Image Processing for Interventional MRI

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Image Processing for Interventional MRI

• Derek Hill
• Professor of Medical Imaging Sciences

Kings College London
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Image Processing for Interventional MRI

• Derek Hill
• Professor of Medical Imaging Sciences

University College London
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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

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Context

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

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Overview

• Background to XMR guided interventions
• Integrating x-ray and MRI
• Automatic cathether tracking
• Integration of image analysis in acquisition

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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

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XMR suite at Guys(funded of JREI, Philips
Medical Systems and Charitable Foundation of
Guys St Thomas)
Staff
Patient
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XMR System at Guys Hospital

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

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XMR suite at Guys
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Catheter manipulation
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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

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Catheter Manipulation
Images acquired with standard Philips real time
or interactive sequences
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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
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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

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Registration Matrix Calculation

• Overall registration transform is composed of a
  series of stages
• Calibration tracking during intervention

M1
?T
Scanner Space
3D Image Space
X
-
ray Table Space
M2
X
-
ray C
-
arm
RP
Space
M3
2D Image Space
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XMR RegistrationSoftware Overview
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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
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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
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XMR RegistrationMR Overlay on X-Ray
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XMR Registration3D Reconstruction
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XMR RegistrationPhantom Validation

• T1-weighted MR volume 5 pairs of tracked x-ray
  images using calibration object as a phantom
• 2D RMS Error 4.2mm (n35), Range 1.4 to 8.0
  mm
• 3D RMS Error 4.6mm (n17), 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.

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Clinical Example

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

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MR Imaging - Anatomy

• SSFP three-dimensional multiphase sequence
• 5 phases
• 256x256 matrix
• 152 slices
• resolution1.33 x 1.33 x 1.4 mm
• TR3.0 ms
• TE1.4 ms
• flip angle45?

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MR Imaging - Motion

• SPAMM tagged imaging sequence
• 59 phases SA 50 phases LA
• 256x256 matrix
• 11 slices SA 4 slices LA
• resolution1.33 x 1.33 x 8.0 mm
• TR11.0 ms
• TE3.5 ms
• flip angle13?
• tag spacing8 mm

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X-ray Imaging Electrical Mapping

• Contact electrical mapping system
• Constellation catheter (Boston Scientific)

LAO View
AP View
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MR Anatomy Overlay
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Catheter Reconstruction
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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

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Visualising the Electrical Data

• Cycle 1 - normal
• Cycle 2 - ectopic

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Instantiation of model
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Simulation results
LV volume
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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

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Is there an image analysis solution?

• Find catheter automatically in modulus image?
• Is it easier to find in a phase image?

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Better solution change nucleus

• Fluorine is not present in body
• High NMR sensitivity
• Safe blood subsitutes available (eg PFOB)

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Catheter tracking
SSFP proton image plus fluorine projections
Phantom setup
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Catheter tracking
Phantom setup
Automatic superposition Of catheter tip on proton
image
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Lumen visible
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Dynamic scan
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• Catheter Tracking and Visualization Using19F
  Nuclear Magnetic Resonance
• Sebastian Kozerke1,2, Sanjeet Hegde3, Tobias
  Schaeffter4, Rolf Lamerichs5, Reza Razavi3,
  Derek L. Hill2
• Magn. Reson. Med. 2004 (in press)

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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?

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Real time MRI with slice tracking

• Real time undersampled radial acquisitions

Navigator Slice tracking
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Registration to compensate for motion
Rigid body then non-rigid registration to correct
motion During scanning
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Demonstration on gated volunteer heart images
(n4)

• Undersampled images

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Demonstration on gated volunteer heart images
(n4)

• Combined with no registration

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Demonstration on gated volunteer heart images
(n4)

• Combined with rigid registration

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Demonstration on gated volunteer heart images
(n4)

• Combined with rigid then non-rigid registration

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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