2007
Vosburgh KG, Stylopoulos N, Estepar RSJ, Ellis RE, Samset E, Thompson CC.
EUS with CT improves efficiency and structure identification over conventional EUS. Gastrointest Endosc 2007;65(6):866-70.
AbstractBACKGROUND: EUS is complicated because of the subtleties of US interpretation, small fields of observation, and uncertainty of probe position and orientation.
OBJECTIVE: Improved EUS performance is sought by providing contextual information to support US probe positioning and identification of features in US images. Our aims were to demonstrate the feasibility of the image registered gastroscopic US (IRGUS) system in a porcine model and to compare the effectiveness and the efficiency of IRGUS with traditional EUS.
DESIGN: Animal feasibility study.
INTERVENTIONS: The IRGUS system uses preprocedure CT and miniature US probe trackers to create real-time synthetic displays of the position of the probe tip and a matched slice of CT data for comparison with the US image. Participants used EUS and IRGUS systems in a porcine model to evaluate the speed and accuracy of structure identification.
MAIN OUTCOME MEASUREMENTS: The performance and utility of IRGUS were determined by the number of correctly identified structures in a timed trial, kinematic variables, and a structured survey.
RESULTS: IRGUS was twice as effective as EUS in localizing and identifying individual structures. In timed trials, IRGUS users identified over 25% more structures than EUS users. Improvement in examination efficiency and accuracy of feature identification was statistically significant, and 90% of the users preferred IRGUS to EUS for these tasks.
CONCLUSIONS: IRGUS appears feasible and may be superior to conventional EUS in efficiency and accuracy of probe positioning and in image interpretation. IRGUS has the potential to shorten the EUS learning curve and to broaden the adoption of EUS techniques by gastroenterologists.
Dransfield MT, Washko GR, Foreman MG, Estepar RSJ, Reilly J, Bailey WC.
Gender differences in the severity of CT emphysema in COPD. Chest 2007;132(2):464-70.
AbstractBACKGROUND: The hallmark of COPD is airflow obstruction, but this can develop on the basis of airway disease, emphysema, or both. There are gender differences in the natural history of COPD, and these may in part be explained by differences in the pathophysiology of airflow obstruction. We aimed to determine if there are gender differences in the severity of CT emphysema among COPD patients.
METHODS: Current and former smokers enrolled in the National Lung Screening Trial (NLST) at the University of Alabama at Birmingham were recruited at the time of an annual screening CT examination. We recorded demographics and smoking history, and subjects performed spirometry. Subjects were classified into modified (prebronchodilator) Global Initiative for Chronic Obstructive Lung Disease stages, and their CT scans were analyzed to determine regional and total emphysema (defined as the percentage of low attenuation areas [LAA%]; < - 950 Hounsfield units). Differences between genders were examined, and univariate and multivariate predictors of LAA% were determined.
RESULTS: A total of 396 subjects participated. Men had more regional and total CT emphysema at all stages of COPD than women (stage 0, 3.9% vs 2.4%, p = 0.001; stage I, 7.0% vs 3.7%, p = 0.015; stage II, 7.8% vs 5.5%, p = 0.063; stages III/IV, 15.8% vs 8.7%, p = 0.024). In multivariate regression analysis, only gender (p < 0.001) and FEV(1)/FVC ratio (p < 0.001) predicted total LAA%.
CONCLUSIONS: At all stages of COPD severity, men have more CT emphysema than women. This difference in radiologic expression may in part explain gender differences in the presentation and natural history of COPD. The NLST (NCT00047385) is registered at
www.clinicaltrials.gov. Registered at
www.clinicaltrials.gov; no.NCT00047835.
Kindlmann G, San José Estépar R, Niethammer M, Haker S, Westin C-F.
Geodesic-loxodromes for diffusion tensor interpolation and difference measurement. Med Image Comput Comput Assist Interv 2007;10(Pt 1):1-9.
