Treatment-Related Changes in Left Atrial Structure in Atrial Fibrillation: Findings From the CABANA Imaging Substudy

[Figure: see text].

Validation of the BRODERS classifier (Benign versus aggRessive nODule Evaluation using Radiomic Stratification), a novel HRCT-based radiomic classifier for indeterminate pulmonary nodules

INTRODUCTION

Implementation of low-dose chest computed tomography (CT) lung cancer screening and the ever-increasing use of cross-sectional imaging are resulting in the identification of many screen- and incidentally detected indeterminate pulmonary nodules. While the management of nodules with low or high pre-test probability of malignancy is relatively straightforward, those with intermediate pre-test probability commonly require advanced imaging or biopsy. Noninvasive risk stratification tools are highly desirable.

METHODS

We previously developed the BRODERS classifier (Benign versus aggRessive nODule Evaluation using Radiomic Stratification), a conventional predictive radiomic model based on eight imaging features capturing nodule location, shape, size, texture and surface characteristics. Herein we report its external validation using a dataset of incidentally identified lung nodules (Vanderbilt University Lung Nodule Registry) in comparison to the Brock model. Area under the curve (AUC), as well as sensitivity, specificity, negative and positive predictive values were calculated.

RESULTS

For the entire Vanderbilt validation set (n=170, 54% malignant), the AUC was 0.87 (95% CI 0.81-0.92) for the Brock model and 0.90 (95% CI 0.85-0.94) for the BRODERS model. Using the optimal cut-off determined by Youden's index, the sensitivity was 92.3%, the specificity was 62.0%, the positive (PPV) and negative predictive values (NPV) were 73.7% and 87.5%, respectively. For nodules with intermediate pre-test probability of malignancy, Brock score of 5-65% (n=97), the sensitivity and specificity were 94% and 46%, respectively, the PPV was 78.4% and the NPV was 79.2%.

CONCLUSIONS

The BRODERS radiomic predictive model performs well on an independent dataset and may facilitate the management of indeterminate pulmonary nodules.

Effect of Catheter Ablation vs Antiarrhythmic Drug Therapy on Mortality, Stroke, Bleeding, and Cardiac Arrest Among Patients With Atrial Fibrillation: The CABANA Randomized Clinical Trial

IMPORTANCE

Catheter ablation is effective in restoring sinus rhythm in atrial fibrillation (AF), but its effects on long-term mortality and stroke risk are uncertain.

OBJECTIVE

To determine whether catheter ablation is more effective than conventional medical therapy for improving outcomes in AF.

DESIGN, SETTING, AND PARTICIPANTS

The Catheter Ablation vs Antiarrhythmic Drug Therapy for Atrial Fibrillation trial is an investigator-initiated, open-label, multicenter, randomized trial involving 126 centers in 10 countries. A total of 2204 symptomatic patients with AF aged 65 years and older or younger than 65 years with 1 or more risk factors for stroke were enrolled from November 2009 to April 2016, with follow-up through December 31, 2017.

INTERVENTIONS

The catheter ablation group (n = 1108) underwent pulmonary vein isolation, with additional ablative procedures at the discretion of site investigators. The drug therapy group (n = 1096) received standard rhythm and/or rate control drugs guided by contemporaneous guidelines.

MAIN OUTCOMES AND MEASURES

The primary end point was a composite of death, disabling stroke, serious bleeding, or cardiac arrest. Among 13 prespecified secondary end points, 3 are included in this report: all-cause mortality; total mortality or cardiovascular hospitalization; and AF recurrence.

RESULTS

Of the 2204 patients randomized (median age, 68 years; 37.2% female; 42.9% had paroxysmal AF and 57.1% had persistent AF), 89.3% completed the trial. Of the patients assigned to catheter ablation, 1006 (90.8%) underwent the procedure. Of the patients assigned to drug therapy, 301 (27.5%) ultimately received catheter ablation. In the intention-to-treat analysis, over a median follow-up of 48.5 months, the primary end point occurred in 8.0% (n = 89) of patients in the ablation group vs 9.2% (n = 101) of patients in the drug therapy group (hazard ratio [HR], 0.86 [95% CI, 0.65-1.15]; P = .30). Among the secondary end points, outcomes in the ablation group vs the drug therapy group, respectively, were 5.2% vs 6.1% for all-cause mortality (HR, 0.85 [95% CI, 0.60-1.21]; P = .38), 51.7% vs 58.1% for death or cardiovascular hospitalization (HR, 0.83 [95% CI, 0.74-0.93]; P = .001), and 49.9% vs 69.5% for AF recurrence (HR, 0.52 [95% CI, 0.45-0.60]; P < .001).

