Rob MacLeod | University of Utah (original) (raw)

Papers by Rob MacLeod

Research paper thumbnail of The influence of volume conduction effects on the EEG/MEG reconstruction of the sources of the Early Left Anterior Negativity

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2004

To achieve a deeper understanding of language processing in the human brain, scientists and clini... more To achieve a deeper understanding of language processing in the human brain, scientists and clinicians use Electroencephalography (EEG) and Magnetoencephalography (MEG) inverse methods to reconstruct sources of Event Related Potentials. There exists a persistent uncertainty regarding the influence of volume conduction effects such as the anisotropy of tissue conductivity of the skull and the white matter layers on the inverse results. In this paper, we will study the sensitivity to anisotropy of the source reconstruction of the Early Left Anterior Negativity (ELAN) component in language processing. For EEG, the presence of tissue anisotropy substantially compromises the restoration ability of an L1-norm current density approach. The centers of activity are strongly shifted along the Sylvian fissure in the anterior direction. In contrast, MEG in combination with the L1 norm approach is able to reconstruct the main features of the ELAN source distribution even in the presence of aniso...

Research paper thumbnail of Improved EEG source analysis using low-resolution conductivity estimation in a four-compartment finite element head model

Human Brain Mapping, 2009

Bioelectric source analysis in the human brain from scalp electroencephalography (EEG) signals is... more Bioelectric source analysis in the human brain from scalp electroencephalography (EEG) signals is sensitive to geometry and conductivity properties of the different head tissues. We propose a low resolution conductivity estimation (LRCE) method using simulated annealing optimization on high resolution finite element models that individually optimizes a realistically-shaped four-layer volume conductor with regard to the brain and skull compartment conductivities. As input data, the method needs T1-and PD-weighted magnetic resonance images for an improved modeling of the skull and the cerebrospinal fluid compartment and evoked potential data with high signal-tonoise ratio (SNR). Our simulation studies showed that for EEG data with realistic SNR, the LRCE method was able to simultaneously reconstruct both the brain and the skull conductivity together with the underlying dipole source and provided an improved source analysis result. We have also demonstrated the feasibility and applicability of the new method to simultaneously estimate brain and skull conductivity and a somatosensory source from measured tactile somatosensory evoked potentials of a human subject. Our results show the viability of an approach that computes its own conductivity values and thus reduces the dependence on assigning values from the literature and likely produces a more robust estimate of current sources. Using the LRCE method, the individually optimized four-compartment volume conductor model can in a second step be used for the analysis of clinical or cognitive data acquired from the same subject.

Research paper thumbnail of Influence of tissue conductivity anisotropy on EEG/MEG field and return current computation in a realistic head model: A simulation and visualization study using high-resolution finite element modeling

NeuroImage, 2006

To achieve a deeper understanding of the brain, scientists, and clinicians use electroencephalogr... more To achieve a deeper understanding of the brain, scientists, and clinicians use electroencephalography (EEG) and magnetoencephalography (MEG) inverse methods to reconstruct sources in the cortical sheet of the human brain. The influence of structural and electrical anisotropy in both the skull and the white matter on the EEG and MEG source reconstruction is not well understood.

Research paper thumbnail of New Magnetic Resonance Imaging-Based Method for Defining the Extent of Left Atrial Wall Injury After the Ablation of Atrial Fibrillation

In this paper, we describe a delayed enhancement MRI method which detects left atrial wall injury... more In this paper, we describe a delayed enhancement MRI method which detects left atrial wall injury following ablation in patients with atrial fibrillation. We imaged and quantified the extent of injury in 46 patients using a respiratory navigated MRI sequence. There was a strong relationship noted between the degree of left atrial wall injury and freedom from the arrhythmia at three month follow-up. Using the described methodology, it appears possible to image and assess the degree of injury due to RF injury following ablation therapy for atrial fibrillation.

