Loss-angle-based determination of a medium viscoelastic parameter in sub-hertz frequency range with the use of local creep response

A method for ultrasound imaging of a compressed target object, the method comprising:

• with an automated compression device comprising a back plate coupled to an ultrasound transducer, a pressure plate to directly contact a surface of the target object and having an opening that receives the ultrasound transducer such that the ultrasound transducer contacts the surface of the target object when the pressure plate directly contacts the surface of the target object, and at least one load sensor arranged between and coupling the back plate to the pressure plate, applying force to the target object while varying said force over a duration of less than one second from an initial value to the a final predetermined value and, once the final predetermined value is reached, maintaining said force at a substantially constant level;
• receiving an ultrasound wave from the target object, insonated with the ultrasound transducer during a period of time while the target object is compressed with said force;
• with an ultrasound imaging system, recording a sequence of ultrasound image data frames during said period, based on data from said ultrasound wave, wherein the ultrasound image data frames represent a region of interest (ROI) of said target object;
• and
• with a programmable computer processor, operably cooperated with at least the compression device and the ultrasound imaging system, determining a value of local stress at each target object point, that has been insonated with said ultrasound transducer, as a function of time.

A method for ultrasound imaging of a compressed target object, the method comprising:

• with an automated compression device, applying force to the target object while varying said force over a duration of less than one second from an initial value to the a final predetermined value and, once the final predetermined value is reached, maintaining said force at a substantially constant level;
• receiving an ultrasound wave from the target object, insonated with an ultrasound transducer of an ultrasound probe during a period of time while the target object is compressed with said force;
• with an ultrasound imaging system, recording a sequence of ultrasound image data frames during said period, based on data from said ultrasound wave, wherein the ultrasound image data frames represent a region of interest (ROI) of said target object;
• with a programmable computer processor operably cooperated with at least the compression device and the ultrasound imaging system, determining a value of local stress at each target object point, that has been insonated with said ultrasound transducer, as a function of time;
• calculating a complex shear modulus at each ultrasonically-imaged point of the target object by at least one of:
• (i) in frequency domain by directly converting values of local stress into Fourier domain;
• (ii) from a profile of values of the local stress in time domain;
• once the complex shear modulus has been determined, calculating a loss angle parameter based on a ratio of imaginary and real parts of the complex shear modulus and forming a map of said loss angle parameter across an imaged portion of the target object;
• marking a lesion area in at least one of the ultrasound image frames, acquired with the ultrasound imaging system, said marking provided as an external input to the programmable computer processor of the system;
• transferring said marking to the map of the loss angle parameter to identify said lesion area on the map;
• and
• determining a first average value of the loss angle parameter within the lesion area of the map and a second average value of the loss angle parameter in a remaining portion of the map while not accounting for data at such points on the map at which a slope of time-dependence of said value of local stress has a negative sign.