CONCLUSIONS AND RELEVANCE

Among patients with AF, the strategy of catheter ablation, compared with medical therapy, did not significantly reduce the primary composite end point of death, disabling stroke, serious bleeding, or cardiac arrest. However, the estimated treatment effect of catheter ablation was affected by lower-than-expected event rates and treatment crossovers, which should be considered in interpreting the results of the trial.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00911508.

Correction: Novel high-resolution computed tomography-based radiomic classifier for screen-identified pulmonary nodules in the National Lung Screening Trial

[This corrects the article DOI: 10.1371/journal.pone.0196910.].

Novel high-resolution computed tomography-based radiomic classifier for screen-identified pulmonary nodules in the National Lung Screening Trial

Purpose

Optimization of the clinical management of screen-detected lung nodules is needed to avoid unnecessary diagnostic interventions. Herein we demonstrate the potential value of a novel radiomics-based approach for the classification of screen-detected indeterminate nodules.

Material and methods

Independent quantitative variables assessing various radiologic nodule features such as sphericity, flatness, elongation, spiculation, lobulation and curvature were developed from the NLST dataset using 726 indeterminate nodules (all ≥ 7 mm, benign, n = 318 and malignant, n = 408). Multivariate analysis was performed using least absolute shrinkage and selection operator (LASSO) method for variable selection and regularization in order to enhance the prediction accuracy and interpretability of the multivariate model. The bootstrapping method was then applied for the internal validation and the optimism-corrected AUC was reported for the final model.

Results

Eight of the originally considered 57 quantitative radiologic features were selected by LASSO multivariate modeling. These 8 features include variables capturing Location: vertical location (Offset carina centroid z), Size: volume estimate (Minimum enclosing brick), Shape: flatness, Density: texture analysis (Score Indicative of Lesion/Lung Aggression/Abnormality (SILA) texture), and surface characteristics: surface complexity (Maximum shape index and Average shape index), and estimates of surface curvature (Average positive mean curvature and Minimum mean curvature), all with P<0.01. The optimism-corrected AUC for these 8 features is 0.939.

Conclusions

Our novel radiomic LDCT-based approach for indeterminate screen-detected nodule characterization appears extremely promising however independent external validation is needed.

Catheter Ablation versus Antiarrhythmic Drug Therapy for Atrial Fibrillation (CABANA) Trial: Study Rationale and Design

The Catheter Ablation Versus Anti-arrhythmic Drug Therapy for Atrial Fibrillation (CABANA, NCT00911508)(1) trial is testing the hypothesis that the treatment strategy of percutaneous left atrial catheter ablation for the purpose of eliminating atrial fibrillation (AF) is superior to current state-of-the-art pharmacologic therapy. This international 140-center clinical trial was designed to randomize 2200 patients to a strategy of catheter ablation versus state-of-the-art rate or rhythm control drug therapy. Inclusion criteria include: 1) age > 65, or ≤65 with≥ 1 risk factor for stroke, 2) documented AF warranting treatment, and 3) eligibility for both catheter ablation and≥ 2 anti-arrhythmic or≥ 2 rate control drugs. Patients were followed every 3 to 6 months (median 4 years) and underwent repeat trans-telephonic monitoring, Holter monitoring, and CT/MR in a subgroup of patient studies to assess the impact of treatment on AF recurrence and atrial structure.

With 1100 patients in each treatment arm, CABANA is projected to have 90% power for detecting a 30% relative reduction in the primary composite endpoint of total mortality, disabling stroke, serious bleeding, or cardiac arrest. Secondary endpoints include total mortality; mortality or cardiovascular hospitalization; a combination of mortality, stroke, hospitalization for heart failure or acute coronary artery events; cardiovascular death alone; and heart failure death, as well as AF recurrence, quality of life, and cost effectiveness. At a time when AF incidence is rising rapidly, CABANA will provide critical evidence with which to guide therapy and shape health care policy related to AF for years to come.

Noninvasive Computed Tomography-based Risk Stratification of Lung Adenocarcinomas in the National Lung Screening Trial

RATIONALE

Screening for lung cancer using low-dose computed tomography (CT) reduces lung cancer mortality. However, in addition to a high rate of benign nodules, lung cancer screening detects a large number of indolent cancers that generally belong to the adenocarcinoma spectrum. Individualized management of screen-detected adenocarcinomas would be facilitated by noninvasive risk stratification.

OBJECTIVES

To validate that Computer-Aided Nodule Assessment and Risk Yield (CANARY), a novel image analysis software, successfully risk stratifies screen-detected lung adenocarcinomas based on clinical disease outcomes.

METHODS

We identified retrospective 294 eligible patients diagnosed with lung adenocarcinoma spectrum lesions in the low-dose CT arm of the National Lung Screening Trial. The last low-dose CT scan before the diagnosis of lung adenocarcinoma was analyzed using CANARY blinded to clinical data. Based on their parametric CANARY signatures, all the lung adenocarcinoma nodules were risk stratified into three groups. CANARY risk groups were compared using survival analysis for progression-free survival.

