Optical monitoring of ultrasound interaction with blood vessels in transparent fish after injection with contrast agents

The goal of this research is to study the ultrasonic therapeutic effects on the blood vessels of animals whose vessels are optically transparent. Glass catfish were used in these experiments Anaesthetized fish were injected with Optison using microinjection techniques. Two focused transducers were used to cover a frequency range of 0.7-3.3 MHz. An inverted microscope combined with a digital camera and video monitor was used to optically monitor and record ultrasound interaction with the blood vessels in the tail of the anaesthetized fish at 200x magnification. The fish were insonified at average acoustic pressures ranging from 0.6-15 MPa. Sonications were pulsed with various burst lengths and a pulse repetition frequency of 1 Hz for 20 sec duration. For the 1.091 MHz sonications, the first type of damage that occurred due to the ultrasound interaction was structural damage to the cartilage rods that comprise the tail of the fish and was characterized by a disintegration of the lining of the rod. Damage to the rods occurred starting at 4.0 MPa, 4.4 MPa, 4.7 MPa, and 6.8 MPa for the 100 msec, 10 msec, 1 msec, and 100 μsec sonications, respectively. The formation of large gas bubbles was observed in the blood vessels of the fish at threshold values of 4.4 MPa, 4.4 MPa, and 6.1 MPa, for the 100 msec, 10 msec, and 1 msec sonications, respectively. At 1.091 MHz, hemorrhage thresholds were observed at 4.7 MPa, 5.4 MPa, and 7.1 MPa, respectively, for the three burst lengths. No damage was observed in any fish using a 10 μsec burst length at 1.091 MHz or the 3.273 MHz sonications at the pressures applied. The 2.273 MHz sonications induced very little damage, only to the cartilage rods in the tail.