DaFHSPECTOpt

Chair for Computer Aided Medical Procedures & Augmented Reality
Lehrstuhl für Informatikanwendungen in der Medizin & Augmented Reality

Optimization of models in Freehand SPECT reconstructions

Thesis by:
Advisor: Nassir Navab
Supervision by: Alexander Hartl

Abstract

Nuclear imaging is a commonly used tool in today's diagnostics and therapy planning, giving necessary information about metabolic functions in the patient's body. They employ radioactive tracers which are injected to the patient and follow there a specific metabolic pathway. With the use of radiation detectors these tracers can then be imaged, for interventional use however the current methods suffer from drawbacks which limit their application. Tomographic systems like PET (Positron Emission Tomography) and SPECT (Single Photon Emission Computed Tomography) have too high acquisition times and are too bulky for intra operative use while nuclear probes and gamma cameras only provide 1D and 2D information. Over the last years a new imaging modality, called freehand SPECT, was developed at our chair to overcome these shortcomings. Freehand SPECT combines a nuclear probe with an optical tracking system to obtain its position and orientation in space synchronized with its reading. These informations can be used to compute a tomographic reconstruction of an activity distribution. This is done by discretizing the volume of interest into voxels xi with unknown activity values a(xi) so the readings of the probe can be regarded as a linear combination of the contribution of each voxel c(xi) to that reading r:

r = c(xi)a(xi)

A set of measurements then yields a system of linear equations and by inverting that system the activity in each voxel is obtained. For the inversion then the contribution of each voxel to each measurement is needed. That contribution is approximated by models of the detection physics. With a known ground truth of the activity distribution the system of linear equations can also be solved for the contribution of a voxel to the reading, by using the existing models as boundary conditions. The computed contributions could then be again used to optimize the models used for reconstruction which is the goal of this work.

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Students.ProjectForm
Title: Optimization of models in Freehand SPECT reconstructions
Abstract: Nuclear imaging is a commonly used tool in today's diagnostics and therapy planning, giving necessary information about metabolic functions in the patient's body. They employ radioactive tracers which are injected to the patient and follow there a specific metabolic pathway. With the use of radiation detectors these tracers can then be imaged, for interventional use however the current methods suffer from drawbacks which limit their application. Tomographic systems like PET (Positron Emission Tomography) and SPECT (Single Photon Emission Computed Tomography) have too high acquisition times and are too bulky for intra operative use while nuclear probes and gamma cameras only provide 1D and 2D information. Over the last years a new imaging modality, called freehand SPECT, was developed at our chair to overcome these shortcomings. Freehand SPECT combines a nuclear probe with an optical tracking system to obtain its position and orientation in space synchronized with its reading. These informations can be used to compute a tomographic reconstruction of an activity distribution. This is done by discretizing the volume of interest into voxels xi with unknown activity values a(xi) so the readings of the probe can be regarded as a linear combination of the contribution of each voxel c(xi) to that reading r:

r = c(xi)a(xi)

A set of measurements then yields a system of linear equations and by inverting that system the activity in each voxel is obtained. For the inversion then the contribution of each voxel to each measurement is needed. That contribution is approximated by models of the detection physics. With a known ground truth of the activity distribution the system of linear equations can also be solved for the contribution of a voxel to the reading, by using the existing models as boundary conditions. The computed contributions could then be again used to optimize the models used for reconstruction which is the goal of this work.
Student:  
Director: Nassir Navab
Supervisor: Alexander Hartl
Type: DA/MA/BA
Area: Medical Imaging, Molecular Imaging, Computer-Aided Surgery
Status: draft
Start: 01.01.2012
Finish:  
Thesis (optional):  
Picture:  


Edit | Attach | Refresh | Diffs | More | Revision r1.1 - 16 Jan 2012 - 15:27 - AlexanderHartl