***TASK*** the task is to summarize an input biomedical literature in six sentences 
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    Input: Abstract Objectives Compare public perceptions and intentions to undergo colorectal cancer screening tests following detailed information regarding CT colonography ( CTC ; after non-laxative preparation or full-laxative preparation ) , optical colonoscopy ( OC ) or flexible sigmoidoscopy ( FS ) . Methods A total of 3,100 invitees approaching screening age ( 45 - 54 years ) were r and omly allocated to receive detailed information on a single test and asked to return a question naire . Outcomes included perceptions of preparation and test tolerability , health benefits , sensitivity and specificity , and intention to undergo the test . Results Six hundred three invitees responded with valid question naire data . Non-laxative preparation was rated more positively than enema or full-laxative preparations [ effect size ( r ) = 0.13 to 0.54 ; p < 0.0005 to 0.036 ] ; both forms of CTC and FS were rated more positively than OC in terms of test experience ( r = 0.26 to 0.28 ; all p-values < 0.0005 ) . Perceptions of health benefits , sensitivity and specificity ( p = 0.250 to 0.901 ) , and intention to undergo the test ( p = 0.213 ) did not differ between tests ( n = 144 - 155 for each test ) . Conclusions Despite non-laxative CTC being rated more favourably , this study did not find evidence that offering it would lead to substantially higher uptake than full-laxative CTC or other methods . However , this study was limited by a lower than anticipated response rate . Key Points• Improving uptake of colorectal cancer screening tests could improve health benefits • Potential invitees rate CTC and flexible sigmoidoscopy more positively than colonoscopy • Non-laxative bowel preparation is rated better than enema or full-laxative preparations • These positive perceptions alone may not be sufficient to improve uptake • Health benefits and accuracy are rated similarly for preventative screening The disease natural history of colorectal neoplasm regarding two opposing theories , adenoma – carcinoma sequence and de novo carcinoma theory , is controversial and rarely quantified . The aims of this study are therefore to estimate the dwelling times of adenoma – carcinoma sequence by adenoma size and histological type , taking de novo carcinoma into account . The efficacy of polypectomy  was therefore estimated making allowance for two pathways . A case – cohort design , underpinning a cohort with 13 908 subjects ( including 10 496 normal subjects , 2652 polyps , 760 colorectal cancers ) who underwent the first examination of colonoscopy between 1979 and 1998 , was devised to estimate parameters associated with two opposing theories by r and omly selecting 305 normal subjects , 300 patients with polyps , and 116 colorectal cancers from the cohort . All the 2652 polyps were linked to national cancer registry to ascertain 25 invasive carcinomas after polypectomy . For the five-state model associated with adenoma size , dwelling times of small ( 0.6–1 cm ) and large adenoma ( > 1 cm ) are 7.75 and 5.27 years for the model without considering de novo , and 17.48 and 15.90 years for the model taking de novo carcinoma into account . Similar findings are observed for the model associated with histological type . The estimated proportions of de novo carcinoma are 31.87 % from the model by adenoma size and 27.81 % from the model by histological type . Compared to size less than 5 mm , patients with adenoma size between 6 and 10 mm and patients with adenoma size larger than 1 cm have 2.17-fold ( 0.67–10.74 ) and 4.25-fold ( 1.23–14.70 ) , respectively , for the risk of malignant transformation . There are similar findings for the model by histological type . The estimates of overall efficacy of colonoscopy in reducing CRC is 73 % for the model allowing for de novo carcinoma and 88 % for the model without considering de novo carcinoma theory . The efficacy of diminutive adenoma and small adenoma increases with follow-up years , whereas the efficacy of large adenoma decreases with follow-up years . In conclusion , about 30 % of cancers arising from de novo sequence are demonstrated . This finding , together with the adenoma – carcinoma sequence associated with adenoma size and