IEEE Robotics & Automation Magazine - September 2023 - 86

rbpc ;;=+ Tballoon@
rb ^h 6
n 00
(3)
where cnrb ^h is the HIFU origin in the robot base RF
(that is available from the robot forward kinematics
rb Tee and registration
eeT )hifu and balloonT
is equal to
0.05 m (to take into account the encumbrance of the
coupling balloon). Additionally, the electronic steering
T s of the HIFU beam is applied as
T=-u^^
s
rb cn
rb tn cn fhh 0
rb
(4)
where tnrb u^h is the estimated target position in the robot
base RF at time n,
^h is the HIFU origin in the
robot base RF, and f0 is the nominal focal length of the
HIFU transducer (i.e., 0.12 m).
4) HIFU sonication: In static and motion-compensated conditions,
the acoustic coupling between the HIFU transducer
and patient is checked before enabling HIFU sonication
(see the " HIFUSK Safety Measures " section). Afterward,
treatment can be performed. Sonication parameters, i.e.,
intensity, duration, and duty cycle, can be selected through
the GUI to produce a thermal and/or mechanical effect on
the target [23]. After the physician's acknowledgment, the
HIFU sonication is executed.
HIFUSK SAFETY MEASURES
The following measures were implemented to verify the safety
of the full procedure, i.e., the global safety (GS), as well as
during specific steps of the treatment, i.e., functionality-specific
safety (FS):
■ GS (force monitoring): The interaction force between the
transducer and patient (or in general, the external environment)
is checked throughout the full procedure. This verifies
that this force falls into the safety interval for the
patient's body, namely, lower than 9 N [24].
■ GS (emergency button): The physician always has supervision
over the procedure: he or she can stop the robot
motion and HIFU sonication by pressing an emergency
button on the GUI.
■ FS (motion amplitude during automatic targeting): Before
enabling the motion of the robot for matching the focus of
the HIFU transducer with the selected target, verification
of the motion amplitude is conducted. This step aims at
avoiding the loss of the acoustic window and coupling
after this adjustment. A safety threshold is set on the robot
translation rbT by imposing its norm to be lower than
3 cm. If this condition is not met, a popup will appear on
the GUI to inform the physician that the selected target is
not reachable in the current robot pose. The physician can
Echo
t
ROI
HIFU
Image-Based
Tracking
Trajectory
Learning
Robot
Control
ROI, im∆ROI-t
imROI(n)
rbt(n)
(a)
HIFU Transducer
Coupling Device
Pivot Point, p
HIFU Beam
Target, t
-∆ xx0
Angular Motion
Compensation
Rotation
Angle
α = cos-1
i
+∆
x
f0
(t(n) - p).(t(n - 1) - p)
~~
(t(n) - p).(t(n - 1) - p)
~~
(b)
FIGURE 6. The architecture of the HIFUSK motion compensation functionality. (a) The physician selects the target (t) and a surrounding
ROI in a frozen echographic image. Then,
im
T
imaging frame (im). The image-based tracking finds that ROI in the following images. At any sample n, this
rbtnr
eeTn+Tdelay
rb
T of the HIFU beam is applied to match the target (t).
ROI- t defines the rigid transformation between the ROI barycenter and target in the
im RO ()nI
is provided back to
the GUI for the physician's visual inspection, and it is converted in target position () in the robot base (rb) RF. This trajectory is later
rbtnu
estimated as () by sinus interpolation. This estimation (together with the control delay, Tdelay , i.e., 100 ms) is used to define the robot
pose () for motion compensation. (b) The robot rotates the HIFU transducer and attached coupling device around a pivotal
point (p), and the electronic steering ()s
86 IEEE ROBOTICS & AUTOMATION MAGAZINE SEPTEMBER 2023
i
t(n-1)
t(n)
∆s
Electronic Steering
c(n)
Mathematical Formulation
c = HIFU Origin
p = Pivot Point
t = Target Point
f0 = Nominal HIFU
Focal Length
c(n-1)
p
α
∆s (n) = it(n) - c(n)i - f0
~
rbt(n + ∆delay)
~
eeTrb(n + ∆delay)
Clinician GUI
IEEE Robotics & Automation Magazine - September 2023

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