Controllable in vivo hyperthermia effect induced by pulsed high intensity focused ultrasound with low
duty cycles
Supplementary Materials
I. Ultrasound Exposure System
The 1.17-MHz HIFU transducer comprised an air-backed, 34.9-mm diameter APC880 PZT disk
(APC International, Ltd., Mackeyville, PA, USA) mounted inside the transducer housing, with
electrical connections on each surface of the PZT disk. The transducer housing consisted of an
aluminum focusing lens with a 5-cm radius of curvature. The driving electronics consisted of a
waveform generator (33120A, Agilent Technologies, Palo Alto, CA, USA) and an RF power
amplifier (AP-400B, ENI, Rochester, NY, USA). Before the experiments, a membrane hydrophone
(MHA 200A, NTR Systems, Inc., Seattle, WA, USA) was used to calibrate the spatial characteristics
of the HIFU beam (-6 dB focal width of 4 mm). The maximum pressure amplitudes achievable were
27 MPa peak positive and 9 MPa peak negative. The ISPPA was determined by integrating the
instantaneous intensity over 20 cycles: I SPPA 
1
nT
 idt = 5300 W/cm2.
nT
During the experiments, the transducer was mounted to a water tank filled with degassed water.
An acoustic absorber crafted from a rubber plate was positioned on the tank wall opposite the
transducer to minimize the acoustic reflection. A custom-built polyamide cone filled with degassed
water was screwed onto the transducer housing to provide acoustic coupling. The cone tip had a
cutting-edge hole (1-cm diameter) that was covered with a polyurethane membrane (12.5-m
thickness, Glad Products Co., Oakland, CA, USA) with an O-ring seal. The distance between the
surface center of the focusing lens and the cone tip was 49 mm, permitting transducer’s focal region
located at the cone tip and the exact focus of the HIFU beam sitting in the vessel.
II. Animal Anesthesia
Following initial sedation with a subcutaneous injection of an acetylpromazine (1.0
mg/kg)/ketamine (22 mg/kg) cocktail, the auricular surfaces were shaved and depilated to facilitate
ultrasound coupling. A 21 gauge catheter was inserted into the proximal auricular vein of one ear
through intravenous (IV) access. The animals were anesthetized with an IV ketamine (35-40
mg/kg)/xylazine (5 mg/kg) cocktail and placed in a lateral decubitus position in preparation for
treatment. Before experiments, in vivo Doppler measurements were first preformed on rabbit auricular
veins to determine the velocity of blood flow, whose average value was measured to be 4.25 cm/s.
Rabbits remained anesthetized throughout the entire experimental protocol. At the end of the
experiment rabbits were euthanized with an overdosed IV injection of ketamine/xylazine.
The purpose of anesthetizing the rabbit was to successfully measure the steady-state temperature
inside the rabbit auricular vein. All the animal preparation procedures were carried out according to
the NIH guidelines and were approved by the University of Washington Animal Care and Use
Committee. The injection dosage of the anesthesia drugs was determined by the body weight of the
animal to insure safety and good anesthetic effect.
It has been reported that an advantage of ketamine was the maintenance of spontaneous
ventilation during anesthesiaS1. However, ketamine is rarely administered alone due to its poor muscle
relaxation. It is most commonly combined with xylazine, acetylpromazine, or diazepam in a wide
range of safety usages, including analgesia, anesthesia, hallucinations, and bronchodilationS2, for
humans and small animals (e.g., cats, dogs, rabbits,rats). Although the administration of the anesthesia
drugs is possible to affect the heart rate and arterial blood pressure of individual animals, the impact
might not be statistically significant as long as the appropriate injection dosage is employedS3,S4.
Especially, since the focus of the current studies is the temperature variations in the rabbit auricular
veins exposed to HIFU pulses rather than investigations on the cardiovascular, pulmonary or neural
issues and the blood flow in the anesthetized rabbit auricular vein was measured with Doppler
instruments right before the experiments, the influence of anesthesia effect could be reasonably
ignored.
References:
S1. T. Aye, B. Milne, Can. J. Anaesth. 49, 283 (2002).
S2. T. E. Peck, S. A. Hill, M. Williams (2008). Pharmacology for anaesthesia and intensive care (3rd
edition). (Cambridge university press, Cambridge, UK, 2008), p. 111.
S3. A. L. Yershov, B. S. Jordan, J. M. Fudge, M. A. Dubick, Veter. Anaesth. Analg., 34, 157 (2007).
S4. C. Baumgartner, M. Bollerhey, J. Ebner, L. Laacke-Singer, T. Schuster, W. Erhardt, Can. J. Vet.
Res. 74, 200, (2010).