The PET facility at the Austin Hospital consists of a medical cyclotron with dedicated
radiochemistry facilities and two whole body PET Scanners.
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Cyclotron
In the 1980's, short-lived radionuclides were available only in the large
physics research centres with access to particle accelerators or nuclear reactors.
The increasing clinical applications of cyclotron produced radioisotopes
have led to the rapid rise in the number of compact cyclotrons
throughout the world. All medical cyclotrons currently available are suitable for
sustaining a major program for PET research and clinical application. Cyclotrons have
been established worldwide, with eight cyclotron facilities
in operation in Australia: three in Melbourne, two in Sydney, one in Perth and two in
Brisbane.
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Specifications of the Austin Health cyclotron production facility:
| Cyclotron: |
IBA Cyclone 10/5 |
| Installation Date: |
1992 |
| Beam: |
50mA 10MeV proton
30mA 5MeV deuteron
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| Targetry: |
Five targets (2 x 18F, 11C,13N & 15O)
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| Hotcell: |
Ten lead-shielded hotcells |
| Radiochemistry: |
Five radiochemistry for 18F nucleophilic substitution;
two for 11C-methylation, one for 15O-water production and
one for radioactive gas delivery.
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| Clean Room: |
One clean room facility for sterile production of 18FDG
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| Radiopharmacy: |
Standard equipment for quality control (Radio-HPLC, Radio-TLC, GC, GC-MS)
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Cyclotron Operation
The cyclotron in operation at the Austin Hospital is a Cyclone 10/5 from
IBA (Louvain-la-Neuve, Belgium). This negative ion design machine accelerates H-
ion to 10 MeV and D- ion to 5 MeV. At the extraction radius, the negative particles
are stripped of their electrons by passing through a very thin carbon foil and the resulting
positively charged ions (H+ or D+) are bent outwards to the target ports,
by the magnetic field. Up to 50 mA of proton and 30
mA of deuteron beam intensity can be extracted onto a single
target or divided between two oppositely mounted targets. The cylindrical magnet return yoke
consisting of 15 cm of steel acts as the primary radiation shield and in addition the machine
is enclosed inside a cylindrical shielding system consisting of 68 cm thickness of boron-doped
water. Experimental measurements indicate that the cyclotron shielding, together with the 60 cm
thick concrete wall of the vault, is sufficient to keep the radiation dose level outside the
cyclotron vault to a safe level. In public areas, measurements of neutron and gamma dose rates
were 0.007 µSv/h and 0.24 µSv/h
respectively.
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Targetry
Currently our machine is fitted with 4 targets remotely loaded or unloaded by gas pressures.
Two types of target are used: liquid target for 18F production with 1mL titanium insert;
and gas target for 11C and 15O production with a 20 mL aluminium insert. These gas targets can
be run in either continuous flow or bolus mode at a loading pressure of up to 11 bar.
The radioisotopes produced are automatically transported via narrow bore tubing from the
targets to the chemistry modules in the hotcells laboratory.
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Radiochemistry modules
Radiolabelling of compounds involves considerable amounts of radioactivity and must be
performed by remote control in lead-shielded hotcells. Two types of hotcells have been
installed within the laboratory: two large hotcells with viewing area mainly used for
research and development; and eight small shielded hotcells used to house automated
radiochemistry modules for routine radiopharmaceutical production.
Manufacture and installation of the lead-shielded hotcells were performed by Bucek
Industries (Geelong, Australia).
18F-radiolabelling is performed in fully automated synthesis modules. Five
modules are currently in operation including two from IBA (Ion Beam Applications, Belgium),
one from EBCO Technologies (Richmond, BC, Canada), one from Coincidence SA
(Belgium) and one from GE (GE Medical Systems).
11C-radiolabelling is performed in two in-house built system, with one based on remote
controlled electrovalves that are manually activated by the operator and the other one based on a fully
computerised system.
15O-radiolabelling is performed using in-house chemistry modules located
in the scanner room.
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Radiation Monitoring
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Radiation detectors are installed in all work area and are monitored and logged by a
dedicated computer system. The cyclotron vault is monitored for both neuron and gamma
radiation and the radiochemistry lab and scanner for gamma only. Operation of the
Cyclotron, targets and chemistry modules is carried out automatically by computers to
minimise exposure to workers.
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PET Scanner
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PET is principally different from SPECT by virtue of it ability to determine the line-of-response of a photon by "electronic" rather than "physical" collimation.
Commercial PET scanners operate in either "so-called" two- or three-dimensional acquisition modes. In two-dimensional mode, lead septa are positioned between the rings of detectors to shield against cross-ring coincidences. By retracting the septa, the sensitivity of the scanner can be increased significantly, however, this results in an increase in the scatter and randoms rate.
