To my knowledge, transcranial doppler doesn’t form images. It just gives you a single channel measurement that is very low resolution.

The method we’re proposing would have mm resolution.

A commercial medical ultrasound imaging device in doppler mode can pick up and map onto the image plane some of the vessels in the brain through the skulls. But mostly just through the temporal bones(where the skulls is like 1-2mm thick). (The commercial machines run doppler on lower frequency than imaging signal so you get no s tructural image this way, only the color doppler map(unless you find a place in the skull where an emissary vein passes through the bone table where the image signal can ride through))

Does viable transcranial doppler for poeple without fontanelles actually exist?

Through the temporal bone of most people you can catch some sparse doppler signals with average hospital gear.

The fontanelles enable good ultrasound imaging on an entirely different level. A highres greyscale image vs a few sparse blobs of doppler from major vessels.