Optical Tomography Using Echo Pulses Modulated by Light for Medical Diagnosis

研究了一种利用近红外光与超声波相互作用成像的新方法在医学诊断中的应用。利用5 MHz谐振频率的超声换能器制作了该方法的测量设备，用于光学层析成像的构建。将该方法应用于包括吸收物的生物组织（狗胃）。当激光二极管照射样品时，来自吸收区后边界的超声回波脉冲出现时移。由速度变化重建的图像显示了狗胃吸收区的形状。实验结果表明，该方法具有应用于恶性肿瘤空间分布诊断的可能性。我们的光学断层扫描设备不足以进行组织表征。为了提高空间分辨率，采用20 MHz谐振频率的超声换能器代替5MHz的换能器。在光照强度在皮肤暴露极限范围内的情况下，检测由介质弹性系数变化引起的超声回波脉冲位移。在超声速度变化构造的图像中，鸡肉表面有狭窄的有色琼脂边界。该测量设备具有更高的空间分辨率，有望应用于距离皮肤一定距离处氧血红蛋白分布的测量和肿瘤的空间诊断。高功率激光二极管附在商用超声诊断设备上。利用阵列换能器检测样品中光照引起的超声波速度变化。样品的图像由阵列换能器的波形构成。得到了样品中吸收分布的详细图像。

A new imaging method using the interaction between the near infrared light and the ultrasonic wave was investigated for application to medical diagnosis.A measuring equipment of the method using the ultrasonic transducer of 5 MHz resonant frequency was fabricated for construction of optical tomography. The method was applied to a biological tissue (a dog stomach) including absorbing objects. Ultrasonic echo pulses from the back boundaries of absorption region showed the time shift when the laser diode illuminated the sample. The image reconstructed from the velocity change revealed the shape of the absorption area in the dog stomach. Experimental results show that this method has the possibility for application to diagnosis of the spatial distribution of malignant tumor.Our equipment for optical tomography was insufficient for tissue characterization. An ultrasonic transducer of 20 MHz resonant frequency was employed instead of the transducer of 5MHz for improvement of spatial resolution. The ultrasonic echo pulse shift which was caused by the elastic coefficient change of the medium was detected under the light illumination of intensity within the skin exposure limit. Narrow boundaries of colored agar under chicken meat were observed in the image constructed from ultrasonic velocity change. The measuring equipment with improved spatial resolution is expected to apply to measurement of distribution of oxy-hemoglobin at the specified distance from the skin and spatial diagnosis of tumors.The high power laser diode was attached to the commercial ultrasonic diagnostic equipment. The array transducer of the equipment was employed to detect the ultrasonic velocity shift due to light illumination in the sample. Images of the sample were constructed from waveforms of the array transducer. The detail image of the absorption distribution in the sample was obtained.