Magnetic Particle Imaging

Magnetic Particle ImagingA Novel Fast 3D In Vivo Imaging Modality

based on Magnetic Nano Particle contrast agents

Dr. Nicoleta Baxan

Innovation with Integrity

Magnetic Particle Imaging (MPI)A New Imaging Modality at Bruker

• Bruker has introduced the first commercial MPI scanner

for Preclinical Research.

• MPI complements Bruker’s palette of other Preclinical

Imaging modalities.

MPIMRI MRI X-Ray OpticalµCTPET/SPECT

12.02.2014 Magnetic Particle Imaging 2

Introduction to MPI

• New tracer-based 3D imaging modality

• Uses non-linear magnetization behaviour of clinically approved MRI contrast agents (Super Paramagnetic Iron Oxides, SPIOs)

• High Speed, High Sensitivity

• Quantitative

• Invented at Philips Research Laboratories, Hamburg [1]

• First demonstration of live mouse imaging in 2009 [2]

• Applications:• High speed: Bolus tracking, Angiography, Organ Perfusion

• High sensitivity: Stem cell tracking

• Quantitative: Organ Perfusion (Coronary deseases)

• Functionalized particles: cell targetting

[1] B. Gleich, J. Weizenecker, Nature 2005, 435, 1214-1217

[2] J. Weizenecker, B. Gleich, J. Rahmer, H. Dahnke, J. Borgert, Phys. Med. Biol. 2009, 54, L1-L10


4

Principles of MPI

• Particles exhibit a non-linear magnetization response to an applied magnetic field.

• The magnetization response to an oscillating excitation field contains harmonics of the excitation frequency.

• The harmonics can be detected in the presence of the excitation signal.

• Their intensity is proportional to the particle concentration.

• A bias field saturates the magnetization and suppresses the generation of harmonics.

Magnetic Particle Imaging12.02.2014

Spatial Selection (I)

5

• A gradient field (Selection Field, SF) saturates the particle magnetization everywhere except for a small region in the center (field free point, FFP)

• Only particles in the FFP vicinity respond to a field oscillation generated by an excitation field (Drive Field, DF)

• An image may be generated by mechanically moving the object through the FFP.

FFP


Spatial Selection (II)

6

• Insight: Drive Field actually moves

FFP.

• By three orthogonal DF coils, the

FFP can be moved magnetically

over the object.

• FFP passage causes local

magnetization flip.

• The response for a particle

distribution is the concentration-

weighted sum of the single-site

responses.


Tracer Material

• Super-Paramagnetic Iron Oxide (SPIO)

nanoparticles

• Clinically approved, non-toxic MR contrast

agent

• Magnetite core (5-30 nm), biocompatible

coating (dextran, carboxydextran)

• Can be functionalized for targeting purposes

• Most experiments so far carried out with

ResoVist™ (Bayer-Schering)

• Large potential in tracer improvementsCore

Diameter

Hydrodynamic

Diameter

Core

Fe3

O4

Coating

(Dextran / Carboxydextran)


Visions for MPIMedical Applications

Cardio-Vascular

• Cardiac ejection fraction, wall motion, flow dynamics

• Coronary blood supply

• Quantitative Myocardial perfusion

• Vulnerable plaque detection

Interventional Radiology (3D)

• Stent placement

• Device & disposal tracking (catheter, stents, …)

• Catheter navigation

Neuro-Vascular

• Bleeding detection

• Lung perfusion

• Functional brain imaging

Organ Perfusion Imaging

• Liver perfusion

• Lung perfusion (incl. therapy response assessment)

• Lung ventilation

Oncology

• Micro-vascularization (blood volume)

• Inflow-outflow kinetic (Pharmacokinetics)

