Colonoscopy is widely considered as the main choice for patients with suspected colorectal disease,and for screening those at high risk of colorectal cancer. However， colonoscope examination,especially those unsedated ones for screening,may bring much pain to patients,even induce some severe complications such as perforation.Considering the increasing need of colonoscopy examination for screening purpose,it has been a problem deserving of further study that how to reduce pain and ensure safety during the procedure.Some studies suggest that use of Magnetic endoscopic imaging(MEI) during colonoscopy has the potential to ease patient discomfort and reduce complications.Theoretically,the MEI could accurately depict the position of the scope in three dimensions and help avoid forcefully feeding the colonoscope through loops of vulnerable bowel,thus alleviating patient pain and promoting procedure safety.However,the problem whether MEI system could help reduce patient pain during procedure effectively，especially in inexperienced colonoscopists，still remains controversial for researchers,and no study has been designed to test the hypothesis that MEI may help decrease the risk of some complications,such as colon perforation.In this study we aim to evaluate the he efficacy of magnetic scope navigation on patient pain during unsedated colonoscopy；In addition，we try to construct a simple colon force measurement device ,and by using this device to observe the variation of force exerted on colon loop ,we expect to find the potential mechanism of pain-alleviation and explore the possible effect of complication reduction during colonoscopy under the influence of MEI system.

This clinical trial is planned as two parts:In the first part,consecutive patients would be recruited and randomized to have colonoscopy examination performed by inexperienced colonoscopists (having performed less than 200 procedures) either with or without the assistance of magnetic scope navigation system. The second part would be conducted as a pilot study,we would first construct a simple colon force measurement device;then colonoscopist would be randomized to perform colonoscopy on a colon model either with or without an MEI view while the force measurement device being used to collect data of colon force variation meanwhile. All force variation data would be recorded by a image storage device.No patients would be involved in the second part.In this pilot study, we plan to perform 40 colonoscopy procedures with the assistance of MEI and 40 colonoscopy procedures without the assistance of MEI.

Inclusion Criteria:

colonoscopists: All colonoscopists are selected from the colonoscopy learners in Endoscopy Center of Shanghai Renji Hospital. Only inexperienced colonoscopists (having performed less than 200 procedures) would be allowed to participate in the first part while both inexperienced colonoscopists and experienced colonoscopists (having performed less than 350 procedures) are allowed to participate in the second part.

patients: in the first part: Patients aged between 18 and 75 are recruited to receive unsedated colonoscopy examination with their permission. Written informed consent would be obtained.

in the second part:no patient would participate in this part

Exclusion Criteria： patients:consecutive patients,excluding inpatients,pregnant,who had a known or suspected colonic stricture or obstruction, who had previous history of abdominal surgery,who had severe comorbid cardiopulmonary,kidney,liver conditions,who had pacemakers or internal defibrillators,who were unable to give informed consent,who have active gastrointestinal bleeding are recruited