A system for examining a colon includes a catheter, such as a rectal catheter, having a proximal end, a distal end, and a central lumen extending from the proximal end to the distal end of the catheter, and a flexible tube coupled with the catheter. The system includes a first balloon located adjacent a distal end of the flexible tube, and a second balloon extending around the catheter and being located between the distal and proximal ends of the catheter, whereby the distance between the first and second balloons is adjustable by sliding the flexible tube through the central lumen of the catheter. The first and second balloons are inflatable for isolating a section of a colon, and a gas or contrast agent may be introduced into the isolated colon section for conducting the examination.