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Measurement of polyp size at colonoscopy: a proof-of-concept simulation study to address technology bias
  1. Shinichiro Sakata1,2,3,
  2. Felicity McIvor3,
  3. Kerenaftali Klein4,
  4. Andrew R L Stevenson1,2,
  5. David G Hewett1,3
  1. 1School of Medicine, The University of Queensland, Brisbane, Australia
  2. 2Department of Colon and Rectal Surgery, Royal Brisbane & Women's Hospital, Brisbane, Australia
  3. 3Division of Gastroenterology, The Queen Elizabeth II Jubilee Hospital, Brisbane, Australia
  4. 4Clinical Trials and Biostatistics Unit, QIMR Berghofer Medical Research Institute, Brisbane, Australia
  1. Correspondence to Dr David G Hewett, University of Queensland School of Medicine, Mayne Medical Building, Herston Road, Herston, QLD 4006, Australia; d.hewett{at}uq.edu.au

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We introduce a novel, proof-of-concept polyp measurement device for the design of future colonoscopes. In a simulation study, 50 expert endoscopists used three measurement strategies (method 1: no visual cues; method 2: a snare tip visual cue; method 3: a grid visual cue) to evaluate 120 images of 40 simulated polyps (1–10 mm) presented in random order. Measurement accuracies of each method were 20%, 33% and 90%, respectively (p<0.001). Using the proof-of-concept measurement grid (method 3), endoscopists were 99.8% accurate for high confidence classifications of polyps into clinically relevant size categories. Improvements in colonoscope design are needed to minimise human and technology biases.

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There are increasing concerns about the influence of human bias on the measurement of polyp size at colonoscopy.1–3 A study of 92 124 individual colorectal polyp measurements from the UK bowel cancer screening programme showed that endoscopists, radiologists and pathologists all exhibited terminal digit preference and clustering of polyp measurements at 5mm intervals.1 Although human bias is an acknowledged contributor to the measurement error of polyps, the importance of technology bias remains understated.1–3 Figure 1 illustrates the extent of image distortion from the fish eye lens of modern colonoscopes, where objects in the centre of the display appear magnified and objects at the periphery appear small and warped. It also demonstrates how makeshift measurement tools, such as snare catheters, potentially worsen measurement error from technology bias coupled with illusions of relative size. We hypothesised that both human and technology biases could be addressed by improvements in current colonoscope technology.

Figure 1

Three measurement conditions for a 5 mm simulated polyp taken with an Olympus CF-HQ190L colonoscope at a viewing distance of 10 mm. (A) Method 1—no visual cues, in which the polyp was photographed against a plain, orange background without any …

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