Transcript OTT_Applications in Nuclear Medicine and Radiology

Applications in Nuclear
Medicine and Radiology
Professor Bob Ott
Institute of Cancer Research
and Royal Marsden Hospital
Topics
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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
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
Digital planar X-ray imaging
• Systems have been based on the use of:
storage phosphor plates
flat panel detectors such as amorphous
silicon or selenium
scanning slot devices with CCDs
phosphors 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
Indirect flat panel sensor for x-ray imaging
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
Comparison of afterglow from scintillators used in CT
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 x 0.625
64
40
0.4
Siemens
Sensation 64
28.8
0.37
32
0.4
64 x 0.6
Toshiba Aquilion 64 x 0.5
64
Curved View (1) and X-Section (2) views
showing the calcified plaque on the LAD
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
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.
HiSPECT with
multipinhole
collimator
HiSPECT images of mouse using Tc-99m tracers
Nano-SPECT system
Nano-SPECT images of mouse taken in helical mode
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
SPECT/CT images
The new LabPET system
Made with APDs coupled
to individual scintillating
crystals (LSO)
Properties of the LabPET system
Specification
Ring diam (cm)
LabPET 3.6
LabPET 7.2
15.6
15.6
Aperture (cm)
11
11
Axial FoV (cm)
3.6
7.2
# of APDs
1536
3072
Scint size (mm)
2x2
2x2
Linear spatial
Resolution (mm)
1.1
1.1
Volume
resolution (l)
2.4
2.4
2-12
2-12
Coinc time
window (ns)
Images from the LabPET system
F-18-FDG
F-18 fluoride
HIDAC MWPC PET system
HIDAC MWPC PET system
F-18 fluoride
F-18 FDG
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 nonorthogonal rays
• Coupled to photodiodes
Multi lens array assembly
for a single block
Without (l) and with (r) optical collimator
PET-MOT system
Transaxial
With and without optical collimator
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
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
PET- MR system layout
PET scanner within MR bore
Off-set concentric
PET rings
PET – MR resolutions
15cm
3.4m
3.4m
spatial
1.4-1.9mm
3.4m
pulse height
~45% in 1m
timing
10.9ns
New crystals for PET/SPECT
Crystal
Rel. light
output
1/e decay Peak 
time (ns) (nm)
Refractive Density
index
(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
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
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!!
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
Summary
• Still plenty of mileage in new
detectors for both NM and Radiology
to:
improve image contrast
improve spatial resolution
combine modalities
reduce radiation dose
pixel intelligence