Evaluation of Second-generation HIFU Systems: Less-invasive Fetal Therapy for TRAP Sequence

In this report, the second-generation high-intensity focused ultrasound （HIFU） systems were clinically evaluated for human fetal therapy in two cases of twin reversed arterial perfusion sequence. The HIFU systems comprised an improved lead zirconate-titanate transducer with an imaging phase array sector probe, a Sonachill cooling system, and three phases of HIFU exposure: a trigger pulse, a continuous heating wave, and an idle period to obtain images with the imaging probe set on the transducer. To evaluate skin surface temperature, a thermal camera was used. To evaluate vessel occlusions, blood flow was measured at fixed timings after exposures. Target vessel occlusion was achieved with HIFU in only one of the cases, but recanalization occurred the following day. Both cases were finally treated with radiofrequency ablation and one infant was successfully delivered without any complications. This case highlighted three advantages with the change to second-generation HIFU systems in human fetal therapy: the simplicity of maneuvers by reduced range of motion disturbance; the ability to observe in real time during the exposure; and a decrease in total ultrasonic output. Treatment interruption due to burns or complaints of heat sensation represented an obstruction to treatment completion. This remains an issue to be addressed in the future.