AbstractIn algorithms for processing diffusion tensor images, two common ingredients are interpolating tensors, and measuring the distance between them. We propose a new class of interpolation paths for tensors, termed geodesic-loxodromes, which explicitly preserve clinically important tensor attributes, such as mean diffusivity or fractional anisotropy, while using basic differential geometry to interpolate tensor orientation. This contrasts with previous Riemannian and Log-Euclidean methods that preserve the determinant. Path integrals of tangents of geodesic-loxodromes generate novel measures of over-all difference between two tensors, and of difference in shape and in orientation.
Hersh CP, Washko GR, Jacobson FL, Gill R, Estepar RSJ, Reilly JJ, Silverman EK.
Interobserver variability in the determination of upper lobe-predominant emphysema. Chest 2007;131(2):424-31.
AbstractBACKGROUND: Appropriateness for lung volume reduction surgery is often determined based on the results of high-resolution CT (HRCT) scanning of the chest. At many centers, radiologists and pulmonary physicians both review the images, but the agreement between readers from these specialties is not known.
METHODS: Two thoracic radiologists and three pulmonologists retrospectively reviewed the HRCT scans of 30 patients with emphysema involved in two clinical studies at our institution. Each reader assigned an emphysema severity score and assessed upper lobe predominance, using a methodology similar to that of the National Emphysema Treatment Trial. In addition, the percentage of emphysema at -910 Hounsfield units was objectively determined by density mask analysis.
RESULTS: For the emphysema severity scores, (Spearman) correlation between readers ranged from 0.59 (p = 0.0005) to 0.87 (p < 0.0001), with generally stronger correlations among readers from the same medical specialty. Emphysema severity scores were significantly correlated with prebronchodilator and postbronchodilator spirometry findings, as well as with density mask analysis. In the assessment of upper lobe predominance, kappa statistics for agreement ranged from 0.20 (p = 0.4) to 0.60 (p = 0.0008). Examining all possible radiologist-pulmonologist pairs, the two readers agreed in their assessments of emphysema distribution in 75% of the comparisons. Readers agreed on upper lobe-predominant disease in 9 of the 10 patients in which regional density mask analysis clearly showed upper lobe predominance.
CONCLUSIONS: In a group of patients with varying emphysema severity, interobserver agreement in the determination of upper lobe-predominant disease was poor. Agreement between readers tended to be better in cases with clear upper lobe predominance as determined by densitometry.
Vosburgh KG, San José Estépar R.
Natural Orifice Transluminal Endoscopic Surgery (NOTES): an opportunity for augmented reality guidance. Stud Health Technol Inform 2007;125:485-90.
AbstractLaparoscopic techniques have gained wide acceptance because they offer a safe and less invasive alternative to open surgery. To further reduce the invasiveness of peritoneal access, the next logical step is to eliminate the incision through the abdominal wall using natural orifices as entry points. This Natural Orifice Transluminal Endoscopic Surgery (NOTES) approach has the potential to replace or augment current techniques. Several research groups have cut through the stomach or colon wall (per-oral transgastric or per-anal transcolonic) to perform organ resections in animal models, and some procedures in humans have been reported anecdotally. Widespread use of these techniques will depend on providing the physician with adequate visual feedback, clear indicators of instrument location and orientation, and support in the recognition of anatomic structures. Compared with laparoscopy, successful endoscopy must accommodate several additional complexities: (1) The flexibility of the endoscope tip complicates the understanding of its distal orientation. Successful navigation inside the stomach and in the abdominal cavity generally requires two years of sub-specialty training. (2) Several surgical targets lie in a retrograde position with respect to an incision in the stomach wall. Efficient and safe access to the pancreas, gall bladder, or the kidneys requires detailed knowledge of the tip placement relative to adjacent anatomic structures. (3) Since there is limited direct access to the abdomen, iatrogenic injuries, such as the accidental cutting of an artery, will be more dangerous and difficult to manage. We present here approaches to resolving these limitations though augmented reality techniques using pre-procedure CT or MRI imaging, real time tracking and reference image registration, and display to the operating physician. As an example, the utility of image registration techniques for orientation for the gastric access puncture is discussed in detail. It is anticipated that such augmentation will make intra-cavitary interventional techniques easier to master and use in practice, and thus more likely to be widely adopted.
