Image Processing for Interventional MRI

Derek Hill

Professor of Medical Imaging Sciences

King’s College London

Image Processing for Interventional MRI

Derek Hill

Professor of Medical Imaging Sciences

University College London

The team

• Kawal Rhode• Marc Miquel• Redha Berboutkah• David Atkinson• Maxime Sermesant• Rado

Andriantsimiavona• Kate McLeish• Sebastian Kozerke

• Reza Razavi• Vivek Muthurangu• Sanjeet Hegde• Jas Gill • Pier Lambraise• Cliff Bucknall • Eric Rosenthal• Shaqueel Qureshi

Context

• Interventional MRI provides particular opportunities and challenges for image analysis. – Hostile environment for computers– “real time” requirements– Link between acquisition and analysis

Overview

• Background to XMR guided interventions

• Integrating x-ray and MRI

• Automatic cathether tracking

• Integration of image analysis in acquisition

XMR

• X-ray + cylindrical bore MRI in the same room

• Becoming main platform for MR guided interventions– Resection control in neurosurgery– Endovascular procedures

• Not ideal for percutaneous procedures

Patient

Staff

XMR suite at Guy’s(funded of JREI, Philips Medical Systems and

Charitable Foundation of Guy’s & St Thomas’)

XMR System at Guy’s Hospital

XMR = hybrid X-ray/MR imaging Common sliding patient table Provides path to MR-guided intervention

XMR suite at Guy’s

Catheter manipulation

Visualizing catheters

• Fast imaging (70 msec per frame)– TE = 1.3, TR = 2.6– SSFP sequence (balanced TFE)– Acquisition: 78 x 96, 80% FOV, 80% acq, SENSE factor 2

(ie: only 25 phase encodes!)• Carbon dioxide filled balloon as contrast agent

Catheter Manipulation

Images acquired with standard Philips real time or interactive sequences

Catheter Manipulation

Miquel et al. Visualization and tracking of an inflatable balloon catheter using SSFP in a flow phantom and in the heart and great vessels of patients. Magn Reson. Med. 51(5):988-95 2004

Integrating x-ray and MRI

• XMR provide rapid transfer between modalities

• No capability to integrate the images

• X-ray and MRI provide complementary information

• Combined x-ray and MR has value in complex interventions eg: electrophysiology

T

M1

Registration Matrix Calculation Overall registration transform is composed of a series of stages Calibration + tracking during intervention

M2

M3

3D Image Space X-ray Table Space

X-ray C-arm Space

2D Image Space

Scanner Space

R*P

XMR Registration:Software Overview

XMR Registration: Calibration Acrylic calibration object with 14 markers Interchangeable caps for MR and X-ray imaging Determine geometric relationship between MR and X-ray

system Determine X-ray projection geometry

MR

X-ray

Calibration

(1) Fixing flange for sliding table.

(2) Saline-filled acrylic half cylinder with 20 divot cap markers in a helical arrangement.

(3) Slot in acrylic base plate to allow sliding of half cylinder.

(4) & (5) End stops.

(6) Fixing to allow MR surface coil attachment

XMR Registration:MR Overlay on X-Ray

XMR Registration:3D Reconstruction

XMR Registration:Phantom Validation

T1-weighted MR volume + 5 pairs of tracked x-ray images using calibration object as a phantom

2D RMS Error = 4.2mm (n=35), Range = 1.4 to 8.0 mm

3D RMS Error = 4.6mm (n=17), Range = 1.7 to 9.0 mm

“Registration and Tracking to Integrate X-ray and MR Images in an XMR Facility “, Rhode et al, TMI, Nov 2003.

Clinical Example

• Patient undergoing electrophysiology study prior to RF ablation of heart rhythm abnormality

MR Imaging - Anatomy

SSFP three-dimensional multiphase sequence

5 phases 256x256 matrix 152 slices resolution=1.33 x 1.33

x 1.4 mm TR=3.0 ms TE=1.4 ms flip angle=45

MR Imaging - Motion

SPAMM tagged imaging sequence

59 phases SA & 50 phases LA

256x256 matrix 11 slices SA & 4 slices

LA resolution=1.33 x 1.33

x 8.0 mm TR=11.0 ms TE=3.5 ms flip angle=13 tag spacing=8 mm

X-ray Imaging + Electrical Mapping

LAO View AP View

Contact electrical mapping systemConstellation catheter (Boston Scientific)

MR Anatomy Overlay

Catheter Reconstruction

Refining the Registration

Errors due to limitations of registration technique and patient motion

Basket point cloud meshed

Rigid surface-to-image registration used to realign the basket mesh

Visualising the Electrical Data

Cycle 1 - normal

Cycle 2 - ectopic

Instantiation of model

Simulation results

LV volume

Catheters re-visited

• Essential properties of catheters– Clearly visible– Safe

• mechanically• electrically • Magnetically

• Desirable properties– Automatic localization– Tip and length visible

• CO2 filled balloon catheters are safe

• Tip location ambiguous

• Length not visible

• Cannot be localized automatically

Is there an image analysis solution?

• Find catheter automatically in modulus image?

• Is it easier to find in a phase image?

Better solution: change nucleus

• Fluorine is not present in body

• High NMR sensitivity• Safe blood subsitutes

available (eg: PFOB)

Catheter tracking

(a)(a)(b)(b)

(c)(c)

++

SSFP proton image plus fluorine projections

Phantom setup

Catheter tracking

(a)(a)(b)(b)

(c)(c)

Automatic superpositionOf catheter tip on proton image

Phantom setup

Lumen visible

Dynamic scan

Catheter Tracking and Visualization Using

19F Nuclear Magnetic Resonance•

Sebastian Kozerke1,2, Sanjeet Hegde3, Tobias Schaeffter4, Rolf Lamerichs5, Reza Razavi3, Derek L. Hill2

Magn. Reson. Med. 2004 (in press)

Image analysis combined with acquisition

• Real time MRI can provide high temporal resolution, but low quality

• Can we subsequently combine real time images to generate high image quality?

Real time MRI with slice tracking

• Real time undersampled radial acquisitions

Navigator Slice tracking

Registration to compensate for motion

Rigid body then non-rigid registration to correct motion During scanning

Demonstration on gated volunteer heart images (n=4)

• Undersampled images

Demonstration on gated volunteer heart images (n=4)

• Combined with no registration

Demonstration on gated volunteer heart images (n=4)

• Combined with rigid registration

Demonstration on gated volunteer heart images (n=4)

• Combined with rigid then non-rigid registration

Conclusions

• Interventional MRI is fertile area for image analysis

• Real time requirements• New applications (eg: RF ablation)• Improving guidance• Novel acquisition and reconstruction

incorporating image analysis