Diploma thesis kick-off presentation
Fast and efficient error correction
of electromagnetic tracking
and its application in prostate cancer treatment
Claudia Thormann
director:
Prof. Dr. Navab
supervisor:
J篓org Traub
medical partner: Prof. Kneschaurek
(Radiation Therapy Department, Rechtsder Isar)
Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
Outline
1. Medical application: prostate cancer treatment
2. Error correction
3. Aim of this diploma thesis
4. Proposed method
Step1: Device calibration
Step2: Creating the Lookup-table
Step3: Onlineerror correction
5. Summary and vision for the future
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
1. Medical application: prostate cancer treatment
00rostate located in front of the rectum, under the bladder, encloses the urethra
00 : male patients and older than 50 years
source of the picture: http://en.wikipedia.org/wiki/Prostate cancer
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
1.1 Medicalprocedure of treatment: Status Quo
00ballooncatheter is inserted into the rectum.
00heballoonis inflated to adjust the prostate in its position.
00CT ofthepatient is done.
00heareaof radiation is calculated (software).
00adiation of the calculated area every weekday with X-rays
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
1.2 Limitations of this treatment
00ectumandurethra should not be radiated, but both are close to the prostate.
00he prostate always moves inside the body, even if it is fixed with the balloon.
00edical statusquo:
The area of radiation has to be enlarged a little bit to ensure the radiation of
the whole cancer.
) A more precise knowledge of the location of the prostate is needed.
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
1.3 Remedy
00racking inside the human body
) electromagnetic tracking system used
00agnetic sensor attached to the balloon catheter
) magnetic sensor visible on the CT
00ptical tracking system used for the computation of the error function
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
2. Error correction1,2
00rror correction needed for the electromagnetic tracking system
reason: gantry and metal always present in the radiation room
00ptical tracking system used as ground truth values
00orkbasedonthe master thesis of Suhkbansbir Kaur:
-analysisoferror correction methods
-the measurement error could be corrected very well
-hermethodnot suitable for prostate cancer scenario
1
"
A survey of electromagnetic position tracker calibration techniques"by Volodymyr V. Kindratenko
2
"
Error Correction for ElectroMagnetic Tracking", Master thesis by Suhkbansbir Kaur, handed in 2006/04/28
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
3. Aim of this diploma thesis
00mproved error correction
(more precise)
00mproved useability
(now: time-consuming and inconvenient)
00avigation interface
-no complicated 3D-GUI is needed
-simple output of
"
table coordinates"
(howthedoctorhas to move the table where the patient is laying)
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
4. Proposed method
Method consists of three steps:
1. Device calibration
2. Creating the lookup-table
3. Onlineerror correction
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
Step1: Device Calibration3,4
00evice calibration done only once
00orgetting the translations Xand Y
00quation:
ART
T
S3
路X路MBT
S1
=ARTT
S2
路Y
3
"
Tracking Systems in Surgical Navigation"by Wolfgang Birkfellner, Chapter 5
4
"
Aligning Optical and Electromagnetic Tracking Systems", Diploma thesis by Sintje G
篓
oritz, handed in 2005/08/15
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
Explanation of the picture
00.R.T. =optical tracking system,
Microbird=electromagnetic tracking system (abbreviated
"
MB")
00ntheleft: magnetic field-generator with rigidly attached optical markers (S3)
00ntheright:
"
combined target"=magnetic sensor (S1) with rigidly attached optical markers
(S2)
00=transformation between the coordinate system of the field-generator and the optical
tracking system
00=transformation between the coordinate system of the magnetic sensor and the optical
tracking system
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
Step 1a: HandEyeCalibrati onto get Y
00ombined target is moved around
00ustbedoneinanon-distorted setting
00easurement data collected
at several locations at several timesi, i+1, ...
00easured data used to setup equations and to calculate Y
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
Step 1b: Reorganizing the equation to get X
ART
T
S3
路X路MBT
S1
=ARTT
S2
路Y
X= (ARTT
S3
)
隆1
路ARTT
S2
路Y路 (MBT
S1
)
隆1
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
What'snew
Suhkbansbir'smethod:
00omarkeronthe field-generator
00herefore device calibration was done during online error correction
00andEyeCalibrati on had to be done more than once
00andEyeCalibrati on did work well in non-distorted settings,
butHandEyeCalibrati on did not work in distorted settings
) but: The prostate cancer setting is always distorted because of gantry and metal present in
the radiation room.
Proposed method:
00dditional optical marker attached to the field-generator
00herefore device calibration can be done in the beginning
00evice calibration needs to be done only once
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
Step2: Creating the Lookup-table (LUT)
00eedtobedone whenever the setting changes (metal)
00apping function (incorrect values! corrected values) implemented as LUT
00woentriesper line:
-measurement data of the electromagnetic tracking system
-corresponding transformed measurement data of the optical tracking system
00ptical data needs to be transformed into the magnetic coordinate system:
MB
T
S1
|{z}
measurement data
=X
隆1
路 (ARTT
S3
)
隆1 ART
T
S2
路Y
|
{z
}
ground truth values
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
Step3: Onlineerror correction
00asedonthe entries of the LUT
00ptical tracking system not needed for this step
00lgorithm for theonlineerror correction:
-Iftheactual position of the sensor is available in the LUT:
) use the corrected value from the LUT
-Iftheactual position is not available in the LUT
) perform interpolation (trilinear/Hardy'sMulti-Quadric)
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
5. Summary and vision for the future
00arryontheworkofSuhkbansbir Kaur
00mprovetheerror correction for magnetic tracking
(withthehelpofan optical tracking system used for the ground truth values)
00akethestepsmore useable for the clinicalworkflow
00edical aim:
) enable more precise radiation of the prostate cancer
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Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment
Further information
For more information about my thesis, please visit
http://campar.in.tum.de/Students/DaProstate
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