Kazuya Okamoto

Bio: Kazuya Okamoto is an academic researcher from Nikon. The author has contributed to research in topics: Electromagnetic coil & Signal. The author has an hindex of 19, co-authored 119 publications receiving 2886 citations. Previous affiliations of Kazuya Okamoto include Toshiba.

A precise and fast temperature mapping using water proton chemical shift.

Abstract: A new temperature measurement procedure using phase mapping was developed that makes use of the temperature dependence of the water proton chemical shift. Highly accurate and fast measurements were obtained during phantom and in vivo experiments. In the pure water phantom experiments, an accuracy of more than +/- 0.5 degrees C was obtained within a few seconds/slice using a field echo pulse sequence (TR/TE = 115/13 ms, matrix = 128 x 128, number of slices = 5). The temperature dependence of the water proton chemical shift was found to be almost the same for different materials with a chemical composition similar to living tissues (water, glucide, protein). Using this method, the temperature change inside a cat's brain was obtained with an accuracy of more than +/- 1 degree C and an in-plane resolution of 0.6 x 0.6 mm. The temperature measurement error was affected by several factors in the living system (B0 shifts caused by position shifts of the sample, blood flow, etc.), the position shift effect being the most serious.

Ultrasonic apparatus for thermotherapy with variable frequency for suppressing cavitation

Abstract: An ultrasonic diagnosis apparatus for raising tissue temperature for hypothermic treatments, including an ultrasonic source for generating an ultrasonic treatment wave and a driving means for driving the ultrasonic source such that a frequency of the ultrasonic treatment wave generated by the ultrasonic source changes with time. The frequency of the ultrasonic treatment wave is changed along the time axis. By this change in frequency, some bubbles formed by cavitation as a result of the ultrasonic treatment wave are divided, and some bubbles are collapsed and therefore eliminated. Side effect cavitation and spread of a thermal degeneration area is suppressed, and thermal degeneration can be accurately induced in a desired area, thereby realizing a reliable, safe ultrasonic thermotherapy. Since cavitation is positively suppressed, the total treatment period can be shortened because cavitation would otherwise interfere with and slow down the thermal degeneration process. Therefore, treatment throughput can be improved as compared with a case in which cavitation is left to naturally break and disappear.

Ultrasonic wave medical treatment apparatus suitable for use under guidance of magnetic resonance imaging

Abstract: An ultrasonic wave medical treatment apparatus capable of preventing the displacement of the focal point of the ultrasonic waves from the treatment target portion within the patient, eliminating a need for re-positioning of the ultrasonic wave applicator with respect to the patient, and taking MR images to be utilized during the treatment at a high resolution. In this apparatus, the ultrasonic wave applicator can be integrally incorporated within a treatment table for carrying the patient into the MRI gantry for taking the MR images. The surface coil for taking the MR images can be provided on a surface film of a water bag in the ultrasonic wave applicator, or on a body cavity probe on which the ultrasonic transducer is also provided. The mixing rate of the coupling fluid can be adjusted, and the impedance matching between the ultrasonic transducer and the driving circuit can be maintained by minimizing the reflected electric power from the ultrasonic transducer.

Ultrasound medical treatment apparatus with reduction of noise due to treatment ultrasound irradiation at ultrasound imaging device

Abstract: An ultrasound medical treatment apparatus includes an ultrasound applicator for applying ultrasound irradiation to a treatment target. The treatment apparatus also includes an ultrasound imaging device that transmits ultrasound pulses to image the treatment target. The treatment apparatus is capable of reducing noises occurring at an ultrasound imaging device due to the ultrasound irradiation generated by the ultrasound application during ultrasound medical treatment. The noises may be reduced by increasing a transmission power of the ultrasound pulses. Alternatively, the noises may be reduced by subtracting pre-recorded noise components from the ultrasound pulses received by the ultrasound imaging device, where the pre-recorded noise components are characteristic of noise occurring at the ultrasound imaging device due to the ultrasound irradiation generated by the ultrasound applicator.

Temperature mapping using water proton chemical shift obtained with 3D-MRSI: feasibility in vivo.

Abstract: This article discusses the applicability to a living animal of the temperature mapping method using the water proton chemical shift obtained with three-dimensional magnetic resonance spectroscopic imaging (3D-MRSI). There are several sources of error in obtaining the spectra with 3D-MRSI: signal noise, limitation in the frequency resolution due to the finite signal length, intravoxel inhomogeneity in the static magnetic field, and variation in the magnetic field due to the eddy current magnetic field. A spectral estimation method called phase deduction complex Lorentzian fitting (PD-CLF) was proposed. Numerical simulations demonstrated that this method reduces the error in the chemical shift to one third of that obtained with the simple frequency subtraction method that uses zero-padded first Fourier transformation (FFT). The temperature images obtained using 3D-MRSI with PD-CLF clearly visualized the changes and distribution of temperature in an anesthetized rat.

