colon & code
What if a CT scan
could predict your operation?
In our blinded validation study, two board-certified colorectal surgeons measured the inter-spinous distance on 70 paired axial CT slices. Their 95% limits of agreement spanned −6.28 to +2.94 mm — a window of more than 9 mm of legitimate disagreement between trained raters.
At this much human variability, you cannot tell a difficult pelvis from an easy one by manual measurement alone.
And no model built on top of unstable measurements can be trusted.
Auto-ISD takes a pelvic CT in NIfTI format and runs a deterministic pipeline: bone segmentation, femur-anchored search window, ISD profile sweep, valley detection, compartment metrics. No manual landmarks. No vendor preprocessing.
For every axial slice in a femur-anchored window, Auto-ISD measures inter-spinous distance, smooths the profile, and selects the slice at the narrowest local minimum. When no clear valley exists, it falls back to the longest plateau.
Inter-spinous distance describes the pelvis at one slice. To predict surgical difficulty, the algorithm also computes the pelvic posterior compartment: the region a TME surgeon actually works in.
Triangle bounded by the bilateral ischial spines and the most anterior point of the sacrum. Captures both the transverse narrowing (ISD) and the anteroposterior depth in a single geometry.
Measured at the same axial slice as ISD: the AP span between hip bone and sacrum near the midline. Different metric from triangle depth, captures the AP dimension complementing ISD's transverse one.
Patients with the same ISD can present with very different operative conditions. The pelvic fat occupying the triangle reduces the surgeon's actual working space. pPFA quantifies that occupancy directly from torso fat segmentation.
Triangle area minus bowel and fat occupancy. The residual space theoretically available for instrument maneuvering during posterior mesorectal dissection. A composite of geometry and tissue.
Across 70 cases of blinded manual annotation by two board-certified colorectal surgeons, the automated pipeline's agreement against the manual reference exceeded the agreement between the two raters themselves. Bland–Altman, ICC, and contrast-robustness analyses are in the IJCARS paper.