Novel metal-chelating temperature-responsive ultrafine hydrogel nanoparticles were synthesized and loaded into a solid lipid nanoparticle carrier with various melting points. The temperature sensitive contrast agent was engineered with two consecutive 'off-on' and 'on-off thermal transitions, which delimit a window within which thermotherapy can be applied. An 'off-on' step transition in contrast enhancement was detected at the melting point of the lipid matrix and an 'on-off step transition is present at the lower critical solution temperature (LCST) of the copolymer hydrogel. A single composite gadolinium-hydrogel-lipid hybrid nanoparticle (Gd-HLN), as formulated here, can thus serve to indicate the onset of non-ablative thermotherapy (42-43°C) and to delineate the transition from non-ablative to ablative temperatures (>55°C). Since both the melting point of the lipid matrix and the LCST of the hydrogel are tunable in terms of temperature of phase transition, the intelligent multiparticle relaxation-enhancing system can be engineered to designate the temperature window specific to the goal of the individual thermotherapy.