Research paper thumbnail of Association of Left Atrial Fibrosis Detected by Delayed-Enhancement Magnetic Resonance Imaging and the Risk of Stroke in Patients With Atrial Fibrillation

Journal of The American College of Cardiology, 2011

Objectives-This study tried to determine the association between left atrial (LA) fibrosis, detec... more Objectives-This study tried to determine the association between left atrial (LA) fibrosis, detected using delayed-enhanced magnetic resonance imaging (DE-MRI), and the CHADS 2 score (point system based on individual clinical risk factors including congestive heart failure, hypertension, age, diabetes, and prior stroke) variables, specifically stroke.

Research paper thumbnail of Dark Regions of No-Reflow on Late Gadolinium Enhancement Magnetic Resonance Imaging Result in Scar Formation After Atrial Fibrillation Ablation

Journal of the American College of Cardiology, 2011

Research paper thumbnail of Atrial Fibrosis Helps Select the Appropriate Patient and Strategy in Catheter Ablation of Atrial Fibrillation: A DE-MRI Guided Approach

Journal of Cardiovascular Electrophysiology, 2010

MRI for AF Patient Selection and Ablation Approach. Introduction: Left atrial (LA) fibrosis and a... more MRI for AF Patient Selection and Ablation Approach. Introduction: Left atrial (LA) fibrosis and ablation related scarring are major predictors of success in rhythm control of atrial fibrillation (AF). We used delayed enhancement MRI (DE-MRI) to stratify AF patients based on pre-ablation fibrosis and also to evaluate ablation-induced scarring in order to identify predictors of a successful ablation.Methods and Results: One hundred and forty-four patients were staged by percent of fibrosis quantified with DE-MRI, relative to the LA wall volume: minimal or Utah stage 1; <5%, mild or Utah stage 2; 5–20%, moderate or Utah stage 3; 20–35%, and extensive or Utah stage 4; >35%. All patients underwent pulmonary vein (PV) isolation and posterior wall and septal debulking. Overall, LA scarring was quantified and PV antra were evaluated for circumferential scarring 3 months post ablation. LA scarring post ablation was comparable across the 4 stages. Most patients had either no (36.8%) or 1 PV (32.6%) antrum circumferentially scarred. Forty-two patients (29%) had recurrent AF over 283 ± 167 days. No recurrences were noted in Utah stage 1. Recurrence was 28% in Utah stage 2, 35% in Utah stage 3, and 56% in Utah stage 4. Recurrence was predicted by circumferential PV scarring in Utah stage 2 and by overall LA wall scarring in Utah stage 3. No recurrence predictors were identified in Utah stage 4.Conclusions: Circumferential PV antral scarring predicts ablation success in mild LA fibrosis, while posterior wall and septal scarring is needed for moderate fibrosis. This may help select the proper candidate and strategy in catheter ablation of AF. (J Cardiovasc Electrophysiol, Vol. 22, pp. 16-22, January 2011)

Research paper thumbnail of Evaluation of the left atrial substrate in patients with lone atrial fibrillation using delayed-enhanced MRI: Implications for disease progression and response to catheter ablation

Heart Rhythm, 2010

BACKGROUND-Lone atrial fibrillation (AF) is thought to be a benign type or an early stage of the ... more BACKGROUND-Lone atrial fibrillation (AF) is thought to be a benign type or an early stage of the disease.

Research paper thumbnail of Real-time magnetic resonance imaging–guided radiofrequency atrial ablation and visualization of lesion formation at 3 Tesla

Heart Rhythm, 2011

Background-MRI allows visualization of location and extent of RF ablation lesion, myocardial scar... more Background-MRI allows visualization of location and extent of RF ablation lesion, myocardial scar formation, and real-time (RT) assessment of lesion formation. In this study, we report a novel 3-Tesla RT-MRI based porcine RF ablation model and visualization of lesion formation in the atrium during RF energy delivery.

Research paper thumbnail of Magnetic Resonance Imaging-Confirmed Ablative Debulking of the Left Atrial Posterior Wall and Septum for Treatment of Persistent Atrial Fibrillation: Rationale and Initial Experience

Journal of Cardiovascular Electrophysiology, 2010

LA Debulking for Atrial Fibrillation. Introduction: Though pulmonary vein (PV) isolation has been... more LA Debulking for Atrial Fibrillation. Introduction: Though pulmonary vein (PV) isolation has been widely adopted for treatment of atrial fibrillation (AF), recurrence rates remain unacceptably high with persistent and longstanding AF. As evidence emerges for non-PV substrate changes in the pathogenesis of AF, more extensive ablation strategies need further study.

