[veelenga]

Overview

• add the mri-scanner explainer: one repetition of a spin-echo scan on a 1.5 T closed-bore scanner taking a slice of a head, told in six chapters (the machine, the main magnet, hydrogen leaning and wobbling, the radio pulse and its echo, the gradient coils, echoes turning into a picture), with 3 T as the comparison
• model from a sourced facts sheet: Larmor frequency and the Boltzmann spin surplus per field, a piecewise map from the timeline to real milliseconds for T1 and T2 weighting, the net magnet through tip, dephasing, refocus, echo and regrowth, the gradient arithmetic, and a 64 × 64 head drawing whose brightness comes from the spin-echo signal equation and is rebuilt line by line through a Fourier transform (fft.js)
• scene: a scanner in its copper-lined room with a table, patient and head coil, a wedge cutaway through the vacuum vessel, heat shield, liquid helium, main and shield coils, gradient shells and body coil, a cold head and quench pipe, flowing field lines with the 0.5 mT ring on the floor, a magnified cube of spin arrows with the net magnet, radio and echo rings, gradient coils that light along their own axis, and a wall monitor showing the picture as it builds
• controls: 1.5 T or 3 T, T1 or T2 weighting, cutaway, field lines and labels toggles, a tip angle slider, tissue, moment, coil and line count chips, a k-space and picture canvas with text alternatives, gauge readouts for the frequency, the time in the repetition and the lines filled
• copy in all eight languages, reviewed and then rewritten from the English meaning by a native writer each, with zero dashes and descriptions within the limits
• cover and link preview image
• build: keep a package that only one explainer imports out of the shared chunk, so fft.js does not weigh on the other pages

Notes

Lint, the full test suite (3,592 tests) and the build with the site check pass. The largest page (uk) loads about 271 kB of gzipped JavaScript against the 300 kB budget.

Browser QA on desktop 1440 × 900 and iPhone 13 in English, Ukrainian and Japanese: no page or console errors, no untranslated keys, no horizontal overflow, every dock choice, toggle and chip row checked on the real scene, and free orbit from above, behind and the far side in the first two chapters.

Known rough edges: the three gradient coil labels in chapter 5 point at one spot on the cut face, and the cover image is taken from a fairly steep angle.