• Interventional oncology

• Ablation monitoring

• Highly localized heating for therapy and thermally trigger local

drug release

Breast Imaging

• Sentinel lymph node detection

• Screening

Cell Tracking

• Bleeding detection

• White blood cell tracking – inflammation detection

• Therapeutic (stem) cell tracking


Visions for MPIMolecular Imaging in Comparison to other Modalities

Radiation

used

Spatial

Resolution

Temporal

Resolution

Sensitivity Quantity of

Contrast Agent

used

Summary / Comments

Positron Emission

Tomography

high-energy

g - rays

1-2 mm

10 Seconds to

Minutes

10

-11

– 10

-12

mole/liter

Nanograms

Sensitive

Quantitative

Needs Cyclotron

Single Photon

Emission

Tomography

low-energy

g - rays 1-2 mm Minutes

10

-10

– 10

-11

mole/liter Nanograms Many available probes

Computed

Tomography

X-rays 50-200 µm Minutes

Not well

characterized

Not applicable

Good for bone, tumors, not for

soft tissue

Magnetic

Resonance

Imaging

radio waves 25-100 µm

Minutes to

Hours

10

-3

– 10

-5

mole/liter

Micrograms to

Nanograms

Highest resolution

morphological and functional

imaging, low sensitivity, slow

Magnetic Particle

Imaging

Radio waves 200-500 µm

Seconds to

minutes

10

-11

– 10

-12

mole/liter Nanograms

Quantitative

Good sensitivity,

fast good resolution

no tissue contrast

From: K. Krishnan, IEEE Transactions on Magnetics 2010, 48, 2523-2558


• Imaging volume 20.4 ×12 ×16.8 mm3

• Frame rate ~ 46 fps

• Bolus can be following through body

• Signal is modulated by heart beat (partial volume effect)

J. Weizenecker, B. Gleich, J. Rahmer, H. Dahnke, J. Borgert, Phys. Med. Biol. 2009, 54, L1-L10

3D mouse imaging

10Magnetic Particle Imaging12.02.2014

MPI

Open research areas

11

� Radiologists and non-technical researchers need more access to MPI scanners.

� German Research Foundation (DFG) is funding the installation of MPI scanners for

application oriented research.

New contrast

agents

MPI application

protocols

Diagnostic and

Interventional

imaging

Comparison to

other modalities

Reconstruction

techniques

Sequence

design


Current state of MPIToday’s MPI Scanners world wide

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Installed base of working home-

built research scanners:

• Berkeley

• Braunschweig

• Hamburg

• Lübeck

• Würzburg

All current scanners are installed in laboratories focused on MPI hardware design and

are operated by physicists and engineers.


Bruker Preclinical MPI SystemTarget specifications

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• AVANCE III / MPI technology

• ParaVision Software

• Full 3D imaging, segmented acquisition capability

• 12 cm free access

• BioSpec™/ClinScan™ compatible Animal Handling

• Integrated calibration robot

• Interfaces for Animal Monitoring and Infusion Pump

Component Target Specs

Scalable Selection Field 0…2.5 T/m

Drive Field X/Y/Z 0…20 mT @ 25 kHz

Focus Field X/Y/Z 0…45/0…45/0…120 mT

Max. FOV Ø 10 cm×10 cm

Bandwidth 1.25 MHz

Speed 46 volumes per second


Magnetic Particle Imaging 14

Scanner Details (I)

Field Generator Design

Drive Field X/Y/Z

• 3 ×20 mT

• Oil cooled

• 12 cm bore

diameter

12.02.2014

Focus Field X/Y

• 2 ×45 mT

• Oil cooled

Focus Field Z

• 120 mT

• Water cooled

Housing

• 50×50×50 cm

Selection Field

• 2.5 T/m

• Water cooled

Magnetic Particle Imaging

Scanner Details (II)

Control electronics

• 5 cabinets

• Room for extensions and upgrades

Animal Handling

• 12 VDC filtered power for infusion

pump and monitoring equipment

• RS-232, Trigger, FO Monitoring

Operating Console

• Turnkey operation

• Complete control from ParaVision

Avance-III-MPI Electronics

• Components reused from

MRI/FTMS

Tune/Match boxes

• Contain capacitor banks

for resonant circuit

System Views

12.02.2014

ParaVision

• Imaging platform for MRI/MPI

• Open for user-implemented MPI

acquisition and reconstruction

15

Bruker MPI Research

16

• Magnetic Particle Spectrometer

• Also commercially available from Bruker

• System design and manufacturing

• Optimized reconstruction algorithms

• Combination MRI/MPI

• Ongoing design study

• Magnet switchable between homogeneous and gradient configuration

• MRI reference image generation in same instrument with minimal time difference to MPI scan


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Innovation with Integrity

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Magnetic Particle Imaging