"The "rho" in the sequence name refers to a "ro"tating frame and the sequence has elements of both T1 and T2 weighting. After the initial 90° RF pulse, tipping the magnetisation vector into the transverse plane, a second pulse is applied parallel to the tipped magnetisation vector. This effectively locks the magnetisation vector into the transverse plane ("ro"tating frame) without phase decay (as with T2 decay). The decay of this locked magnetisation to 0 is the T1 rho time."
"The sequence is sensitive for low-frequency interactions between macromolecules and bulk water, and is predominantly under investigation for use in cartilage imaging. Applications in other areas (e.g. brain, cardiac and liver imaging) are areas of active research."
"Normal T1 relaxation time is dependent on longitudinal magnetisation interactions with surrounding environment (e.g. "spin-lattice"). T1 rho effectively manages to make transverse magnetisation interact with the surrounding environment (sort of a T2 "spin-lattice")."