Research paper thumbnail of MRI based injury characterization immediately following ablation of atrial fibrillation

A major limitation of catheter ablation for atrial fibrillation is the lack of tools to evaluate ... more A major limitation of catheter ablation for atrial fibrillation is the lack of tools to evaluate the efficacy and extent of lesion creation. Late gadolinium enhanced MRI has been used to detect acute injury following ablation, and scar tissue that forms weeks to months later However, at the earliest imaging time point previously feasible in a clinical setting (<; 24

Research paper thumbnail of Low resolution conductivity estimation to improve source localization

International Congress Series, 2007

Bioelectric source localization in the brain is sensitive to geometry and conductivity properties... more Bioelectric source localization in the brain is sensitive to geometry and conductivity properties of the different head tissues. We propose a method that individually optimizes a realisticallyshaped volume conductor with regard to the conductivities using a simulated annealing optimizer in discrete parameter space. We show that the method is able to simultaneously reconstruct two reference sources and a reference skull:brain conductivity ratio even in the presence of realistic noise. The individually optimized head model can then be used for the analysis of clinical or cognitive data.

Research paper thumbnail of Acute injury immediately post atrial fibrillation ablation defined by MRI

Journal of Cardiovascular Magnetic Resonance, 2010

Research paper thumbnail of SELECTION OF ATRIAL FIBRILLATION ABLATION STRATEGY BASED ON ATRIAL STRUCTURAL REMODELING: A LATE GADOLINIUM ENHANCEMENT-MRI BASED MODEL

Journal of The American College of Cardiology, 2011

Category: 26. Clinical Electrophysiology-Supraventricular Arrhythmias Session-Poster Board Number... more Category: 26. Clinical Electrophysiology-Supraventricular Arrhythmias Session-Poster Board Number: 1123-419

Research paper thumbnail of Dark Regions of No-Reflow on Late Gadolinium Enhancement Magnetic Resonance Imaging Result in Scar Formation After Atrial Fibrillation Ablation

Journal of The American College of Cardiology, 2011

The aim of this study was to assess acute ablation injuries seen on late gadolinium enhancement (... more The aim of this study was to assess acute ablation injuries seen on late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) immediately post-ablation (IPA) and the association with permanent scar 3 months post-ablation (3moPA).

Research paper thumbnail of Echocardiographic left atrial reverse remodeling after catheter ablation of atrial fibrillation is predicted by preablation delayed enhancement of left atrium by magnetic resonance imaging

American Heart Journal, 2010

The substrate for atrial fibrillation (AF) is atrial fibrosis, the hallmark of structural remodel... more The substrate for atrial fibrillation (AF) is atrial fibrosis, the hallmark of structural remodeling (SRM) (1,2). AF begets AF and increasing AF burden leads to structural and functional remodeling, creating a substrate that is favorable for sustaining AF propagation (3) and paroxysmal AF eventually becomes persistent or permanent AF. Catheter ablation of AF results in improvement of symptoms and quality of life, in addition to significantly lowering recurrence rate of AF (4,5). The goal of ablation is to identify and eliminate the AF trigger(s) and modify the substrate of AF to halt the vicious cycle of arrhythmia and remodeling.

Research paper thumbnail of C-REACTIVE PROTEIN LEVELS AND PROGRESSION OF ATRIAL FIBROSIS DETECTED BY DE-MRI IN PATIENTS WITH ATRIAL FIBRILLATION

Journal of The American College of Cardiology, 2011

: 177 patients (109 male; 68.5±0.7 years old) underwent DE-MRI to quantify left atrial structural... more : 177 patients (109 male; 68.5±0.7 years old) underwent DE-MRI to quantify left atrial structural remodeling (SRM) as a marker for atrial fibrosis. Based on the degree of SRM patients were staged into 4 groups: Utah I (≤5% LA wall enhancement), Utah II (>5% to ≤20%), Utah III (>20% to ≤35%) and Utah IV (>35%) . CRP was measured 5±33 days to DE-MRI examination. Highest level of CRP was found in patients with Utah II (0.61±0.71 mg/dl). Course of CRP showed a significant increase from Utah I to Utah II (0.2±0.17 mg/dl vs. 0.61±0.71 mg/dl; p=0.021) and a decrease from Utah II. To Utah III and to Utah IV ). Levels of CRP were comparable in Utah I and Utah IV (0.2±0.17 vs. 0.43±0.53 mg/dl; p =0.338) Conclusion: From our preliminary experience inflammation process is involved in the early stages of atrial structural remodeling in patients with AF as detected using DE-MRI.

