Introduction 1 2 1 1 3 4 5 6 7 1 8 Fig. 1 a arrows arrowheads b arrowheads  Therapeutic options Surgery The anatomic position of the rectum in the true pelvis and its vicinity to adjacent anatomy, in particular the sphincter muscles, poses a challenge for the surgeon regardless of the surgical technique used. Surgical treatment of rectal cancer is a difficult balancing act between minimizing the risk of local recurrence and the preservation of anorectal and genitourinary function. Total mesorectal excision (TME) 9 10 Circumferential resection margin (CRM) and local recurrence 11 12 14 15 17 15 Adjuvant/neoadjuvant therapy 18 19 20 21 22 21 22 23 Local tumor staging 24 6 1 2 2 3 4 5 4 5 6 7 8 Table 1 TNM classification for colorectal cancer Type Description T1 Tumor involves submucosa T2 Tumor involves muscularis propria T3 Tumor beyond muscularis propria T4 Tumor reaches peritoneal surface or invades adjacent organ N0 No involved nodes N1 Up to three perirectal/colic nodes N2 Four or more perirectal/colic nodes Table 2 UICC staging of rectal carcinoma Stage Description Stage 0 Tis N0 M0 Stage I T1 N0 M0 T2 N0 M0 Stage IIA T3 N0 M0  B T4 N0 M0 Stage IIIA T1, T2 N1 M0  B T3, T4 N1 M0  C Every T N2 M0 Stage IV Every T Every N M1 Fig. 2 a arrowhead b c 2 a  Fig. 3 Paraxial T2-weighted FSE (TSE) sequence. Tumor of the rectal wall. Fibrous strands into the mesorectum represent desmoplastic reaction (arrow). A differention between desmoplastic reaction and tumor infiltration of the mesorectum can be difficult  Fig. 4 arrow arrowheads  Fig. 5 arrow arrowhead  Fig. 6 a b arrows  Fig. 7 arrow  Fig. 8 arrowhead  Staging modalities Endorectal ultrasound (EUS) 25 35 28 36 Computed tomography (CT) 32 37 41 42 43 MRI 39 44 46 31 47 49 The advent of powerful gradient systems and, above all, the development of high-resolution phased array surface coil systems in recent years brought the breakthrough in the staging of rectal cancer by MRI. The use of these phased-array surface coils combines a very high spatial resolution with a large FOV that allows not only detailed evaluation of the intestinal wall but also depicts surrounding anatomy including the mesorectal fascia. Imaging technique 50 At our department, we administer a spasmolytic agent (butylscopolamine) at a dose of 20–40 mg to prevent artifacts caused by peristalsis of the small intestine and to distend the sigmoid and rectum. The agent has a short half-life and is therefore injected intramuscularly immediately before MRI. For efficient planning of the pulse sequences to be employed, the radiologist performing the examination should beforehand obtain information about the approximate tumor localization (distance from anocutaneous line in cm) from the referring surgeon and ask the patient about any previous surgery or diseases of the pelvic organs. The patient is positioned comfortably on the back and a phased-array surface coil is placed on the pelvis in such a way that the lower edge of the coil comes to lie well below the pubic bone. The coil is kept in place with belts and the patient is then advanced head-first into the bore of the magnet. 51 52 Since differentiation with the T2-weighted sequences is based on the contrast between the high-signal-intensity mesorectal fatty tissue and the rather low signal intensity of the tumor, spectral fat suppression techniques are not needed. The duration of the MRI protocol as just outlined is about 25–30 min, including planning. T-staging 53 56 3 49 54 57 27 54 57 60 59 54 61 54 61 60 54 60 62 N-staging 9 10 11 63 16 64 65 66 Fig. 9 arrow  Fig. 10 asterisk  Fig. 11 arrows  10 25 26 30 32 34 35 37 67 32 39 68 69 32 39 47 53 55 60 70 71 9 Future perspectives USPIO 12 72 73 Fig. 12 a arrows b arrows  Whole-body MRI 74 77 62 Diffusion/perfusion-weighted MRI and PET 78 81 82 Conclusion The advances that have been made in the treatment of rectal cancer in recent years and that have considerably improved the prognosis of affected patients rely on differentiated pretherapeutic tumor staging. Despite its known limitations in T-staging, MRI is currently the only imaging modality that enables highly accurate evaluation of the topographic relationship between lateral tumor extent and the mesorectal fascia and to thus make a prediction about the CRM. In this way it is possible to carefully select those patients who will benefit from neoadjuvant therapy and to avoid overtreatment or undertreatment.