Simultaneous B-mode/subharmonic imaging and 3D subharmonic imaging on a modified commercial ultrasound scanner

The ability to generate signals at half the insonation frequency is exclusive to ultrasound contrast agents (UCA). Hence, subharmonic imaging (SHI; transmitting at f₀ and receiving at f₀/2) provides improved visualization of UCA within the vasculature by suppressing tissue signals. Despite the clinical advantages of this technique, use of SHI is currently limited by a lack of tissue landmarks for sonographical navigation and the use of a 2D representation of vasculature. Thus, the goal of this work is to demonstrate the feasibility of both dual grayscale/SHI and 3D SHI on a commercial ultrasound scanner. All scanning was performed on a modified Logiq9 US scanner (GE Healthcare, Milwaukee, WI). Dual 2D imaging was performed with a 4C curvilinear probe using several UCA in vitro in a flow phantom, and in vivo using Sonazoid (GE Healthcare, Oslo) in patients with suspected portal hypertension. Preliminary 3D SHI was implemented on the unit using a 4D10L probe. 3D imaging of Definity (Lantheus Medical Imaging, N. Billerica, MA) was performed in a flow phantom and canine kidneys and compared to harmonic imaging to show proof of concept. 2D dual imaging results showed a subharmonic amplitude response as a function of acoustic output to match the S-curve behavior described in the literature, with a maximum subharmonic amplitude of 33.9 ± 5.2 dB in humans relative to the noise floor. Noticeable tissue suppression was also observed, although this varied greatly on a case by case basis. In vitro and in vivo 3D SHI results showed better segmentation of vessels compared to harmonic imaging due to improved tissue suppression. These improvements should make SHI more translatable to future clinical applications.