MEASUREMENTS AND MAIN RESULTS

A total of 294 patients were included in the analysis. Kaplan-Meier analysis of all the 294 adenocarcinoma nodules stratified into the Good, Intermediate, and Poor CANARY risk groups yielded distinct progression-free survival curves (P < 0.0001). This observation was confirmed in the unadjusted and adjusted (age, sex, race, and smoking status) progression-free survival analysis of all stage I cases.

CONCLUSIONS

CANARY allows the noninvasive risk stratification of lung adenocarcinomas into three groups with distinct post-treatment progression-free survival. Our results suggest that CANARY could ultimately facilitate individualized management of incidentally or screen-detected lung adenocarcinomas.

Rezūm System Water Vapor Treatment for Lower Urinary Tract Symptoms/Benign Prostatic Hyperplasia: Validation of Convective Thermal Energy Transfer and Characterization With Magnetic Resonance Imaging and 3-Dimensional Renderings

OBJECTIVE

To evaluate by magnetic resonance imaging the physical effects of convective thermal energy transfer with water vapor as a means of treating lower urinary tract symptoms due to benign prostatic hyperplasia.

METHODS

Sixty-five men with lower urinary tract symptoms were treated with the Rezūm System by transurethral intraprostatic injection of water vapor. A group of 45 of these men consented to undergo a series of gadolinium-enhanced magnetic resonance imagings of the prostate after treatment to monitor the size and location of ablative lesions, their time course of resolution, and the corresponding change in prostate tissue volume. Visualization was conducted at 1 week, 1, 3, and 6 months after treatment.

RESULTS

Outcomes were available for 44 patients. Convective thermal lesions were limited to the transition zone and correlated with targeted treatment locations. At 1 week after treatment, the mean volume of ablative lesions was 8.2 cm(3) (0.5-24.0 cm(3)). At 6 months, whole prostate volume was reduced by a mean of 28.9% and transition zone volume by 38.0% as compared with baseline 1-week images. At 3 and 6 months after treatment, the lesion volumes had reduced by 91.5% and 95.1%, respectively. Lesions remained within the targeted treatment zone without compromising integrity of the bladder, rectum, or striated urinary sphincter.

CONCLUSION

This imaging study confirms the delivery of convective water vapor technology to create thermal lesions in the prostate tissue. Lesions generated underwent near complete resolution by 3 and 6 months after treatment with a concomitant one-third reduction in overall prostate and transition zone volumes.

Active relearning for robust supervised training of emphysema patterns

Radiologists are adept at recognizing the character and extent of lung parenchymal abnormalities in computed tomography (CT) scans. However, the inconsistent differential diagnosis due to subjective aggregation necessitates the exploration of automated classification based on supervised or unsupervised learning. The robustness of supervised learning depends on the training samples. Towards optimizing emphysema classification, we introduce a physician-in-the-loop feedback approach to minimize ambiguity in the selected training samples. An experienced thoracic radiologist selected 412 regions of interest (ROIs) across 15 datasets to represent 124, 129, 139 and 20 training samples of mild, moderate, severe emphysema and normal appearance, respectively. Using multi-view (multiple metrics to capture complementary features) inductive learning, an ensemble of seven un-optimized support vector models (SVM) each based on a specific metric was constructed in less than 6 s. The training samples were classified using seven SVM models and consensus labels were created using majority voting. In the active relearning phase, the ensemble-expert label conflicts were resolved by the expert. The efficacy and generality of active relearning feedback was assessed in the optimized parameter space of six general purpose classifiers across the seven dissimilarity metrics. The proposed just-in-time active relearning feedback with un-optimized SVMs yielded 15 % increase in classification accuracy and 25 % reduction in the number of support vectors. The average improvement in accuracy of six classifiers in their optimized parameter space was 21 %. The proposed cooperative feedback method enhances the quality of training samples used to construct automated classification of emphysematous CT scans. Such an approach could lead to substantial improvement in quantification of emphysema.

The effect of elastic modulus on ablation catheter contact area

Cardiac ablation consists of navigating a catheter into the heart and delivering RF energy to electrically isolate tissue regions that generate or propagate arrhythmia. Besides the challenges of accurate and precise targeting of the arrhythmic sites within the beating heart, limited information is currently available to the cardiologist regarding intricate electrode-tissue contact, which directly impacts the quality of produced lesions. Recent advances in ablation catheter design provide intra-procedural estimates of tissue-catheter contact force, but the most direct indicator of lesion quality for any particular energy level and duration is the tissue-catheter contact area, and that is a function of not only force, but catheter pose and material elasticity as well. In this experiment, we have employed real-time ultrasound (US) imaging to determine the complete interaction between the ablation electrode and tissue to accurately estimate contact, which will help to better understand the effect of catheter pose and position relative to the tissue. By simultaneously recording tracked position, force reading and US image of the ablation catheter, the differing material properties of polyvinyl alcohol cryogel^[1] phantoms are shown to produce varying amounts of tissue depression and contact area (implying varying lesion quality) for equivalent force readings. We have shown that the elastic modulus significantly affects the surface-contact area between the catheter and tissue at any level of contact force. Thus we provide evidence that a prescribed level of catheter force may not always provide sufficient contact area to produce an effective ablation lesion in the prescribed ablation time.

