Hyung Sik Kim

Measurement of Two-Dimensional Photon Beam Distributions Using a Fiber-Optic Radiation Sensor for Small Field Radiation Therapy

In this study, a fiber-optic radiation sensor with an organic scintillator is fabricated to measure high-energy photon beam from a clinical linear accelerator (CLINAC) and a fiberoptic sensor array is also fabricated to measure two-dimensional, high-resolution and real-time dose distributions for small field radiotherapy dosimetry. The scintillating lights generated from each organic sensor probe embedded and arrayed in a water phantom are guided by 10 m plastic optical fibers to the light- measuring device. The two-dimensional photon beam distributions in a water phantom are measured with different energies and field sizes of photon beams. Also, percent depth dose curves for 6 and 15 MV photon beams are obtained.

Intra- and inter-hemispheric effective connectivity in the human somatosensory cortex during pressure stimulation

BackgroundSlow-adapting type I (SA-I) afferents deliver sensory signals to the somatosensory cortex during low-frequency (or static) mechanical stimulation. It has been reported that the somatosensory projection from SA-I afferents is effective and reliable for object grasping and manipulation. Despite a large number of neuroimaging studies on cortical activation responding to tactile stimuli mediated by SA-I afferents, how sensory information of such tactile stimuli flows over the somatosensory cortex remains poorly understood. In this study, we investigated tactile information processing of pressure stimuli between the primary (SI) and secondary (SII) somatosensory cortices by measuring effective connectivity using dynamic causal modeling (DCM). We applied pressure stimuli for 3 s to the right index fingertip of healthy participants and acquired functional magnetic resonance imaging (fMRI) data using a 3T MRI system.ResultsDCM analysis revealed intra-hemispheric effective connectivity between the contralateral SI (cSI) and SII (cSII) characterized by both parallel (signal inputs to both cSI and cSII) and serial (signal transmission from cSI to cSII) pathways during pressure stimulation. DCM analysis also revealed inter-hemispheric effective connectivity among cSI, cSII, and the ipsilateral SII (iSII) characterized by serial (from cSI to cSII) and SII-level (from cSII to iSII) pathways during pressure stimulation.ConclusionsOur results support a hierarchical somatosensory network that underlies processing of low-frequency tactile information. The network consists of parallel inputs to both cSI and cSII (intra-hemispheric), followed by serial pathways from cSI to cSII (intra-hemispheric) and from cSII to iSII (inter-hemispheric). Importantly, our results suggest that both serial and parallel processing take place in tactile information processing of static mechanical stimuli as well as highlighting the contribution of callosal transfer to bilateral neuronal interactions in SII.

Measurement of two-dimensional photon beam distributions using a fiber-optic radiation sensor for small field radiation therapy

In this study, we fabricated a fiber-optic radiation sensor with an organic scintillator to measure the high-energy photon beam from a clinical linear accelerator, and a two-dimensional fiber-optic sensor array to measure high-resolution and real-time dose distributions for small field radiotherapy dosimetry. The scintillating lights generated from each organic sensor probe embedded and arrayed in a water phantom are guided by 10 m plastic optical fibers to the light-measuring device. Two-dimensional photon beam distributions in a water phantom were measured for photon beams with different energies and field sizes. Also, percent depth dose curves for 6 and 15 MV photon beams were obtained.

Development of Two-dimensional Fiber-optic Radiation Sensor for High Energy Photon Beam Therapy Dosimetry

In this study, we have developed two-dimensional fiber-optic radiation sensors using organic scintillators and plastic optical fibers for high energy photon beam therapy dosimetry. The scintillating lights generated from each organic sensor probe embedded and arrayed in a polymethylmethacrylate phantom are guided by 10 m plastic optical fibers to the light-measuring devices such as 25 channel photodiode-amplifiers system. Two-dimensional photon beam distributions in a polymethylmethacrylate phantom are measured with different energies and field sizes of photon beam. Also, percent depth dose curves for 6 and 15 MV photon beams are obtained using a two-dimensional fiber-optic sensor. This sensor has many advantages such as high resolution, real-time measurement, two-dimensional dose measurement and ease calibration over conventional radiation measurement devices.

A Simple Finger Stimulator for Simultaneous Vibration and Heat Stimulation

In this study, we developed a simple finger stimulator that can simultaneously control vibration and heat stimulation. The newly developed stimulator consists of three parts, namely the control unit, drive unit, and an actuator. The control unit controls the stimulation type, frequency, intensity, and time. The drive unit amplifies the stimulation signal that drives the actuator. The actuator displays the vibration and heat stimuli quantitatively and simultaneously. Although the developed stimulator is simple, it has a wide frequency range of 0-400 Hz comprising 40 levels, and vibration stimulation intensity comprising 50 levels. The control temperature and stimulation temperature used for heat stimulation comprise four and eight levels, respectively. In addition, the developed stimulator has many advantages in terms of the overall system, stimulation control, and safety. Therefore, the developed stimulator can be used for integrative tactile perception and cognition studies on various vibration and heat sensations.

A Study on the Characteristics of a Vibrator Using Flat PCB-Coil

In this study, we developed and evaluateda vibrator using a flat PCB-coil. The flat PCB-coil vibrator was fabricated on a printed circuit board using and etching process. The spiral pattern was etched on a fiberglass cloth with an epoxy resin. To evaluatethe flat PCB-coil vibrator, we generated a sine wave, saw-tooth, and square wave through a custom made wave generator and amplified the waveforms using a power amplifier. A three-axis accelerometer was used to evaluate the performance of the developed vibrator. Even though the developed vibrator is simple, it has a wide range of vibration frequency (50~500 Hz) and vibration amplitude (0~5 V). The vibration amplitude does not change due to frequency change. It is expected that the developed vibrator can be used in a wide variety of applications such as in a tactile stimulator, in elastography, energy harvesting, and in a cooling system.

A MR-Compatible Finger Stimulator for Simultaneous Pressure and Heat Stimulation

In this study, a Magnetic Resonance (MR)-compatible finger stimulator was developed that can display pressure and heat stimulation simultaneously. The developed finger stimulator consists of three parts: a main controller, drive units, and tactors. The main controller controls stimulation parameters such as stimulation intensity and time. The drive units operate pressure and heat tactors in response to commands from the main controller. The tactors display various pressure and heat stimulation quantitatively and simultaneously. The developed stimulator has many advantages in overall system, stimulation control, and tactor aspects. The new stimulator operated stably in MR circumstance without affecting MR images. Therefore, it can be used for the various intra-and inter-finger functional magnetic resonance imaging (fMRI) studies on pressure and heat sensation.

Movement Measurement Systems for fMRI Motion Studies

In this study, functional magnetic resonance image (fMRI)-compatible movement measurement system was developed. The movement measurement system consisted of a sensor module with a three-axis accelerometer and a two-axis gyroscope, a modulator, and a demodulator. Velcro was used to attach the sensor module to a finger or wrist. Interactive effects in a human subject were tested by measuring fMRI and motion signals simultaneously. Images were obtained using the field echo planar imaging method using a 3 T MR scanner and the signal-to-noise ratio was calculated. The entire system can be made with low cost, and its direct implementation is available in a clinical MR scanner without any additional installation. Various kinematic variables, such as angle, acceleration, and jerk, can be measured and calculated by using the movement measurement system. Therefore, it is expected that this system could be used for the study of the relationship between various kinematic variables and brain function.