Sudhakar Chelikani - Academia.edu (original) (raw)

Papers by Sudhakar Chelikani

Research paper thumbnail of Constrained non-rigid registration for use in image-guided adaptive radiotherapy

Medical Image Analysis, 2009

A constrained non-rigid registration (CNRR) algorithm for use in prostate image-guided adaptive r... more A constrained non-rigid registration (CNRR) algorithm for use in prostate image-guided adaptive radiotherapy is presented in a coherent mathematical framework. The registration algorithm is based on a global rigid transformation combined with a series of local injective non-rigid multi-resolution cubic B-spline Free Form Deformation (FFD) transformations. The control points of the FFD are used to non-rigidly constrain the transformation to the prostate, rectum, and bladder. As well, the control points are used to rigidly constrain the transformation to the estimated position of the pelvis, left femur, and right femur. The algorithm was tested with both 3D conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) dose plan data sets. The 3DCRT dose plan set consisted of 10 fan-beam CT (FBCT) treatment-day images acquired from four different patients. The IMRT dose plan set consisted of 32 cone-beam CT (CBCT) treatment-day images acquired from 4 different patients. The CNRR was tested with different combinations of anatomical constraints and each test significantly outperformed both rigid and non-rigid registration at aligning constrained bones and critical organs. The CNRR results were used to adapt the dose plans to account for patient positioning errors as well as inter-day bone motion and intrinsic organ deformation. Each adapted dose plan improved performance by lowering radiation distribution to the rectum and bladder while increasing or maintaining radiation distribution to the prostate.

Research paper thumbnail of Constrained Non-Rigid (NR) Registration for Use in Aligning Critical Organs in External Beam Radiotherapy (EBRT) for Prostate Cancer

International Journal of Radiation Oncology Biology Physics, Nov 1, 2007

Research paper thumbnail of Integrated Segmentation and Nonrigid Registration for Application in Prostate Image-Guided Radiotherapy

Lecture Notes in Computer Science, 2010

Many current image-guided radiotherapy (IGRT) systems incorporate an in-room cone-beam CT (CBCT) ... more Many current image-guided radiotherapy (IGRT) systems incorporate an in-room cone-beam CT (CBCT) with a radiotherapy linear accelerator for treatment day imaging. Segmentation of key anatomical structures (prostate and surrounding organs) in 3DCBCT images as well as registration between planning and treatment images are essential for determining many important treatment parameters. Due to the image quality of CBCT, previous work typically uses manual segmentation of the soft tissues and then registers the images based on the manual segmentation. In this paper, an integrated automatic segmentation/constrained nonrigid registration is presented, which can achieve these two aims simultaneously. This method is tested using 24 sets of real patient data. Quantitative results show that the automatic segmentation produces results that have an accuracy comparable to manual segmentation, while the registration part significantly outperforms both rigid and non-rigid registration. Clinical application also shows promising results.

Research paper thumbnail of An integrated approach to segmentation and nonrigid registration for application in image-guided pelvic radiotherapy

Medical Image Analysis, Oct 1, 2011

External beam radiotherapy (EBRT) has become the preferred options for non-surgical treatment of ... more External beam radiotherapy (EBRT) has become the preferred options for non-surgical treatment of prostate cancer and cervix cancer. In order to deliver higher doses to cancerous regions within these pelvic structures (i.e. prostate or cervix) while maintaining or lowering the doses to surrounding non-cancerous regions, it is critical to account for setup variation, organ motion, anatomical changes due to treatment and intra-fraction motion. In previous work, manual segmentation of the soft tissues is performed and then images are registered based on the manual segmentation. In this paper, we present an integrated automatic approach to multiple organ segmentation and nonrigid constrained registration, which can achieve these two aims simultaneously. The segmentation and registration steps are both formulated using a Bayesian framework, and they constrain each other using an iterative conditional model strategy. We also propose a new strategy to assess cumulative actual dose for this novel integrated algorithm, in order to both determine whether the intended treatment is being delivered and, potentially, whether or not a plan should be adjusted for future treatment fractions. Quantitative results show that the automatic segmentation produced results that have an accuracy comparable to manual segmentation, while the registration part significantly outperforms both rigid and non-rigid registration. Clinical application and evaluation of dose delivery show the superiority of proposed method to the procedure currently used in clinical practice, i.e. manual segmentation followed by rigid registration.