Simulated evaluation of an intraoperative surface modeling method for catheter ablation by a real phantom simulation experiment

In this work, we propose a phantom experiment method to quantitatively evaluate an intraoperative left-atrial modeling update method. In prior work, we proposed an update procedure which updates the preoperative surface model with information from real-time tracked 2D ultrasound. Prior studies did not evaluate the reconstruction using an anthropomorphic phantom. In this approach, a silicone heart phantom (based on a high resolution human atrial surface model reconstructed from CT images) was made as simulated atriums. A surface model of the left atrium of the phantom was deformed by a morphological operation - simulating the shape difference caused by organ deformation between pre-operative scanning and intra-operative guidance. During the simulated procedure, a tracked ultrasound catheter was inserted into right atrial phantom - scanning the left atrial phantom in a manner mimicking the cardiac ablation procedure. By merging the preoperative model and the intraoperative ultrasound images, an intraoperative left atrial model was reconstructed. According to results, the reconstruction error of the modeling method is smaller than the initial geometric difference caused by organ deformation. As the area of the left atrial phantom scanned by ultrasound increases, the reconstruction error of the intraoperative surface model decreases. The study validated the efficacy of the modeling method.

Analysis of Left Atrial Respiratory and Cardiac Motion for Cardiac Ablation Therapy

Cardiac ablation therapy is often guided by models built from preoperative computed tomography (CT) or magnetic resonance imaging (MRI) scans. One of the challenges in guiding a procedure from a preoperative model is properly synching the preoperative models with cardiac and respiratory motion through computational motion models. In this paper, we describe a methodology for evaluating cardiac and respiratory motion in the left atrium and pulmonary veins of a beating canine heart. Cardiac catheters were used to place metal clips within and near the pulmonary veins and left atrial appendage under fluoroscopic and ultrasound guidance and a contrast-enhanced, 64-slice multidetector CT scan was collected with the clips in place. Each clip was segmented from the CT scan at each of the five phases of the cardiac cycle at both end-inspiration and end-expiration. The centroid of each segmented clip was computed and used to evaluate both cardiac and respiratory motion of the left atrium. A total of three canine studies were completed, with 4 clips analyzed in the first study, 5 clips in the second study, and 2 clips in the third study. Mean respiratory displacement was 0.2±1.8 mm in the medial/lateral direction, 4.7±4.4 mm in the anterior/posterior direction (moving anterior on inspiration), and 9.0±5.0 mm superior/inferior (moving inferior with inspiration). At end inspiration, the mean left atrial cardiac motion at the clip locations was 1.5±1.3 mm in the medial/lateral direction, and 2.1±2.0 mm in the anterior/posterior and 1.3±1.2 mm superior/inferior directions. At end expiration, the mean left atrial cardiac motion at the clip locations was 2.0±1.5 mm in the medial/lateral direction, 3.0±1.8 mm in the anterior/posterior direction, and 1.5±1.5 mm in the superior/inferior directions.

Measurements of the left atrium and pulmonary veins for analysis of reverse structural remodeling following cardiac ablation therapy

RATIONALE AND OBJECTIVES

Geometric analysis of the left atrium and pulmonary veins is important for assessing reverse structural remodeling following cardiac ablation therapy. Most volumetric analysis techniques, however, require laborious manual tracing of image cross-sections. Pulmonary vein diameters are typically measured at the junction between the left atrium and pulmonary veins, called the pulmonary vein ostia, with manually drawn lines on volume renderings or in image slices. In this work, we describe a technique for making semi-automatic measurements of left atrial volume and pulmonary vein diameters from high resolution CT scans and demonstrate its use for analyzing reverse structural remodeling following cardiac ablation therapy.

METHODS

The left atrium and pulmonary veins are segmented from high-resolution computed tomography (CT) volumes using a 3D volumetric approach and cut planes are interactively positioned to separate the pulmonary veins from the body of the left atrium. Left atrial volume and pulmonary vein ostial diameters are then automatically computed from the segmented structures. Validation experiments are conducted to evaluate accuracy and repeatability of the measurements. Accuracy is assessed by comparing left atrial volumes computed with the proposed methodology to a manual slice-by-slice tracing approach. Repeatability is assessed by making repeated volume and diameter measurements on duplicated and randomized datasets. The proposed techniques were then utilized in a study of 21 patients from the Catheter Ablation versus Antiarrhythmic Drug Therapy for Atrial Fibrillation Trial (CABANA) pilot study who were scanned both before and approximately 3 months following ablation therapy.

