MSc project Janneke Ansems 21-08-2007 Intensity and Feature Based 3D Rigid Registration of Pre- and Intra-Operative MR Brain Scans Committee: Prof. dr. ir. B.M. ter Haar Romeny Prof. dr. ir. F.N. van de Vosse Dr. ir. B. Platel Dr. ir. G.J. Strijkers
Jan 15, 2016
MSc project Janneke Ansems
21-08-2007
Intensity and Feature Based 3D Rigid Registration
of Pre- and Intra-Operative MR Brain Scans
Committee:Prof. dr. ir. B.M. ter Haar RomenyProf. dr. ir. F.N. van de VosseDr. ir. B. PlatelDr. ir. G.J. Strijkers
Two 3-D point sets are given: fpi g and fp0i g; i = 1, 2, : : :, N. The equation
that needs to be solved is then:
p0i = Rpi + T + Ni (1)
where R is a 3£3 rotation matrix, T a translation vector (3£1 column matrix)and Ni a noisevector. Therotation R and translation T haveto befound suchthat the following equation is minimized:
§ 2 =NX
i=1
k p0i ¡ (Rpi + T) k2: (2)
First the point sets are translated such that both point sets have the samecentroid. Then the rotation matrix R is calculated using the singular valuedecomposition (SVD). Finally the translation vector T is computed. Theregis-tration is completed by transforming the entire dataset using the just found Rand T.
RMS =1N
kp0i ¡ (Rpi + T)k: (3)
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Outline Introduction Registration Materials and Methods Results Discussion and Conclusion Recommendations
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IntroductionMedical Background
Brain tumors Cancer is 2nd major cause of death in the Netherlands at
present time Each year 1000 people in the Netherlands are diagnosed with a
brain tumor
Treatment Radiotherapy Resection surgery
Figure 1: benign (left) and malignant tumor
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IntroductionImage-Guided Surgery
Image-Guided Surgery The use of images to guide a surgeon during the procedure
Medtronic Stealth Station Surgeon is able to verify the location
of a tumor directly with the imagesusing an image guided probe
But: pre-operative images do not alwaysresemble the real-time situation duringsurgery!
Figure 2: Medtronic Stealth Station
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IntroductionIntra-Operative Imaging
Brain shift Intra-operative imaging during surgery gives a more
accurate view on the real-time situation
Figure 3: Axial slices during a craniotomy showing brain shift.
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IntroductionIntra-Operative MRI
The Polestar N20 open intra-operative MR scanner (Medtronic Inc.) Field strength: 0.15 Tesla Resolution: 128x128x64 Field of view: 20x20x19 cm
Chosen for its: Relative low cost Open access to the patient Mobility Local shielding Compatibility with Medtronic
Stealth Station Compromise: image qualityFigure 4: The Polestar N20 system in the operating
room.
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IntroductionImage quality Polestar
Due to low field the Polestar scanner is susceptible to noise and artifacts Intensity Gradient Distortions
Figure 5: Images of Phantoms scanned by the polestar N20 showing distortion (left) and intensity gradient.
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IntroductionAim
Register 3D pre-operative high resolution MR data and the intra-operative MR data from the Polestar N20 with maximum accuracy.
In this way high resolution accurate information is available for navigational purposes during neurosurgery, focus on datasets with skull intact.