Research paper thumbnail of Atrial Fibrosis Helps Select the Appropriate Patient and Strategy in Catheter Ablation of Atrial Fibrillation: A DE-MRI Guided Approach

Journal of Cardiovascular Electrophysiology, 2010

MRI for AF Patient Selection and Ablation Approach. Introduction: Left atrial (LA) fibrosis and a... more MRI for AF Patient Selection and Ablation Approach. Introduction: Left atrial (LA) fibrosis and ablation related scarring are major predictors of success in rhythm control of atrial fibrillation (AF). We used delayed enhancement MRI (DE-MRI) to stratify AF patients based on pre-ablation fibrosis and also to evaluate ablation-induced scarring in order to identify predictors of a successful ablation.Methods and Results: One hundred and forty-four patients were staged by percent of fibrosis quantified with DE-MRI, relative to the LA wall volume: minimal or Utah stage 1; <5%, mild or Utah stage 2; 5–20%, moderate or Utah stage 3; 20–35%, and extensive or Utah stage 4; >35%. All patients underwent pulmonary vein (PV) isolation and posterior wall and septal debulking. Overall, LA scarring was quantified and PV antra were evaluated for circumferential scarring 3 months post ablation. LA scarring post ablation was comparable across the 4 stages. Most patients had either no (36.8%) or 1 PV (32.6%) antrum circumferentially scarred. Forty-two patients (29%) had recurrent AF over 283 ± 167 days. No recurrences were noted in Utah stage 1. Recurrence was 28% in Utah stage 2, 35% in Utah stage 3, and 56% in Utah stage 4. Recurrence was predicted by circumferential PV scarring in Utah stage 2 and by overall LA wall scarring in Utah stage 3. No recurrence predictors were identified in Utah stage 4.Conclusions: Circumferential PV antral scarring predicts ablation success in mild LA fibrosis, while posterior wall and septal scarring is needed for moderate fibrosis. This may help select the proper candidate and strategy in catheter ablation of AF. (J Cardiovasc Electrophysiol, Vol. 22, pp. 16-22, January 2011)

Research paper thumbnail of USING REAL TIME MRI TO VISUALIZE AND ABLATE GAPS IN RADIOFREQUENCY ABLATION LESION SETS IN THE ATRIUM

Journal of The American College of Cardiology, 2011

A is a delayed enhancement coronal image showing the two lesions and the gap in between. Lesions ... more A is a delayed enhancement coronal image showing the two lesions and the gap in between. Lesions indicated by green and white arrowheads were made in the EP lab using fluoroscopy. Panel B shows the real time MRI catheter guidance screen shot showing the lesions made in the EP lab and the MRI compatible catheter. Panel C is a delayed enhancement coronal image after ablation confirming the ablation of the gap area. Yellow arrowhead indicates the lesion made in the MRI scanner. Panel D is gross pathology showing the two lesions made in the EP lab with the gap ablated in the MRI.

Research paper thumbnail of REVERSE REMODELING OF LEFT ATRIUM AFTER CATHETER ABLATION OF ATRIAL FIBRILLATION IN EARLY AND ADVANCED STAGES OF LEFT ATRIAL STRUCTURAL REMODELING BY DELAYED ENHANCEMENT-MRI

Journal of The American College of Cardiology, 2010

Background: Atrial fibrosis is a hallmark of atrial structural remodeling (SRM) and leads to func... more Background: Atrial fibrosis is a hallmark of atrial structural remodeling (SRM) and leads to functional impairment of left atrium (LA) and persistence of atrial fibrillation (AF). This study assesses LA reverse remodeling after catheter ablation of AF in early and advanced stages of LA SRM.

