Endourethral MRI.
Although high-resolution MRI with phased array pelvic, endorectal, and endovaginal coils has dramatically enhanced the ability to visualize abnormalities of the female urethra and periurethral tissues, controversy still remains about the anatomy of this region. This study introduces an endourethral approach for ultra-high-resolution MRI of the female urethra and the periurethral tissues. To this end, two different radiofrequency (RF) receiver coil designs for an endourethral insertion have been developed: a single-loop coil and a phased array/quadrature coil. Both designs feature a flexible coil circuit, small loss tuning and matching directly at the coil, active decoupling, and the integration of a lambda/4 coaxial choke to decrease unbalanced currents and limit potential RF heating effects. Effective reduction of the mutual inductance between the two coils of the phased array design was achieved by introducing a metallic "paddle" to steer the flux between the coils. The performance of the coils has been evaluated in female human cadaver studies and in an in vivo pig experiment. The novel endourethral approach enabled a dramatic increase of the signal-to-noise ratio (SNR) at the region of interest (ROI). High-resolution MR images of the female urethra have been acquired with a spatial resolution down to 78 x 78 microm. Histologic correlation was achieved for the MR images generated. The achieved high local SNR and resulting high spatial resolution will add valuable information to the discussion of female urethral anatomy. Magn Reson Med 45:138-146, 2001.