Research paper thumbnail of Impact of margin allocation on uncertainty in tumor control probability (TCP) in external beam radiotherapy (EBRT) of prostate cancer

International Journal of Radiation OncologyBiologyPhysics

Research paper thumbnail of Integrated segmentation and nonrigid registration for application in prostate image-guided radiotherapy

Many current image-guided radiotherapy (IGRT) systems incorporate an in-room cone-beam CT (CBCT) ... more Many current image-guided radiotherapy (IGRT) systems incorporate an in-room cone-beam CT (CBCT) with a radiotherapy linear accelerator for treatment day imaging. Segmentation of key anatomical structures (prostate and surrounding organs) in 3DCBCT images as well as registration between planning and treatment images are essential for determining many important treatment parameters. Due to the image quality of CBCT, previous work typically uses manual segmentation of the soft tissues and then registers the images based on the manual segmentation. In this paper, an integrated automatic segmentation/constrained nonrigid registration is presented, which can achieve these two aims simultaneously. This method is tested using 24 sets of real patient data. Quantitative results show that the automatic segmentation produces results that have an accuracy comparable to manual segmentation, while the registration part significantly outperforms both rigid and non-rigid registration. Clinical application also shows promising results.

Research paper thumbnail of An integrated approach to segmentation and nonrigid registration for application in image-guided pelvic radiotherapy

Medical Image Analysis, 2011

External beam radiotherapy (EBRT) has become the preferred options for non-surgical treatment of ... more External beam radiotherapy (EBRT) has become the preferred options for non-surgical treatment of prostate cancer and cervix cancer. In order to deliver higher doses to cancerous regions within these pelvic structures (i.e. prostate or cervix) while maintaining or lowering the doses to surrounding non-cancerous regions, it is critical to account for setup variation, organ motion, anatomical changes due to treatment and intra-fraction motion. In previous work, manual segmentation of the soft tissues is performed and then images are registered based on the manual segmentation. In this paper, we present an integrated automatic approach to multiple organ segmentation and nonrigid constrained registration, which can achieve these two aims simultaneously. The segmentation and registration steps are both formulated using a Bayesian framework, and they constrain each other using an iterative conditional model strategy. We also propose a new strategy to assess cumulative actual dose for this novel integrated algorithm, in order to both determine whether the intended treatment is being delivered and, potentially, whether or not a plan should be adjusted for future treatment fractions. Quantitative results show that the automatic segmentation produced results that have an accuracy comparable to manual segmentation, while the registration part significantly outperforms both rigid and non-rigid registration. Clinical application and evaluation of dose delivery show the superiority of proposed method to the procedure currently used in clinical practice, i.e. manual segmentation followed by rigid registration.

Research paper thumbnail of Constrained Non-Rigid (NR) Registration for Use in Aligning Critical Organs in External Beam Radiotherapy (EBRT) for Prostate Cancer

International Journal of Radiation Oncology*Biology*Physics, 2007

Research paper thumbnail of Tracking organ overlap for a constrained non-rigid registration algorithm

This paper tracks organ (prostate, rectum, bladder) overlap in a constrained non-rigid registrati... more This paper tracks organ (prostate, rectum, bladder) overlap in a constrained non-rigid registration (NRR) algorithm to register computed tomographic (CT) images used in external beam prostate radiotherapy. The local motion of the organs is described by a hierarchical multi-resolution FFD based on cubic B-splines. Registration is achieved by minimizing a cost function which is a combination of three functions representing the overlap of the critical organs, image similarity and smoothness of the transformation. The constrained NRR algorithm generated better registration results when compared to an unconstrained NRR algorithm.

