Specific Energy Dose (Sed); Heat Load Induced By Ultrasound; Cooling The Patient - Profound Sonalleve MR-HIFU Instructions For Use Manual

2. Safety > 2.3. Heat and Specific Absorption Rate (SAR)

2.3.2. Specific Energy Dose (SED)

The amount of radio frequency (RF) energy absorbed by the body, per unit mass, is called the
Specific Energy Dose (SED). The SED is determined by the SAR and scan duration. The SED is
expressed in kJ/kg.
NOTICE
In some MR imaging protocols the total SED can become so high that it limits the use of the
protocol.

2.3.3. Heat load induced by ultrasound

Also the ultrasound energy delivered to the patient is ultimately absorbed and transformed to
thermal energy inside the patient.
The total thermal energy over the course of the treatment can be reduced by:
Using feedback cells instead of regular cells.
Using larger treatment cells.
Short term heat load over the course of a few minutes can be reduced by:
Increasing the cooling interval between sonications.
Using smaller treatment cells.
Note that increasing the cooling interval between sonications increases the total treatment time.

2.3.4. Cooling the patient

WARNING
Always leave sufficient cooling intervals between sonications.
Failure to do so may cause heat buildup in the near field or far field, leading to skin burn or
other unwanted tissue damage.
The system visualizes temperature changes relative to the start of each sonication, not absolute
temperature. Estimates of heat buildup and predictions of cumulative heating in the near field are
calculated internally and affect cooling times.
NOTICE
Refer to 4.5. Temperature monitoring for more information on the temperature measurement
method and to 4.5.4. Cooling time for more information on cooling time.
The Sonalleve MR-HIFU systems include an active Direct Skin Cooling (DISC) device. The
purpose of the device is to facilitate faster tissue cooling by keeping the patient interface at a
constant temperature throughout the treatment. This effect is taken into account when the system
calculates cooling time recommendations. In most cases, active cooling will shorten the system-
recommended cooling times. Thus using the DISC device may shorten the total treatment time.
The operational status of DISC is displayed in the System Status Display (see 5.9.1. System Status
Display).
Instructions for Use
109745C2 / 02-2022
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