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Outline Introduction
Registration Materials and Methods Results Discussion and Conclusion Recommendations
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Registration Definition:
Given a reference image R and a template image T, find a suitable transformation y such that the transformed image T[y] looks similar to the reference image R
ReferenceTemplate
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RegistrationTransformation Model
Definition: A mapping of locations of one image to new locations in another
image
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RegistrationSimilarity Measure Definition:
Equation that measures how much two images are alike
Intensity-based Methods Sum of Squared Differences:
Gradient-based Methods Normalized Gradient Field:
x
2SSD ))( - )(( T] [R,S xRxT
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2NGF
),(
))(())(( T] [R,S
T
TxTn
xTnxRn
Reference Template
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RegistrationSimilarity Measure
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RegistrationOptimizing Scheme
Definition: An optimizing scheme calculates the transformation
parameters to achieve maximum similarity
Steepest Descent Gauss-Newton Levenberg-Marquardt
Figure 6: A comparison of steepest descent (green) and Gauss-Newton's method (red) for minimizing a function
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OptimizationGauss-Newton
The objective function f (w), w are transformation parameters:
f (w) =12
k T(y(w)) ¡ R k22 : (1)
Updatew by s, thesecond order Taylor approximation is:
f (w+ s) = f (w) + sr f (w) +12sT r 2f (w)s: (2)
The derivativeof s is taken and set to zero:
s =¡ r f (w)r 2f (w)
; (3)
in which r f (w) and r 2f (w) are:
r f (w) = Tyyw(T(y(w)) ¡ R) and r 2f (w) = (Tyyw)T (Tyyw): (4)
By updating w by s the new transformation parameters w are calculated.
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RegistrationMultilevel approach
Definition: Register from coarse to fine to optimize for speed and
robustness
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RegistrationSummary Intensity Based
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RegistrationFeatures Definition:
Features are a finite number of pixels or groups of pixels that are unique and exist in both images.
Given features r1, … , rn in reference image and t1, … , tn in template image, find a transformation y such that:ntyr ii ,...,1ifor )(
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Automatic feature detection Scale Invariant Feature Transform (SIFT) by Lowe 2D version gave promising results
RegistrationFeatures
Figure 6: Matches found by SIFT algorithm in Polestar data (left) and high resolution data
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Manual feature selection Transformation using Arun’s algorithm
Demo Brainmark
RegistrationFeatures
test
p0i = Rpi + T + Ni (1)
where R is a 3£3 rotation matrix, T a translation vector (3£1 column matrix)and Ni a noisevector. The rotation R and translation T haveto be found suchthat the following equation is minimized:
§ 2 =NX
i=1
k p0i ¡ (Rpi + T) k2: (2)
test
Two 3D point sets are given, the equation that needs to be solved is then:
ri = Rti + T (1)
Root mean square error (RMS):
RMS =1N
kri ¡ (Rti + T)k: (2)
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Outline Introduction Registration
Materials and Methods Results Discussion and Conclusion Recommendations
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Materials and MethodsDatasets
Four datasets: Pre-operative 1.5 Tesla and intra-operative 0.15 Tesla MR data Two datasets of healthy volunteers Two partial datasets of patients
Figure 7: Mid-sagittal slices of the high and low resolution MR data of a healthy volunteer (left) and patient.
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Materials and MethodsPreprocessing
Initial Alignment Important for optimization scheme Gravity point of nonzero voxels in sagittal direction
Gradient removal Skull removal
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Materials and MethodsPreprocessing
Global Intensity Gradient Removal Subtract peaks from Gaussian blurred image
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Materials and MethodsPreprocessing
Gradient Removal Subtract peaks from Gaussian blurred image
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Materials and MethodsPreprocessing
‘Skull’ stripping Dilation and erosion of a binary mask
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Materials and MethodsPreprocessing
‘Skull’ stripping Dilation and erosion of a binary mask
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Materials and MethodsRegistration programs
Intensity-based registration programs: Rigid transformation model Sum of Squared Differences and Normalized Gradient Field Gauss-Newton optimization scheme Multilevel approach
Feature-based registration program: Manual selection of 10-15 features Arun’s algorithm for transformation
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Materials and MethodsExperiments
Intensity-based registrations Four datasets were registered using the SSD and NGF
programs Multilevel approach: 1, 2 and 3 levels (resolution steps) were
used
Feature-based registration Four datasets were registered The results will be used as initial parameter guess for the
optimizing scheme of the NGF program to register the patient datasets
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Materials and MethodsVisualization
To inspect registration results, a Graphical User Interface (GUI) was built
Figure 8: A screenshot of Regview to inspect registration results visually. The green lines indicate the cross-section with the other two views.
