A 2D-3D Registration Framework for Freehand TRUS-Guided Prostate Biopsy

A 2D-3D Registration Framework for Freehand TRUS-Guided Prostate BiopsySiavash Khallaghi, C. Antonio Snchez, Saman Nouranian, Samira Sojoudi, Silvia Chang, Hamidreza Abdi, Lindsay Machan, Alison Harris, Peter Black, Martin Gleave, Larry Goldenberg, S. Sidney Fels, and Purang Abolmaesumi

Robotics and Control Laboratory,University of British Columbia, Vancouver, Canada

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Roger S Kirby and Manish I Patel. Fast facts: Prostate cancer. Health Press, 2012Most common cancer in men(excluding non-melanoma skin cancer)Prostate CancerAffects 1 in 8 during lifetimeScreening and Diagnosis:Digital rectal examHigh PSACore needle biopsyRoger S Kirby and Manish I Patel. Fast facts: Prostate cancer. Health Press, 2012

Prostate

Prostate Cancer (PCa) is the most common non-cutaneous cancer in North American men,affecting 1 in 8 men in their lifetime. (http://www.crs-src.ca/page.aspx?pid=1325&gclid=CNv34dvhwcUCFRSUfgod-ZQAkg, Canadian Cancer Statistics 2014)

There are several methods of screening, but the gold standard for diagnosis is the core needle biopsy2

NeedleBiopsy GunNeedle GuideEndocavity Ultrasound Probe

The biopsy is most often guided using a 2D endocavity ultrasound probe, like this one, with an attached biopsy gun3

4Tissue samples tested in labProstate Biopsy30% false negativesRoger S Kirby and Manish I Patel. Fast facts: Prostate cancer. Health Press, 2012Frequent need to re-biopsy

The probe is inserted in through the rectum, and a needle is fired to collect a tissue sample. This sample is sent for histopathological analysis.Unfortunately, the current method has a high false negative rateSo patients are frequently asked to repeat the uncomfortable procedure4

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3D GuidancePlan:Tracked TRUS probeRoger S Kirby and Manish I Patel. Fast facts: Prostate cancer. Health Press, 2012

TargetPrevious Core

3D guidance is needed to Improve targeting accuracyAnd for re-biopsy patients, to integrate the previous core locations

This is done using spatial tracking of the probe and the 2D image to target and record biopsy cores5

6Roger S Kirby and Manish I Patel. Fast facts: Prostate cancer. Health Press, 2012Challenge:2D 3D registration required Prostate moves and deformsProbe tracking not sufficient

Unfortunately, during the freehand biopsy procedure, the prostate moves and deformsSo, spatial tracking of the probe is not enough:We need to use the 2D image information to maintain alignment with the biopsy plan63D Freehand Guidance Framework

Reference VolumeSlice-to-Volume Registration

Rigid registration for bulk motionNon-rigid registration for deformationsPre-procedure axial sweepVolume reconstructionTarget planning

Target registration error: 3.15 0.81 mm

We present a 2D-3D registration framework for use in freehand prostate biopsies.

First, we generate a 3D ultrasound from a tracked axial sweep. This reference volume used for target planning

Next, we perform the slice-to-volume registration, consisting of 2 stepsA rigid registration to account for the bulk of the prostate motion;A non-rigid registration to account for deformations.

Currently, we achieve a mean target registration error of around 3mm for the combined method7Trajectory-based constraint:Pre-procedure axial sweep traces rectal wall Live 2D slice should also fall on rectal wall Constrain probe tip to trajectoryImage-based metricSum-of-squared distances (SSD)Local minima due to:Limited spatial informationLow SNR of TRUS

Rigid Registration

For the rigid alignment step, we minimize the sum-of-squared distances between image intensitiesThis method alone is highly susceptible to local minima due tothe limited spatial informationAnd the low signal-to-noise ratio of ultrasound

So, we introduce a constraint:We know that the pre-procedure sweep traces the rectal wallDuring the procedure, the live 2D slice is also somewhere on the rectal wallThus, we constrain the probe to the pre-procedure trajectory,This accounts for any large spatial offset, ensuring the rectal walls coincide8Finite element-based method:Incorporates physical properties of the tissueSimultaneously minimize strain and image SSD

Non-Rigid Registration

For residual motion and for deformations, we use a FEM-based methodThis allows us to incorporate material properties of the prostate and surrounding tissue, letting it deform physicallyThe FEM is driven by image forces, as we simultaneously minimize the total strain and the SSD metric.9

Example Registration

This is the algorithm in action

The 2D slice slides along the trajectory from the 3D volume, finding the best match based on image intensitiesThe finite element method then takes over, moving and bending the volume to achieve a better fit10

2D Target SliceInitializationExample Registration

Here we see the 2D target slice, and the initial guess within the volume, based solely on spatial tracking. As you can see, the boundaries of the prostate appear quite different between the images.11

2D Target SliceRigid RegistrationExample Registration

After rigid registration, the prostate boundaries are much more similar, and there is a calcification visible at the same location in both images12

2D Target SliceDeformable RegistrationExample Registration

Following finite-element correction, the calcification is brighter in the middle. The volume has also deformed to better match the boundary features.13Registration Results

TargetInitialRigidFEM-Based

Both stages of the registration method play significant rolesThe trajectory-based rigid registration helps avoid local minima, bringing us to a good starting point for the FEM-based registration to take over

Our method is shown to robust, locating some of the finer details present in the slice14

C. Antonio SnchezDept. of Elec. & Comp. Eng.University of British ColumbiaVancouver, BC, Canadaantonios@ece.ubc.caSiavash KhallaghiDept. of Elec. & Comp. Eng.University of British ColumbiaVancouver, BC, Canadasiavashk@ece.ubc.ca

If youd like to find out more about our work, please come and find us. We would be delighted to discuss the details of the method, and answer any of your questions.

Thank-you.15