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4. Treatment methods > 4.4. Electronic deflection
4.4. Electronic deflection
The Sonalleve MR-HIFU system is able to steer electronically the position of the treatment point
within a limited range around the natural focus of the transducer. This method is called electronic
deflection. The system automatically uses electronic deflection to extend the reach of sonications
depthwise along the transducer's X coordinate axis. With positive electronic X deflection it
becomes possible to place treatment cells deeper than what the mechanical movement range of
the transducer allows. Negative electronic X deflection makes it possible to place treatment cells
closer to the patient's skin. The system automatically chooses electronic deflection based on the
user-selected cell location. Electronic X deflection is possible with 4, 8, 12 and 14 mm cells, but not
with 16 mm cells.
4.5. Temperature monitoring
The Sonalleve console shows the temperature increase of the tissue during sonication, improving
the safety and predictability of the treatment.
Temperature measurements are based on MR signal phase changes. This is called the PRF
(Proton Resonance Frequency) shift method. The temperature is calculated from the phase
difference of two subsequent dynamic images (Δφ, in radians) and the MR protocol echo time TE
(t
, in seconds) as:
E
where α = 0.0094 ppm/°C, γ = 42.58 MHz/T, B
This technique measures relative changes in temperature with respect to the initial temperature. In
the beginning of each sonication, the temperature calculation assumes that the initial temperature
of the tissue is the body reference temperature. A sufficient cooling time is necessary to avoid an
unwanted heat buildup.
Unexpected temperature changes may occur when there is a change in the measured signal
phase. Such changes can be caused by patient movement or by magnetic field changes due to
external or internal disturbances. The Sonalleve Software can detect and correct slow changes
(drift), but sudden changes may compromise the temperature information. The Sonalleve Software
will issue a warning at the onset of a sudden change.
4.5.1. Thermal dose limits
The Sonalleve Software calculates the thermal dose from temperature maps using the formula:
Instructions for Use
109745C2 / 02-2022
ΔT =
α γ B₀ t 2 π
0
Δφ
E
= 1.5 T or 3.0 T.
49 (192)
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