JPH05154154A - Optical ct device using wavelength variable laser - Google Patents

Abstract

(57) [Summary] [Structure] A laser beam obtained from a semiconductor laser-excited all-solid-state tunable pulse laser is applied to a living body to detect the temporal spread and temporal intensity of a light pulse transmitted through the living tissue. Optical CT device for imaging the oxygen concentration distribution in the body [Effect] This device uses an all-solidified tunable pulse laser that oscillates stably in a wide wavelength range, so that the spatial resolution of the oxygen concentration distribution in the living body can be improved. A high and stable image distribution is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention obtains a three-dimensional distribution of tissue oxygen concentration in a living body using a semiconductor laser-excited all-solid-state titanium-doped sapphire (Ti: Al ₂ O ₃ ) tunable pulse laser as a light source. Optical CT device capable of

With this device, hemoglobin in blood,
Alternatively, it is possible to image (CT image) the oxygen concentration distribution in tissue oxygen from myoglobin in muscle (for example, brain oxygen distribution), and in the medical field, diagnoses such as ischemia, cerebral infarction, myocardial infarction, and cancer It is expected to be applied to diagnosis. Furthermore, the non-invasive measurement of oxygen concentration in the living body is expected to be applied to three-dimensional analysis of oxygen metabolism in the living body in medicine.

[0003]

2. Description of the Related Art Recently, near-infrared light CT for imaging oxygen concentration distribution in living tissue has been studied. The light source used in this optical CT is a semiconductor laser, a dye laser, a titanium-doped sapphire laser excited by an argon laser, or the like.

By the way, biological substances that regulate the oxygen concentration are usually hemoglobin, myoglobin, and cytochrome oxidase, but their absorption spectra have a wide wavelength band of 750 nm to 1100 nm. There are basically two possible methods for realizing the optical CT of such a substance. One of them is an X-ray CT algorithm that extracts the concentration of the absorber existing in the optical path, the absorption coefficient, and the absorption of the straight-ahead component that determines the optical path length from the light (including scattered light) that has passed through the biological tissue. Method using
The other one is to detect the light transmitted through the tissue in the shortest time by irradiation-light reception arranged on a straight line (180 °) using short pulse light (picosecond to femtosecond region), and use this as the straight component. Then, it is a method using an X-ray CT algorithm.

However, in any of the above-mentioned methods using a laser, since the absorption spectrum of biological substances such as hemoglobin is wide, oxygen concentration is calculated, and the resolution of the image is further improved. In order to realize CT, it is necessary to use multi-wavelength laser light (the higher the wavelength, the higher the image resolution, and in this case, preferably 100 wavelengths or more).
There is a need for a wavelength tunable laser that stably oscillates in the 0 nm wavelength region.

At present, one semiconductor laser used for research can change the wavelength only within a range of about ten and several nm. However, it is possible to cover 700 to 1100 nm by using several tens of semiconductor lasers, but in this case, there is a drawback that it is difficult to match the optical axis of each laser.

The wavelength tunable dye laser has a wavelength tunable range of 50 to 100 nm, but not only is the laser oscillation output lowered and fluctuated due to the photodegradation of the dye in use, it is unstable, and the life is also shortened. Short and not easy to maintain.
The titanium-doped sapphire laser excited by an argon laser has an excitation light source of an argon laser and a gas laser,
There are problems such as the life of gas and frequent maintenance.

A titanium-doped sapphire laser excited by a flash lamp-excited neodymium-doped solid-state laser (for example, Nd: YAG, Nd: YLF) can be considered, but when using a flash lamp, the high voltage required is in a hospital. Then, there is a problem that the measurement of the electrocardiogram is affected.

[0009]

DISCLOSURE OF THE INVENTION The present invention has less of the above-mentioned problems, that is, excellent biopermeability, and is from 700 to
Oxygen concentration in biological tissue using a wavelength tunable pulse laser of titanium sapphire as a light source that oscillates stably with high efficiency and long life by tunable wavelength in the range of 1100 nm and does not affect measurements such as electrocardiograms in hospitals. It is an object of the present invention to provide an optical CT device capable of imaging a distribution.

[0010]

DISCLOSURE OF THE INVENTION As a result of intensive studies on the optical CT apparatus, the present inventors have found that a semiconductor laser-excited all-solid-state tunable titanium-doped sapphire pulse laser has a wavelength in the range of 700 to 1100 nm. It has been found that the above problems can be solved by oscillating variable and with high efficiency and using this as a light source, and completed the present invention.

That is, the present invention is a light for irradiating a living body with a laser beam obtained from a semiconductor laser-excited all-solid-state tunable pulse laser, detecting light transmitted through a living tissue, and imaging an oxygen concentration distribution in the living body. The present invention relates to a CT device.

Next, the basic structure of the present invention will be described in more detail with reference to embodiments. FIG. 1 is a diagram schematically showing the configuration of the optical CT apparatus of the present invention. In the figure, 1 is a semiconductor laser-excited all-solid-state titanium-doped sapphire wavelength tunable laser, 2 is a laser power source, 3 is an optical fiber, 4 is a gantry and a living body fixing stand, 5 is a photodetector (for example, a photomultiplier tube, 6 is a target tube). An inspection human body, 7 is a data processing computer, 8 is an image plotter, 9 is a display, and 10 is a data recording device.