Research paper thumbnail of The influence of volume conduction effects on the EEG/MEG reconstruction of the sources of the Early Left Anterior Negativity

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2004

To achieve a deeper understanding of language processing in the human brain, scientists and clini... more To achieve a deeper understanding of language processing in the human brain, scientists and clinicians use Electroencephalography (EEG) and Magnetoencephalography (MEG) inverse methods to reconstruct sources of Event Related Potentials. There exists a persistent uncertainty regarding the influence of volume conduction effects such as the anisotropy of tissue conductivity of the skull and the white matter layers on the inverse results. In this paper, we will study the sensitivity to anisotropy of the source reconstruction of the Early Left Anterior Negativity (ELAN) component in language processing. For EEG, the presence of tissue anisotropy substantially compromises the restoration ability of an L1-norm current density approach. The centers of activity are strongly shifted along the Sylvian fissure in the anterior direction. In contrast, MEG in combination with the L1 norm approach is able to reconstruct the main features of the ELAN source distribution even in the presence of aniso...

Research paper thumbnail of Improved EEG source analysis using low-resolution conductivity estimation in a four-compartment finite element head model

Human Brain Mapping, 2009

Bioelectric source analysis in the human brain from scalp electroencephalography (EEG) signals is... more Bioelectric source analysis in the human brain from scalp electroencephalography (EEG) signals is sensitive to geometry and conductivity properties of the different head tissues. We propose a low resolution conductivity estimation (LRCE) method using simulated annealing optimization on high resolution finite element models that individually optimizes a realistically-shaped four-layer volume conductor with regard to the brain and skull compartment conductivities. As input data, the method needs T1-and PD-weighted magnetic resonance images for an improved modeling of the skull and the cerebrospinal fluid compartment and evoked potential data with high signal-tonoise ratio (SNR). Our simulation studies showed that for EEG data with realistic SNR, the LRCE method was able to simultaneously reconstruct both the brain and the skull conductivity together with the underlying dipole source and provided an improved source analysis result. We have also demonstrated the feasibility and applicability of the new method to simultaneously estimate brain and skull conductivity and a somatosensory source from measured tactile somatosensory evoked potentials of a human subject. Our results show the viability of an approach that computes its own conductivity values and thus reduces the dependence on assigning values from the literature and likely produces a more robust estimate of current sources. Using the LRCE method, the individually optimized four-compartment volume conductor model can in a second step be used for the analysis of clinical or cognitive data acquired from the same subject.

Research paper thumbnail of Influence of tissue conductivity anisotropy on EEG/MEG field and return current computation in a realistic head model: A simulation and visualization study using high-resolution finite element modeling

NeuroImage, 2006

To achieve a deeper understanding of the brain, scientists, and clinicians use electroencephalogr... more To achieve a deeper understanding of the brain, scientists, and clinicians use electroencephalography (EEG) and magnetoencephalography (MEG) inverse methods to reconstruct sources in the cortical sheet of the human brain. The influence of structural and electrical anisotropy in both the skull and the white matter on the EEG and MEG source reconstruction is not well understood.

Research paper thumbnail of New Magnetic Resonance Imaging-Based Method for Defining the Extent of Left Atrial Wall Injury After the Ablation of Atrial Fibrillation

In this paper, we describe a delayed enhancement MRI method which detects left atrial wall injury... more In this paper, we describe a delayed enhancement MRI method which detects left atrial wall injury following ablation in patients with atrial fibrillation. We imaged and quantified the extent of injury in 46 patients using a respiratory navigated MRI sequence. There was a strong relationship noted between the degree of left atrial wall injury and freedom from the arrhythmia at three month follow-up. Using the described methodology, it appears possible to image and assess the degree of injury due to RF injury following ablation therapy for atrial fibrillation.

Research paper thumbnail of Association of Left Atrial Fibrosis Detected by Delayed-Enhancement Magnetic Resonance Imaging and the Risk of Stroke in Patients With Atrial Fibrillation

Journal of The American College of Cardiology, 2011

Objectives-This study tried to determine the association between left atrial (LA) fibrosis, detec... more Objectives-This study tried to determine the association between left atrial (LA) fibrosis, detected using delayed-enhanced magnetic resonance imaging (DE-MRI), and the CHADS 2 score (point system based on individual clinical risk factors including congestive heart failure, hypertension, age, diabetes, and prior stroke) variables, specifically stroke.

