Developmental changes in proton magnetic resonance relaxation times of cardiac and skeletal muscle.

Proton magnetic resonance relaxation time measurements were used to study developmental changes in rabbit cardiac and skeletal muscles during the last days of gestation and at several postnatal times. Tissue water content decreased steadily during late fetal and early postnatal stages of development. During this period T1 and T2 for cardiac and skeletal muscles also decreased. The relaxation times stabilized after the 20th postnatal day, and at this juncture the T1 and T2 values for myocardium remained consistently higher than for skeletal muscle. The developmental changes in proton relaxation time probably represent changes in water distribution and mobility as well as macromolecular structure during muscle maturation.