Baki Karaboce

Focused ultrasound temperature effect in tissue-mimicking material and sheep liver

The temperature distribution produced by a HIFU (High Intensity Focused Ultrasound) transducer has been investigated by a set up using T type thermocouple temperature sensors in the automated scanning system. The temperature change and the temperature distribution due to applied ultrasound power have been characterized. The temperature measurements were carried out in a tissue-mimicking material (TMM) that has characteristics very similar to human tissue and in ex vivo tissue. A temperature measurement set up in a tissue phantom has been constructed at TÜBİTAK UME (The Scientific and Technological Research Council of Turkey, the National Metrology Institute) Ultrasound laboratory. Burning and removing the tissue by high power ultrasound have been showed.

Investigation of temperature rise in tissue — Mimicking material induced by a HIFU transducer

In this study, temperature distribution inside a tissue - mimicking material induced by a HIFU (High Intensity Focused Ultrasound) transducer was investigated with two different methods. In first method T-type thermocouple (TC) temperature sensors and in second method, infrared (IR) camera system was used for determining the temperature distribution on the tissue-mimicking material (TMM). Temperature increase and distribution in the TMM have been characterized during the ultrasonic power application. Temperature measurements were actualized inside a TMM which has characteristics very similar to human liver tissue. Temperature rise has been characterized for different input ultrasonic powers and durations. Two different temperature measuring tools were compared and consistency between these methods was presented.

High pressure focused ultrasound field characterization

High intensity focused ultrasound (HIFU) transducers are novel and very attractive tools for cancer therapy. They produce very high pressure acoustic fields up to tens of MPa at the focus; thus, acoustic characterization of HIFU fields must be investigated in order to ensure the safe and effective use in clinical applications. A needle hydrophone has been used for HIFU transducer characterization in the newly designed home made system at TUBITAK UME (The Scientific and Technological Research Council of Turkey, the National Metrology Institute) Ultrasound laboratory. TUBITAK UME HIFU measurement system was controlled by a Labview based data translation program. The driving signal was generated by signal generation card and output from the hydrophone was fed directly into a DSO oscilloscope card. The controlling program executed a “capture-analyze-move” cycle, allowing a large number of measurements to be made. Field scanning measurements are made between 1 MPa, 2 MPa, and 3 MPa pressures. Theoretical model...

Inspection and Testing of Respirators and Anaesthesia Machines

Respirators are used in intensive care units and in operating rooms. It consists of filtering, air compression, and humidifying control board units. A respirator is a device that combines the patient’s respiratory tract to assist the respiratory system in conditions where the patient has difficulty in breathing or after operations. The device supplies controlled air to the patient by the inner compressor. The breakdown of the oxygen sensor and the heating of the circuit boards (if the filter is not cleaned) are the most common problems in respirators. They may not stabilize with required values over time and the tester is used to maintain stability. The device must be calibrated regularly or if the gauge of the test device does not match the standard values of gas flow, volume, pressure and oxygen parameters. The anaesthesia machine delivers pressurised medical gases like air, oxygen, nitrous oxide, heliox etc. and controls the gas flow individually. It composes a known and controlled gas mixture at a known flow rate and then delivers it to the gas outlet of the machine. Therefore, the fresh gas flow is serviced to the anaesthesia circle breathing system in order to make artificial respiration in the patient and monitor vital functions closely. For patient safety, the most important thing is to check out the system regularly and in pre-use and to ensure that there exists a ready and functioning alternative solution for ventilating the patient’s lungs.

Experimental investigations of viscous heating effect of thermocouples under focused ultrasound applications

Realization of temperature characterization on focused ultrasound treatment devices by using tissue-mimicking phantom systems (Tissue-Mimicking Material, TMM) is indispensible in pre-clinical studies. In this survey, in order to examine the viscous heating effect of thermocouples, temperature rise due to excitation of a HIFU transducer has been measured by using two different types of T-type thermocouples embedded inside the TMM. In order to obtain the temperature values from the thermocouples more effectively, a PC-based multi-channel data acquisition and monitoring interface were developed by using LabVIEW graphical development platform. Measurements were carried out inside a TMM which has characteristics like human liver tissue. Temperature rise has been characterized for the different input ultrasonic powers (25 W, 38 W and 50 W) and frequencies (1,1 MHz and 3.3 MHz) and the time intervals applied (1 s, 2 s and 3 s). The temperature values obtained from two different types of T-type thermocouple were compared to each other and discrepancies between these two different thermocouple measurements were shown with the study.