Research paper thumbnail of Constrained non-rigid registration using Lagrange multipliers for application in prostate radiotherapy

ABSTRACT This paper presents a novel free-form deformation registration algorithm with non-rigid ... more ABSTRACT This paper presents a novel free-form deformation registration algorithm with non-rigid constraints to capture the transformation between the planning day and treatment day CT images used for external beam radiotherapy for prostate cancer. The non-rigid registration is constrained to the predetermined motion of segmented soft tissues, and the constrained optimization problem is solved by the method of Lagrange multipliers. The ultimate goal is for the nonrigid transformation to be used to update the radiotherapy plan to take into account soft tissue deformation. The performance of this hard-constrained nonrigid registration (H-CNRR) algorithm has been compared to those achieved using rigid, fully non-rigid, and soft-constrained nonrigid registration (S-CNRR). The results clearly indicate that this Lagrange multipliers based hard-constrained nonrigid registration algorithm presented in this paper performed better at capturing the motion of the constrained organs.

Research paper thumbnail of Constrained Non-rigid Registration (CNRR): An Image Guided Method to Update Prostate External Beam Radiotherapy (EBRT) Plans

International Journal of Radiation Oncology*Biology*Physics, 2008

Conclusions: The 3D-CRT plan could be further improved if a better choice of beam angles was made... more Conclusions: The 3D-CRT plan could be further improved if a better choice of beam angles was made. The 3D-CRT plans were able to meet the RTOG criteria, which suggests the added time and expense of IMRT planning was not justified for these cases. However, it is true that allowing the TPS to work toward the RTOG criteria achieved a more homogeneous dose inside the target volume. To rationalize the use of IMRT treatment when a 3D conformal plan would suffice, the FCCC criteria could be used to fully exploit the benefits IMRT offers.

Research paper thumbnail of A constrained non-rigid registration algorithm for use in prostate image-guided radiotherapy

A constrained non-rigid registration (CNRR) algorithm for use in updating prostate external beam ... more A constrained non-rigid registration (CNRR) algorithm for use in updating prostate external beam image-guided radiotherapy treatment plans is presented in this paper. The developed algorithm is based on a multi-resolution cubic B-spline FFD transformation and has been tested and verified using 3D CT images from 10 sets of real patient data acquired from 4 different patients on different treatment days. The registration can be constrained to any combination of the prostate, rectum, bladder, pelvis, left femur, and right femur. The CNRR was tested with 5 different combinations of constraints and each test significantly outperformed both rigid and non-rigid registration at aligning constrained bones and critical organs. The CNRR was then used to update the treatment plans to account for articulated, rigid bone motion and non-rigid organ deformation. Each updated treatment plan outperformed the original treatment plan by increasing radiation dosage to the prostate and lowering radiation dosage to the rectum and bladder.

Research paper thumbnail of POSTER PRESENTATION Open Access Comparison of electroanatomic voltage mapping with late gadolinium enhancement CMR

Atrial fibrillation (AF) is associated with atrial remodel-ing, including atrial cellular patholo... more Atrial fibrillation (AF) is associated with atrial remodel-ing, including atrial cellular pathology [1,2], left atrial enlargement [3], and low voltage on electroanatomic mapping (EAM)[4]. Recent studies have identified late gadolinium enhancement (LGE) in AF subjects pre-PVI as novel evidence of LA remodeling [5]. One study com-pared voltage by EAM obtained prior to a pulmonary vein isolation (PVI) procedure with the extent of atrial fibrosis using LGE [6]. Our goal was to further correlate EAM voltages with LGE. Methods Sixteen AF patients were imaged on a 1.5T scanner (Achieva, Philips Healthcare, NL) using high resolution LGE [7], prior to their first PVI. Left atrial LGE was obtained using an ECG-triggered, navigator-gated 3D GRE inversion recovery (IR) sequence obtained 10-20 minutes after the administration of 0.2 mmol/kg of Gd-DTPA, with spatial resolution of 1.3 × 1.3 × 4 mm 3. The left atrial cavity and enhanced tissue were segmented on the LGE images, using a threshold co...

