Would dual-energy X-ray absorptiometry be useful if performed on a crab?
Stream of thoughts:
no
Dual-energy X-ray absorptiometry is typically used to diagnose and follow osteoporosis.

Osteoporosis is a disease in which bone weakening increases the risk of a broken bone.

Crabs are invertebrates.

Invertebrates do not have bones.

.

So, the answer is no