Scatter Corrections for Cone Beam Optical Computed Tomography

1
Scatter Corrections for Cone Beam Optical
Computed Tomography

• Tim Olding1, Oliver Holmes1, and L. John
  Schreiner2,3
• 1Department of Physics, Queens University
• 2Medical Physics Department, Cancer Centre of
  Southeastern Ontario
• 3Departments of Physics and Oncology, Queens
  University, Kingston, ON, Canada

2
VISTA Scanner

• uses 630 nm red or 590 nm amber LEDs in a diffuse
  light box/panel
• Projection data acquired with 1024x768 pixel
  10-bit monochrome camera (410 projections over
  360o).

Wolodzko et al. (1999) Med. Phys. 26, 2508 Jordan
et al. (2006) DOSGEL 2006, 138
3
Scatter Management Strategies

• Polarizer Scatter Reduction
• 90o Side Transmission
• Beam Pass Array (BPA)
• Beam Stop Array (BSA)

4
BSA Scatter Correction
Projections (Reference Data)
Scatter Maps
5
Scatter Correction Strategies
A Scatter Solution B Polarizer Corrected C
BSA Corrected D Dye Solution
6
Scatter Correction Strategies
A Scatter Solution B Polarizer Corrected C
BSA Corrected D Dye Solution
7
Polymer Gel Scatter Map Corrections
500 cGy delivery
4T polymer gel dosimeter
2 mm BSA corrected
8
Test Phantoms
2 cm finger
0.10 g/L scattering solution
courtesy of Modus Medical Ltd.
9
Test Phantoms
2 cm finger
0.10 g/L scattering solution
2 cm double finger
courtesy of Modus Medical Ltd.
10
Test Phantoms
2 cm finger
0.10 g/L scattering solution
2 cm double finger
5 cm finger
courtesy of Modus Medical Ltd.
11
Test Phantoms
2 cm finger
0.10 g/L scattering solution
2 cm double finger
5 cm finger
9 cm jar
courtesy of Modus Medical Ltd.
12
5cm Finger Phantom Scatter Correction
0.10 g/L scattering solution
1 mm BSA corrected
Raw Data
13
5cm Finger Phantom Scatter Correction
0.10 g/L scattering solution
Actual
Expected
1 mm BSA corrected
Raw Data
14
5 cm Finger Phantom Scatter Correction
2
3
1
0.10 g/L scattering solution
15
5cm Finger Phantom Scatter Correction
9 cm raw data
5 cm raw data
Scatter () map
Scatter () map
16
5cm Finger Phantom Scatter Correction
?P3 , ?S3
Raw Data
?P2 , ?S2
?P1 , ?S1
Scatter () Map
17
Are we ready to correct for scatter?
18
Conclusions

• Beam stop array (BSA) method works well for
  scatter correction of uniformly attenuating
  dosimeters
• More sophisticated use of scatter information
  required for BSA scatter corrections in
  clinically relevant dosimetry

19
Acknowledgements

• Funding Canadian Institutes for Health Research
• Thanks to CCSEO Medical Physics Group

20
Polarizer Scatter Reduction (in front behind
tank)
Polarized
Non-Polarized
Extends the linear range of the scanner, but adds
scan artifacts.
21
BPA Scatter Correction (0.10 g/L)
Scatter Maps
Projections (Reference Data)
22
Scatter Correction of Dye Solution
Raw Data
1 mm BSA Corrected
23
Polymer Gel Scatter Map Corrections
500 cGy delivery
OptCT projection (4T dosimeter)
24
Choosing BSA Sizing