Fast for 12h before the examination and take 8ml of Simethicone Emulsion (Berlin-Chemie, Germany, containing 40 mg simethicone in 1mL emulsion) with 250ml water 30min before capsule ingestion.CE are performed with the Pillcam SB2 capsule endoscopy system (Given Imaging Co. Ltd., Yoqnem, Israel).

the same as protocol A plus 1L Polyethylene glycol 11-12h before VCE. CE are performed with the Pillcam SB2 capsule endoscopy system.

the same as protocol A plus 2L Polyethylene glycol 10-12h before VCE. CE are performed with the Pillcam SB2 capsule endoscopy system.

Group D: the same as protocol A plus 1L Polyethylene glycol 3-4h before VCE. CE are performed with the Pillcam SB2 capsule endoscopy system.

Group E: the same as protocol A plus 2L Polyethylene glycol 2-4h before VCE. CE are performed with the Pillcam SB2 capsule endoscopy system.

The image quality was evaluated only in cases in which the capsule reached the cecum within the examination period. All CE images will be assessed at low speed (10 frames/s) under the AutoView mode of the RAPID workstation (Given Imaging). The intestinal mucosa is defined as clean if, less than 25% of the mucosal surface was covered by dark liquid, bubbles or debris. Using a timer, the investigators record the exact time period during which the small intestinal mucosa was clean. The definition of "excellent" is at least 90% of the overall small bowel mucosa is clean (the sum of "clean" time /total small bowel transit time>90%). And the definition of "good" is at least 80% of the overall small bowel mucosa is clean. We considered that "excellent" or "good" preparation is adequate to make an accurate diagnosis.

A visual analogical scale (VAS) is used to evaluate the degree of patients' discomfort. The numerical scale between 0 and 10, with 0 being no burden at all and 10 indicating an intolerable procedure.

The questionnaire provide information about whether they experienced nausea, bloating, or any discomfort during the bowel preparation, difficulty to complete the preparation, their willingness to repeat the same preparation in the future (yes or no)and did it affect their daily activity and nocturnal rest.