San José Estépar R, Stylopoulos N, Ellis R, Samset E, Westin C-F, Thompson C, Vosburgh K.
Towards scarless surgery: an endoscopic ultrasound navigation system for transgastric access procedures. Comput Aided Surg 2007;12(6):311-24.
AbstractOBJECTIVE: Scarless surgery is an innovative and promising technique that may herald a new era in surgical procedures. We have created a navigation system, named IRGUS, for endoscopic and transgastric access interventions and have validated it in in vivo pilot studies. Our hypothesis is that endoscopic ultrasound procedures will be performed more easily and efficiently if the operator is provided with approximately registered 3D and 2D processed CT images in real time that correspond to the probe position and ultrasound image.
MATERIALS AND METHODS: The system provides augmented visual feedback and additional contextual information to assist the operator. It establishes correspondence between the real-time endoscopic ultrasound image and a preoperative CT volume registered using electromagnetic tracking of the endoscopic ultrasound probe position. Based on this positional information, the CT volume is reformatted in approximately the same coordinate frame as the ultrasound image and displayed to the operator.
RESULTS: The system reduces the mental burden of probe navigation and enhances the operator's ability to interpret the ultrasound image. Using an initial rigid body registration, we measured the mis-registration error between the ultrasound image and the reformatted CT plane to be less than 5 mm, which is sufficient to enable the performance of novice users of endoscopic systems to approach that of expert users.
CONCLUSIONS: Our analysis shows that real-time display of data using rigid registration is sufficiently accurate to assist surgeons in performing endoscopic abdominal procedures. By using preoperative data to provide context and support for image interpretation and real-time imaging for targeting, it appears probable that both preoperative and intraoperative data may be used to improve operator performance.
Kindlmann G, San Jose Estépar R, Niethammer M, Haker S, Westin C-F.
Geodesic-loxodromes for diffusion tensor interpolation and difference measurement. Medical image computing and computer-assisted intervention : MICCAI .. International Conference on Medical Image Computing and Computer-Assisted InterventionMedical image computing and computer-assisted intervention : MICCAI .. International Conference 2007;10:1-9.
AbstractIn algorithms for processing diffusion tensor images, two common ingredients are interpolating tensors, and measuring the distance between them. We propose a new class of interpolation paths for tensors, termed geodesic-loxodromes, which explicitly preserve clinically important tensor attributes, such as mean diffusivity or fractional anisotropy, while using basic differential geometry to interpolate tensor orientation. This contrasts with previous Riemannian and Log-Euclidean methods that preserve the determinant. Path integrals of tangents of geodesic-loxodromes generate novel measures of over-all difference between two tensors, and of difference in shape and in orientation.
Vosburgh KKGG, Estépar RSJR.
Natural Orifice Transluminal Endoscopic Surgery (NOTES): an opportunity for augmented reality guidance. Studies in health technology and informaticsStudies in health technology and informatics 2007;125:485-490.
AbstractLaparoscopic techniques have gained wide acceptance because they offer a safe and less invasive alternative to open surgery. To further reduce the invasiveness of peritoneal access, the next logical step is to eliminate the incision through the abdominal wall using natural orifices as entry points. This Natural Orifice Transluminal Endoscopic Surgery (NOTES) approach has the potential to replace or augment current techniques. Several research groups have cut through the stomach or colon wall (per-oral transgastric or per-anal transcolonic) to perform organ resections in animal models, and some procedures in humans have been reported anecdotally. Widespread use of these techniques will depend on providing the physician with adequate visual feedback, clear indicators of instrument location and orientation, and support in the recognition of anatomic structures. Compared with laparoscopy, successful endoscopy must accommodate several additional complexities: (1) The flexibility of the endoscope tip complicates the understanding of its distal orientation. Successful navigation inside the stomach and in the abdominal cavity generally requires two years of sub-specialty training. (2) Several surgical targets lie in a retrograde position with respect to an incision in the stomach wall. Efficient and safe access to the pancreas, gall bladder, or the kidneys requires detailed knowledge of the tip placement relative to adjacent anatomic structures. (3) Since there is limited direct access to the abdomen, iatrogenic injuries, such as the accidental cutting of an artery, will be more dangerous and difficult to manage. We present here approaches to resolving these limitations though augmented reality techniques using pre-procedure CT or MRI imaging, real time tracking and reference image registration, and display to the operating physician. As an example, the utility of image registration techniques for orientation for the gastric access puncture is discussed in detail. It is anticipated that such augmentation will make intra-cavitary interventional techniques easier to master and use in practice, and thus more likely to be widely adopted.
