Andrei Nomerotski

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Instrumentation for Medical Applications

Andrei Nomerotski (Oxford Particle Physics)

VC Forum, 17 November 2009

Andrei Nomerotski

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Particle Detectors in Medicine Energy scales of modern particle physics are much

beyond needs of medicine but detection techniques are similar High energy particles cascade to low energy particles

Detection of visible light and X-rays is in demand both in medical imaging and particle physics

Medical imaging Slow rates (~Hz) Modest # of frames per second Complicated processing Each frame is a lot of information High data rates

Andrei Nomerotski

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Driving Factors Huge progress in micro (nano) electronics

New silicon technologies New types of detectors

Complicated processing at sensor level

New materials

Computing faster CPU Taking advantage of Moore’s law Software sophistication

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Outline

In the following will talk about

Positron Emission Tomography

Medical Imaging using silicon detectors

In Vivo Dosimetry

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Positron Emission Tomography (PET)

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• Cancer diagnostic tool

• Distinguish normal and cancerous tissue on the basis of their biological function

Andrei Nomerotski

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FDG-PET: basic principle

Two opposite PET detectors operating in coincidence

511 keV

511 keV -ray

511 keV -ray

18F-fluoro-deoxy-glucose

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Whole Body PET

Usually combined with Computer Tomography (CT)

PET accuracy ~5 mm Overlaid images give better accuracy CT allow for attenuation corrections

2M scans annually 20% per year growth

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Scintillator:Converts 511 keV gamma-rays into the light

PMTs: Convert the scintillation light into a measurable electrical voltage pulse

511 keVgamma-rays

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PET detector componentsPET detector components

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Solid-State PET Detectors

• Avalanche photodiode (APD)

High detection efficiency (~50%)

Wide dynamic range

Low gain (~100)

• Silicon Photomultiplier (SiPM)

Work in Geiger mode

Gain is comparable to PMTs (~106)

High speed (similar to PMTs)

Limited dynamic range

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Silicon Photomultiplier (SiPM)

SiPM devices SiPM microcells

Schematic diagram

1mm x 1mm

HAMAMATSU Inc.

• Geiger mode operated silicon arrays on a common substrate• Invented in 90’s• Last years – big improvements in parameters and available bareas

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Silicon Photomultiplier

Hamamatsu MPPC

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New Fast Scintillators

Promising new scintillators: PreLudeTM420 (LYSO) and BrilLanCeTM380 (LaBr3(Ce)) By Saint-Gobain Cristaux et Detecteurs

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Time Of Flight PET

Use time information to localize interaction with ~few cm precision

Allows for better image quality for same dose

Or lower dose (=higher throughput) for same image quality

Need to achieve ~100 ps timing accuracy

Currently ~400 ps

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Combined PET & MRI Difficult to combine due to strong magnetic field and high

frequency interference SiPMs work in strong magnetic field PET scanner inside

MRI scanner Advantage over PET/CT - lower dose

From S.Cherry, Advances in PET Imaging Technology

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PET R&D Activities in Oxford Physics Ongoing R&D on SiPM can be used for

PET

Preparing a bid to Wellcome/STFC to build a TOF-PET demonstrator

Discussing common R&D projects with Churchill

Offer SiPM/TOF-PET MPhys project in Physics

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Medical Imaging

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Medical Imaging Concentrate on X-ray imaging with silicon detectors Nicely demonstrates advances in silicon industry

Not driven by science any more rather by telecommunications and PlayStation users

Nowadays use processes with 0.09 m = 90 nm min feature size with 45 nm in sight

Medipix – silicon pixel detector with integrated electronics and readout Started at CERN in 90’s as by-product of R&D for future

LHC experiments Very successful with dozens of applications outside of PP

(and medicine)

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X-Rays in Silicon Visible photon range few m 20keV X-ray range 5 m 100 keV X-ray range 80 m For larger energies need different materials (higher Z)

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Hybrid-Pixel DetectorsHybrid-Pixel Detectors

p+

n-

ASICn-well

p-substrate

Semiconductor detector

Bump-bond contact

Charged particle

gm

Iin Vout

Pulse processing electronics provides simultaneously fast and noise free images

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Medipix2 Bump BondingMedipix2 Bump Bonding

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Preamp

Disc1

Disc2

Double Disc logic

Vth Low

Vth High

13 bits

Shift Register

Input

Ctest

Testbit

Test Input

Maskbit

Maskbit

3 bits threshold

3 bits threshold

Shutter

Mux

Mux

ClockOut

Previous Pixel

Next Pixel

Conf

8 bits configuration

Polarity

Analog Digital

Preamp

Disc1

Disc2

Double Disc logic

Vth Low

Vth High

13 bits

Shift Register

Input

Ctest

Testbit

Test Input

Maskbit

Maskbit

3 bits threshold

3 bits threshold

Shutter

Mux

Mux

ClockOut

Previous Pixel

Next Pixel

Conf

8 bits configuration

Polarity

Analog Digital

Charge sensitive preamplifier with individual leakage current compensation

2 discriminators with globally adjustable threshold

3-bit local fine tuning of the threshold per discriminator

1 test and 1 mask bit

External shutter activates the counter

13-bit counter

1 Overflow bit

Signal ~ few 1000 electrons (!)

