interventional imaging in igt · miccai 2009 medical robotics tutorial nmr • nuclear magnetic...

MICCAI 2009 Medical Robotics Tutorial

Interventional Imaging in IGT

Terry PetersRobarts Research Institute

University of Western OntarioLondon, Canada


Overview• Introduction to Modalities

– Computed Tomography– Magnetic Resonance Imaging– Ultrasound

• How they work• What they do• How they are used in image-guided

interventions• Where to from here?


The Beginnings of CT

• Johann Radon 1917 – “The Radon Transform”– Mathematical underpinnings of CT

• Ronald Bracewell 1956– Radio Astronomy– Reconstruction of radio sources from radio-

telescope signals– Mathematics similar to CT reconstruction – Reconstructed images using mechanical

calculator! (3 instructions/min?!)


Sir Godfrey Hounsfield• Engineer for EMI PLC

– (the music company)• Nobel Prize 1979 (with

Alan Cormack)• Knighted 1981


CT PrinciplesTwo minutes of CT Physics!


Central Slice Theorem

2D FT

φ

Projection at angle φ 1D FT of Projection at angle φ

1D FT

φ


Cross-section of head

Vertical projection of this cross-section Modified (filtered) projection

FT ⏐ρ⏐ Inv FT

Back-project filtered projections (at all angles)

Filtered Back Projection

Or convolve with


Clinical Acceptance of CT!?

• Radiology colleagues less than enthusiastic

• Dr James Ambrose 1972– Radiologist, Atkinson -

Morley’s Hospital London– Recognised potential of

EMI-scanner“• Maybe potential world

market for 6 CT machines”– EMI 1972


Then ……………and Now

• 1974• 80 x 80 image• 3 mm pixels• 13 mm thick slices• Two simultaneous

slices!!!• 80 sec scan time per

slice• 80 sec recon time

• 2009• 1024 x 1024 image• <1mm slice thickness• <0.5mm pixels• 0.25 sec rotation• 0.1 sec recon per slice• Isotropic resolution• Volume scanning - up to

320 slices in 350ms


So what good is it?

• Images electron density• Good high contrast discrimination• Great for bones• Not so good in brain (poor white/grey matter

contrast)• High spatial resolution• High temporal resolution (2-3 images/sec)• High radiation dose• Use for image-guidance

– Pre-operative imaging for modeling– Limited for intra-operative guidance – dose restrictions


CT Angiography (CTA)

Normal Coronary CTA

Jason Cole M.D., Cardiology Associates

Image vessels in 3DInject contrast agent


Plaque in LAD Artery

Jason Cole M.D., Cardiology Associates


CT in RoboticallyCT in Robotically--Assisted CABGAssisted CABG


Port Placement AlgorithmPort Placement Algorithm

• Potential port locations (intercostalspaces) and targets (IMA & LAD) defined as splines

• Optimization based on robot kinematics, tool design, intercostal spaces & target locations, etc

• Optimal locations defined assuming targets do not move (i.e., CT accurately represents OR situation)


Visualization for PlanningVisualization for Planning

• 64 slice preoperative CT: – Mid diastole only– Slice thickness, in-

plane resolution• Currently limited to slice-

by-slice axial views, combined with a volumetric display

• Major challenge:– incorporating robot

kinematics– Incorporate change in

geometry pre-op/intra-op


Magnetic Resonance Imaging


NMR

• Nuclear Magnetic Resonance• Imaging through magnetic properties of tissue• Roots in Physics and Chemistry labs• Built on mathematical foundations similar to CT• Became MRI in medical imaging community ….

“Nuclear” not considered politically correct!• “Most important medical breakthrough since the

invention of X rays”


MRI (formally NMR imaging)• Paul Lautebur 1975

– Presented at Stanford CT meeting

– “Zeugmatography”• Magnets!?• Gradients?!• Clinical Applications?

• Raymond Damadian 1977 – relaxation times and cancer

• Sir Peter Mansfield 1980– Slice-selection– Echo-planar imaging

Zeugmatographyimage of water-filled

test tubes

Early MansfieldThorax Image

Lautebur and Mansfield Shared Nobel Prize in Medicine for MRI in 2003

Object Reconstruction


Two minutes of MR Physics!