THE BRIGHAM AND WOMEN S HOSPITAL INC.
MEASUREMENT OF THIN-LAYERED STRUCTURES IN X-RAY COMPUTER TOMOGRAPHY. 2007.
Abstract... MEASUREMENT OF THIN-LAYERED STRUCTURES IN X-RAY COMPUTER TOMOGRAPHY RELATED APPLICATIONS [0001] This application is a PCT application claiming the ...
Vosburgh KG, Stylopoulos N, San Jose Estépar R, Ellis RE, Samset E, Thompson CC.
EUS with CT improves efficiency and structure identification over conventional EUS. Gastrointestinal endoscopyGastrointestinal endoscopy 2007;65:866-870.
AbstractBACKGROUND: EUS is complicated because of the subtleties of US interpretation, small fields of observation, and uncertainty of probe position and orientation. OBJECTIVE: Improved EUS performance is sought by providing contextual information to support US probe positioning and identification of features in US images. Our aims were to demonstrate the feasibility of the image registered gastroscopic US (IRGUS) system in a porcine model and to compare the effectiveness and the efficiency of IRGUS with traditional EUS. DESIGN: Animal feasibility study. INTERVENTIONS: The IRGUS system uses preprocedure CT and miniature US probe trackers to create real-time synthetic displays of the position of the probe tip and a matched slice of CT data for comparison with the US image. Participants used EUS and IRGUS systems in a porcine model to evaluate the speed and accuracy of structure identification. MAIN OUTCOME MEASUREMENTS: The performance and utility of IRGUS were determined by the number of correctly identified structures in a timed trial, kinematic variables, and a structured survey. RESULTS: IRGUS was twice as effective as EUS in localizing and identifying individual structures. In timed trials, IRGUS users identified over 25% more structures than EUS users. Improvement in examination efficiency and accuracy of feature identification was statistically significant, and 90% of the users preferred IRGUS to EUS for these tasks. CONCLUSIONS: IRGUS appears feasible and may be superior to conventional EUS in efficiency and accuracy of probe positioning and in image interpretation. IRGUS has the potential to shorten the EUS learning curve and to broaden the adoption of EUS techniques by gastroenterologists.
gastrointest._endosc._2007_vosburgh.pdf Dransfield MT, Washko GR, Foreman MG, San Jose Estépar R, Reilly J, Bailey WC.
Gender differences in the severity of CT emphysema in COPD. ChestChest 2007;132:464-470.
AbstractBACKGROUND:The hallmark of COPD is airflow obstruction, but this can develop on the basis of airway disease, emphysema, or both. There are gender differences in the natural history of COPD, and these may in part be explained by differences in the pathophysiology of airflow obstruction. We aimed to determine if there are gender differences in the severity of CT emphysema among COPD patients.METHODS:Current and former smokers enrolled in the National Lung Screening Trial (NLST) at the University of Alabama at Birmingham were recruited at the time of an annual screening CT examination. We recorded demographics and smoking history, and subjects performed spirometry. Subjects were classified into modified (prebronchodilator) Global Initiative for Chronic Obstructive Lung Disease stages, and their CT scans were analyzed to determine regional and total emphysema (defined as the percentage of low attenuation areas [LAA%]; < - 950 Hounsfield units). Differences between genders were examined, and univariate and multivariate predictors of LAA% were determined.RESULTS:A total of 396 subjects participated. Men had more regional and total CT emphysema at all stages of COPD than women (stage 0, 3.9% vs 2.4%, p = 0.001; stage I, 7.0% vs 3.7%, p = 0.015; stage II, 7.8% vs 5.5%, p = 0.063; stages III/IV, 15.8% vs 8.7%, p = 0.024). In multivariate regression analysis, only gender (p < 0.001) and FEV(1)/FVC ratio (p < 0.001) predicted total LAA%.CONCLUSIONS:At all stages of COPD severity, men have more CT emphysema than women. This difference in radiologic expression may in part explain gender differences in the presentation and natural history of COPD. The NLST (NCT00047385) is registered at www.clinicaltrials.gov. Registered at www.clinicaltrials.gov; no.NCT00047835.