Research paper thumbnail of CMR-Verified Lower LA Strain in the Presence of Regional Atrial Fibrosis in Atrial Fibrillation

JACC. Cardiovascular imaging, Jan 6, 2016

Research paper thumbnail of Voxel-based logistic analysis of PPMI control and Parkinson's disease DaTscans

Research paper thumbnail of Lower left atrial strain in the presence of regional atrial fibrosis: an MRI study of patients with atrial fibrillation

Journal of Cardiovascular Magnetic Resonance, 2016

Research paper thumbnail of Atrial fibrosis segmentation thresholds: a theoretical and empirical study

Journal of Cardiovascular Magnetic Resonance, 2016

Research paper thumbnail of CMR-Verified Lower LA Strain in the Presence of Regional Atrial Fibrosis in Atrial Fibrillation

JACC. Cardiovascular imaging, Jan 6, 2016

Research paper thumbnail of Support Vector Machine Density Estimator as a Generalized Parzen Windows Estimator for Mutual Information based Image Registration

Lecture Notes in Computer Science, 2003

Mutual Information is perhaps the most widely used multimodality image registration method. A cru... more Mutual Information is perhaps the most widely used multimodality image registration method. A crucial step in mutual information is the estimation of the probability density function (pdf). In most cases, the Parzen window estimator is employed for this purpose which results in an excessive computational cost. In this paper we demonstrate that replacing the Parzen density estimator with a Support Vector Machine (SVM) density estimation will result in a significant reduction of the computational time. We verified this by registering 2D portal images to DRRs (digitally reconstructed radiographs) projected from 3D CT volumetric data.

Research paper thumbnail of Design and optimization of a Compton camera for nuclear medicine applications

A major limitation in conventional SPECT imaging is the poor sensitivity. The lead collimators us... more A major limitation in conventional SPECT imaging is the poor sensitivity. The lead collimators used in Anger cameras allow the detection of approximately 1 out of every 10000 photons that arrive to the front face of the collimator. Consequently, to offset this disadvantage, the radiation dosage given to the patient can be considerable. It is apparent that the performance of the camera will improve if the collimator is removed. A completely redesigned camera, without the lead collimator, has been introduced, and is referred to as a Compton camera. The Compton camera, in addition to increased sensitivity, can allow, from a single position, the simultaneous acquisition of data from multiple angular views. This reduces the possibility of artifacts due to camera motion and also eliminates the time wasted between angular positions. The increased sensitivity allows the use of lower activity levels and isotopes with shorter half- lives. The essential design of a Compton camera consists of 2...

Research paper thumbnail of Constrained non-rigid registration for use in image-guided adaptive radiotherapy

Medical Image Analysis, 2009

A constrained non-rigid registration (CNRR) algorithm for use in prostate image-guided adaptive r... more A constrained non-rigid registration (CNRR) algorithm for use in prostate image-guided adaptive radiotherapy is presented in a coherent mathematical framework. The registration algorithm is based on a global rigid transformation combined with a series of local injective non-rigid multi-resolution cubic B-spline Free Form Deformation (FFD) transformations. The control points of the FFD are used to non-rigidly constrain the transformation to the prostate, rectum, and bladder. As well, the control points are used to rigidly constrain the transformation to the estimated position of the pelvis, left femur, and right femur. The algorithm was tested with both 3D conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) dose plan data sets. The 3DCRT dose plan set consisted of 10 fan-beam CT (FBCT) treatment-day images acquired from four different patients. The IMRT dose plan set consisted of 32 cone-beam CT (CBCT) treatment-day images acquired from 4 different patients. The CNRR was tested with different combinations of anatomical constraints and each test significantly outperformed both rigid and non-rigid registration at aligning constrained bones and critical organs. The CNRR results were used to adapt the dose plans to account for patient positioning errors as well as inter-day bone motion and intrinsic organ deformation. Each adapted dose plan improved performance by lowering radiation distribution to the rectum and bladder while increasing or maintaining radiation distribution to the prostate.

