Towards a better understanding of pelvic system disorders using numerical simulation

International audienceGenital prolapse is a pathologic hyper-mobility of the organs that forms the pelvic system. Although this is common condition, the pathophysiology of this disorder is not well known. In order to improve the understanding of its origins, we recreate - virtually - this biomechanical pathology using numerical simulation. The approach builds on a finite element model with parameters measured on several fresh cadavers. The meshes are created from a MRI of a healthy woman and the simulation includes the mechanical interactions between organs (contacts, ligaments, adhesion...). The model is validated through comparison of functional mobilities of the pelvic system observed on a dynamic MRI. We then propose to modify, step by step, the model and its parameters to produce a pathologic situation and have a better understanding of the process. It is not a formal proof but the numerical experiments reinforce the clinical hypothesis on the multifactorial origins of the pathology

Automatic analysis of transperineal ultrasound images

This thesis focuses on the automatic image analysis of transperineal ultrasound (TPUS) data, which is used to investigate female pelvic floor problems. These problems have a high prevalence, but the understanding of pelvic floor (dys-)function is limited. TPUS analysis of the pelvic floor is done manually, which is time-consuming and observer dependent. This hinders both the research into interpretation of TPUS data and its clinical use. To overcome these problems we use automatic image analysis. Currently, one of the main methods used, to analyse the TPUS is manually selecting and segmenting the slice of minimal hiatal dimensions (SMHD). In the first chapter of this thesis we show that reliable automatic segmentation of the urogenital hiatus and the puborectalis muscle in the SMHD can be successfully implemented, using deep learning. Furthermore, we show that this can also be used to successfully automate the process of selecting and segmenting the SMHD. 4D TPUS is available in the clinical practice but by the aforementioned method only provides 1D and 2D parameters. Therefore, information stored within TPUS about the volume appearance of the pelvic floor muscles and muscle functionality is not analyzed. In the third chapter of this thesis we propose a reproducible manual 3D segmentation protocol of the puborectalis muscle. The resulting manual segmentations can be used to train active appearance models and convolutional neural networks, these algorithms can be used for reliable automatic 3D segmentation. In the fifth chapter of we show that on this data it is possible to identify all subdivisions of the main pelvic floor muscle group, the levator ani muscles, on new TPUS data. In the last chapter we apply unsupervised deep learning to our data and show that this can be used for classification of the TPUS data. The segmentation results presented in this thesis are an important step to reduce the TPUS analysis time and will therefore ease the study of large populations and clinical TPUS analysis. The 3D identification and segmentation of the levator ani muscle subdivisions helps to identify if they are still intact. This is an important step to better informed clinical decision-making

Shifting and Shaping Perceptions: Towards the Characterization and Literacy of Female Pelvic Organ Support

Pelvic Organ Prolapse (POP) is a pelvic floor condition characterized by the unnatural descent of pelvic organs into the vagina. It occurs as the result of compromised connective tissues and musculature following vaginal delivery and/or changes in tissue composition due to aging. Approximately 50% of women in the United States experience some degree of POP during their lifetime, with symptoms that include altered urination and defecation, physical discomfort, depression, and anxiety. Over the last decade, POP treatments have gained public notoriety due to surgical complications and recurrence of prolapse after surgical repair. Both outcomes stem, in part, from gaps in knowledge regarding the complex interactions of pelvic viscera, tissues, and musculature, and is exacerbated by the significant time span between events surrounding vaginal birth injuries and symptomatic prolapse. Over the last century, fields such as cardiovascular medicine and orthopedics have made significant strides to improve the human condition through the application of biomechanics, diagnostic imaging techniques, and modeling. Such methods have been used to reliably differentiate normal and diseased anatomy with respect to orientation, location, and other geometric attributes. In contrast, urogynecology remains decades behind as a result of a failure to adopt new interdisciplinary methods, limiting our ability to effectively treat POP. Thus, approximately 80% of women with symptomatic POP choose to suffer in silence. This is troubling, given that POP and related disorders will become increasingly prevalent due to the advancing age of the global population. This dissertation explores the assessment and development of diagnostic tools that improve our ability to quantify the position of the vagina with respect to physiologic changes that may occur over the lifespan within the normal range. These tools provide valuable information regarding the physical changes that occur over time and the differences between populations while serving as a potential standard by which pelvic anatomy can be quantified. Furthermore, this work explores our knowledge, perceptions, and attitudes regarding female pelvic health to challenge misconceptions surrounding normal and abnormal physiological functions, foster attitudes of empathy and acceptance for disorders, and improve health literacy by illustrating the impact that it has on lives worldwide

Mechanical Characterization of Synthetic Mesh for Pelvic Organ Prolapse Repair

Pelvic organ prolapse (POP) is characterized by the abnormal descent of the pelvic organs into the vaginal canal. POP is associated with urinary, defacatory, and sexual dysfunction, in addition to psychological disorders including depression. Prolapse is quite common, with ~50% of women over the age of 50 exhibiting some degree of prolapse, and over 200,000 surgical repairs in the United States annually. During surgical repair, a graft is used to restore support to the vagina, re-approximating the normal anatomy. Given the high failure rate of native tissue repair, use of polypropylene mesh has become widespread. Despite the prevalence of synthetic mesh, complication rates are ~20%, with little known about its behavior following implantation. Therefore, this dissertation aims to rigorously characterize the mechanical behavior of synthetic mesh, with the goal of optimizing device design for use in the pelvic floor. First, micro- and macro-level deformation of mesh was assessed in response to mechanical loads using uniaxial testing and 3D reconstruction. Upon loading, mesh pores significantly deformed, yielding textile dimensions that are known to heighten the foreign body response. In addition, point loads significantly wrinkled the mesh surface, further reducing mesh dimensions and producing configurations consistent with those found clinically. Next, a finite element model for synthetic mesh was developed, using a novel method to allow for textile properties to be measured in-silico. This model was validated using a custom testing apparatus to simultaneously load and image transvaginal mesh products. Evaluation of mesh deformation found experimental and computational results to be similar, demonstrating the predictive capabilities of this model. The validated model was then used to examine the sensitivity of mesh behavior to variable loading conditions. Here the magnitude and orientation of tensile forces were found to significantly predict undesired deformations. Finally, computational mesh models were combined with MRI reconstructions of patient specific anatomy to simulate the development of prolapse and mesh repair. Again, mesh pores experienced significant deformation upon anatomical fixation, corresponding with clinical sites of exposure and pain. In total, this dissertation provides a tool for the evaluation and optimization of synthetic mesh devices prior to implantation and pre-surgical evaluation of mesh procedures

Unraveling the Pelvic Floor:Obstetric injury, Symptoms and Imaging Techniques

Research into risk factors for the development of pelvic floor (residual) injury and urogynecological complaints after a vaginal delivery with and without obstetric anal sphincter injury. Comparison between conventional perineal pelvic floor ultrasound and virtual reality imaging of the pelvic floor