How much exposure to radiation is needed for this? Their brochure indicates 20-80 mGy/mSv. But a typical clinical head CT is only 2 mGy. AFAIK, exposures that high would not be acceptable for clinical human use.

It's probably inevitable that a 'spectral' scanner requires greater exposure than clinical CT scanners since the intensity of a spectral X-ray source apparently varies during the scan. This implies slower scans and more X-ray exposure than a conventional CT.

Apparently that's why MARS' current product is intended for preclinical (non-human) use only.