histological type , is important for the estimation of dwelling times , the efficacy of colonoscopy , and the surveillance of polyp after polypectomy BACKGROUND Screening for colorectal cancer is widely recommended , but the preferred strategy remains unidentified . We aim ed to compare participation and diagnostic yield between screening with colonoscopy and with non-cathartic CT colonography . METHODS Members of the general population , aged 50 - 75 years , and living in the regions of Amsterdam or Rotterdam , identified via the registries of the regional municipal administration , were r and omly allocated ( 2:1 ) to be invited for primary screening  for colorectal cancer by colonoscopy or by CT colonography . R and omisation was done per household with a minimisation algorithm based on age , sex , and socioeconomic status . Invitations were sent between June 8 , 2009 , and Aug 16 , 2010 . Participants assigned to CT colonography who were found to have one or more large lesions ( ≥10 mm ) were offered colonoscopy ; those with 6 - 9 mm lesions were offered surveillance CT colonography . The primary outcome was the participation rate , defined as number of invitees undergoing the examination relative to the total number of invitees . Diagnostic yield was calculated as number of participants with advanced neoplasia relative to the total number of invitees . Invitees and screening centre employees were not masked to allocation . This trial is registered in the Dutch trial register , number NTR1829 . FINDINGS 1276 ( 22 % ) of 5924 colonoscopy invitees participated , compared with 982 ( 34 % ) of 2920 CT colonography invitees ( relative risk [ RR ] 1·56 , 95 % CI 1·46 - 1·68 ; p<0·0001 ) . Of the participants in the colonoscopy group , 111 ( 9 % ) had advanced neoplasia of whom seven ( < 1 % ) had a carcinoma . Of CT colonography participants , 84 ( 9 % ) were offered colonoscopy , of whom 60 ( 6 % ) had advanced neoplasia of whom five ( < 1 % ) had a carcinoma ; 82 ( 8 % ) were offered surveillance . The diagnostic yield for all advanced neoplasia was 8·7 per 100 participants for colonoscopy versus 6·1 per 100 for CT colonography ( RR 1·46 , 95 % CI 1·06 - 2·03 ; p=0·02 ) and 1·9 per 100 invitees for colonoscopy and 2·1 per 100 invitees for CT colonography ( RR 0·91 , 0·66 - 2·03 ; p=0·56 ) . The diagnostic yield for advanced neoplasia of 10 mm or more was 1·5 per 100 invitees for colonoscopy and 2·0 per 100 invitees for CT colonography , respectively ( RR 0·74 , 95 % CI 0·53 - 1·03 ; p=0·07 ) . Serious adverse events related to the screening procedure were post-polypectomy bleedings : two in the colonoscopy group and three in the CT colonography group . INTERPRETATION Participation in colorectal cancer screening with CT colonography was significantly better than with colonoscopy , but colonoscopy identified significantly more advanced neoplasia per 100 participants than did CT colonography .  The diagnostic yield for advanced neoplasia per 100 invitees was similar for both strategies , indicating that both techniques can be used for population -based screening for colorectal cancer . Other factors such as cost-effectiveness and perceived burden should be taken into account when deciding which technique is preferable . FUNDING Netherl and s Organisation for Health Research and Development , Centre for Translational Molecular Medicine , and the Nuts Ohra Foundation OBJECTIVES : Visualizing the entire colorectum in screening is an advantage of colonoscopy , and also computed tomographic ( CT ) colonography , another potentially suitable screening test . Our objective was to compare screening CT colonography and colonoscopy in an asymptomatic average-risk population , and to determine whether providing a choice of tests increased participation . METHODS : One thous and and four hundred subjects from the general community , r and omly selected from the parliamentary electoral roll , were allocated one of three screening groups : colonoscopy , CT colonography , or a choice of these tests , and were sent an institutional letter of invitation . Those with symptoms , colorectal cancer in first-degree relatives , or colonoscopy within 5 yr were ineligible . Outcome measures were participation , acceptability of screening , and yield for advanced colorectal neoplasia in participants . RESULTS : Of the subjects , 24.9 % were ineligible ; the overall participation rate was 18.2 % ( 184/1,009 ) . Participation in each screening group was not different . Both tests were accompanied by the same high levels of acceptability ; most participants found colonoscopy ( 87 % ) and CT colonography ( 67 % , p < 0.001 ) less unpleasant than expected . About 29 % ( 26/89 ) CT colonography subjects had a positive screening test . The yield of advanced colorectal neoplasia was 8.7 % ( 95 % CI 5–14 % ) , with no difference in yield between tests . CONCLUSION : Colorectal neoplasia screening by colonoscopy or CT colonography was associated with modest participation , high levels of acceptability , and similar yield for advanced colorectal neoplasia . Providing a choice of test did not increase participation BACKGROUND Colonoscopy is the gold-st and ard test for investigation of symptoms suggestive of colorectal cancer ; computed tomographic colonography ( CTC ) is an alternative , less invasive test . However , additional investigation after CTC is needed to confirm suspected colonic lesions , and this is an important factor in establishing the feasibility of CTC as an alternative to colonoscopy . We aim ed to compare rates of additional colonic investigation after CTC or colonoscopy for detection of colorectal cancer or large ( ≥10 mm ) polyps in symptomatic patients in clinical practice . METHODS This pragmatic multicentre r and omised trial recruited patients with symptoms suggestive of colorectal cancer from 21 UK hospitals . Eligible patients were aged 55 years or older and regarded by their referring clinician as suitable for colonoscopy . Patients were r and omly assigned ( 2:1 ) to colonoscopy or CTC by computer-generated r and om numbers , in blocks of six , stratified by trial centre and sex . We analysed the primary outcome -the rate of additional colonic investigation-by intention to treat . The trial is an International St and ard R and omised Controlled Trial , number 95152621 . FINDINGS 1610 patients were r and omly assigned to receive either colonoscopy  ( n=1072 ) or CTC  ( n=538 ) . 30 patients withdrew consent , leaving for analysis 1047 assigned to colonoscopy and 533 assigned to CTC . 160 ( 30.0 % ) patients in the CTC group had additional colonic investigation compared with 86 ( 8.2 % ) in the colonoscopy group ( relative risk 3.65 , 95 % CI 2.87 - 4.65 ; p<0.0001 ) . Almost half the referrals after CTC were for small ( < 10 mm ) polyps or clinical uncertainty , with low predictive value for large polyps or cancer . Detection rates of colorectal cancer or large polyps in the trial cohort were 11 % for both procedures . CTC missed 1 of 29 colorectal cancers and colonoscopy missed none ( of 55 ) . Serious adverse events were rare . INTERPRETATION Guidelines are needed to reduce the referral rate  after CTC . For most patients , however , CTC provides a similarly sensitive , less invasive alternative to colonoscopy . FUNDING NIHR Health Technology Assessment Programme , NIHR Biomedical Research Centres funding scheme , Cancer Research UK , EPSRC Multidisciplinary Assessment of Technology Centre for Healthcare , and NIHR Collaborations for Leadership in Applied Health Research and Care Background Bowel preparation is an important part of computed tomographic colonography ( CTC ) ; we evaluated two small-volume preparations for screening CTC with regard to quality of preparation and patient acceptability . Methods Asymptomatic subjects at average risk for colorectal cancer from a community-based CTC screening program were r and  omized to bowel preparation comprising magnesium/bisacodyl/picolax or polyethylene glycol (PEG)/picolax . CTC images were evaluated by a blinded investigator for residual feces and fluid ; subjects completed a question naire regarding acceptability of the preparation . Results In 176 subjects r and omized to magnesium/bisacodyl/picolax ( n = 82 ) or PEG/picolax ( n = 94 ) , the former preparation was discontinued because of syncope or presyncope in four ( 5 % ) subjects . Another 137 subjects received PEG/picolax without a significant adverse event . There were no other major differences in acceptability of the preparations as reported by subjects . The quality of bowel preparations for reporting C 
    Output:
    
CTC is an option for CRC screening in asymptomatic patients .