How to determine if there is a cavity inside a metal body, if the metal from which the body is made is known?

If the metal from which the body is made is known, then its density is also known. Therefore, to find out if the cavity is inside the body, you must first measure its mass and volume, then use the formula p = m / V to calculate the real density of the body and compare it with the density of the metal from which it is made. If the calculated density of the body is less than the density of the metal, then there are cavities in it.