<prompt> Which of the following is the investigation of choice for assessment of depth of penetration and perirectal nodes in rectal cancerTrans rectal ultrasoundCT Scan pelvisMRI ScanDouble contrast Barium enema  <response>: Investigations for Rectal Carcinoma For Diagnosis -Best diagnosed by sigmoidoscopy rigid, not flexible Biopsy of tumorBarium enemaFor stagingTRUS transrectal ultrasonographyCTMRITRUS transrectal ultrasonographyThe depth of tumor invasion can be accurately determined by TRUSBut it cannot detect cancer metastasis in lymph node though it can detect enlarged lymph node, but it cannot predict if cancer infiltration is present or not.CTCT scan is also helpful for evaluation of cancer extension.But again, CT also cannot tell clearly about lymph node invasion by cancer cell.MRIIt has become the most useful investigation tool especially with the use of transrectal coils for rectal carcinoma.It can very well predict the invasion of tumor in the rectal wall as well as lymph node invasion with high accuracy. 