Calibration of therapeutic ultrasonic transducers with the modified radiation force balance system

A modified radiation force balance (RFB) system was established for physiotherapy and high intensity therapeutic ultrasound (HITU) power measurements in the Medical Metrology Laboratory at the National Metrology Institute of Turkey (UME). The system was found to be highly stable up to a power level of 500 Watts. The measuring system consists of a Plexiglas cylindrical balancer, target mounted scale disks, conical reflector and absorbent targets, adjustable nuts and a hanging monofilament line‥ The balance is entirely symmetric with identical sizes and weight targets on both sides of the equilibrium point. The balance of the balance arm can be adjusted with adjustment screws on each side. The transducer was mounted beneath the water reservoir. Absorbing liners were used in the bottom and the near walls of the tank for reflecting target case. Ultrasound force is applied to a scale of equilibrium to which the reflector/absorber target is mounted, and the corresponding force is measured on the other scale of the equilibrium to which the equilibrium is connected by a thin wire while standing on a thin resting support. Ultrasound power of a HITU transducer at frequencies of 1.1 MHz was measured with conventional and new system. The measurement results were compared and uncertainty components were evaluated in this paper. A lower uncertainty value has been achieved in ultrasound power measurements for physiotherapy and HITU.

Investigation of ultrasonic fields produced by HIFU transducers used in cancer therapy

Ultrasonic fields induced by HIFU (High Intensity Focused Ultrasound) have been studied. Effect of input electrical power, harmonics and nonlinear propagation of the ultrasound fields has been quantized. Asymmetric waveforms with peak (+) pressures and peak (-) pressures were obtained both numerically and experimentally. Nonlinear propagation with harmonics output was dominant at higher intensities that leads to an increase of the compressional wave and a decrease of rarefactional wave. All measurements have been realized in the constructed system at National Metrology Institute of Turkey, TÜBİTAK UME. Set up includes a water reservoir, positioning system, HIFU transducers, needle hydrophone, power amplifier, signal generator, measurement and control devices which are all controlled by LabVIEW 8.1 software. P+, P- and P pressures have been determined theoretically for each waveform. Wave behaviors generated by the Khoklov-Zabolotskaya-Kuznetsov model (KZK model) and from experiments match in general. Decrease in size of focus point was shown in 3rd harmonic.

The calibration of a prototype occluded ear simulator designed for neonatal hearing assessment applications

An innovative family of ear simulators has been conceived for the calibration and traceability of audiometric equipment. Each device within the family has been designed for a particular key age group, covering neonates through to adults. The age-specific ear simulators are intended to improve the quality of hearing assessment measurements for all test subject age groups, and will be proposed as the next generation of standardised ear simulators for audiometric applications. The family of ear simulators shares a common design and modeling approach, and the first prototype devices for neonatal applications have been manufactured. The objectives of this study were to develop calibration methods, verify conformance to the design goals, demonstrate that the device is capable of being calibrated reliably, and show that its performance is ultimately suitable for international standardisation and eventual adoption into clinical practices. Four national measurement institutes took part in a round-robin calibration comparison and an analysis of the results showed that these objectives were achieved.

Investigation of the temperature effect of ultrasound used in cancer therapy

In present study, temperature rise in a tissue — mimicking material induced by a HIFU (High Intensity Focused Ultrasound) transducer was examined with two different methods. In order to determine the temperature rise inside and distribution on the surface of a Tissue-Mimicking Material (TMM), T-type thermocouple (TC) temperature sensors and infrared (IR) camera system was used in the first and second method respectively. During the ultrasonic power application, temperature increase and distribution in the TMM have been represented. Temperature measurements were realized inside a TMM which has characteristics very similar to human liver tissue. Temperature rise has been measured for different input ultrasonic powers and durations. Two different temperature measuring tools were compared and consistency between these methods was presented.

Portable ultrasonic wattmeter for ultrasonic prob calibration

In our country, in many different brands and types of ultrasound devices are used very intensely in the health sector. However, these ultrasound devices do not pass a mandatory/legal or voluntarily technical measurements /controls. In order to verify the indicated performance and safety of the ultrasonic probes that is the most important part of ultrasound devices, measurements/controls are required to be done as per strong scientific parameters and standards. For this reason, Portable Ultrasonic Wattmeter device has been designed, manufactured and tested. The device works in the distilled water and probe tests are done by operating the probes in this water tank. In the installation system, powers of ultrasonic probes that have an approximate power range between 15 W and 150 W have been measured. In this paper, information will be given and experiences will be shared about the production of ultrasonic wattmeter that measures the power of ultrasonic probes as portable.