Research paper thumbnail of Dark Regions of No-Reflow on Late Gadolinium Enhancement Magnetic Resonance Imaging Result in Scar Formation After Atrial Fibrillation Ablation

Journal of the American College of Cardiology, 2011

Research paper thumbnail of Atrial Fibrosis Helps Select the Appropriate Patient and Strategy in Catheter Ablation of Atrial Fibrillation: A DE-MRI Guided Approach

Journal of Cardiovascular Electrophysiology, 2010

MRI for AF Patient Selection and Ablation Approach. Introduction: Left atrial (LA) fibrosis and a... more MRI for AF Patient Selection and Ablation Approach. Introduction: Left atrial (LA) fibrosis and ablation related scarring are major predictors of success in rhythm control of atrial fibrillation (AF). We used delayed enhancement MRI (DE-MRI) to stratify AF patients based on pre-ablation fibrosis and also to evaluate ablation-induced scarring in order to identify predictors of a successful ablation.Methods and Results: One hundred and forty-four patients were staged by percent of fibrosis quantified with DE-MRI, relative to the LA wall volume: minimal or Utah stage 1; <5%, mild or Utah stage 2; 5–20%, moderate or Utah stage 3; 20–35%, and extensive or Utah stage 4; >35%. All patients underwent pulmonary vein (PV) isolation and posterior wall and septal debulking. Overall, LA scarring was quantified and PV antra were evaluated for circumferential scarring 3 months post ablation. LA scarring post ablation was comparable across the 4 stages. Most patients had either no (36.8%) or 1 PV (32.6%) antrum circumferentially scarred. Forty-two patients (29%) had recurrent AF over 283 ± 167 days. No recurrences were noted in Utah stage 1. Recurrence was 28% in Utah stage 2, 35% in Utah stage 3, and 56% in Utah stage 4. Recurrence was predicted by circumferential PV scarring in Utah stage 2 and by overall LA wall scarring in Utah stage 3. No recurrence predictors were identified in Utah stage 4.Conclusions: Circumferential PV antral scarring predicts ablation success in mild LA fibrosis, while posterior wall and septal scarring is needed for moderate fibrosis. This may help select the proper candidate and strategy in catheter ablation of AF. (J Cardiovasc Electrophysiol, Vol. 22, pp. 16-22, January 2011)

Research paper thumbnail of Evaluation of the left atrial substrate in patients with lone atrial fibrillation using delayed-enhanced MRI: Implications for disease progression and response to catheter ablation

Heart Rhythm, 2010

BACKGROUND-Lone atrial fibrillation (AF) is thought to be a benign type or an early stage of the ... more BACKGROUND-Lone atrial fibrillation (AF) is thought to be a benign type or an early stage of the disease.

Research paper thumbnail of Real-time magnetic resonance imaging–guided radiofrequency atrial ablation and visualization of lesion formation at 3 Tesla

Heart Rhythm, 2011

Background-MRI allows visualization of location and extent of RF ablation lesion, myocardial scar... more Background-MRI allows visualization of location and extent of RF ablation lesion, myocardial scar formation, and real-time (RT) assessment of lesion formation. In this study, we report a novel 3-Tesla RT-MRI based porcine RF ablation model and visualization of lesion formation in the atrium during RF energy delivery.

Research paper thumbnail of Magnetic Resonance Imaging-Confirmed Ablative Debulking of the Left Atrial Posterior Wall and Septum for Treatment of Persistent Atrial Fibrillation: Rationale and Initial Experience

Journal of Cardiovascular Electrophysiology, 2010

LA Debulking for Atrial Fibrillation. Introduction: Though pulmonary vein (PV) isolation has been... more LA Debulking for Atrial Fibrillation. Introduction: Though pulmonary vein (PV) isolation has been widely adopted for treatment of atrial fibrillation (AF), recurrence rates remain unacceptably high with persistent and longstanding AF. As evidence emerges for non-PV substrate changes in the pathogenesis of AF, more extensive ablation strategies need further study.

