan plane (60°, Pitchx = 1.5, 16 x 1.5 mm

acquisition, 5 mm image)

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SLIDE 26

CTUG Nov 06

Testing the cone beam artefact

  • Should this be a described test ?
  • In a specified phantom ?
  • How often?
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SLIDE 27

CTUG Nov 06

Beyond IPEM 91

  • All the slices ?
  • MPRs (+3-D), AEC, cone beam artefacts

– Should these be included in routine testing ?

  • Should there be anything else ?

0.48 0.5 0.52 0.54 0.56 0.58 0.6 0.62

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Slice number fwhm (mm)

End view Side view

CT scanner couch Catphan carrying case