Hersh CP, Washko GR, Jacobson FL, Gill R, San Jose Estépar R, Reilly JJ, Silverman EK.
Interobserver variability in the determination of upper lobe-predominant emphysema. ChestChest 2007;131:424-431.
AbstractBACKGROUND:Appropriateness for lung volume reduction surgery is often determined based on the results of high-resolution CT (HRCT) scanning of the chest. At many centers, radiologists and pulmonary physicians both review the images, but the agreement between readers from these specialties is not known.METHODS:Two thoracic radiologists and three pulmonologists retrospectively reviewed the HRCT scans of 30 patients with emphysema involved in two clinical studies at our institution. Each reader assigned an emphysema severity score and assessed upper lobe predominance, using a methodology similar to that of the National Emphysema Treatment Trial. In addition, the percentage of emphysema at -910 Hounsfield units was objectively determined by density mask analysis.RESULTS:For the emphysema severity scores, (Spearman) correlation between readers ranged from 0.59 (p = 0.0005) to 0.87 (p < 0.0001), with generally stronger correlations among readers from the same medical specialty. Emphysema severity scores were significantly correlated with prebronchodilator and postbronchodilator spirometry findings, as well as with density mask analysis. In the assessment of upper lobe predominance, kappa statistics for agreement ranged from 0.20 (p = 0.4) to 0.60 (p = 0.0008). Examining all possible radiologist-pulmonologist pairs, the two readers agreed in their assessments of emphysema distribution in 75% of the comparisons. Readers agreed on upper lobe-predominant disease in 9 of the 10 patients in which regional density mask analysis clearly showed upper lobe predominance.CONCLUSIONS:In a group of patients with varying emphysema severity, interobserver agreement in the determination of upper lobe-predominant disease was poor. Agreement between readers tended to be better in cases with clear upper lobe predominance as determined by densitometry.
San Jose Estépar R, Stylopoulos N, Ellis R, Samset E, Westin C-F, Thompson C, Vosburgh K.
Towards scarless surgery: an endoscopic ultrasound navigation system for transgastric access procedures. Computer aided surgery : official journal of the International Society for Computer Aided SurgeryComputer aided surgery : official journal of the International Society for Computer Aided Surgery 2007;12:311-324.
AbstractOBJECTIVE: Scarless surgery is an innovative and promising technique that may herald a new era in surgical procedures. We have created a navigation system, named IRGUS, for endoscopic and transgastric access interventions and have validated it in in vivo pilot studies. Our hypothesis is that endoscopic ultrasound procedures will be performed more easily and efficiently if the operator is provided with approximately registered 3D and 2D processed CT images in real time that correspond to the probe position and ultrasound image. MATERIALS AND METHODS: The system provides augmented visual feedback and additional contextual information to assist the operator. It establishes correspondence between the real-time endoscopic ultrasound image and a preoperative CT volume registered using electromagnetic tracking of the endoscopic ultrasound probe position. Based on this positional information, the CT volume is reformatted in approximately the same coordinate frame as the ultrasound image and displayed to the operator. RESULTS: The system reduces the mental burden of probe navigation and enhances the operator's ability to interpret the ultrasound image. Using an initial rigid body registration, we measured the mis-registration error between the ultrasound image and the reformatted CT plane to be less than 5 mm, which is sufficient to enable the performance of novice users of endoscopic systems to approach that of expert users. CONCLUSIONS: Our analysis shows that real-time display of data using rigid registration is sufficiently accurate to assist surgeons in performing endoscopic abdominal procedures. By using preoperative data to provide context and support for image interpretation and real-time imaging for targeting, it appears probable that both preoperative and intraoperative data may be used to improve operator performance.
