Our research on respiratory motion mitigation methods in non-invasive surgery using boiling histotripsy has been published in a highly rated journal IEEE Transactions on Ultrasonics, Ferroelectric, and Frequency Control (Q1, IF 3.0): “Respiratory motion effects and mitigation strategies on boiling histotripsy in porcine liver and kidney”.

Boiling histotripsy (BH) is a novel method that allows for non-invasive (i.e., incisionless) disruption of unwanted tissues in the human body (e.g., tumors) using high-intensity focused ultrasound (HIFU). The target tissue at the focus is turned into liquid as in a “remote blender”.

Boiling histotripsy can be applied for non-invasive mechanical disruption of tumors, including those in the abdominal cavity, for example, in liver and kidneys. However, tissue motion and deformation with respiration can reduce the accuracy of focus positioning relatively to the target and, therefore, may result in failure to fully ablate the planned volume and/or in damage to surrounding healthy tissues.

A number of strategies have been proposed to address this issue, including, for example, pulse gating which synchronizes delivery of BH pulses with respiratory phase when the tissue is relatively immobile (e.g., during expiratory pause), as typically evaluated using ultrasound imaging. During transcutaneous BH exposure, a reliable reference for ultrasound imaging-based respiration tracking can be the interface between the coupling water and the skin surface closest to the target organ. However, due to the periodic pausing of the pulses, this approach lengthens the treatment time.

Another option can be active motion compensation which tracks target motion in real time and continuously adjusts the position of the BH array mechanically, for example, by a robotic arm, or electronically steers the BH focus by phasing its elements. Unlike treatment gating, active motion compensation does not increase the treatment times, but it is more challenging to implement.

The goal of the study, therefore, was to compare the performance of the two approaches to mitigate the respiratory motion, both based on unidirectional ultrasound imaging-based motion tracking during BH treatments in porcine liver and kidney in vivo.

The results showed that:

• Due to predominance of respiratory motion across the BH axis, active motion compensation only along the axis was insufficient to avoid off-target tissue damage across the axis.
• Due to synchronization of respiratory motion in both directions, pulse gating during inhalation enhanced the treatment accuracy while increasing treatment time by only 24%.

Thus, respiration-based BH pulse gating is an adequate approach for BH treatments in organs with pronounced 3D respiratory motion and can be useful in further clinical practice to ensure completeness and accuracy of non-invasive BH procedures taking into account the patient’s breathing.

For more details, see the text of the paper and our talk at «ISTU-2025».