I've watched a video about this recently. The problem is, most detectors were based on X-rays in the past decades. Liquid explosives are pretty close to the density (and/or other properties) of water, and you can't tell for sure whether there's toothpaste or boom juice in that tube.

However, some airports started using expensive ~~MRI~~ MRI like X-ray* machines that can see stuff in more detail, plus, it lets you to make cross sections from different angles and therefore have a 3D model that you can rotate on your screen (it's rather cool).

EDIT: I just realised someone else linked this, too. I would leave it here, it's still educational.

[–] Darkassassin07@lemmy.ca 3 points 5 months ago (1 children)

I'd just like to clarify: the new machines aren't MRI (the magnets in those would prohibit all metal objects being within 100ft).

The new machines are also xray; but the xray emiters and detector are now on a spinning carriage similar to an MRI. This allows you to build a 3d model of the object and calculate it's volume, which when combined with the density measurements gives much more reliable material detection.

This also means your stuff doesn't have to be removed from bags to ensure items aren't blocking each other from the scanner.

[–] Dicska@lemmy.world 2 points 5 months ago

You're so right, it makes perfect sense. Thanks for the correction!