Applications in Nuclear Medicine and Radiology Professor Bob Ott - - PowerPoint PPT Presentation

Applications in Nuclear Medicine and Radiology

Professor Bob Ott Institute of Cancer Research and Royal Marsden Hospital

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

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
• f 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
• r 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

0.4 32 64 x 0.5 Toshiba Aquilion 64 0.37 28.8 64 x 0.6 Siemens Sensation 64 0.4 40 64 x 0.625 Philips Brilliance 64 0.35 40 64 x 0.625 GE Lightspeed VCT Rotation speed (s) Axial length (mm) Channels Scanner

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

• f <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

2-12 2-12

Coinc time window (ns)

2.4 2.4

Volume resolution (µl)

1.1 1.1

Linear spatial Resolution (mm)

2 x 2 2 x 2

Scint size (mm)

3072 1536

# of APDs

7.2 3.6

Axial FoV (cm)

11 11

Aperture (cm)

15.6 15.6

Ring diam (cm)

LabPET 7.2 LabPET 3.6 Specification

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 non-
• rthogonal 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

spatial pulse height timing 1.4-1.9mm ~45% in 1m 10.9ns

15cm 3.4m 3.4m 3.4m

New crystals for PET/SPECT

3.79 ~1.9 350 28 0.7-0.9 LaCl3(Ce) 6.71 1.85 430 60 0.2 GSO 4.88 1.5 195/310 0.6/630 0.05/0.16 BaF2 5.29 ~1.9 380 26 1.3 LaBr3(Ce) 7.4 1.82 420 40 0.75 LSO 7.13 2.15 480 300 0.2 BGO 3.67 1.85 415 250 1.0 NaI (Tl) Density (g.ml) Refractive index Peak λ (nm) 1/e decay time (ns)

• Rel. light
• utput

Crystal

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 (<5µ) 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