1. A dual energy x-ray absorptiometry (DEXA) method for determining intramuscular fat of a selected sub-volume of an intramuscular fat volume of a patient, which intramuscular fat volume is surrounded by a subcutaneous fat volume and together therewith forms a total volume of a patient's limb, comprising: acquiring x-ray measurements of the patient's limb for respective pixel positions related to a two-dimensional projection image of said total volume, wherein at least some of the measurements are dual-energy x-ray measurements of the subcutaneous fat and the intramuscular fat to thereby make subcutaneous fat and intramuscular fat regions of the patient visible in a dual-energy image of the patient's limb; placing a plurality of regions relative to the image; computer processing said dual-energy x-ray measurements to determine a metric of intramuscular fat contained in said sub-volume of the intramuscular fat volume that also contains material that is not intramuscular fat; and providing and displaying selected results related to said intramuscular fat metric.