RESULTS

In the high resolution CT scans the left atrial volume measurements show high accuracy with a mean absolute difference of 2.3±1.9 cm(3) between volumes computed with the proposed methodology and a manual slice-by-slice tracing approach. In the intra-rater repeatability study, the mean absolute difference in left atrial volume was 4.7±2.5 cm(3) and 4.4±3.4 cm(3) for the two raters. Intra-rater repeatability for pulmonary vein diameters ranged from 0.9 to 2.3 mm. The inter-rater repeatability for left atrial volume was 5.8±5.1 cm(3) and inter-rater repeatability for pulmonary vein diameter measurements ranged from 1.4 to 2.3 mm. In the patient study, significant (p<.05) decreases in left atrial volume and all four pulmonary vein diameters were observed. The absolute change in LA volume was 20.0 cm(3), 95%CI [12.6, 27.5]. The left inferior pulmonary vein diameter decreased 2.1 mm, 95%CI [0.4, 3.7], the left superior pulmonary vein diameter decreased 3.2 mm, 95%CI [1.0, 5.4], the right inferior pulmonary vein diameter decreased 1.5 mm, 95%CI [0.3, 2.7], and the right superior pulmonary vein diameter decreased 2.8 mm, 95%CI [1.4, 4.3].

CONCLUSIONS

Using the proposed techniques, we demonstrate high accuracy of left atrial volume measurements as well as high repeatability for left atrial volume and pulmonary vein diameter measurements. Following cardiac ablation therapy, a significant decrease was observed for left atrial volume as well as all four pulmonary vein diameters.

Comparison of manual and semiautomated techniques for analyzing gastric volumes with MRI in humans

Gastric emptying, accommodation, and motility can be quantified with magnetic resonance imaging (MRI). The first step in image analysis entails segmenting the stomach from surrounding structures, usually by a time-consuming manual process. We have developed a semiautomated process to segment and measure gastric volumes with MRI. Gastric images were acquired with a three-dimensional gradient echo MRI sequence at 5, 10, 20, and 30 min after ingestion of a liquid nutrient (Ensure, 296 ml) labeled with gadolinium in 20 healthy volunteers and 29 patients with dyspeptic symptoms. The agreement between gastric volumes measured by manual segmentation and our new semiautomated algorithm was assessed with Lin's concordance correlation coefficient (CCC) and the Bland Altman test. At 5 min after a meal, food volumes measured by manual (352 ± 4 ml) and semiautomated (346 ± 4 ml) techniques were correlated {CCC[95% confidence interval (CI)] 0.70 (0.52, 0.81)}; air volumes measured by manual (88 ± 6 ml) and semiautomated (84 ± 6 ml) techniques were also correlated [CCC (95% CI) 0.89 (0.82, 0.94)]. Findings were similar at subsequent time points. The Bland Altman test was not significant. The time required for semiautomated segmentation ranged from an average of 204 s for the 5-min images to 233 s for the 20-min images. These times were appreciably smaller than the typical times of many tens of minutes, even hours, required for manual segmentation. To conclude, a semiautomated process can measure gastric food and air volume using MRI with comparable accuracy and far better efficiency than a manual process.

Quantitative stratification of diffuse parenchymal lung diseases

Diffuse parenchymal lung diseases (DPLDs) are characterized by widespread pathological changes within the pulmonary tissue that impair the elasticity and gas exchange properties of the lungs. Clinical-radiological diagnosis of these diseases remains challenging and their clinical course is characterized by variable disease progression. These challenges have hindered the introduction of robust objective biomarkers for patient-specific prediction based on specific phenotypes in clinical practice for patients with DPLD. Therefore, strategies facilitating individualized clinical management, staging and identification of specific phenotypes linked to clinical disease outcomes or therapeutic responses are urgently needed. A classification schema consistently reflecting the radiological, clinical (lung function and clinical outcomes) and pathological features of a disease represents a critical need in modern pulmonary medicine. Herein, we report a quantitative stratification paradigm to identify subsets of DPLD patients with characteristic radiologic patterns in an unsupervised manner and demonstrate significant correlation of these self-organized disease groups with clinically accepted surrogate endpoints. The proposed consistent and reproducible technique could potentially transform diagnostic staging, clinical management and prognostication of DPLD patients as well as facilitate patient selection for clinical trials beyond the ability of current radiological tools. In addition, the sequential quantitative stratification of the type and extent of parenchymal process may allow standardized and objective monitoring of disease, early assessment of treatment response and mortality prediction for DPLD patients.

