Medinria diffusion weighted imaging6/16/2023 ![]() Passive continence is the involuntary aspect of micturition since no conscious effort is required to achieve continence. Urodynamic studies reveal that the resting tone of the urethral muscles maintains a favorable pressure relative to the bladder when urethral pressure exceeds bladder pressure ( 7). To maintain continence, urethral closure pressure must be greater than bladder pressure, both at rest and during increases in abdominal pressure, to retain urine in the bladder( 7). ![]() In addition to information on microstructure that can be derived from the DTI data, it is also possible to evaluate tissue architecture such as fiber length and density. It is possible to infer qualitative changes in the fiber diameter and in the extracellular fraction from the macroscopic diffusion measurements while careful diffusion modeling can enable one to extract quantitative values of these parameters. This information is represented by a diffusion tensor that provides insights into the micro-structure and characteristics of the underlying tissue. In addition, by application of diffusion sensitizing gradients along different directions, one can infer direction dependent diffusion. The anatomical positions of the different components of the urethral complex relative to the other components in the larger anatomical field of view can be appreciated.Īmongst the available imaging modalities (X-ray computed tomography, ultrasound, nuclear medicine), MRI is unique in that it enables the mapping of the molecular diffusion of water molecules ( 5, 6). ![]() (b) MRI high-resolution proton-density image of the mid-sagittal anatomy at a location comparable to that of the schematic (except for a larger field of view) is labeled with the relevant anatomy including the urethral complex, and shows the proximo-distal extent imaged in the present study. (a) Schematic of median section of bladder and urethra where the relative anatomic positions of the bladder, the lisso-sphincter, the prostate and rhabdo-sphincter are indicated. These findings have been plagued by the inevitable distortions and alterations of the anatomical structures in cadaveric dissections of bony elements due to the inaccessible location in the deep pelvis ( 4). Such descriptions have undergone several revisions since it was first described more than 150 years ago, since previous conclusions were mostly derived from cadaveric dissection of adult male pelvis ( 3). Prior to characterization of the age-related changes in the sphincters, the anatomical description of the normal male urethral sphincter has to be established. Urinary incontinence is a major clinical problem affecting a very large portion of the aging population, particularly due to age-related apoptotic changes to the sphincter muscles ( 1, 2). A schematic of anatomic structures in the median section through the bladder and urethra, with different relevant structures labeled, is shown in Fig. Urethral sphincters, namely the proximal lisso-sphincter and the striated external (EUS) or rhabdo-sphincter, as well as pelvic floor muscles, play an important role in urinary incontinence ( 1).
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