The Austin Hospital in Melbourne operated a Siemens/CTI 951 (Knoxville, TN, USA) from 1992 to 2003. The ECAT-951/31R consisted of 16 rings of BGO detectors (Bi4Ge3O12), an axial range of 10.8 cm and a ring aperture of 56.7 cm diameter. It featured a retractable septa so that it could be operated in 2- or 3-D mode. The scanner was used principally in 2-D mode for clinical studies and 3-D mode for research studies.
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Specifications:
| PET Scanner: |
Siemens/CTI 951 |
| Number of Detector rings: |
16 |
| Number of crystals: |
8192 BGO |
| Crystal dimensions: |
6.25 (Transaxial) x 6.75 (Axial) x 30 (Radial) mm3 |
| Detector Ring diameter: |
1020 mm |
| Patient portal diameter: |
567 mm |
| Axial FOV: |
108 mm |
| Number of Image Planes: |
31 |
| Plane Spacing: |
3.375 mm |
Resolution (18FDG):
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Transaxial |
off-axis |
0cm |
5.8 mm |
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10 cm |
6.4 mm |
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20 cm |
7.7 mm |
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Axial |
off-axis |
0 cm |
5.0 mm |
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10 cm |
5.7 mm |
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20 cm |
7.1 mm |
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| Sensitivity (2D, 250 keV LLD): |
110 kcps/mCi/cc, 2970 cps/kBq/cc |
| Transmission source: |
3 rotating Ge-68 rods @ 0.5 mCi/rod |
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In July 2002, the Austin Hospital Centre for PET commissioned a Philips Allegro PET scanner. The following year in September 2003, the Centre further commissioned a Philips Gemini PET/CT scanner. These Allegro/Gemini PET cameras are fully 3-D and comprise of 29 rings of GSO (Gd2SiO5) detectors with an axial extent of 180 mm and a patient aperture of 565 mm.
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Specifications:
| PET Scanner: |
Philips Allegro/Gemini |
| Number of Detector rings: |
29 |
| Number of crystals: |
17864 GSO |
| Number of PMT's: |
420 |
| Crystal dimensions: |
4 (Transaxial) x 6 (Axial) x 20 (Radial) mm3 |
| Detector Ring diameter: |
800 mm |
| Patient portal diameter: |
565 mm |
| Axial FOV: |
180 mm |
| Number of Image Planes: |
90 or 45 |
| Plane Spacing: |
2 or 4 mm |
Resolution (18FDG):
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Transaxial |
off-axis |
0cm |
4.73 mm |
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10 cm |
5.59 mm |
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Axial |
off-axis |
0 cm |
4.74 mm |
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10 cm |
5.89 mm |
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| NEMA-1994 Sensitivity : |
19.7 kcps/kBq/mL |
| NEMA-1994 Scatter fraction : |
32% |
| NEMA-2001 Sensitivity : |
4.6 cps/kBq |
| NEMA-2001 Scatter fraction : |
39% |
| Transmission source: |
Rotating 740 MBq 137Cs point source |
| Reconstruction Algorithms: |
FORE3D+ FBP |
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FORE3D + OSEM, AW-OSEM |
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FORE3D + RAMLA2D |
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RAMLA3D |
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Data Processing
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Emission and transmission data are acquired by the PET scanner hardware and stored on the acquisition computer sub-system. Coincidence events are stored in acquisition memory in either histogram or listmode format.
In histogram mode, events are incrementally binned whilst in listmode, the binning stage is performed off-line. The binning stage converts the event from the coincident detector pairs to a Line Of Response to give an angle and offset of the event.
This so-called ‘sinogram’ representation of the data corresponds to sets of 2-dimensional projections of the tracer distribution. Whole body scans are performed by acquiring multiple ‘beds’ where the patient is scanned sequentially by moving the bed to cover the region of interest.
After emission and transmission acquisition for each bed are acquired, the data are reconstructed using dedicated high performance hardware. The transmission data are used to generate attenuation correction data to be applied to the emission data.
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The reconstruction of the attenuation corrected emission data gives a volume where each voxel represents the concentration of radio-isotope at that location in the volume. A range of algorithms are used from analytic methods such as FBP (Filtered Back Projection) to Iterative methods such as OSEM (Ordered Subsets Expectation Maximisation) and RAMLA (Row Action Maximum Likelihood Algorithm).
Using bio-mathematical models, the PET data can be further transformed into information with physiological, pathological or pharmacological significance. In addition, a full determination of the quantitative information available from the image requires a kinetic model of the transport mechanism and of the physiological and biochemical processes in which each radiopharmaceutical participates.
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