Jeong Ki Seo

Development of Respiration Sensors Using Plastic Optical Fiber for Respiratory Monitoring Inside MRI System

In this study, we have fabricated two types of non-invasive fiber-optic respiration sensors that can measure respiratory signals during magnetic resonance (MR) image acquisition. One is a nasal-cavity attached sensor that can measure the temperature variation of air-flow using a thermochromic pigment. The other is an abdomen attached sensor that can measure the abdominal circumference change using a sensing part composed of polymethyl-methacrylate (PMMA) tubes, a mirror and a spring. We have measured modulated light guided to detectors in the MRI control room via optical fibers due to the respiratory movements of the patient in the MR room, and the respiratory signals of the fiber-optic respiration sensors are compared with those of the BIOPAClTEXg

Measurements of Relative Depth Doses Using Fiber-Optic Radiation Sensor and EBT Film for Brachytherapy Dosimetry

^{(R)}

Development of a Cerenkov radiation sensor to detect low-energy beta-particles.

l/TEXg system. We have verified that respiratory signals can be obtained without deteriorating the MR image. It is anticipated that the proposed fiber-optic respiration sensors would be highly suitable for respiratory monitoring during surgical procedures performed inside an MRI system.

Spectroscopic study on the development of fiber-optic pH sensor

In this study, we have fabricated a fiber-optic radiation sensor using an organic scintillator for brachytherapy dosimetry. Organic scintillators are made from a polystyrene base with wavelength-shifting fluors, and they do not disturb the radiation field due to their tissue or water-equivalent characteristics in a wide range of energies. The fiber-optic radiation sensor developed for this study provides a fast real-time response and convenient usage for brachytherapy dosimetry. For more accurate measurement, we have measured Cerenkov light using a dummy fiber and avoided dose measurement errors arising from high dose gradients in brachytherapy dosimetry. The Cerenkov light has been eliminated using a modified subtraction method. Also, the relative depth dose without the dose generated from Cerenkov lights is measured and compared with the results obtained using conventional EBT dosimetry films.

Development of a 2-Channel Embedded Infrared Fiber-Optic Temperature Sensor Using Silver Halide Optical Fibers

We fabricated a novel fiber-optic Cerenkov radiation sensor using a Cerenkov radiator for measuring beta-particles. Instead of employing a scintillator, transparent liquids having various refractive indices were used as a Cerenkov radiator to serve as a sensing material. The experimental results showed that the amount of Cerenkov radiation due to the interaction with beta-particles increased as the refractive index of the Cerenkov radiator was increased as a results of a decrease of the Cerenkov threshold energy for electrons.

Measurement of relative dose irradiated from a Co-60 source using a scintillating fiber-optic dosimeter

In this study, we have fabricated a fiber-optic pH sensor which is composed of a light source, plastic optical fibers and a spectrometer. As an indicator, a phenol red is used, and a pH liquid solution is prepared by mixing of phenol red and various kinds of pH buffer solutions in these experiments. The emitting light from a light source is guided by plastic optical fibers to the pH liquid solution, and the optical characteristic of a light is changed in the pH liquid solution according to its color change. Therefore, we have measured the intensities and wavelength shifts of the modulated lights, which are changed due to the color variations of phenol red at different pH values, by using of a spectrometer for spectral analysis. Also, the relationships between the pH values of liquid solutions and the optical properties of modulated light according to the change of color of phenol red are obtained.

Development of Reflection-type Fiber-optic pH Sensor Using Sol-gel Film

A 2-channel embedded infrared fiber-optic temperature sensor was fabricated using two identical silver halide optical fibers for accurate thermometry without complicated calibration processes. In this study, we measured the output voltages of signal and reference probes according to temperature variation over a temperature range from 25 to 225 °C. To decide the temperature of the water, the difference between the amounts of infrared radiation emitted from the two temperature sensing probes was measured. The response time and the reproducibility of the fiber-optic temperature sensor were also obtained. Thermometry with the proposed sensor is immune to changes if parameters such as offset voltage, ambient temperature, and emissivity of any warm object. In particular, the temperature sensing probe with silver halide optical fibers can withstand a high temperature/pressure and water-chemistry environment. It is expected that the proposed sensor can be further developed to accurately monitor temperature in harsh environments.

Measurements of relative depth dose rates for a brachytherapy Ir-192 sourceusing an organic scintillator fiber-optic radiation sensor

In this study, we have fabricated a scintillating fiber-optic dosimeter for a radiotherapy dosimetry. And -rays generated by a Co-60 are measured using a scintillating fiber-optic dosimeter and percent depth dose curves are obtained according to the different depths of solid water phantoms. Also, Cerenkov radiations generated by primary or secondary electrons are measured at different depths of water phantom using a background optical fiber.

Chalcogenide optical fiber based sensor for non-invasive monitoring of respiration

A reflection-type fiber-optic pH sensor, which is composed of a pH sol-gel film, plastic optical fibers, a mirror, a light source and a spectrometer, is developed in this study. As pH indicators, a bromthymol blue, a cresol red and a thymol blue are used, and they are immobilized in the sol-gel films. The emitted light from a light source is guided by a fiber-optic Y-coupler and plastic optical fibers to the pH sol-gel film in a pH sensing probe. The pH change in the sensing probe gives rise to a change in the color of the pH sol-gel film, and the optical characteristic of reflected light through the pH sol-gel film is also changed. Therefore, we have measured the spectra of reflected lights, which are changed according to the color variations of the pH sol-gel films with different pH values, by using of a spectrometer. Also, the relationships between the pH values and the intensities of reflected lights are obtained on the basis of the color variations of the pH sol-gel films.

Measurements and comparisons of PDDs using ion chamber and fiber-optic dosimeter irradiated by high energy photon beam

In this study, we have fabricated a fiber-optic radiation sensor using an organic scintillator and plastic optical fiber for brachytherapy dosimetry. Also, we have measured relative depth dose rates of Ir-192 source using a fiber-optic sensor and compared them with the results obtained using a conventional EBT film. Cerenkov lights which can be a noise in measuring scintillating light with a fiber-optic sensor are measured and eliminated by using of a background optical fiber. It is expected that a fiber-optic radiation sensor can be used in brachytherapy dosimetry due to its advantages such as a low cost, simple usage and a small volume.