SURLAS: A new clinical grade ultrasound system for sequential or concomitant thermoradiotherapy of superficial tumors: Applicator description
SURLAS applicator. (a) Side view of SURLAS illustrating basic operation principle for an en face clinical setup. Another often-used clinical configuration is one with photon beam coming tangential to the patient surface. (b) Exploded CAD solid model view of the SURLAS applicator. LFA=low frequency array; HFA=high frequency array. (c) Photograph of constructed applicator.
(a) Urethane belt and sandwich rubber mounts minimized vibration transfer from the motor to the applicator’s body. (b) Acoustical (audible) noise for various tested stepping motors and mountings.
Solid model diagram depicting the radiation force balance measurement setup. The three A, B, C arrows at the bottom view diagram of the SURLAS applicator show the three reflector positions selected for pressure and radiation force measurements. The distance between the array and the reflector was 5.5 cm (arrow A), 13.5 cm (B), and 21.5 cm (C). The total distance the ultrasound beam had to travel to reach the measurement plane was 8.5 cm (A), 16.5 cm (B), and 24.5 cm (C).
Electrical impedance for one of the SURLAS 4.9 MHz elements (a) without and (b) with matching circuit. The matched impedance magnitude was 50.6 Ω at 5° impedance phase.
Electrical signal measured at measurement location Probe 1 (applicator input) for the generator’s channel A at 1.957 MHz, and electrical signal measured at location Probe 2 (applicator ultrasound transducer electrode) for the same generator's channel. By comparing both plots, it can be seen how the matching circuit acts as a low-pass filter attenuating the parasitic higher harmonics emanating from the Labthermics M216 channel A output. Similar results were obtained for the remaining 15 channels.
50% iso-bars of acoustical pressure measured for the low (1.9 MHz) and the high (4.9 MHz) frequency arrays for the three reflector positions shown in Fig. 4. These measurements were performed with a 0.1-mm-thick silicone rubber coupling water bolus membrane. The hydrophone (0.5 mm active diameter) was mounted on a 3D scanning mechanism to take measurements in a plane perpendicular to the propagation direction at 4 cm below the SURLAS’s lower solid surface (bolus membrane). The data in each plot are normalized to the maximum value measured on that plane. The plots (a), (b), and (c) are for the low frequency array for proximal, central, and distal positions from that array, respectively. The plots (d), (e), and (f) are for the high frequency array for proximal, central, and distal positions from that array, respectively.
Radiation force results as a function of input electrical power. Each datum is an average of five measurements. Each measurement was made with all the array elements on and the result divided by the number of elements (eight). No bolus membrane was used. (a) Ultrasound output power from a representative 1.9 MHz element. (b) Ultrasound output power from a representative 4.9 MHz element. (c) Electro-acoustical efficiency of a representative 1.9 MHz element. (d) Electro-acoustical efficiency of a representative 4.9 MHz element. The maximum standard deviation of the measurement was 3% for all 1.9 MHz elements, and 10% for all 4.9 MHz elements.
Comparison of the Sonotherm and SURLAS applicators.
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