A medical instrument (200, 400, 500) comprising: - a magnetic resonance imaging system for acquiring magnetic resonance data from a subject at least partially within an imaging zone; - a transducer for mechanically vibrating at least a portion of the subject within the imaging zone; - a transducer controller for controlling the amplitude and phase of vibrations of the transducer; - a processor for controlling the medical instrument; - a memory for storing machine executable instructions (264, 266, 268, 270) for execution by the processor, wherein execution of the instructions causes the processor to: - control the transducer to vibrate; - control the magnetic resonance imaging system to repeatedly acquire the magnetic resonance data from a first region of interest using a first spatially encoding pulse sequence during vibration of the transducer; - control the magnetic resonance imaging system to acquire navigator data from a second region of interest using a second spatially encoding pulse sequence, wherein the execution of the instructions causes the acquisition of the magnetic resonance data to be interleaved with the acquisition of the navigator data; - construct a set of navigator profiles (258, 804, 904, 1004, 1108, 1208, 1308) using the navigator data; and - reconstruct at least one magnetic resonance rheology image from the magnetic resonance data; said medical instrument being characterised in that execution of the instructions further causes the processor to determine at least one parameter descriptive of transducer vibrations using the set of navigator profiles to provide feedback between the amplitude and phase of vibrations of the transducer and said at least one magnetic resonance rheology image. - a magnetic resonance imaging system for acquiring magnetic resonance data from a subject at least partially within an imaging zone; - a transducer for mechanically vibrating at least a portion of the subject within the imaging zone; - a transducer controller for controlling the amplitude and phase of vibrations of the transducer; - a processor for controlling the medical instrument; - a memory for storing machine executable instructions (264, 266, 268, 270) for execution by the processor, wherein execution of the instructions causes the processor to: - control the transducer to vibrate; - control the magnetic resonance imaging system to repeatedly acquire the magnetic resonance data from a first region of interest using a first spatially encoding pulse sequence during vibration of the transducer; - control the magnetic resonance imaging system to acquire navigator data from a second region of interest using a second spatially encoding pulse sequence, wherein the execution of the instructions causes the acquisition of the magnetic resonance data to be interleaved with the acquisition of the navigator data; - construct a set of navigator profiles (258, 804, 904, 1004, 1108, 1208, 1308) using the navigator data; and - reconstruct at least one magnetic resonance rheology image from the magnetic resonance data; - control the transducer to vibrate; - control the magnetic resonance imaging system to repeatedly acquire the magnetic resonance data from a first region of interest using a first spatially encoding pulse sequence during vibration of the transducer; - control the magnetic resonance imaging system to acquire navigator data from a second region of interest using a second spatially encoding pulse sequence, wherein the execution of the instructions causes the acquisition of the magnetic resonance data to be interleaved with the acquisition of the navigator data; - construct a set of navigator profiles (258, 804, 904, 1004, 1108, 1208, 1308) using the navigator data; and - reconstruct at least one magnetic resonance rheology image from the magnetic resonance data;