Nanoshell-mediated near-infrared thermal therapy of tumors under magnetic resonance guidance

Abstract: Metal nanoshells are a class of nanoparticles with tunable optical resonances. In this article, an application of this technology to thermal ablative therapy for cancer is described. By tuning the nanoshells to strongly absorb light in the near infrared, where optical transmission through tissue is optimal, a distribution of nanoshells at depth in tissue can be used to deliver a therapeutic dose of heat by using moderately low exposures of extracorporeally applied near-infrared (NIR) light. Human breast carcinoma cells incubated with nanoshells in vitro were found to have undergone photothermally induced morbidity on exposure to NIR light (820 nm, 35 W/cm2), as determined by using a fluorescent viability stain. Cells without nanoshells displayed no loss in viability after the same periods and conditions of NIR illumination. Likewise, in vivo studies under magnetic resonance guidance revealed that exposure to low doses of NIR light (820 nm, 4 W/cm2) in solid tumors treated with metal nanoshells reached average maximum temperatures capable of inducing irreversible tissue damage (DeltaT = 37.4 +/- 6.6 degrees C) within 4-6 min. Controls treated without nanoshells demonstrated significantly lower average temperatures on exposure to NIR light (DeltaT < 10 degrees C). These findings demonstrated good correlation with histological findings. Tissues heated above the thermal damage threshold displayed coagulation, cell shrinkage, and loss of nuclear staining, which are indicators of irreversible thermal damage. Control tissues appeared undamaged.

Magnetic resonance imaging device

Abstract: By using a multiple receiving coil composed of receiving coils, an imaging portion of a subject is subjected to a first pulse sequence to create n sensitivity images (701 to 703) fewer than the examination images. When these sensitivity images are created, an NMR signal is measured for only the low-frequency region of the k space. A second pulse sequence from which a phase encode step is removed is conducted to create m (m>n) examination images (704, 705) of the subject by using the receiving coils. When sensitivity distributions (707, 708) of the receiving coils are determined for the sensitivity images (701 to 703), and if there are no sensitivity distributions corresponding to the slice positions of the examination images (704, 705), they are determined by slice interpolation using the sensitivity distributions (701 to 703), and the aliasing artifacts of the examination images (704, 705) are removed by matrix operation by using the sensitivity distributions (707, 708).

Noninvasive MR Imaging-Guided Focal Opening of the Blood-Brain Barrier in Rabbits

Abstract: PURPOSE: To determine if focused ultrasound beams can be used to locally open the blood-brain barrier without damage to surrounding brain tissue and if magnetic resonance (MR) imaging can be used to monitor this procedure. MATERIALS AND METHODS: The brains of 18 rabbits were sonicated (pulsed sonication) in four to six locations, with temporal peak acoustic power ranging from 0.2 to 11.5 W. Prior to each sonication, a bolus of ultrasonographic (US) contrast agent was injected into the ear vein of the rabbit. A series of fast or spoiled gradient-echo MR images were obtained during the sonications to monitor the temperature elevation and potential tissue changes. Contrast material–enhanced MR images obtained minutes after sonications and repeated 1–48 hours later were used to depict blood-brain barrier opening. Whole brain histologic evaluation was performed. RESULTS: Opening of the blood-brain barrier was confirmed with detection of MR imaging contrast agent at the targeted locations. The lowest power leve...

Surgical generator for ultrasonic and electrosurgical devices

Abstract: A control circuit of a surgical device is disclosed. The control circuit includes a first circuit portion coupled to at least one switch operable between an open state and a closed state. The first circuit portion communicates with a surgical generator over a conductor pair to receive a control signal to determine a state of the at least one switch.

A precise and fast temperature mapping using water proton chemical shift.

Abstract: A new temperature measurement procedure using phase mapping was developed that makes use of the temperature dependence of the water proton chemical shift. Highly accurate and fast measurements were obtained during phantom and in vivo experiments. In the pure water phantom experiments, an accuracy of more than +/- 0.5 degrees C was obtained within a few seconds/slice using a field echo pulse sequence (TR/TE = 115/13 ms, matrix = 128 x 128, number of slices = 5). The temperature dependence of the water proton chemical shift was found to be almost the same for different materials with a chemical composition similar to living tissues (water, glucide, protein). Using this method, the temperature change inside a cat's brain was obtained with an accuracy of more than +/- 1 degree C and an in-plane resolution of 0.6 x 0.6 mm. The temperature measurement error was affected by several factors in the living system (B0 shifts caused by position shifts of the sample, blood flow, etc.), the position shift effect being the most serious.