Matching layer optimization between ultrasound transducer and human tissues

Several volume rendering methods have been developed for CT, MRI and PET in recent years, however, very limited research has been undertaken successfully with the applications in volume rendering of ultrasound images. One of the major problems is in overcoming severe noise contamination in conventional 2D real time ultrasound images. The authors have studied a method to improve the transmission of ultrasound waves to human body. It is found that a Solid Gel matching layer with thickness in multiple quarters of a wavelength and an matching impedance between the ultrasound transducer surface and body surface could maximize the transmitted ultrasound pulse amplitude into the body. Theoretical analysis indicates that for the matching layer the thickness should be a multiples of 0.036 mm to 0.11 mm depending on transducer used (conventional frequency range from 3.5 MHz to 10 Mhz). The impedance of the matching layer should be correspondingly 1.58*10⁶ Kg/m²Sec to 30*10⁶ Kg/m²Sec. In order to confirm the theoretical prediction, the authors performed computer simulations and experiments using a type of Solid Silica Gel with a thickness of 33 mm and impedance of 6.90*10⁶ Kg/m²Sec for a 3.5 Mhz ultrasound convex transducer