LSO from Discovery to Commercial Development

1
LSO - from Discovery to Commercial Development

• C. L. Melcher
• CTI, Inc.
• Knoxville, TN, USA

2
Acknowledgments

• Schlumberger-Doll Research, Ridgefield
• J. S. Schweitzer, R. A. Manente, C. A. Peterson
• California Institute of Technology, Pasadena
• T. A. Tombrello, H. Suzuki
• LETI, Grenoble
• J. J. Aubert, Ch. Wyon
• CTI, Inc., Knoxville
• R. Nutt, M. Andreaco
• St. Petersburg State Technical University, St.
  Petersburg
• P. A. Rodnyi and co-workers
• Institute of Single Crystals, Kharkov
• B. Minkov, M. V. Korzhik, and co-workers
• Ural State Technical University, Ekaterinburg
• B. V. Shulgin and co-workers

3
Properties of the ideal scintillator

• High light output
• Fast decay time
• High density
• High atomic number
• Good energy resolution
• Suitable emission wavelength
• Good mechanical strength
• Non-hygroscopic
• Practical crystal growth
• Low cost

4
Strengths/weaknesses of various scintillators
5
Search strategy for new scintillators

• Identify suitable luminescent center
• Suitable emission wavelength
• High transition probability
• Compatible with host material
• Identify candidates for host material
• High density
• High atomic number
• Transparent
• Non-hygroscopic
• Practical crystal growth
• Synthesize candidates
• Solid state synthesis by sintering powders
• Characterize scintillation properties
• Single crystal growth

6
Powder synthesis of candidate materials
7
Ce3 activators

• 4f 5d transition
• Allowed dipole transition
• Typically high quantum efficiency
• Typically 20-60 ns decay time
• Emission wavelength usually 350 450 nm depending
  on crystal field of host e.g. GSOCe, BaF2Ce,
  CeF3

8
Ln2SiO5 host materials
Growth of lanthanide oxyorthosilicate single
crystals and their structural and optical
characteristics, G. V. Ananeva, A. M. Korovkin,
T. I. Merkulyaeva, A. M. Morozova, M. V. Petrov,
I. R. Savinova, V. R. Startsev, and P. P.
Feofilov, Akademii Nauk SSSR, Izvestiya, Seriya
Neorganicheskie Materialy, V 17, N 6, p. 754-8,
June 1981.

• Czochralski crystal growth of Ln2SiO5, Ln Y,
  Gd-Lu
• Crystal structure
• Physical characteristics
• Melting point
• Density
• Refractive Index
• Doping with Nd3, Ho3, Er3, Tm3, Yb3

9
Early papers

• Melcher, U.S. Patent No. 4,958,080 (1990)
• Melcher and Schweitzer, IEEE Conf. Rec. (1991)
• Rodnyi (1992)
• Minkov, Functional Materials (1994)
• Shulgin et al. (1990)
• Melcher and Schweitzer, IEEE Trans. Nucl. Sci.
  (1992)
• Melcher and Schweitzer, Nucl. Instr. Meth. (1992)

10
Crystal structure vs. RE radius
11
Crystal structure Lu2SiO5 (LSO)
Monoclinic C Space group C2/c   Lattice
constants a 14.254 Å b 6.641 Å c 10.241
Å   b 122.2º
12
Crystal growth practical requirements

• Congruent melting (solid and liquid have same
  composition in equilibrium)
• Reasonable melting point (compatible with
  crucible and furnace materials)
• Mechanically strong material
• Reasonable distribution coefficient for dopant

13
Dopant concentration vs fraction of melt pulled
14
Czochralski growth of single crystals
Pull 1 mm/hr
Rotation 5 rpm
Seed crystal
Iridium crucible
Crystal
melt
Induction heater
Insulation
15
Czochralski growth of single crystal LSO
2070oC
16
Transmission of pure and Ce-doped LSO
17
Low temperature (11K) excitation spectra
18
Low temperature (11K) emission spectra
19
Ce1 Ce2 gamma ray emission
20
Pulse height spectrum of 137Cs
21
Coincidence resolving time (511 keV)
22
Intrinsic background radiation

• 2.6 of naturally occurring Lu is Lu-176
• Beta decay with primary gamma rays of 88, 202,
  307 keV
• Count-rate from Lu-176
• 0 1000 keV 40 counts/sec/g

23
Scintillation efficiency h bSQ
Lempicki et al., Nucl. Instr. Meth. A333,
304-311 (1994)
24
Scintillator properties
25
Photon interaction cross sections
26
Emission spectra at room temperature
27
Scintillation decay times
28
Coincidence resolving time
29
Commercialization issues

• Raw materials
• Availability of large quantities
• Low cost
• Recycling of scrap
• Factory
• Low cost growth stations
• Reliable electrical power
• Cooling water system
• Growth control system
• Detector processing

30
Abundance of Lu
Element Abundance
(ppmw) Lu 0.8 I 0.45 Tl 0.85 Cd
0.15 W 1.25 Bi 0.009 Ge 1.5 Hg
0.085
31
Raw materials
Lu2O3
32
LSO factory
33
Electrical power
Battery backup
Dual electrical service (3 MW)
34
Cooling water system
1000 gpm
35
Cooling towers
36
Nitrogen supply
37
Crystal boules
38
LSO production boules
Picture of 50 boules
39
Light output of all LSO crystals - 2002
40
Energy resolution of all LSO crystals - 2002
41
LSO decay time
42
Light output uniformity within a boule
43
Energy resolution uniformity within a boule
44
Decay time uniformity within a boule
45
Detector processing
46
Detector processing robotic assembly of pixels
47
Detector processing Ultraviolet light cures
adhesive
48
Detector with PMTs
49
LBNL PET detector modules

• PD Array Identifies Crystal of Interaction
• PMT Provides Timing Pulse and Energy
  Discrimination
• PDPMT Measures Energy Deposit
• PD / (PDPMT) Measures Depth of Interaction

1 square PMT
PD array
64 element LSO array
Custom IC
Courtesy of W. W. Moses, LBNL - CFI
50
UCLA
Courtesy of UCLA Crump Institute
51
Finished crystals
52
Commercial products - Accel

• Clinical applications
• 9216 LSO crystals
• High throughput
• 20 minute whole body scan

53
Commercial products - HRRT

• High Resolution Research Tomograph
• 119,808 LSO crystals
• Depth of interaction
• 2.5 mm resolution

54
PET images