Toward Standardized Mapping for Left Atrial Analysis and Cardiac Ablation Guidance

In catheter-based cardiac ablation, the pulmonary vein ostia are important landmarks for guiding the ablation procedure, and for this reason, have been the focus of many studies quantifying their size, structure, and variability. Analysis of pulmonary vein structure, however, has been limited by the lack of a standardized reference space for population based studies. Standardized maps are important tools for characterizing anatomic variability across subjects with the goal of separating normal inter-subject variability from abnormal variability associated with disease. In this work, we describe a novel technique for computing flat maps of left atrial anatomy in a standardized space. A flat map of left atrial anatomy is created by casting a single ray through the volume and systematically rotating the camera viewpoint to obtain the entire field of view. The technique is validated by assessing preservation of relative surface areas and distances between the original 3D geometry and the flat map geometry. The proposed methodology is demonstrated on 10 subjects which are subsequently combined to form a probabilistic map of anatomic location for each of the pulmonary vein ostia and the boundary of the left atrial appendage. The probabilistic map demonstrates that the location of the inferior ostia have higher variability than the superior ostia and the variability of the left atrial appendage is similar to the superior pulmonary veins. This technique could also have potential application in mapping electrophysiology data, radio-frequency ablation burns, or treatment planning in cardiac ablation therapy.

Statistical SPECT processing in MRI-negative epilepsy surgery

OBJECTIVE

To evaluate the benefit of statistical SPECT processing over traditional subtraction methods, we compared ictal-interictal SPECT analyzed by statistical parametric mapping (SPM) (ISAS), statistical ictal SPECT coregistered to MRI (STATISCOM), and subtraction ictal-interictal SPECT coregistered with MRI (SISCOM) in patients with MRI-negative focal temporal lobe epilepsy (nTLE) and extratemporal lobe epilepsy (nETLE).

METHODS

We retrospectively identified 49 consecutive cases of drug-resistant focal epilepsy that had a negative preoperative MRI and underwent interictal and ictal SPECT prior to resective epilepsy surgery. Interictal and ictal SPECT scans were analyzed using SISCOM, ISAS, and STATISCOM to create hyperperfusion and hypoperfusion maps for each patient. Reviewers blinded to clinical data and the SPECT analysis method marked the site of probable seizure origin and indicated their confidence in the localization.

RESULTS

In nTLE and nETLE, the hyperperfusions detected by STATISCOM (71% nTLE, 57% nETLE) and ISAS (67% nTLE, 53% nETLE) were more often colocalized with surgery resection site compared to SISCOM (38% nTLE, 36% nETLE). In nTLE, localization of the hyperperfusion to the region of surgery was associated with an excellent outcome for STATISCOM (p = 0.005) and ISAS (p = 0.027), but not in SISCOM (p = 0.071). This association was not present in nETLE for any method.

CONCLUSION

In an unselected group of patients with normal MRI and focal epilepsy, SPM-based methods of SPECT processing showed better localization of SPECT hyperperfusion to surgical resection site and higher interobserver agreement compared to SISCOM. These results show the benefit of statistical SPECT processing methods and further highlight the challenge of nETLE.

Quantitative modeling of the accuracy in registering preoperative patient-specific anatomic models into left atrial cardiac ablation procedures

PURPOSE

In cardiac ablation therapy, accurate anatomic guidance is necessary to create effective tissue lesions for elimination of left atrial fibrillation. While fluoroscopy, ultrasound, and electroanatomic maps are important guidance tools, they lack information regarding detailed patient anatomy which can be obtained from high resolution imaging techniques. For this reason, there has been significant effort in incorporating detailed, patient-specific models generated from preoperative imaging datasets into the procedure. Both clinical and animal studies have investigated registration and targeting accuracy when using preoperative models; however, the effect of various error sources on registration accuracy has not been quantitatively evaluated.

METHODS

Data from phantom, canine, and patient studies are used to model and evaluate registration accuracy. In the phantom studies, data are collected using a magnetically tracked catheter on a static phantom model. Monte Carlo simulation studies were run to evaluate both baseline errors as well as the effect of different sources of error that would be present in a dynamic in vivo setting. Error is simulated by varying the variance parameters on the landmark fiducial, physical target, and surface point locations in the phantom simulation studies. In vivo validation studies were undertaken in six canines in which metal clips were placed in the left atrium to serve as ground truth points. A small clinical evaluation was completed in three patients. Landmark-based and combined landmark and surface-based registration algorithms were evaluated in all studies. In the phantom and canine studies, both target registration error and point-to-surface error are used to assess accuracy. In the patient studies, no ground truth is available and registration accuracy is quantified using point-to-surface error only.

RESULTS

The phantom simulation studies demonstrated that combined landmark and surface-based registration improved landmark-only registration provided the noise in the surface points is not excessively high. Increased variability on the landmark fiducials resulted in increased registration errors; however, refinement of the initial landmark registration by the surface-based algorithm can compensate for small initial misalignments. The surface-based registration algorithm is quite robust to noise on the surface points and continues to improve landmark registration even at high levels of noise on the surface points. Both the canine and patient studies also demonstrate that combined landmark and surface registration has lower errors than landmark registration alone.