Medipix2 Pixel Cell SchematicMedipix2 Pixel Cell Schematic

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Medipix2 Cell LayoutMedipix2 Cell Layout

55 m

55 m

55 m

55 m

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Medipix2 Chip ArchitectureMedipix2 Chip Architecture

IO

Logic

LVDS

Input

LVDS

Output32-bi t C MOS Output

256-bi t Fast Shift Register

3328

-bit

Pix

el C

olum

n-0

13 8-bi t DACs

14111 m

3328

-bit

Pix

el C

olum

n-1

3328

-bit

Pix

el C

olum

n-1

1612

0

m

IO

Logic

LVDS

Input

LVDS

Output32-bi t C MOS Output

256-bi t Fast Shift Register

3328

-bit

Pix

el C

olum

n-0

13 8-bi t DACs

14111 m

3328

-bit

Pix

el C

olum

n-1

3328

-bit

Pix

el C

olum

n-1

1612

0

m

256 x 256 pixels

5ms readout time(serial @ 200MHz)

300s readout time (parallel @ 100MHz)

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Medipix Data Acquisition

Max frame rates ~ 1 kHz USB interface- easy to use

X-ray detector

Medipix with USB interface

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Sample ImagesSample Images

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High resolution X-ray imaging using a micro-High resolution X-ray imaging using a micro-focus X-ray sourcefocus X-ray source

Needle holding the sample

Edges are enhanced by phase contrast effect

S. Pospisil, J. Jakubek and co-workers, IEAP, CTU, Prague, CZ

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Future Trends

Microelectronics becomes more and more complex Intelligence at pixel level

Medipix3 introduce corrections to amplitude to improve amplitude resolution

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Charge summing and allocation concept

55µm

The winner takes all

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Medipix3 SimulationMedipix3 Simulation

Much improved amplitude resolution Immune to threshold variations

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Material Reconstruction in CTMaterial Reconstruction in CT

Photon counting at8 keV threshold

water /non iodine

iodine

Brightness = density of materials (g/cm3)

Measurements in collaboration with the University of Canterbury, Christchurch

G. Anton, T. Michel and co-workers, Univ. Erlangen, D

Amplitude information important to distinguish between different materials

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In Vivo Dosimetry A lot of interest given JAI activities on

therapy of cancer using particle accelerators

TLD, diodes, MOSFETs TLDs are complicated to process Diodes need a cable and continuous

readout New: MOSFET

Metal Oxide Semiconductor Field Effect Transistors

Absorbed dose change characteristics of MOSFET

Compact ~1 mm

Much needed instrument with a lot of room for improvement and new ideas

scanditronix-wellhofer.com

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Medipix Activities in Oxford Area Several Medipix/Timepix users

Diamond Light Source for crystal diffraction studies Oxford Chemistry/Physics for Ion Imaging Mass

Spectrometry Oxford Engineering for Mammography

Talking to each other, may think about joining the Medipix collaboration

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Future: Monolithic Sensors

Future trend is in integration of detector and electronics in one sensor, MAPS (Monolithic Active Pixel Sensor)

Pixels

Bump Bonds

Readout Electronics

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Monolithic Sensors with 3D Integration

Technologies becoming available to thin silicon wafers to 10 microns and to bond them together

New approach to monolithic sensors: 3D integration Precision 1 m alignment Interconnection of wafers by metal vias

Opto Electronics

Digital layer

Analog Layer

Sensor Layer

Optical Fiber I n Optical Fiber Out

Designer’s Dream

50 um

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Ultra Thin Devices First attempts to produce ultra-thin devices in industry and for

particle detection are under way hopefully will make its way to medical applications as well

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Summary Enormous progress in detector technologies and

nanoelectronics which can be applied to medical applications Especially to imaging

A lot of interest from Physics side to apply better detectors to medicine

Medical applications are driven by practical needs and economics benefit from communications between two communities

Acknowledgements: Medipix collaboration