BGO PET System

1
BGO PET System
Initial Results
2
The BGO System

• Two banks of 8 BGO tubes
• -ve 900V
• 22Na point sources
• Turntable 5o increments
• Performance
• DE 30 (170keV _at_ 511keV)
• Dt 25ns FWHM
• Singles 750cps _at_ 5cm
• Coincidence 13 cps _at_ 5cm
• two tubes

3
Electronics

• Logical OR of each bank of tubes
• AND from coincidence unit
• Singles/Coincidence Trigger
• Disc. threshold 60 keV (241Am)
• 16 channel CAEN Amplifier

4
Data Acquisition

• Sources rotated 5o increments
• Data collection for 2 hours per angle
• Singles Mode
• Mg 2 filter in sort
• Coincidence between directly opposite tubes
• LORs defined

5
22Na Spectrum

• Gain-matched spectrum
• 45o angular position

• Poor energy resolution
• Good PT ratio Mg2

6
First Images - FBP
Ramp Filtered Image (Linear Interpolation)

• Very Poor Image
• Limited number of LORs
• - 35 angles x 8 projections 280 LORs
• Insufficient Projections

7
First Images ML-EM
Greyscaled image 16 iterations

• Good Image
• - No artefacts
• - Strong source resolved
• - Small amount of blurring
• - good spatial resolution
• System matrix copes with limited data
• Weak source not present in scaled image

8
Image Matrix

• Output image matrix prior to greyscaling
• Manipulate data (v, 3v, 4v,..)
• Surface Plot
• - clearly identify sources
• Image
• - Greyscale or Colourmap

9
Surface Plots
data
v(data)
3v(data)
4v(data)
10
Modified Images
4v(data) Scaled Images
Greyscale
Colormap
11
Modified Images

• Background matrix defined
• Mean and s calculated
• Background removed pixel by pixel
• Only sources remain in image

12
Further Work

• Investigate effect of gate width
• - Statistics v True coincidence
• How important is system energy resolution to
  image quality?
• - scatter rejection
• - major selling point of smartPET!
• - iterative reconstruction
• Define LORs between more detector pairs

13
Preliminary Results
Mg2 Matrices
Narrow photopeak gate
No gate
14
No Gate
Compton Gate