Research paper thumbnail of Constrained Non-Rigid (NR) Registration for Use in Aligning Critical Organs in External Beam Radiotherapy (EBRT) for Prostate Cancer

International Journal of Radiation Oncology Biology Physics, Nov 1, 2007

Research paper thumbnail of Integrated Segmentation and Nonrigid Registration for Application in Prostate Image-Guided Radiotherapy

Lecture Notes in Computer Science, 2010

Many current image-guided radiotherapy (IGRT) systems incorporate an in-room cone-beam CT (CBCT) ... more Many current image-guided radiotherapy (IGRT) systems incorporate an in-room cone-beam CT (CBCT) with a radiotherapy linear accelerator for treatment day imaging. Segmentation of key anatomical structures (prostate and surrounding organs) in 3DCBCT images as well as registration between planning and treatment images are essential for determining many important treatment parameters. Due to the image quality of CBCT, previous work typically uses manual segmentation of the soft tissues and then registers the images based on the manual segmentation. In this paper, an integrated automatic segmentation/constrained nonrigid registration is presented, which can achieve these two aims simultaneously. This method is tested using 24 sets of real patient data. Quantitative results show that the automatic segmentation produces results that have an accuracy comparable to manual segmentation, while the registration part significantly outperforms both rigid and non-rigid registration. Clinical application also shows promising results.

Research paper thumbnail of An integrated approach to segmentation and nonrigid registration for application in image-guided pelvic radiotherapy

Medical Image Analysis, Oct 1, 2011

External beam radiotherapy (EBRT) has become the preferred options for non-surgical treatment of ... more External beam radiotherapy (EBRT) has become the preferred options for non-surgical treatment of prostate cancer and cervix cancer. In order to deliver higher doses to cancerous regions within these pelvic structures (i.e. prostate or cervix) while maintaining or lowering the doses to surrounding non-cancerous regions, it is critical to account for setup variation, organ motion, anatomical changes due to treatment and intra-fraction motion. In previous work, manual segmentation of the soft tissues is performed and then images are registered based on the manual segmentation. In this paper, we present an integrated automatic approach to multiple organ segmentation and nonrigid constrained registration, which can achieve these two aims simultaneously. The segmentation and registration steps are both formulated using a Bayesian framework, and they constrain each other using an iterative conditional model strategy. We also propose a new strategy to assess cumulative actual dose for this novel integrated algorithm, in order to both determine whether the intended treatment is being delivered and, potentially, whether or not a plan should be adjusted for future treatment fractions. Quantitative results show that the automatic segmentation produced results that have an accuracy comparable to manual segmentation, while the registration part significantly outperforms both rigid and non-rigid registration. Clinical application and evaluation of dose delivery show the superiority of proposed method to the procedure currently used in clinical practice, i.e. manual segmentation followed by rigid registration.

Research paper thumbnail of Impact of margin allocation on uncertainty in tumor control probability (TCP) in external beam radiotherapy (EBRT) of prostate cancer

International Journal of Radiation OncologyBiologyPhysics

Research paper thumbnail of Integrated segmentation and nonrigid registration for application in prostate image-guided radiotherapy

Many current image-guided radiotherapy (IGRT) systems incorporate an in-room cone-beam CT (CBCT) ... more Many current image-guided radiotherapy (IGRT) systems incorporate an in-room cone-beam CT (CBCT) with a radiotherapy linear accelerator for treatment day imaging. Segmentation of key anatomical structures (prostate and surrounding organs) in 3DCBCT images as well as registration between planning and treatment images are essential for determining many important treatment parameters. Due to the image quality of CBCT, previous work typically uses manual segmentation of the soft tissues and then registers the images based on the manual segmentation. In this paper, an integrated automatic segmentation/constrained nonrigid registration is presented, which can achieve these two aims simultaneously. This method is tested using 24 sets of real patient data. Quantitative results show that the automatic segmentation produces results that have an accuracy comparable to manual segmentation, while the registration part significantly outperforms both rigid and non-rigid registration. Clinical application also shows promising results.

Research paper thumbnail of An integrated approach to segmentation and nonrigid registration for application in image-guided pelvic radiotherapy

