Industrial CT would probably be pretty effective at giving a density distribution and identifying voids, but that may be overkill - a couple planes of X-ray ima

Industrial CT would probably be pretty effective at giving a density distribution and identifying voids, but that may be overkill - a couple planes of X-ray imaging may be sufficient. Ultrasound would also be a solid bet, but it depends how many points you need to sample if it would be time efficient.