Bladder wall flattening with conformal mapping for MR cystography

Magnetic resonance visual cystoscopy or MR cystography (MRC) is an emerging tool for bladder tumor detection, and 3D endoscopic views on the inner bladder surface are being investigated by researchers. In this paper, we further investigate an innovative strategy of visualizing the inner surface by flattening the 3D surface into a 2D display, where conformal mapping, a mathematically-proved algorithm with shape preserving, is used. The original morphological, textural and even geometric information can be visualized in the flattened 2D image. Therefore, radiologists do not have to manually control the view point and angle to locate the possible abnormalities like what they do in the 3D endoscopic views. Once an abnormality is detected on the 2D flattened image, its locations in the original MR slice images and in the 3D endoscopic views can be retrieved since the conformal mapping is an invertible transformation. In such a manner, the reading time needed by a radiologist can be expected to be reduced. In addition to the surface information, the bladder wall thickness can be visualized with encoded colors on the flattened image. A normal volunteer and a patient studies were performed to test the reconstruction of 3D surface, the conformal flattening, and the visualization of the color-coded flattened image. A bladder tumor of 3 cm size is so obvious on the 2D flattened image such that it can be perceived only at the first sight. The patient dataset shows a noticeable difference on the wall thickness distribution than that of the volunteer’s dataset.