A laser beam is guided to a gantry to which a living body is fixed by an optical system such as an optical fiber or a mirror,
Irradiate the living body to be inspected. At this time, the laser light is applied to the living body from various angles by rotating the gantry. The irradiated light penetrates the living body while causing scattering and the like in the living tissue. At that time, the irradiation-light receiving system arranged in a straight line detects the time-spreading of the transmitted pulse or the temporal intensity of the pulse to detect the rectilinear component that has passed through the biological tissue in the shortest time, and the tissue transmission. Measure time and absorbance. After that, these data and the spread of light are calculated to create a CT image.

Examples of semiconductor laser-excited all-solid-state tunable pulse laser used as a light source in the present invention include the following.

(1) Wavelength 1.08 μm produced by ⁴ F _3/2 → ⁴ I _11/2 transition in a neodymium-doped yttrium aluminum perovskite (Nd: YAlO ₃ , Nd: YAP) laser excited by a quasi-continuous oscillation semiconductor laser. K switch pulse laser of K
An all-solid-state titanium-doped sapphire (Ti: Ti: P) having a second harmonic pulsed light generated by doubling under 90 ° phase matching condition by a TiOPO ₄ (KTP) crystal as an excitation source.
Al ₂ O ₃ ) Tunable pulsed laser.

(2) With a continuous wave semiconductor laser,
Neodymium-added yttrium aluminum garnet (Nd: Y ₃ Al ₅ O ₁₂ , Nd: YAG), neodymium-added yttrium aluminum vanadate (Nd: Y
VO ₄ ) and neodymium-doped yttrium aluminum perovskite (Nd: YAlO ₃ , Nd: YAP) are excited to continuously oscillate, and the oscillated laser light is forcibly mode-locked by an acousto-optic device to generate pulsed light. KTiOPO ₄ (KTP), β-barium borate (β-BaB ₂ O ₄ , BBO), lithium borate (LiB ₃ O ₅ , LBO), potassium niobium oxide (KN)
bO ₃ , KN) and the like, pulsed light generated by doubling with a non-linear optical element such as bO ₃ , KN) is used as excitation light, and synchronous excitation mode-locked all-solid-state titanium-doped sapphire (Ti: Al ₂ O) is used.
₃ ) Tunable pulsed laser.

(3) ⁴ F in a Nd: YAP tunable laser pumped by a quasi-continuous oscillation semiconductor laser
1.0 of the wavelength generated by the _3/2 → ⁴ I _11/2 transition
Second-harmonic pulsed light generated by doubling an 8 μm Q-switched laser pulse under 90 ° phase matching conditions by a KTP crystal, or Nd: YAG, neodymium-doped yttrium lithium fluoride excited by a quasi-continuous oscillation semiconductor laser. Ride (Nd: YLiF ₄ )
Laser Q switch pulse is KTP, BBO, LB
Using a crystal such as O or KN, the pulsed light of a titanium-doped sapphire wavelength tunable laser whose excitation source is the pulsed light of the second harmonic generated by doubling under phase matching conditions A laser obtained by a system in which pulse compression or frequency chirping is applied on the order of seconds by an optical fiber and then compressed on the order of picoseconds by a dispersion circuit such as a diffraction grating pair.

The laser light used in the present invention has a variable wavelength range of 700 to 1100 nm and a pulse width of several ns.
ec to several tens of psec, preferably picosecond order, pulse repetition rate 100 Hz to several MHz, preferably 100 Hz order, pulse energy is several μJ /.
It is preferable to use one having a range of p to several mJ / p.

In particular, the pulse width is preferably in the picosecond order, which is to increase the repetition rate of the pulse in the nonasecond order by using an optical fiber exhibiting the above optical Kerr effect, or a pair of diffraction gratings as an optical fiber and a dispersion circuit. Without (100 Hz order), it can be compressed into a picosecond order pulse.

Although pulsed light on the picosecond order can be obtained even by using the method of synchronous excitation mode locking, in this case the repetition rate is on the order of MHz, so that the laser pulsed lights irradiated in the living body do not overlap. Laser pulses for CT are obtained by thinning the pulses.

FIG. 2 is a diagram showing a configuration example of a quasi-continuous oscillation semiconductor laser pumped titanium sapphire laser. FIG. 3 is a diagram showing another configuration example of a titanium sapphire laser pumped by a quasi-continuous oscillation semiconductor laser, which is 1.08 μm of an Nd: YAP laser excited by a quasi-continuous oscillation semiconductor laser.
Of the all-solid-state tunable pulse laser that doubles the Q-switched laser pulse in KTP by KTP and compresses the pulsed light of the titanium sapphire laser that uses the generated second harmonic as the excitation source to the picosecond order by the single mode optical fiber. Here is an example. Further, FIG. 4 shows an example of a synchronously pumped mode-locked titanium sapphire laser.

