*2.2.1 Bad diagnosis always begins with bad patient preparation*

Contrary to what is still being claimed, preparation of the bowel by means of enema (clyster or micro clyster) immediately prior to the examination is extremely important. We want to perform a high-precision examination similar to colonoscopy in a clean medium and not in a contaminated organ. The patient will always be informed in detail about the exact procedure of the examination, and this ensures active cooperation in most cases. This way, we minimize restlessness and movement artifacts. After flushing with Microlax Rectal Solution, the rectum is filled with warm tap water. Water is an excellent contrast medium without risking distension of the intestinal wall. In our department, we only use ultrasound gel for MRI defaecography, but not for tumor diagnosis, as the expansion of the rectum due to compression may restrict the assessment of the mesorectal space. Water as contrast medium allows an exact detection of even small flat lesions, which may be the case after RCT. Another advantage is the elimination of air besides stool residues. This procedure also creates perfect conditions for high quality DWI, which plays a particularly important role in restaging. Air is an enemy and real falsificator of DWI measurements! Last but not least, we prepare an infusion for administration of butylscopolamine to reduce intestinal motility, and for administration of contrast agent, if necessary.

Having this done, specially trained medical-technical staff accompanied by doctors trained in rectal MRI perform the actual MRI examination. They always follow a standardized protocol with particular attention to angulation. The main axial layers must always be orthogonal to the tumor. Only in this way can the MRI results correspond with histology in terms of local tumor staging, and measurement of infiltration depth and distance to the mesorectal fascia. Furthermore, it is important to ensure that the restaging examination is always performed with the same equipment as the primary staging examination was done. Our experience has shown that different devices (e.g. Siemens vs. Phillips) deliver different DWI, which can make precise restaging difficult. These organizational challenges can only be overcome if we are all aware of them.
