Medical City · Device Lab 34 of 69
Endoscope
A coherent bundle of some twenty-three thousand fibres carries the image up the insertion tube to an eyepiece, and two incoherent bundles carry light the other way from a lamp in the stack. The objective forms a real image on the distal face of the image guide, every fibre relays one picture element of it, and what a person looks at is the proximal face of the same bundle.
- 10 parts
- 2 configurations in the Device Lab
- Also called: Gastroscope, Flexible Endoscope
Configurations
The versions in the Device Lab.
Fibre-optic image guide, eyepiece and light bundles
A coherent bundle of some twenty-three thousand fibres carries the image up the insertion tube to an eyepiece, and two incoherent bundles carry light the other way from a lamp in the stack. The objective forms a real image on the distal face of the image guide, every fibre relays one picture element of it, and what a person looks at is the proximal face of the same bundle.
Chip-on-tip sensor and distal light-emitting diode
The objective forms its image directly on a sensor three millimetres behind it, inside the distal tip. What travels up the insertion tube is a signal on a cable six tenths of a millimetre across, and the light comes from a diode at the tip rather than from a lamp in the stack, so no glass runs the length of the scope at all.
How it works
Explore it in the Device Lab.
The exponent that decides everything
Put every lumen in one shaft side by side and compare their resistances, then feed them all from one fitting and watch where the delivery goes.
Why a flush carries rather than scrubs
Raise the flush rate on the working channel until the flow stops being laminar, and then try the same thing on a lumen under a millimetre across.
Where the image is formed decides how wide the channel is
Add up the cross-sectional area of everything the image path occupies on each configuration, take the difference, and spend it on the working channel.
A hole nobody can see
Pressurise the interior to a couple of hundred millimetres of mercury, submerge the instrument, and angulate it fully while watching for bubbles. Then work out how small a hole that finds.
The elegant half, and why it is not the problem
Compute the acceptance angle from two refractive indices, the packing fraction from a core and a pitch, the resolution from a sampling grid, and the depth of field from the same grid. Then note that not one of them is a failure mode.
The parts
Part by part.
Distal tip and its four apertures
A black moulded cylinder about ten millimetres across and fourteen long, at the end of a metre of dark flexible tube. Look at it end-on and there are four openings in the face, each a different size, and one of them has a tiny bent spout beside it.
Objective lens assembly and the field of view
Three glass elements smaller than a grain of sugar with an aperture stop between them, sitting behind the window in the distal face. The whole assembly is about five millimetres long and there is no focus control anywhere on the instrument.
Bending section, articulation rings and outer sheath
The last ten centimetres before the tip, and it is obviously different from the rest of the shaft: softer, more willing, and it stays where it is put. Squeeze it and you can feel discrete rings under the rubber.
Angulation wires, coil pipes and the control knobs
Two knobs on the side of the control body, one inside the other. The large one is up and down, the small one is left and right, and each has a lever beside it that locks it.
Insertion tube: helical band, braid and sheath
A metre of dark, slightly matt tube about the thickness of a finger, marked with pale rings every five centimetres. It feels almost incompressible along its length and quite willing to curve.
Biopsy and suction channel
A pale fluoropolymer tube running the length of the instrument, two and a half to three and a half millimetres across, from a port on the control body to the largest opening in the distal face. On the instrument you never see it.
Instrument port, biopsy valve and the suction branch
A short boss angled forward off the top of the control body with a soft rubber cap in it. The cap has a slit in it.
Air and water channels, nozzle and valve
A blue-capped button on the control body with a hole in the top of it, and two narrow lumens under a millimetre across running the whole length of the instrument and the cord. Leave the button alone and nothing happens.
Suction valve and the suction line
A red-capped valve on the control body next to the blue one, a hose leaving the connector section, a translucent jar on the bottom shelf of the trolley with a float in it, and a pump behind the jar with a gauge and a regulator. Press the red valve and fluid appears in the jar within a second.
Water bottle, air pump and the irrigation path
A translucent bottle of a couple of hundred millilitres clipped to the trolley column, with a blue cap carrying two tubes: one short, one reaching nearly to the bottom. A line runs from the cap towards the light source.
Simulations
Where it appears in the simulations.
Standards
The standards for this device.
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