Foreign Object (FO) Definition
==============================
A foreign object (FO) is any object fully introduced into the patient's body
cavity during surgery that must be retrieved or accounted for. Importantly,
standard surgical instruments that remain connected to the external environment
(e.g., graspers, scissors, trocars, staplers, cameras) are not considered foreign
objects. Furthermore, we exclude detachable parts of surgical instruments,
particularly anvil components of staplers.


Foreign Object Classes
======================

Sponge
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A soft, absorbent material used to soak up fluids. They are typically white when
fresh and can become reddish-brown when saturated with blood.

Clip
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A small metal or polymer device used to seal vessels or ducts. May potentially
remain in the body. Clips only count as foreign objects once placed in the
abdomen. They do not count as foreign objects while loaded within the clip
applier instrument.

Specimen Bag
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A sterile pouch used to collect and retrieve resected tissue or organs from the
body cavity. Only consider the pouch itself as foreign object and ignore the
string attached to it.

Silicone Loop
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A soft and flexible, typically white band used to encircle and control blood
vessels or structures for isolation and traction.

External Drain
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A clear or fluid-filled tube used to evacuate fluids from the surgical site to
the outside of the body. Its tip may be temporarily visible within the surgical
field during placement or adjustment.

Needle
------
A sharp, pointed metal instrument, straight or curved, used for placing sutures.
If only the string of the needle is visible, it does not count as "the needle is
visible". Only if the needle itself is visible in the video.

Gallstone
---------
Calcified concretion originating from the gallbladder with a roundish,
white/yellow appearance. Gallstones that are within a specimen bag count as
retrieved. Specimen bags are annotated separately.

Specimen
--------
Excised biological tissue (e.g. appendix, resected bowel segment) that must be
retrieved from the body cavity before procedure completion. As soon as every
connection to other body anatomy is cut, the cut off tissue/organ counts as
specimen. This excludes fat or blood. Specimens that are within a specimen bag
count as retrieved. Specimen bags are annotated separately.

Mesh
----
A screen-like patch that surgeons use to reinforce a weak area in the body's
muscle wall. This differs from a sponge which appears more like a tightly woven
cloth. It is an implantable foreign body that is not removed at the end of the
surgery.
