Alejandro Roldán Alzate
University of Wisconsin-Madison
Presenting in Track 11: Fluids Engineering
Presentation Title: Lower Urinary Tract Biomechanics - Uro-Dynamic MRI
Abstract: Multichannel urodynamics (UDS) with and without fluoroscopic imaging has been the gold standard for assessment of the bladder and the urethra. Dynamic MRI has successfully been used in several modalities to evaluate bladder biomechanics. Bladder function and specifically detrusor contraction has always been thought about as a deflating balloon, where the bladder uniformly and concentrically contracts. The goal of this study is to identify and characterize patterns in anatomical changes in the bladder during voiding using Uro-Dynamic MRI. During Uro-Dynamic MRI subjects are equipped with a condom catheter connected to a 1L bag attached to their leg for urine collection. Subjects are then instructed to void in the MRI scanner in a supine position. Acquired images are collected in a 3T MRI scanner (Premier, GE Healthcare, Waukesha, WI) using a high-density flexible array coil (AIR Coil, GE Healthcare) following the Uro-Dynamic MRI protocol. Protocol consists of a DIfferential Subsampling with Cartesian Ordering (DISCO) 3D acquisition sequence (Spatial Resolution=1x1x2, Slice Spacing=1mm, TE=1.116, TR=3.62, Flip Angle=7) that images 41 timesteps. DICOM files are imported into MIMICS where one 3D segmentation of the bladder is semiautomatically performed at every time point within each voiding event (17±4 timesteps in each voiding). Volume and surface area (SA) were collected for each 3D model of the bladder. The bladder volumes were then used to calculate flow rate and sphericity index. Urinary flow rate is calculated using the backward difference method while sphericity index used the SA of the bladder divided by the SA of a sphere with the same volume as the bladder, thus giving an indication of how “spherical” the bladder is at each timestep. So far, subjects recruited for this study exhibited large variations in flow rate characteristics allowing for a comprehensive characterization of bladder biomechanics and behavior during voiding. Sphericity index analysis has shown a distinct parabolic pattern indicating the bladder becoming “more spherical” and then returning to a “less spherical” state while emptying.
Biography: Alejandro Roldán-Alzate is an Associate Professor in the Departments of Radiology and Mechanical Engineering at the University of Wisconsin – Madison. Professor Roldán-Alzate is also the director of the Cardiovascular Fluid Dynamics Laboratory, which has the main interest of coupling engineering tools with medical imaging to non-invasively characterize the hemodynamics in different physiological and pathological conditions. More recently Dr. Roldán-Alzate has worked on developing non-invasive ways of assessing the biomechanics of the lower urinary tract using MRI in combination with computational fluid dynamics. He uses advanced optical imaging and computational fluid dynamics for enhancement and validation of quantitative flow imaging including 4D Flow MRI. Critical validation of Flow MRI metrics as well as enhancing their quantitative power is crucial for the future of clinical Flow MRI. Finally, Dr. Roldán-Alzate is the past chair of the fluid dynamics technical committee in the biofluids division of the American Society of Mechanical Engineers.