Research paper thumbnail of MRI based injury characterization immediately following ablation of atrial fibrillation

A major limitation of catheter ablation for atrial fibrillation is the lack of tools to evaluate ... more A major limitation of catheter ablation for atrial fibrillation is the lack of tools to evaluate the efficacy and extent of lesion creation. Late gadolinium enhanced MRI has been used to detect acute injury following ablation, and scar tissue that forms weeks to months later However, at the earliest imaging time point previously feasible in a clinical setting (<; 24

Research paper thumbnail of Low resolution conductivity estimation to improve source localization

International Congress Series, 2007

Bioelectric source localization in the brain is sensitive to geometry and conductivity properties... more Bioelectric source localization in the brain is sensitive to geometry and conductivity properties of the different head tissues. We propose a method that individually optimizes a realisticallyshaped volume conductor with regard to the conductivities using a simulated annealing optimizer in discrete parameter space. We show that the method is able to simultaneously reconstruct two reference sources and a reference skull:brain conductivity ratio even in the presence of realistic noise. The individually optimized head model can then be used for the analysis of clinical or cognitive data.

Research paper thumbnail of Acute injury immediately post atrial fibrillation ablation defined by MRI

Journal of Cardiovascular Magnetic Resonance, 2010

Research paper thumbnail of SELECTION OF ATRIAL FIBRILLATION ABLATION STRATEGY BASED ON ATRIAL STRUCTURAL REMODELING: A LATE GADOLINIUM ENHANCEMENT-MRI BASED MODEL

Journal of The American College of Cardiology, 2011

Category: 26. Clinical Electrophysiology-Supraventricular Arrhythmias Session-Poster Board Number... more Category: 26. Clinical Electrophysiology-Supraventricular Arrhythmias Session-Poster Board Number: 1123-419

Research paper thumbnail of Dark Regions of No-Reflow on Late Gadolinium Enhancement Magnetic Resonance Imaging Result in Scar Formation After Atrial Fibrillation Ablation

Journal of The American College of Cardiology, 2011

The aim of this study was to assess acute ablation injuries seen on late gadolinium enhancement (... more The aim of this study was to assess acute ablation injuries seen on late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) immediately post-ablation (IPA) and the association with permanent scar 3 months post-ablation (3moPA).

Research paper thumbnail of Echocardiographic left atrial reverse remodeling after catheter ablation of atrial fibrillation is predicted by preablation delayed enhancement of left atrium by magnetic resonance imaging

American Heart Journal, 2010

The substrate for atrial fibrillation (AF) is atrial fibrosis, the hallmark of structural remodel... more The substrate for atrial fibrillation (AF) is atrial fibrosis, the hallmark of structural remodeling (SRM) (1,2). AF begets AF and increasing AF burden leads to structural and functional remodeling, creating a substrate that is favorable for sustaining AF propagation (3) and paroxysmal AF eventually becomes persistent or permanent AF. Catheter ablation of AF results in improvement of symptoms and quality of life, in addition to significantly lowering recurrence rate of AF (4,5). The goal of ablation is to identify and eliminate the AF trigger(s) and modify the substrate of AF to halt the vicious cycle of arrhythmia and remodeling.

Research paper thumbnail of C-REACTIVE PROTEIN LEVELS AND PROGRESSION OF ATRIAL FIBROSIS DETECTED BY DE-MRI IN PATIENTS WITH ATRIAL FIBRILLATION

Journal of The American College of Cardiology, 2011

: 177 patients (109 male; 68.5±0.7 years old) underwent DE-MRI to quantify left atrial structural... more : 177 patients (109 male; 68.5±0.7 years old) underwent DE-MRI to quantify left atrial structural remodeling (SRM) as a marker for atrial fibrosis. Based on the degree of SRM patients were staged into 4 groups: Utah I (≤5% LA wall enhancement), Utah II (>5% to ≤20%), Utah III (>20% to ≤35%) and Utah IV (>35%) . CRP was measured 5±33 days to DE-MRI examination. Highest level of CRP was found in patients with Utah II (0.61±0.71 mg/dl). Course of CRP showed a significant increase from Utah I to Utah II (0.2±0.17 mg/dl vs. 0.61±0.71 mg/dl; p=0.021) and a decrease from Utah II. To Utah III and to Utah IV ). Levels of CRP were comparable in Utah I and Utah IV (0.2±0.17 vs. 0.43±0.53 mg/dl; p =0.338) Conclusion: From our preliminary experience inflammation process is involved in the early stages of atrial structural remodeling in patients with AF as detected using DE-MRI.

