- In magnetic resonance, the time for 63% of longitudinal relaxation to occur; the value is a function of magnetic field strength and the chemical environment of the hydrogen nucleus; for protons in fat and in water, in a 1.5T magnet, about 250 msec and 3000 msec, respectively. A T.-weighted image will have a bright fat signal.* * *breast tumor smaller than 2 cm [TNM (tumor-node-metastasis) classification]; longitudinal relaxation time
* * *tricuspid valve closure; see first heart sound, under sound.
Medical dictionary. 2011.