The adult large bowel: describing environment morphology for effective biomedical device development

Abstract

An understanding of the biological environment, and in particular the physical morphology, is crucial for those developing medical devices and software applications. It not only informs appropriate design inputs, but provides the opportunity to evaluate outputs via virtual or synthetic models before investing in costly clinical investigations. The large bowel is a pertinent example, having a major demand for effective technological solutions to clinical unmet needs. Despite numerous efforts in this area, there remains a paucity of accurate and reliable data in literature. This work reviews what is available, including both processed datasets and raw medical images, before providing a comprehensive quantitative description of the environment for biomedical engineers in this and related regions of the body. Computed tomography images from 75 patients, and a blend of different mathematical and computational methods, are used to calculate and define several crucial metrics, including: a typical adult size (abdominal girth) and abdominal shape, location (or depth) of the bowel inside the abdomen, large bowel length, lumen diameter, flexure number and characteristics, volume and anatomical tortuosity. These metrics are reviewed and defined by both gender and body posture, as well as-wherever possible-being spilt into the various anatomical regions of the large bowel. The resulting data can be used to describe a realistic 'average' adult large bowel environment and so drive both design specifications and high fidelity test environments.

Keywords: colon specifications; endoscopy; large bowel; medical image analysis; morphology; virtual anatomy.

Fig. 8.

The separation distance (or depth) of the bowel lumen inside the abdominal cavity w.r.t the bowel perimeter. MALE patients, SUPINE body position, ANTERIOR measurement direction.

Fig. 9.

The separation distance (or depth) of the bowel lumen inside the abdominal cavity w.r.t the bowel perimeter. FEMALE patients, SUPINE body position, ANTERIOR measurement direction.

Fig. 1.

A diagram summarizing the large bowel regions. a. The regions defined on a model of an actual large bowel from CT imaging, b. A typical representation of the large bowel anatomy in literature next to c. An example of a tortuous large bowel.

Fig. 2.

The size of the patient population analyzed in this work. a. Size of the male population, b. Size of the female population.

Fig. 3.

An overview of the DICOM image processing showing a. a raw CT image, b. the segmented and labelled image and c. the 3D model (point cloud) with centerline overlaid.

Fig. 4.

Extracting metrics from the abdominal sections. a. the various metrics defined on each image slice, including perimeter of the abdominal wall and the relative location of the lumen center; b. the definition of patient directions for distance measurements.

Fig. 5.

The large bowel lumen is sampled in thin sections orthogonal to the centerline to calculate the diameter.

Fig. 6.

A large bowel centerline with all flexures (green) identified. Red lines indicate no distinct flexure.

Fig. 7.

A demonstration of flexure severity being a function of flexure angle, bend radius and lumen diameter.