Ultrasound Technologies: FUS vs. fUS
While their similar abbreviations can cause confusion, focused ultrasound (FUS) and functional ultrasound (fUS) are distinct technologies with different purposes, histories, and technical operations. Recent research has also explored their complementary use in preclinical studies.
Technology Overview and History
Focused Ultrasound (FUS) is a therapeutic technique first developed in the 1940s. Its clinical application advanced significantly in the 1990s with the development of imaging-based guidance.
FUS uses focused beams of low-frequency ultrasound, typically in the range of 0.2–3 MHz, to deliver concentrated energy to a specific target within the body.
Functional Ultrasound (fUS) is an imaging technology initially developed in the early 2010s. The concept was proposed in 2011, and the company Iconeus was founded in 2016 to commercialize it.
fUS uses high-frequency ultrasound pulses, typically around 15 MHz for small-animal imaging, delivered as unfocused plane-waves.
Technical and Application Comparison
The core differences between the two technologies are summarized below:
Aspect Focused Ultrasound (FUS) Functional Ultrasound (fUS) Primary Purpose Therapy (e.g., tumor treatment, neuromodulation) Imaging (neurovascular and neurofunctional mapping) Frequency Range 0.2–3 MHz Typically ~15 MHz Energy & Focusing Uses transmit focusing to concentrate high energy on a small target. Does not use transmit focusing; employs low-energy, distributed insonification. Use of Reflections Does not detect ultrasound reflections for its primary therapeutic function. Relies on detecting echoes from red blood cells to generate 2D or 3D images. Primary Application Area Applied body-wide, including the brain, soft tissues, and organs. Used almost exclusively for brain imaging, due to high sensitivity for neurovascular coupling. Development Stage Has established clinical therapies; others are under investigation. Currently at the preclinical research stage; clinical applications are in development.Current Applications
FUS Applications include High-Intensity Focused Ultrasound (HIFU) for creating tissue lesions in tumor ablation and Low-Intensity Focused Ultrasound (LIFU) for neuromodulation and tissue stimulation.
fUS Applications in preclinical research include studying brain responses to sensory or drug stimulation, investigating resting-state functional connectivity, and generating detailed maps of the neurovascular network.
Complementary Research
A 2024 study demonstrated the combined use of these technologies, using fUS imaging to monitor hemodynamic responses in the mouse brain induced by FUS stimulation.
The authors of the study noted that this approach could lead to more guided and effective FUS neuromodulation protocols.
Terminology Clarification
The article notes that "functional ultrasound" has historically been abbreviated as 'fUS', which can lead to confusion with the therapeutic 'FUS'. To clarify this distinction, it is suggested that the imaging technology be referred to as 'fUS imaging' or 'fUSI'.
Commercial Development
Iconeus, a Paris-based company founded in 2016, manufactures fUS imaging systems. The company's technology is used in preclinical brain research, and efforts are underway to develop clinical applications for imaging cerebral blood flow and microvasculature.