Technology behind the Haifu System

The figure shows the Haifu transducer (yellow) focusing the ultrasound beam (green lines) into the liver (brown) The patient is positioned on his right-hand side, over the treatment head.

The therapeutic principles of the Haifu System

The Haifu System uses high-intensity focused ultrasound (HIFU) to treat solid tumour deposits. Ultrasound has two unique properties, which allow it to be used for the ablation of solid tumours: it passes harmlessly through soft tissue yet, when directed through a lens, may deposit enough energy in the focal region to cause localised tissue ablation. The fine balance between transmission and deposition of energy is utilised by the Haifu System to ablate solid tumour deposits non-invasively.

Mechanisms of tissue destruction induced by the Haifu System

• Thermal effect
  Tissue temperature within the local region is instantly elevated to 65-100^oC within 1 second of HIFU exposure; coagulation necrosis is, therefore, immediately induced in the tumour.
• Cavitation
  Due to the depression caused by the negative part of the ultrasound wave, intercellular water may enter the gaseous phase, which would lead to the development of micro bubbles. When they reach the size of resonance, these bubbles suddenly collapse and produce high pressure shock waves, destroying tumour tissue.
• Damage to tumour blood vessels
  Small tumour blood vessels, of diameter less than 2mm, can be completely destroyed by the Haifu System, resulting in secondary effects of HIFU on the target tumour.

The core theory of HIFU therapeutic dosimetry: Biological Focal Region (BFR)

The focus formed by focused ultrasound in the ideal acoustic field such as degassed water is called the Acoustic Focal Region (AFR), which is unchangeable in size and shape. However, while HIFU is performed to induce thermal ablation at a target tissue, changes in HIFU acoustic energy, exposure time, frequency, focal length, and depth of target tissue can cause lesions of different shapes and sizes - in vitro and in vivo. The lesion resulting from the interaction of these factors and the tissue structure and function is known as the biological focal region (BFR). Because the BFR is variable, knowing how to adjust the variable size and shape of the BFR becomes a key point in achieving a successful treatment of tumours of different sizes and shapes. Dr Zhi-Biao Wang first proposed the concept of the BFR in the world, and hoped that it could describe the relationship between the acoustic dose of HIFU and biological effects on tissue. The characteristics of the BFR are listed as follows:

• Variability
  Tumours can be completely ablated using variable BFR, which is achieved by adjusting the ultrasound frequency, acoustic energy, the exposure time and the therapeutic modes.
• Visibility
  When the coagulation necrosis of a target tumour is induced, obvious changes in tissue gray-scale on the ultrasound imaging can be directly seen.
• Real-time monitor
  During the HIFU procedure, the volume of coagulation necrosis can be immediately evaluated by real-time ultrasound imaging.
• Controllable
  Changes in therapeutic parameters can control the size and shape of the BFR. A real-time feedback controlling system provides the accurate assessment of therapeutic effect on the target tissue, and the control of the therapeutic energy.

Seen under an electronic microscope, the cytomembrane and karyotheca lost their integrity, and rupture occurred in membranous structure.

Seen under a light microscope, endothellal cells of vascular wall were severely damaged and thrombus in blood vessels was observed.

Microscopic examination showed that elastic and collagen fibres in vascular wall were damaged and disrupted.

A BFR (coagulation necrosis) was induced in tissue using the Haifu System.