CONCLUSIONS

In this work, we describe a model for evaluating the impact of noise variability on the input parameters of a registration algorithm in the context of cardiac ablation therapy. The model can be used to predict both registration error as well as assess which inputs have the largest effect on registration accuracy.

Biomechanical evaluation of an injectable and biodegradable copolymer P(PF-co-CL) in a cadaveric vertebral body defect model

A novel biodegradable copolymer, poly(propylene fumarate-co-caprolactone) [P(PF-co-CL)], has been developed in our laboratory as an injectable scaffold for bone defect repair. In the current study, we evaluated the ability of P(PF-co-CL) to reconstitute the load-bearing capacity of vertebral bodies with lytic lesions. Forty vertebral bodies from four fresh-frozen cadaveric thoracolumbar spines were used for this study. They were randomly divided into four groups: intact vertebral body (intact control), simulated defect without treatment (negative control), defect treated with P(PF-co-CL) (copolymer group), and defect treated with poly(methyl methacrylate) (PMMA group). Simulated metastatic lytic defects were made by removing a central core of the trabecular bone in each vertebral body with an approximate volume of 25% through an access hole in the side of the vertebrae. Defects were then filled by injecting either P(PF-co-CL) or PMMA in situ crosslinkable formulations. After the spines were imaged with quantitative computerized tomography, single vertebral body segments were harvested for mechanical testing. Specimens were compressed until failure or to 25% reduction in body height and ultimate strength and elastic modulus of each specimen were then calculated from the force-displacement data. The average failure strength of the copolymer group was 1.83 times stronger than the untreated negative group and it closely matched the intact vertebral bodies (intact control). The PMMA-treated vertebrae, however, had a failure strength 1.64 times larger compared with the intact control. The elastic modulus followed the same trend. This modulus mismatch between PMMA-treated vertebrae and the host vertebrae could potentially induce a fracture cascade and degenerative changes in adjacent intervertebral discs. In contrast, P(PF-co-CL) restored the mechanical properties of the treated segments similar to the normal, intact, vertebrae. Therefore, P(PF-co-CL) may be a suitable alternative to PMMA for vertebroplasty treatment of vertebral bodies with lytic defects.

Anatomic surface reconstruction from sampled point cloud data and prior models

In this paper, we propose an approach for reconstruction of an anatomic surface model from point cloud data using the Screened Poisson Surface Reconstruction algorithm, which requires a collection of points and their normal vectors. Various algorithms exist for estimating normal vectors for point cloud data; however, in this work we describe a novel approach to estimating the normal vectors from a high-resolution prior model. In many medical applications, a preoperative high-resolution scan is acquired for diagnostic and planning purposes, whereas intraoperative, lower fidelity imaging is utilized during the procedure. This approach assumes an already existing registration between intra-operatively acquired data and the preoperative model. We conducted simulation experiments to evaluate the effect of registration error, point sampling rate, and noise levels on the acquired point cloud data samples. In addition, we evaluated the effect of using both the closest point, as well as a neighborhood of closest points on the prior model for estimating the normal. Our results showed that surface reconstruction error increases with higher registration error; however, acceptable performance was achieved with clinically-acceptable registration error. In addition, the best reconstruction was obtained when estimating the normal using only the closest point on the prior model, as opposed to utilizing a neighborhood of points. When combining the effect of all factors (Gaussian sampling noise of zero mean and σ=1.8mm; Gaussian translational error of zero mean and σ=2.0mm; and Gaussian rotational error of zero mean and σ=3°) the overall RMS reconstruction error was 0.88±0.03mm.

Quantitative computed tomography imaging of interstitial lung diseases

PURPOSE

High-resolution chest computed tomography (HRCT) is essential in the characterization of interstitial lung disease. The HRCT features of some diseases can be diagnostic. Longitudinal monitoring with HRCT can assess progression of interstitial lung disease; however, subtle changes in the volume and character of abnormalities can be difficult to assess. Accuracy of diagnosis can be dependent on expertise and experience of the radiologist, pathologist, or clinician. Quantitative analysis of thoracic HRCT has the potential to determine the extent of disease reproducibly, classify the types of abnormalities, and automate the diagnostic process.

MATERIALS AND METHODS

Novel software that utilizes histogram signatures to characterize pulmonary parenchyma was used to analyze chest HRCT data, including retrospective processing of clinical CT scans and research data from the Lung Tissue Research Consortium. Additional information including physiological, pathologic, and semiquantitative radiologist assessment was available to allow comparison of quantitative results, with visual estimates of the disease, physiological parameters, and measures of disease outcome.

RESULTS

Quantitative analysis results were provided in regional volumetric quantities for statistical analysis and a graphical representation. These results suggest that quantitative HRCT analysis can serve as a biomarker with physiological, pathologic, and prognostic significance.