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Materials and MethodsVisualization
Three different settings to inspect registration results
Figure 9: Checkerboard (left), fusion (middle) and transition visualization.
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Outline Introduction Registration Materials and Methods
Results Discussion and Conclusion Recommendations
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ResultsTable 1.1: Results from the SSD program.
Dataset Nr of Nr of F inal SSD Computing Quality Commentsresolution iterations value time [s] A ssessment
steps V isualInspection
VolunteerNeuro001 3 9+11+3=23 1539509 65 Good2 24+3=27 1539294 66 Good1 35 1540095 196 Average
VolunteerNeuro002 3 16+13+10=39 1427983 82 Bad No skull2 44+9=53 1378021 91 Average removal1 35 1378671 378 Bad
PatientNeuro003 3 54+47+6=107 759877 98 Good Manual2 125+7=132 983955 370 Bad initial1 154 1059637 730 Bad alignment
PatientNeuro004 3 - - - Unable2 - - - Unable1 - - - Unable
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Results Influence of resolution steps, VolunteerNeuro002
One resolution step
Two resolution steps
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ResultsTable 1.2: Results from the NGF program.
Dataset Nr of Nr F inal NGF Computing Quality A ssessmentresolution steps iterations value time [s] V isual Inspection
VolunteerNeuro001 3 18+11+10=39 20,13 117 Bad2 13+5=18 8,97 117 Excellent1 31 8,97 205 Excellent
VolunteerNeuro002 3 15+12+7=34 8,59 168 Good2 14+7=21 8,59 138 Excellent1 22 17,64 172 Bad
PatientNeuro003 3 40+20+10=70 40,96 195 Bad2 14+30=44 98,84 233 Bad1 7 121,0 88 Bad
PatientNeuro004 3 - - - Unable2 - - - Unable1 - - - Unable
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ResultsRegistration of VolunteerNeuro001
using NGF, two resolution steps:
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ResultsTable 1.3: Results from the feature-based program.Dataset Nr of selected R M S error [cm] Quality A ssessment Comments
features V isual InspectionVolunteerNeuro001 5 0.157 Poor
10 0.166 Average15 0.128 Average
VolunteerNeuro002 5 0.203 Poor10 0.130 Average15 0.093 Average
PatientNeuro003 4 0.119 Poor5 0.120 Poor6 0.121 Poor7 0.162 Poor8 0.139 Average8 - Good After NGF
PatientNeuro004 4 0.201 Poor5 0.161 Poor6 0.146 Poor7 0.136 Poor8 0.130 Poor9 0.124 Average10 0.150 Average10 - Excellent After NGF
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Results
After manual selection of 10 features
Using feature based initialization for NGF registration program
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Results The intensity-based registration programs managed to
register the datasets of the healthy volunteers
However both intensity-based programs were not able to register the partial datasets of the patients without manual initial parameter guess
Best results were obtained by using a feature-based registration as initial parameter guess for the intensity-based programs.
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Outline Introduction Registration Materials and Methods Results
Discussion and Conclusion Recommendations
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Conclusion and Discussion All datasets are registered, results were inspected using
visual inspection
Preprocessing important for intensity-based programs
Accuracy of the voxelsize is feasible in the center of the field of view
However this accuracy is not attainable at the edge of the field of view due to distortions and artifacts resulting from the low field of the Polestar N20
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Outline Introduction Registration Materials and Methods Results Discussion and Conclusion
Recommendations
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Recommendations Image quality Polestar
Currently a phantom is developed to measure and correct the distortion
Next step: registration after skull opening but before tumor resection Non rigid transformation model Computation time Validation
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Thank you for your attention!Questions?