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21COE プログラム「機械システム・イノベーション」平成17年度第5回公開セミナーを開催いたします。ご参加いただきますようどうぞ宜しくお願い申し上げます。

講師 Professor Lihong V. Wang, Ph.D.
(Biomedical Engineering & Electrical Engineering, Texas A&M University)
題目 High-resolution Biophotonic Imaging
日時 2005年9月7日(水) 17:00〜18:30
場所 工学部8号館・226号会議室
講演要旨

We develop novel biophotonic tomography for early-cancer detection and functional imaging using physically combined non-ionizing electromagnetic and ultrasonic waves. Unlike ionizing x-ray radiation, non-ionizing electromagnetic waves, such as optical and radio waves, pose no health hazard and, at the same time, reveal new contrast mechanisms. For example, our spectroscopic oblique-incidence reflectometry can detect skin cancers accurately based on functional hemoglobin parameters and cell nuclear size. Unfortunately, electromagnetic waves in the non-ionizing spectral region do not penetrate biological tissue in straight paths as x-rays do. Consequently, high-resolution tomography based on non-ionizing electromagnetic waves alone, as demonstrated by confocal microscopy and two-photon microscopy as well as optical coherence tomography, is limited to superficial imaging within about one transport mean free path (~1mm) into biological tissues. Ultrasonic imaging, on the contrary, furnishes good image resolution but has strong speckle ultrasound-mediated imaging modalities by combining electromagnetic and ultrasonic waves synergistically to overcome the above problems. The hybrid modalities yield speckle-free images of high electromagnetic contrast at high ultrasonic resolution in relatively large volumes of biological tissues. The specific technologies to be reviewed in the talk are summarized below.

Mueller optical coherence tomography provides microscopic-scale depth-resolved tomographic images of the complete polarization properties in scattering biological tissues.Polarization properties are related to the orientation and density of fibril structures (such as collagen) in skin, retina, cartilage, muscle, and other anisotropic biological tissues.Potential applications include the imaging of burns, detection of glaucoma, study of osteoporosis, and detection of cancer.

In ultrasound-modulated optical tomography, a focused ultrasonic wave tags diffuse laser light in scattering biological tissue, which is analogous to the encoding concept in MRI.Because the tagged photons that carry the ultrasonic frequency originate from the localized ultrasonic wave, they can be extracted from the observed optical speckles to achieve high-resolution tomographic imaging.

In photo-acoustic tomography, an expanded pulsed laser beam diffuses into the biological tissue and generates a small but rapid temperature rise, which causes the emission of ultrasonic waves as a result of thermoelastic expansion.The short-wavelength ultrasonic waves are then detected to form diffraction -limited high-resolution tomographic images.

Thermo-acoustic tomography is similar to photo-acoustic tomography except that low-energy radio-frequency pulses, instead of laser pulses, are used.Although the long-wavelength radio-frequency waves diffract rapidly in the tissue, the short-wavelength ultrasonic waves provide high spatial resolution.

参加者 RA3を含めて9名
主な議論 光を用いた生体内測定についてのレビューのあと、光と超音波を組み合わせた 生体測定であるphoto-acoustic tomograph (PAT)が紹介された。
光を用いた生体内の非侵襲測定は生体内での光の散乱が大きいことと 光の吸収解像度が波長によって制限されるために、従来は限界があった。
ところが,光の吸収を超音波で測定することによって高解像度の測定が可能となった。
また,照射する光の波長を変えることで静脈と動脈を区別する測定なども可能である。
紹介された血管の3次元的な詳細な測定結果は大変インパクトがあった。
皮膚の表面からどの程度の深さまで測定できるかとの質問に対して、 10mm程度との回答があった。


本件連絡先

  東京大学工学系研究科機械工学専攻 丸山 茂夫
  E-mail:maruyama@photon.t.u-tokyo.ac.jp
  TEL:03-5841-6421


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