A handheld oscillation applicator (40) for use in a magnetic resonance rheology imaging system (10), for applying mechanical oscillations to at least a portion of a subject of interest (20), the handheld oscillation applicator (40) comprising a housing (54), at least one transducer unit (48) configured to output mechanical energy, a piston (68) that is mechanically linked to the at least one transducer unit (48), the piston (68) including a first end (70), a second end (72), and an opening (74) that extends between the first end (70) and the second end (72), wherein the housing (54) comprises at least one opening (60), and the at least one opening (60) of the housing (54) and the opening (74) of the piston (68) at least partially overlap with regard to a housing opening direction (66) defined by an opening center (62) of the opening (60) of the housing (54) at a first surface (56) and an opening center (64) of the opening (60) of the housing (54) at a second surface (58)； and an oscillation applicator system (38), including: a handheld oscillation applicator (40), a transducer driving unit (42) for energizing the at least one transducer unit (48), a sensing unit (50) configured to determine a physical quantity that is representative of an amplitude of mechanical oscillations being applied to at least the portion of the subject of interest (20), and to provide an output signal representing the determined physical quantity, at least one closed-loop control circuit for maintaining a mechanical displacement amplitude of the transducer unit (48) at a selected level, wherein the closed-loop control circuit is configured to provide an output signal for controlling the transducer driving unit (42), based on the output signal received from the sensing unit (50).L'invention concerne un applicateur d'oscillation à main (40) destiné à être utilisé dans un système d'imagerie de rhéologie par résonance magnétique (10), pour appliquer des oscillations mécaniques à au moins une par
