IEEE Robotics & Automation Magazine - September 2023 - 80

medicine for diagnostic imaging has been well established
since the second half of the past century. On the other hand,
the therapeutic use of US is a domain that has ample room for
research and innovation. In this scenario, FUS plays a paramount
role. The FUS principle is analogous to the one of a
convex lens that focuses a beam of sunlight on a single spot.
If this spot lies on a piece of paper, the paper will be locally
burned. In a similar way, FUS uses an acoustic lens to focus
multiple beams of US on a certain target,
causing a negligible effect where the
individual beams pass through but
resulting in a relevant amount of energy
being delivered to the focal spot. If this
spot is located deep in the human body,
it is possible to produce a localized relevant
biological effect while preserving
the integrity of the surrounding tissues
[1], as in Figure 1.
Neurological disorders, including essential tremors, Par "
MEDICAL
APPLICATIONS
FUS could potentially change the treatment
paradigm of several medical conditions.
Indeed, at low to medium acoustic
intensities, FUS can be used for triggering
drug delivery. Localized drug release can be activated by
applying FUS on nanosized carriers, such as thermosensitive
liposomes [2]. In case of high amounts of energy at the focal
spot (i.e., from 1 to 10 kW/cm2) and a frequency in the range
of 0.5-3 MHz, FUS is usually referred to as high-intensity
focused ultrasound (HIFU) [3].
ROBOTIC CONTROL AND
MACHINE LEARNING
ALGORITHMS ENSURE
SAFETY EVEN IN CASE
OF TARGET MOTIONS
DURING THERAPY.
„
kinson's disease, and neuropathic pain can be approached
by HIFU. In addition, new emerging applications have been
recently investigated, namely, vessel blockage, to control
hemorrhages, thrombolysis, and abscesses [4]. However, one
of the most promising fields of HIFU application is cancer
therapy. Indeed, the possibility to noninvasively-without
any incision or the use of ionizing radiation-focus a highintensity
beam within the human body
sets HIFU as a valid alternative to traditional
cancer surgical treatments, both
for benign and malignant tumors. Liver,
kidney, pancreas, uterine, thyroid, bone,
brain, prostate, and soft tissue malignancies
can be addressed using HIFU
[5]. Figure 2 reports the main anatomical
sites where HIFU surgery has been
applied for tumor treatment, along with
the number of treatments, the state of the
research, and regulatory approvals [1].
IMAGE GUIDANCE TECHNIQUES
The quality of HIFU treatments is
strictly related to precision and accuracy
FUS Transducer
Coupling Medium
Patient's Body
Target to Treat
FUS Focal Spot
in target identification as well as for the monitoring of
energy deposition throughout the therapy [3]. This can be
achieved by image guidance, which can be carried out by
using magnetic resonance (MR) and US imaging. Excellent
soft tissue contrast together with an ability to monitor
HIFU-induced temperature changes make MR guidance
attractive for some clinical applications. However, the integration
of a HIFU therapy unit into an MR scanner is challenging,
and it calls for complicated and expensive
technology (e.g., the Exablate system). On the other hand,
using US imaging for target identification and therapy
monitoring leads to relevant advantages: 1) ease of use, 2)
relatively low cost, 3) portability, and 4) wide patient
access. In addition, US guidance is intrinsically safe
because it enables visualizing only what can be treated
(i.e., having the same acoustic window for monitoring and
treatment). Additionally, it provides methods of tissue analysis
(such as elastography [6]) that can be useful to assess
therapeutic effects. Finally, the refresh rate of US imaging
is higher if compared to MR, thus enabling online corrections
to the treatment plan. With the final aim to develop a
flexible platform for HIFU treatment, the US imaging
modality may represent the most suitable solution both for
cost and applicability.
FIGURE 1. A medical application of FUS. A transducer generates
a beam of FUS. An acoustic coupling medium guarantees the
correct propagation of this beam from the therapeutic device (i.e.,
the FUS transducer) to the patient's inner body. The FUS beam
has a negligible effect on the tissues it propagates through, except
for its focal spot, where a mechanical or thermal lesion occurs.
This focal spot, which can be positioned in the target to treat,
typically has the size of a grain of rice.
80 IEEE ROBOTICS & AUTOMATION MAGAZINE SEPTEMBER 2023
COMMERCIAL HIFU PLATFORMS WITH US GUIDANCE
US-guided HIFU (USgHIFU) takes advantage of a US
imaging probe coaxially mounted with respect to the HIFU
therapeutic transducer. Currently, USgHIFU systems come
with two possible designs (Figure 3). In earlier systems, the
patient lies on the operating table, partially immersed in a
degassed water bath. The transducer and confocal imaging
IEEE Robotics & Automation Magazine - September 2023

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