Medical Image Analysis, 2011

External beam radiotherapy (EBRT) has become the preferred options for non-surgical treatment of ... more External beam radiotherapy (EBRT) has become the preferred options for non-surgical treatment of prostate cancer and cervix cancer. In order to deliver higher doses to cancerous regions within these pelvic structures (i.e. prostate or cervix) while maintaining or lowering the doses to surrounding non-cancerous regions, it is critical to account for setup variation, organ motion, anatomical changes due to treatment and intra-fraction motion. In previous work, manual segmentation of the soft tissues is performed and then images are registered based on the manual segmentation. In this paper, we present an integrated automatic approach to multiple organ segmentation and nonrigid constrained registration, which can achieve these two aims simultaneously. The segmentation and registration steps are both formulated using a Bayesian framework, and they constrain each other using an iterative conditional model strategy. We also propose a new strategy to assess cumulative actual dose for this novel integrated algorithm, in order to both determine whether the intended treatment is being delivered and, potentially, whether or not a plan should be adjusted for future treatment fractions. Quantitative results show that the automatic segmentation produced results that have an accuracy comparable to manual segmentation, while the registration part significantly outperforms both rigid and non-rigid registration. Clinical application and evaluation of dose delivery show the superiority of proposed method to the procedure currently used in clinical practice, i.e. manual segmentation followed by rigid registration.

Research paper thumbnail of Constrained Non-Rigid (NR) Registration for Use in Aligning Critical Organs in External Beam Radiotherapy (EBRT) for Prostate Cancer

International Journal of Radiation Oncology*Biology*Physics, 2007

Research paper thumbnail of Tracking organ overlap for a constrained non-rigid registration algorithm

This paper tracks organ (prostate, rectum, bladder) overlap in a constrained non-rigid registrati... more This paper tracks organ (prostate, rectum, bladder) overlap in a constrained non-rigid registration (NRR) algorithm to register computed tomographic (CT) images used in external beam prostate radiotherapy. The local motion of the organs is described by a hierarchical multi-resolution FFD based on cubic B-splines. Registration is achieved by minimizing a cost function which is a combination of three functions representing the overlap of the critical organs, image similarity and smoothness of the transformation. The constrained NRR algorithm generated better registration results when compared to an unconstrained NRR algorithm.

Research paper thumbnail of Constrained non-rigid registration using Lagrange multipliers for application in prostate radiotherapy

ABSTRACT This paper presents a novel free-form deformation registration algorithm with non-rigid ... more ABSTRACT This paper presents a novel free-form deformation registration algorithm with non-rigid constraints to capture the transformation between the planning day and treatment day CT images used for external beam radiotherapy for prostate cancer. The non-rigid registration is constrained to the predetermined motion of segmented soft tissues, and the constrained optimization problem is solved by the method of Lagrange multipliers. The ultimate goal is for the nonrigid transformation to be used to update the radiotherapy plan to take into account soft tissue deformation. The performance of this hard-constrained nonrigid registration (H-CNRR) algorithm has been compared to those achieved using rigid, fully non-rigid, and soft-constrained nonrigid registration (S-CNRR). The results clearly indicate that this Lagrange multipliers based hard-constrained nonrigid registration algorithm presented in this paper performed better at capturing the motion of the constrained organs.

Research paper thumbnail of Constrained Non-rigid Registration (CNRR): An Image Guided Method to Update Prostate External Beam Radiotherapy (EBRT) Plans

International Journal of Radiation Oncology*Biology*Physics, 2008

Conclusions: The 3D-CRT plan could be further improved if a better choice of beam angles was made... more Conclusions: The 3D-CRT plan could be further improved if a better choice of beam angles was made. The 3D-CRT plans were able to meet the RTOG criteria, which suggests the added time and expense of IMRT planning was not justified for these cases. However, it is true that allowing the TPS to work toward the RTOG criteria achieved a more homogeneous dose inside the target volume. To rationalize the use of IMRT treatment when a 3D conformal plan would suffice, the FCCC criteria could be used to fully exploit the benefits IMRT offers.

Research paper thumbnail of A constrained non-rigid registration algorithm for use in prostate image-guided radiotherapy

A constrained non-rigid registration (CNRR) algorithm for use in updating prostate external beam ... more A constrained non-rigid registration (CNRR) algorithm for use in updating prostate external beam image-guided radiotherapy treatment plans is presented in this paper. The developed algorithm is based on a multi-resolution cubic B-spline FFD transformation and has been tested and verified using 3D CT images from 10 sets of real patient data acquired from 4 different patients on different treatment days. The registration can be constrained to any combination of the prostate, rectum, bladder, pelvis, left femur, and right femur. The CNRR was tested with 5 different combinations of constraints and each test significantly outperformed both rigid and non-rigid registration at aligning constrained bones and critical organs. The CNRR was then used to update the treatment plans to account for articulated, rigid bone motion and non-rigid organ deformation. Each updated treatment plan outperformed the original treatment plan by increasing radiation dosage to the prostate and lowering radiation dosage to the rectum and bladder.