In these figures, 11 is a semiconductor laser, 1
2 is a condenser lens, 13 is Nd: YAP, 14 is a Q switch, 15 is a KTP crystal, 16 is a reflection mirror, 17 is a condenser lens, 18 is a reflection mirror, 19 is a titanium sapphire crystal, 20 is a wavelength selection element, 21 and 22 are reflection mirrors, 2
3 is a wavelength selection element, 24 is a reflection mirror, 25 is a beam splitter mirror, 26 is a condenser lens, 27 is a single mode optical fiber, 28 is a condenser lens, 29 is a reflection mirror, 30 is an electro-optic modulator, 31 is 31 Nd: YAG or N
d: YLF, 32 is a photodetector, and 33 is an electro-optic modulator power supply.

[0023]

Since the apparatus of the present invention uses an all-solidified wavelength tunable pulse laser that stably oscillates in a relatively wide wavelength range, a stable image distribution such as oxygen concentration distribution in a living body can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the configuration of an optical CT device of the present invention.

FIG. 2 is a diagram showing a configuration example of a titanium sapphire laser pumped by a quasi-continuous oscillation semiconductor laser.

FIG. 3 is a view showing another configuration example of a quasi-continuous oscillation semiconductor laser-excited titanium sapphire laser.

FIG. 4 is a diagram showing an example of a synchronously pumped mode-locked titanium sapphire laser.

[Explanation of symbols]

1: Semiconductor laser-excited all-solid-state titanium-doped sapphire wavelength tunable laser 2: Laser power supply 3: Optical fiber 4: Gantry and living body fixing stand 5: Photodetector 6: Human body to be inspected 7: Data processing computer 8: Image plotter 9 : Display 10: Data recording device 11: Semiconductor laser 12: Condenser lens 13: Nd: YAP 14: Q switch 15: KTP crystal 16: Reflection mirror 19: Titanium sapphire crystal 20: Wavelength selection element 25: Beam splitter mirror 27: Single-mode optical fiber 30: Electro-optic modulator 31: Nd: YAG or Nd: YLF 32: Photodetector 33: Electro-optic modulator power supply

Claims (4)

[Claims] 1. A laser beam obtained from a semiconductor laser-excited all-solid-state tunable pulse laser is irradiated to a living body, and the temporal intensity of the pulsed light transmitted through the living tissue is detected to image the oxygen concentration distribution in the living body. Optical CT device that does. 2. A semiconductor laser-excited all-solid-state tunable laser in a neodymium-doped yttrium aluminum perovskite (Nd: YAlO ₃ ) laser excited by a quasi-continuous oscillation semiconductor laser is ⁴ F _3/2 → ⁴
A Q-switched laser pulse with a wavelength of 1.08 μm caused by the I _11/2 transition was generated by KTiOPO ₄ crystal.
2. An all-solid-state titanium-doped sapphire (Ti: Al ₂ O ₃ ) wavelength tunable pulse laser using a second harmonic pulse light generated by doubling under 0 ° phase matching condition as an excitation source. Optical CT device. 3. A semiconductor laser-excited all-solid-state tunable laser is a continuous wave semiconductor laser, which is used to produce yttrium aluminum garnet (Nd: Y ₃
Al ₅ O ₁₂ ), neodymium-added yttrium vanadate (Nd: YVO ₄ ), and neodymium-added yttrium aluminium perovskite (Nd: YAlO ₃ ) are excited to continuously oscillate, and forced mode synchronization is performed.
The generated pulsed light is converted into KTiOPO ₄ , β barium borate (β-BaB ₂ O ₄ ), lithium borate (LiB
₃ O ₅ ), potassium niobium oxide (KNbO ₃ ), which is a all-solid-state titanium-doped sapphire wavelength tunable pulse laser that is synchronously excited and mode-locked by using as pulsed light pulsed light that is doubled by a nonlinear optical element. The optical CT apparatus according to claim 1. 4. A semiconductor laser-excited all-solidified tunable solid-state laser is a ⁴ F _3/2 in a neodymium-doped yttrium aluminum perovskite (Nd: YAlO ₃ ) laser excited by a quasi-continuous oscillation semiconductor laser.
→ ⁴ I _11/2 Q-switched laser pulse with a wavelength of 1.08 μm doubled under 90 ° phase matching condition by KTiOPO ₄ crystal, or pulsed light of second harmonic, or quasi-continuous oscillation semiconductor Q of laser-excited neodymium-doped yttrium aluminum garnet or neodymium-doped yttrium lithium fluoride (Nd: YLiF ₄ ) laser
Switch pulse to potassium titanium phosphate (KTiOPO
₄ ), β barium borate (β-BaB ₂ O ₄ ), lithium borate (LiB ₃ O ₅ ), potassium niobate (KNb)
A crystal selected from O ₃ ) is used, and the pulsed light of the titanium sapphire wavelength tunable pulse laser whose excitation source is the pulsed light of the second harmonic generated by doubling under phase matching conditions The optical CT apparatus according to claim 1, wherein the optical CT apparatus is a system in which pulse compression or frequency chirping is applied on the order of seconds by an optical fiber and then compressed on the order of picoseconds by a dispersion circuit such as a diffraction grating pair.