2006
San José Estépar R, Washko GG, Silverman EK, Reilly JJ, Kikinis R, Westin C-F.
Accurate airway wall estimation using phase congruency. Med Image Comput Comput Assist Interv 2006;9(Pt 2):125-34.
AbstractQuantitative analysis of computed tomographic (CT) images of the lungs is becoming increasingly useful in the medical and surgical management of subjects with Chronic Obstructive Pulmonary Disease (COPD). Current methods for the assessment of airway wall work well in idealized models of the airway. We propose a new method for airway wall detection based on phase congruency. This method does not rely on either a specific model of the airway or the point spread function of the scanner. Our results show that our method gives a better localization of the airway wall than "full width at a half max" and is less sensitive to different reconstruction kernels and radiation doses.
Mulkern RV, Davis PE, Haker SJ, Estepar RSJ, Panych LP, Maier SE, Rivkin MJ.
Complementary aspects of diffusion imaging and fMRI; I: structure and function. Magn Reson Imaging 2006;24(4):463-74.
AbstractStudying the intersection of brain structure and function is an important aspect of modern neuroscience. The development of magnetic resonance imaging (MRI) over the last 25 years has provided new and powerful tools for the study of brain structure and function. Two tools in particular, diffusion imaging and functional MRI (fMRI), are playing increasingly important roles in elucidating the complementary aspects of brain structure and function. In this work, we review basic technical features of diffusion imaging and fMRI for studying the integrity of white matter structural components and for determining the location and extent of cortical activation in gray matter, respectively. We then review a growing body of literature in which the complementary aspects of diffusion imaging and fMRI, applied as separate examinations but analyzed in tandem, have been exploited to enhance our knowledge of brain structure and function.
Niethammer M, Estepar RSJ, Bouix S, Shenton M, Westin C-F.
On diffusion tensor estimation. Conf Proc IEEE Eng Med Biol Soc 2006;1:2622-5.
AbstractIn this paper we propose a formal formulation for the estimation of Diffusion Tensors in the space of symmetric positive semidefinite (PSD) tensors. Traditionally, diffusion tensor model estimation has been carried out imposing tensor symmetry without constraints for negative eigenvalues. When diffusion weighted data does not follow the diffusion model, due to noise or signal drop, negative eigenvalues may arise. An estimation method that accounts for the positive definiteness is desirable to respect the underlying principle of diffusion. This paper proposes such an estimation method and provides a theoretical interpretation of the result. A closed-form solution is derived that is the optimal data-fit in the matrix 2-norm sense, removing the need for optimization-based tensor estimation.
Niethammer M, Estepar RSJ, Bouix S, Shenton M, Westin C-F.
On diffusion tensor estimation. Conf Proc IEEE Eng Med Biol Soc 2006;Suppl:6707-10.
AbstractIn this paper we propose a formal formulation for the estimation of Diffusion Tensors in the space of symmetric positive semidefinite (PSD) tensors. Traditionally, diffusion tensor model estimation has been carried out imposing tensor symmetry without constraints for negative eigenvalues. When diffusion weighted data does not follow the diffusion model,due to noise or signal drop, negative eigenvalues may arise. An estimation method that accounts for the positive definiteness is desirable to respect the underlying principle of diffusion. This paper proposes such an estimation method and provides a theoretical interpretation of the result. A closed-form solution is derived that is the optimal data-fit in the matrix 2-norm sense,removing the need for optimization-based tensor estimation.
Aja-Fernández S, San José Estépar R, Alberola-López C, Westin C-F.
Image quality assessment based on local variance. Conf Proc IEEE Eng Med Biol Soc 2006;1:4815-8.
AbstractA new and complementary method to assess image quality is presented. It is based on the comparison of the local variance distribution of two images. This new quality index is better suited to assess the non-stationarity of images, therefore it explicitly focuses on the image structure. We show that this new index outperforms other methods for the assessment of image quality in medical images.