Research paper thumbnail of POSTER PRESENTATION Open Access Comparison of electroanatomic voltage mapping with late gadolinium enhancement CMR

Atrial fibrillation (AF) is associated with atrial remodel-ing, including atrial cellular patholo... more Atrial fibrillation (AF) is associated with atrial remodel-ing, including atrial cellular pathology [1,2], left atrial enlargement [3], and low voltage on electroanatomic mapping (EAM)[4]. Recent studies have identified late gadolinium enhancement (LGE) in AF subjects pre-PVI as novel evidence of LA remodeling [5]. One study com-pared voltage by EAM obtained prior to a pulmonary vein isolation (PVI) procedure with the extent of atrial fibrosis using LGE [6]. Our goal was to further correlate EAM voltages with LGE. Methods Sixteen AF patients were imaged on a 1.5T scanner (Achieva, Philips Healthcare, NL) using high resolution LGE [7], prior to their first PVI. Left atrial LGE was obtained using an ECG-triggered, navigator-gated 3D GRE inversion recovery (IR) sequence obtained 10-20 minutes after the administration of 0.2 mmol/kg of Gd-DTPA, with spatial resolution of 1.3 × 1.3 × 4 mm 3. The left atrial cavity and enhanced tissue were segmented on the LGE images, using a threshold co...

Research paper thumbnail of CMR-Verified Lower LA Strain in the Presence of Regional Atrial Fibrosis in Atrial Fibrillation

JACC. Cardiovascular imaging, Jan 6, 2016

Research paper thumbnail of Voxel-based logistic analysis of PPMI control and Parkinson's disease DaTscans

Research paper thumbnail of Lower left atrial strain in the presence of regional atrial fibrosis: an MRI study of patients with atrial fibrillation

Journal of Cardiovascular Magnetic Resonance, 2016

Research paper thumbnail of Atrial fibrosis segmentation thresholds: a theoretical and empirical study

Journal of Cardiovascular Magnetic Resonance, 2016

Research paper thumbnail of CMR-Verified Lower LA Strain in the Presence of Regional Atrial Fibrosis in Atrial Fibrillation

JACC. Cardiovascular imaging, Jan 6, 2016

Research paper thumbnail of Support Vector Machine Density Estimator as a Generalized Parzen Windows Estimator for Mutual Information based Image Registration

Lecture Notes in Computer Science, 2003

Mutual Information is perhaps the most widely used multimodality image registration method. A cru... more Mutual Information is perhaps the most widely used multimodality image registration method. A crucial step in mutual information is the estimation of the probability density function (pdf). In most cases, the Parzen window estimator is employed for this purpose which results in an excessive computational cost. In this paper we demonstrate that replacing the Parzen density estimator with a Support Vector Machine (SVM) density estimation will result in a significant reduction of the computational time. We verified this by registering 2D portal images to DRRs (digitally reconstructed radiographs) projected from 3D CT volumetric data.

Research paper thumbnail of Design and optimization of a Compton camera for nuclear medicine applications

A major limitation in conventional SPECT imaging is the poor sensitivity. The lead collimators us... more A major limitation in conventional SPECT imaging is the poor sensitivity. The lead collimators used in Anger cameras allow the detection of approximately 1 out of every 10000 photons that arrive to the front face of the collimator. Consequently, to offset this disadvantage, the radiation dosage given to the patient can be considerable. It is apparent that the performance of the camera will improve if the collimator is removed. A completely redesigned camera, without the lead collimator, has been introduced, and is referred to as a Compton camera. The Compton camera, in addition to increased sensitivity, can allow, from a single position, the simultaneous acquisition of data from multiple angular views. This reduces the possibility of artifacts due to camera motion and also eliminates the time wasted between angular positions. The increased sensitivity allows the use of lower activity levels and isotopes with shorter half- lives. The essential design of a Compton camera consists of 2...