Research paper thumbnail of Atrial Fibrosis Helps Select the Appropriate Patient and Strategy in Catheter Ablation of Atrial Fibrillation: A DE-MRI Guided Approach

Journal of Cardiovascular Electrophysiology, 2010

MRI for AF Patient Selection and Ablation Approach. Introduction: Left atrial (LA) fibrosis and a... more MRI for AF Patient Selection and Ablation Approach. Introduction: Left atrial (LA) fibrosis and ablation related scarring are major predictors of success in rhythm control of atrial fibrillation (AF). We used delayed enhancement MRI (DE-MRI) to stratify AF patients based on pre-ablation fibrosis and also to evaluate ablation-induced scarring in order to identify predictors of a successful ablation.Methods and Results: One hundred and forty-four patients were staged by percent of fibrosis quantified with DE-MRI, relative to the LA wall volume: minimal or Utah stage 1; <5%, mild or Utah stage 2; 5–20%, moderate or Utah stage 3; 20–35%, and extensive or Utah stage 4; >35%. All patients underwent pulmonary vein (PV) isolation and posterior wall and septal debulking. Overall, LA scarring was quantified and PV antra were evaluated for circumferential scarring 3 months post ablation. LA scarring post ablation was comparable across the 4 stages. Most patients had either no (36.8%) or 1 PV (32.6%) antrum circumferentially scarred. Forty-two patients (29%) had recurrent AF over 283 ± 167 days. No recurrences were noted in Utah stage 1. Recurrence was 28% in Utah stage 2, 35% in Utah stage 3, and 56% in Utah stage 4. Recurrence was predicted by circumferential PV scarring in Utah stage 2 and by overall LA wall scarring in Utah stage 3. No recurrence predictors were identified in Utah stage 4.Conclusions: Circumferential PV antral scarring predicts ablation success in mild LA fibrosis, while posterior wall and septal scarring is needed for moderate fibrosis. This may help select the proper candidate and strategy in catheter ablation of AF. (J Cardiovasc Electrophysiol, Vol. 22, pp. 16-22, January 2011)

Research paper thumbnail of USING REAL TIME MRI TO VISUALIZE AND ABLATE GAPS IN RADIOFREQUENCY ABLATION LESION SETS IN THE ATRIUM

Journal of The American College of Cardiology, 2011

A is a delayed enhancement coronal image showing the two lesions and the gap in between. Lesions ... more A is a delayed enhancement coronal image showing the two lesions and the gap in between. Lesions indicated by green and white arrowheads were made in the EP lab using fluoroscopy. Panel B shows the real time MRI catheter guidance screen shot showing the lesions made in the EP lab and the MRI compatible catheter. Panel C is a delayed enhancement coronal image after ablation confirming the ablation of the gap area. Yellow arrowhead indicates the lesion made in the MRI scanner. Panel D is gross pathology showing the two lesions made in the EP lab with the gap ablated in the MRI.

Research paper thumbnail of REVERSE REMODELING OF LEFT ATRIUM AFTER CATHETER ABLATION OF ATRIAL FIBRILLATION IN EARLY AND ADVANCED STAGES OF LEFT ATRIAL STRUCTURAL REMODELING BY DELAYED ENHANCEMENT-MRI

Journal of The American College of Cardiology, 2010

Background: Atrial fibrosis is a hallmark of atrial structural remodeling (SRM) and leads to func... more Background: Atrial fibrosis is a hallmark of atrial structural remodeling (SRM) and leads to functional impairment of left atrium (LA) and persistence of atrial fibrillation (AF). This study assesses LA reverse remodeling after catheter ablation of AF in early and advanced stages of LA SRM.