CONCLUSIONS

It is likely that quantitative analysis of HRCT can be used in clinical practice as a means to aid in identifying a probable diagnosis, stratifying prognosis in early disease, and consistently determining progression of the disease or response to therapy. Further optimization of quantitative techniques and longitudinal analysis of well-characterized subjects would be helpful in validating these methods.

Automated quantification of radiological patterns predicts survival in idiopathic pulmonary fibrosis

Accurate assessment of prognosis in idiopathic pulmonary fibrosis remains elusive due to significant individual radiological and physiological variability. We hypothesised that short-term radiological changes may be predictive of survival. We explored the use of CALIPER (Computer-Aided Lung Informatics for Pathology Evaluation and Rating), a novel software tool developed by the Biomedical Imaging Resource Laboratory at the Mayo Clinic Rochester (Rochester, MN, USA) for the analysis and quantification of parenchymal lung abnormalities on high-resolution computed tomography. We assessed baseline and follow-up (time-points 1 and 2, respectively) high-resolution computed tomography scans in 55 selected idiopathic pulmonary fibrosis patients and correlated CALIPER-quantified measurements with expert radiologists' assessments and clinical outcomes. Findings of interval change (mean 289 days) in volume of reticular densities (hazard ratio 1.91, p=0.006), total volume of interstitial abnormalities (hazard ratio 1.70, p=0.003) and per cent total interstitial abnormalities (hazard ratio 1.52, p=0.017) as quantified by CALIPER were predictive of survival after a median follow-up of 2.4 years. Radiologist interpretation of short-term global interstitial lung disease progression, but not specific radiological features, was also predictive of mortality. These data demonstrate the feasibility of quantifying interval short-term changes on high-resolution computed tomography and their possible use as independent predictors of survival in idiopathic pulmonary fibrosis.

On mixed reality environments for minimally invasive therapy guidance: systems architecture, successes and challenges in their implementation from laboratory to clinic

Mixed reality environments for medical applications have been explored and developed over the past three decades in an effort to enhance the clinician's view of anatomy and facilitate the performance of minimally invasive procedures. These environments must faithfully represent the real surgical field and require seamless integration of pre- and intra-operative imaging, surgical instrument tracking, and display technology into a common framework centered around and registered to the patient. However, in spite of their reported benefits, few mixed reality environments have been successfully translated into clinical use. Several challenges that contribute to the difficulty in integrating such environments into clinical practice are presented here and discussed in terms of both technical and clinical limitations. This article should raise awareness among both developers and end-users toward facilitating a greater application of such environments in the surgical practice of the future.

Image-based Modeling and Characterization of RF Ablation Lesions in Cardiac Arrhythmia Therapy

In spite of significant efforts to enhance guidance for catheter navigation, limited research has been conducted to consider the changes that occur in the tissue during ablation as means to provide useful feedback on the progression of therapy delivery. We propose a technique to visualize lesion progression and monitor the effects of the RF energy delivery using a surrogate thermal ablation model. The model incorporates both physical and physiological tissue parameters, and uses heat transfer principles to estimate temperature distribution in the tissue and geometry of the generated lesion in near real time. The ablation model has been calibrated and evaluated using ex vivo beef muscle tissue in a clinically relevant ablation protocol. To validate the model, the predicted temperature distribution was assessed against that measured directly using fiberoptic temperature probes inserted in the tissue. Moreover, the model-predicted lesions were compared to the lesions observed in the post-ablation digital images. Results showed an agreement within 5°C between the model-predicted and experimentally measured tissue temperatures, as well as comparable predicted and observed lesion characteristics and geometry. These results suggest that the proposed technique is capable of providing reasonably accurate and sufficiently fast representations of the created RF ablation lesions, to generate lesion maps in near real time. These maps can be used to guide the placement of successive lesions to ensure continuous and enduring suppression of the arrhythmic pathway.

Toward modeling of radio-frequency ablation lesions for image-guided left atrial fibrillation therapy: model formulation and preliminary evaluation

In the context of image-guided left atrial fibrillation therapy, relatively very little work has been done to consider the changes that occur in the tissue during ablation in order to monitor therapy delivery. Here we describe a technique to predict the lesion progression and monitor the radio-frequency energy delivery via a thermal ablation model that uses heat transfer principles to estimate the tissue temperature distribution and resulting lesion. A preliminary evaluation of the model was conducted in ex vivo skeletal beef muscle tissue while emulating a clinically relevant tissue ablation protocol. The predicted temperature distribution within the tissue was assessed against that measured directly using fiberoptic temperature probes and showed agreement within 5°C between the model-predicted and experimentally measured tissue temperatures at prescribed locations. We believe this technique is capable of providing reasonably accurate representations of the tissue response to radio-frequency energy delivery.