A high-resolution time-of-flight clinical PET detection
system using the PMT-quadrant-sharing technology
Wai-Hoi Wong 1, Hongdi Li 2, Yuxuan Zhang 1, Rocio Ramirez 1,
Hossain Baghaei1, Shaohui An2, Chao Wang2, Shitao Liu2, Yun Dong2
1
University of Texas MD Anderson Cancer Center, Houston, TX,
2
Shanghai United Imaging Healthcare Co, Shanghai, China.
The PMT-Quadrant-Sharing (PQS) detector block
System Design
• LYSO is expensive (1/5 the price of gold)
• The Objective is to get higher sensitivity per cc of LYSO
• More efficient use of LYSO by increasing the axial field of view
while reducing the crystal depth
• GEANT4 MC simulation
• But large AFOV increases
PMT and electronics cost
• Use PMT-quadrant-sharing
reducing PMT usage by 75%
for increasing AFOV cheaply
• 15mm deep LYSO, 28-cm AFOV
Detector Ring Design
• To achieve ultrahigh resolution using large PMT to increase AFOV
2.35 x 2.35 mm pitch
38-mm PMT
16 x 16 LYSO block
Achieve decoding 256 crystals per PMT usage
Adapt PMT-Quad-Sharing blocks to a gapless detector-ring geometry
Ring has 24 modules (3 x 7 blocks)
3 blocks in-plane and 7 blocks axial
The edge blocks are half-ground to
fit the quadrant-sharing PMT
27.6-cm axial FOV
A detector module
The “Slab-Sandwich-Slice” (SSS) Detector Production
There are 4 sandwich types
in this 16 x 16 block
Each reflecting mask can be cut into any shape providing
many degrees of freedom to optimize crystal decoding
These are 15 sets of inter-slab irregular reflecting masks for
a 16 x 16 array to decode 256 crystals / PMT
The SSS production method is highly uniform and precise
as shown in the decoding map of these 72 detector blocks
We use the 5th-generation HYPER Pileup-event-recovery
front-end electronics
Hybrid coincidence
NEMA image resolution measurement
Reconstruction algorithm: FBP2D (SSRB)
Pixel Size: 0.3 x 0.3 x 1.22
NEMA Resolution
Expectation (mm)
Measured (mm)
Transaxial (1 cm)
≤2.8 mm
2.72
Axial (1 cm)
≤3.1mm
2.76
Trans Radial (10 cm)
≤3.3mm
3.36
Trans Tangential (10cm)
≤3.2mm
3.05
Axial (10cm)
≤3.6mm
2.96
PSF reconstructed image resolution (mm)
FWHM
0 cm
4 cm
8 cm
Mid plane
P (V)
1.47
1.55
1.64
1.78
1.76
1.89
1.97
2.46
Mid plane
P (H)
1.55
1.44
1.60
1.61
1.56
1.81
1.77
1.79
¼ axis
NP (V)
1.72
1.88
2.09
2.13
2.18
2.12
2.19
2.95
¼ axis
NP (H)
2.00
2.03
2.19
2.28
2.58
3.13
3.90
4.46
V: Vertical
12 cm 16 cm 20 cm 24 cm 28 cm
H: Horizontal
Average time-of-flight resolution 473 ps (+ 36 ps)
Very fine axial sampling, slice-to-slice separation = 1.22 mm
Oncology
3 minutes/bed
4 bed positions
TOF + PSF
PSF
2 min/bed, 2 iterations
3 min/bed, 3 iterations
MIP
TOF + PSF Recon
SNR: TOF/PSF 2 min/bed 2 iterations = PSF 3 min/bed 3 iterations 2/3 scan time, faster recon, no loss of detectability
SNR = (Signal – Background) / SDBackground
See Jakoby, et al, Phys. Med. Biol. 56
Conclusions
• With PMT-quadrant-sharing Detector design we have
developed an ultrahigh resolution TOF PET/CT
• It has a resolution of 2.8 mm using FBP (1.5 mm using PSF)
• Large axial FOV 27.6 cm, ultrafine axial sampling of 1.22 mm
• This large system with ultrahigh resolution uses only 576 PMT
(reducing PMT and electronics cost, while increasing reliability)
• It has 129,024 detectors with a TOF resolution of 473 ps
These developments have been supported by:
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NIH-RO1- EB001038 PHS Grant
NIH-RO1- EB001481 PHS Grant
NIH-RO1- EB004840 PHS Grant
Shanghai United Imaging Healthcare Fund