N

S

Frequency

Spinning nuclei generate rf signals

x

y

z

ω0

FT

0 0.2 0.4 0.6 0.8 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

Sign

al FID

0.2 0.4 0.6 0.8 100

10

20

30

40

50

60

Sign

al spectrum


Gradients provide spatial information

Gx

Sample tube with three regions with different Proton densities Place in Magnetic field + gradientProtons in all regions precess with different frequenciesCan now differentiate between regions by examiningFrequency content of signal (Fourier Transform)

Low frequency

Med frequency

High frequency

Sum


Fourier Transform and Image2D (3D) signal data are samples of a 2D (3D) Fourier Transform of the image


• “Interesting images, but will never be as useful as CT”

– (A different) neuroradiologist, 1982

– (However he rapidly changed his tune!!)

35 Years of MRIFirst brain MR image

Typical T2-weighted MR image

2009 7T image


MRI Scanner


So what good is it?

• Images water behaviour• Basic contrast due to T1 and T2 characteristics• Good soft tissue contrast (esp white/grey matter)• Functional• Diffusion• High spatial resolution• High temporal resolution• No radiation dose• Use for image-guidance

– Pre-operative modeling– Limited application for intra-operative guidance


Intra-operative MRI and NeuroArm RobotIntra-operative MRI and NeuroArm Robot

Images courtesy Dr Garnett Sutherland, Calgary Alberta


Intra-operative MRIIntra-operative MRI

GE “Double Donut” Medtronic Odin Polestar


MR Imaging - more than T1 and T2

• MRA - Magnetic resonance angiography– images of vessels

• MRS - Magnetic resonance spectroscopy– images of chemistry of the brain and muscle metabolism

• fMRI - functional magnetic resonance imaging– image of brain function

• PW MRI – Perfusion-weighted imaging• DW MRI – Diffusion-weighted MRI

– images of nerve pathways


MR Imaging ModalitiesMR Imaging Modalities

Angiography

digitalspotlight.files.wordpress.com

brainimaging.waisman.wisc.edu

Functional MRI

Diffusion Tensor Imaging


Ultrasound

(a) (b)


Two minutes of US Physics!


Scanning and Display Modes


Ultrasound

http://www.ob-ultrasound.net/wright_meyer_arm.html


Ultrasound Transducers


So what good is it?

• Images interfaces between tissues• Relatively inexpensive• Portable• Real time 2D and 3D• Does not pass through air or bone• Doppler – measures blood flow• Difficult to interpret• Use for image-guidance

– Often registered with pre-op image to give context


Colour Doppler Imaging

Carotid Normal Carotid Stenosis

Kidney Liver


3-D Ultrasound Acquisition


33--D Ultrasound AcquisitionD Ultrasound Acquisition


US (and CT/MRI) in intraUS (and CT/MRI) in intra--cardiac interventioncardiac intervention

• Create model from pre-op imaging• Register model to patient• Use Trans-espophageal US for real-time

image guidance• Introduce instruments through chest/heart

wall• Magnetically track US and instruments• Display in VR environment


Intra-cardiac interventionIntraIntra--cardiac interventioncardiac intervention


US-guided intra-cardiac interventionUS-guided intra-cardiac intervention

Valve insertion tool

AuroraTM Field Generator

UCI

Valve insertion tool


IntraIntra--cardiac interventioncardiac intervention


Other modalities• Positron Emission Tomography (PET)

– Records gamma rays emitted when e(-) and e(+) annihilate

– Reconstructs 3D distribution of positron-emitting isotope

• Single Photon Emission Computed Tomography (SPECT)– Records gamma-emitting isotopes directly– 3D distributions

• Displays distribution of functionally active agents

• Cancer diagnosis, metabolic activity


ConclusionConclusion• CT and MRI provide high resolution 3D and

4D data– Not easily adaptable to real time intra-operative

imaging• US is inexpensive, capable of real-time 2D

and 3D imaging– Resolution limitations, lack of context and

artefacts render US unsuitable for most image-guidance


ConclusionConclusion• Future of image-guided procedures will

rely on– Pre-op images registered to patient and intra-

op real-time imaging (US, optical)• Deformable models will be controlled by

real-time images to update pre-op images in real time

• Research challenges lie in – Accurate tracking of intra-op imaging devices

and real-time registration– Deformation of pre-operative models to intra-

operative anatomy.

interventional imaging in igt · miccai 2009 medical robotics tutorial nmr • nuclear magnetic...

Documents