Compatibilità dei Dispositivi Meccatronici nella Risonanza Magnetica Interventistica e Funzionale

Vincenzo PositanoFondazione Toscana Gabriele Monasteriopositano@ifc.cnr.it

Why we should use a mechatronic device inside MRI ?

Interventional MRI (i-MRI)ElastographyfMRI paradigms

State of Art

ISMRM 2008

State of Art

State of Art

Gassert et al, Eng Med Biol Mag, 2008

ISI Web 2008

Real time iMRIHigh image quality

High fieldsHomogeneityFast gradients

Interventional MRI (i-MRI)

3 T

4 TOpen, low field(1.0 T) MRI

7 T

9.4 T

1.5 T

Close, high field MRI

Robotic surgery

Eyes MR Images

Hands Mechatronic Devices

Interventional MRI (i-MRI)

Interventional MRI (i-MRI)

Gassert et al, Eng Med Biol Mag, 2008

Bricault et al, Eng Med Biol Mag, 2008

Surgeon compatibility☺

Functional MRI (fMRI)

StimulusStimulus Response

BOLD Signal

Detects MRI signal variation due to BOLD effect

Very low signal changes (< 5%)

Stimuli knowledge and recording is important

Functional MRI (fMRI)

Audio/video Audio/video Touch Touch

Waveguide

Scanner Room

Shielded Cable

Console Room

AcquisitionSetup: instrumentationampsNI-DAQ Card

Reproducibility, stability, and recording of the imposed stimulaReproducibility, stability, and recording of the imposed stimulation tion paradigm are needed.paradigm are needed.

Mechatronics devices may be employed to meet the requirements Mechatronics devices may be employed to meet the requirements

Functional MRI (fMRI)

Functional MRI (fMRI)

Vanello et al, IEEE Trans Mechatronics, 2008

MARIARC, Liverpool, UK

MR Compatibility

MR safe (no hazard)

MR compatible (preserves image quality)

MR Compatibility

Static magnetic field1.5 -3.0 T

RF63 -126 Mhz

Gradients20-50 mT/s

Safety: static magnetic field

Strong (very strong!) attractive force on ferromagnetic materials

Projectile effect

Safety: Radiofrequency/Gradients

Heating of conductive materials

Shielded electronicsNo wire loops

Giovannetti et al, Concepts Magn Res B, 2004

Safety: Radiofrequency/Gradients

If possible, move components outside the scanner room

WaveguideScanner Room

Shielded Cable

Console Room

AcquisitionSetup: instrumentationampsNI-DAQ Card

MR Compatibility: artefacts

Assessment of image quality with and without the device under testing

Screw

Arunkumat et al, Diagn Neuroradiol, 1998

ROI 1

ROI 2

SNR, CNR

Standard measurements

Image ArtefactsDefines standard sequences for

determining artifact so the amount ofartifact for different devices can becompared

No acceptance criteria:Depending on region of interest,different amounts of artifact are acceptable

In some cases, artifacts are desirable(biopsy needles, image guided surgery)

MR compatibility

ASTM F2052-06 for Measurement of Magnetically InducedDisplacement Force on Medical Devices in the MR Environment

ASTM F2119-01 for Evaluation of MRImage Artifacts from Passive implants

ASTM F2182-02a for Measurement of Measurement of Radio Frequency Induced Heating Near Passive Implants During MRI

ASTM F2213-06 for Measurement of Magnetically Induced Torqueon Medical Devices in the MR Environment

MR compatibility

No ferromagnetic components

Aluminum, copper, etc…

Magnetic susceptibility close to air/human tissue (plastic polymers, fiberglass, carbon fibers)

Actuators(hydrostatic, piezoelectric, cable transmission)

Sensors(optical fibers)

fMRI actuator

Roger Gassert, Laboratory of Robotic Systems, Losanna

The master actuator: DC torque motor (a), master hydraulic cylinder (b), hydraulic pump (c) and circuitry (d) as well as disconnectable hydrostatic transmission (e) and security switches (f)

The slave module: A) open version showing the slave hydraulic piston (a) and the tactile pad (b). The ultrasonic motor is located beneath the tactile pad. B) The closed module showing the touch-pad (c) and the disconnectable (d) hydrostatic transmission

fMRI actuator (design)

Copper tubeCopper tubeDimensions: outer diameter 35.2mm, inner diameter 32mm, length 1Dimensions: outer diameter 35.2mm, inner diameter 32mm, length 140mm.40mm.Following results regard the copper tube into the bore, fixed orFollowing results regard the copper tube into the bore, fixed or in movement (in movement (zz--transltransl.): we can .): we can note that this experiment does not create significant artefacts note that this experiment does not create significant artefacts in the MR images.in the MR images.

Copper fixed tubeCopper fixed tube

Slice nSlice n°°11

22 55 1010 1515

p SNRp SNR 0.01260.0126 0.8850.885 0.310.31 0.73390.7339 0.5550.555

p SDp SD 0.1080.108 0.0650.065 0.8970.897 0.1590.159 0.8850.885

Copper tube in movement (Copper tube in movement (zz--transltransl.).)

Slice nSlice n°° 11 22 55 1010 1515

p SNRp SNR 0.11440.1144 0.03290.0329 0.9780.978 0.580.58 0.770.77

p SDp SD 0.660.66 0.8030.803 0.8370.837 0.980.98 0.590.59

fMRI actuator (design)

Electromagnetic simulator (GEMS)Electromagnetic simulator (GEMS)

Giovannetti et al, Concepts Magn Res B, 2008

fMRI actuator (testing)

Activation maps

No device Non-compatible device. Compatible device

Scan 1 vs. Scan 2 Scan 1 vs. Scan 39% 60%11% 91%

overlapijRsizeijR

Scan 1 Scan 2 Scan 3

Nicola Vanello, University of Pisa

Conclusions

The lack of harmful effects on the patient and the operator make MR well suited for "interventional radiology", where the images produced by an MRI scanner are used to guide a minimally-invasive procedure intraoperativelyand/or interactively.

Robotic may play a significant role in the field, allowing the use of high performance scanners

Design of compatible MRI mechatronics devices is a challenging task

iMRI represents a transformation from conventional hand-eye-coordination to interactive, navigational operations (Virtual Reality)