Applications in Nuclear Medicine and Radiology
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Transcript of Applications in Nuclear Medicine and Radiology
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Applications in Nuclear Medicine and Radiology
Professor Bob Ott
Institute of Cancer Research and Royal Marsden Hospital
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Topics
• Digital x-ray imaging
• Fast CT scanning
• SPECT scanners for small animals
• SPECT/CT scanning
• PET scanners for small animals
• New crystals for PET and SPECT
• Active pixel sensors in medical imaging
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Imaging requirements• X-ray imaging of anatomy
energies between ~20keV and 140keV
performed in integrate mode
contrast between tissues often small• Single photon emission computed
tomography (SPECT) imaging tissue function
gamma ray energies between 80-364 keV• Positron emission tomography (PET) imaging
of tissue function
gamma ray energy 511 keV• PET and SPECT in pulse counting mode
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Digital planar X-ray imaging
• Systems have been based on the use of:storage phosphor platesflat panel detectors such as amorphous
silicon or seleniumscanning slot devices with CCDsphosphors imaged with a CCD or CMOS devices
• Typically 70 microns spatial resolution is possible for breast imaging with ~100% photon detection at ~20keV
• 10 lp/mm possible compared to 15 lp/mm with film
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Indirect flat panel sensor for x-ray imaging
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Diagnostic X-ray CT scanning
• Historically detectors based on the use of CsI coupled to silicon diodes or Xe gas detectors
• More recent developments involve the use of CdWO4 or ceramic scintillators such as Yttrium Gadolinium Oxide which have ~2x the light output of CdWO4
• New fast ceramic detectors use gadolinium oxide (GDOS) have a short decay time and reduced afterglow (by 400 times).
• Can make fast images with 30% less radiation dose
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Comparison of afterglow from scintillators used in CT
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Diagnostic X-ray CT scanning• Main developments are in multi-slice imaging to
speed up scanning allowing heart scanning in 5 beats
Scanner Channels Axial length (mm)
Rotation speed (s)
GE Lightspeed VCT
64 x 0.625 40 0.35
Philips Brilliance 64
64 x 0.625 40 0.4
Siemens Sensation 64
64 x 0.6 28.8 0.37
Toshiba Aquilion 64
64 x 0.5 32 0.4
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Curved View (1) and X-Section (2) views showing the calcified plaque on the LAD
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X-ray CT future developments
• Toshiba have developed a new 256 x 0.5mm row detector array which is soon to be commercial
• GE and Siemens are developing flat panel detector CT systems which can be used for RT planning but are presently too slow for diagnostics
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High resolution animal SPECT
• The HiSPECT system is an add-on to existing NaI(Tl)-based gamma cameras to give multi-pinhole aperture sensitivity and enhanced resolution.
• The Nano-SPECT system is a purpose built (Mediso) small animal imaging gamma camera system with a resolution of <0.8mm and with multi-pinhole sensitivity.
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HiSPECT withmultipinholecollimator
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HiSPECT images of mouse using Tc-99m tracers
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Nano-SPECT system
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Nano-SPECT images of mouse taken in helical mode
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SPECT/CT scanning
• Following the development of PET/CT scanners several SPECT/CT scanners have now been developed
• Provide improved attenuation/scatter correction plus anatomy as well as function
• Siemens and Philips have just connected double headed gamma cameras to conventional CT scanners
• GE have produced a gamma camera gantry incorporating a low cost CT scanner
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SPECT/CT images
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The new LabPET system
Made with APDs coupled to individual scintillating crystals (LSO)
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Properties of the LabPET systemSpecification LabPET 3.6 LabPET 7.2
Ring diam (cm) 15.6 15.6
Aperture (cm) 11 11
Axial FoV (cm) 3.6 7.2
# of APDs 1536 3072
Scint size (mm) 2 x 2 2 x 2
Linear spatial Resolution (mm)
1.1 1.1
Volume resolution (l)
2.4 2.4
Coinc time window (ns)
2-12 2-12
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Images from the LabPET system
F-18-FDG F-18 fluoride
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HIDAC MWPC PET system
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HIDAC MWPC PET system
F-18 fluoride F-18 FDG
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The new PETMOT system
• The system will combine phoswitch- PET and micro-lens array optical tomograph
• Optical lens system is 1cm2 block containing 100 x 1mm lenses
• Optical collimator used to reject non-orthogonal rays
• Coupled to photodiodes
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Multi lens array assembly for a single block
Without (l) and with (r) optical collimator
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PET-MOT system
Transaxial
With and without optical collimator
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PET-MOT system
• Allows both optical and positron emission tomography simultaneously
• The optical system inside the PET array has little effect on the 511keV photons and is insensitive to them
• J Peter and W Semmler, German Cancer Centre, Heidelberg
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An MR compatible PET system for small animals
• LSO multi ring PET system mounted inside the MR magnet with a purpose-built RF coil within PET ring
• 104 2mm x 3mm x 5mm crystals coupled to 2mm diameter optical fibres
• Fibres connected to MC-PMTs mounted in an RF screened box
• Ring diameter 75.5 mm• P Marsden et al at St Thomas’ Hospital
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PET- MR system layout
PET scanner within MR boreOff-set concentric PET rings
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PET – MR resolutions
spatial pulse height timing1.4-1.9mm ~45% in 1m 10.9ns
15cm
3.4m3.4m
3.4m
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New crystals for PET/SPECTCrystal Rel. light
output1/e decay time (ns)
Peak (nm)
Refractive index
Density (g.ml)
NaI (Tl) 1.0 250 415 1.85 3.67
LaCl3(Ce) 0.7-0.9 28 350 ~1.9 3.79
BaF2 0.05/0.16 0.6/630 195/310 1.5 4.88
BGO 0.2 300 480 2.15 7.13
LSO 0.75 40 420 1.82 7.4
GSO 0.2 60 430 1.85 6.71
LaBr3(Ce) 1.3 26 380 ~1.9 5.29
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LaBr3:Ce scintillation camera
• Pani et al have developed a small scintillation camera using this new scintillator coupled to a flat panel PSPMT
• Achieve an energy resolution of 6.5% and a spatial resolution of 1.1mm FWHM
• Efficiency at 140 keV is twice that of NaI(Tl) with a 6mm crystal
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LaBr3:Ce TOF PET scanner
• Karp et al have developed a ring PET scanner using LaBr3:Ce crystals 4mm x 4mm by 30mm coupled via continuous light guide to PMTs
• Energy resolution (8.5%) is better than the equivalent LSO scanner (>20%) leading to a reduced scatter fraction (22% vs 42%)
• Peak NEC rates are better than the LSO scanners
• Timing resolution is ~315ps!!
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Active Pixels Sensors in Medical Imaging
• Active pixel sensors are being developed under the MI-3 basic technology grant
• Will allow on-chip intelligence and ‘individual pixel/ROI’ read-out
• Applications include:High resolution (sub-mm) gamma camera imaging
Digital X-ray imaging
High resolution (<5) digital autoradiography
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Summary
• Still plenty of mileage in new detectors for both NM and Radiology to:
improve image contrastimprove spatial resolutioncombine modalitiesreduce radiation dosepixel intelligence