Photoacoustic tomography

from Wikipedia, the free encyclopedia

The photoacoustic tomography ( PAT , also: optoacoustic imaging , English Photo Acoustic Imaging , PAI ) is a hybrid imaging method which comprises the photoacoustic effect exploited. It works with very fast laser pulses (less than ten nanoseconds ) that generate ultrasound in the tissue to be examined . The difference to conventional ultrasound examinations is that not only are "echoes" examined on the surface of organs, but these generate the sound themselves. The local absorption of the light leads to sudden local heating and the resulting thermal expansion . This ultimately generates broadband acoustic waves . By measuring the outgoing ultrasonic waves with appropriate ultrasonic transducers outside the sample, the original distribution of the absorbed energy can be reconstructed. The images possible with this can achieve the richness of detail of computed tomography without generating harmful radiation. This imaging technique is particularly suitable for soft, biological tissue, as certain tissue components such as blood vessels have a strong contrast to visible or infrared light.

In laboratory experiments, the process (in the form of photoacoustic spectroscopy ) was also used to measure the blood sugar content of diabetics .

Tumor cells appear transparent and are therefore almost invisible. Scientists have genetically modified tumor cells so that they produce the body's own pigment melanin . This makes them recognizable for the photoacoustics . The extremely small detectors generate 3-D images in a very high resolution and enable examinations in tissue regions of living organisms with image depths of up to one centimeter. Previous, purely optical technologies with high resolution, such as microscopy or coherence tomography , could only reach depths of one millimeter.

The application of photoacoustic tomography to detect and diagnose ovarian cancer at an early stage is currently being researched. Two biomarkers are used to characterize the ovaries: the relative total hemoglobin concentration (rHbT), which is directly related to tumor angiogenesis , and the mean oxygen saturation sO 2 . In photoacoustic tomography, the laser light propagates from a transvaginal ultrasound probe , is absorbed by the tumor and generates sound waves that display information about the two biomarkers in the ovaries visible in the ultrasound .

literature

  • J. Märk, H. Dortay, A. Wagener, E. Zhang, J. Buchmann, C. Grötzinger, T. Friedrich, J. Laufer: Dual-wavelength 3D photoacoustic imaging of mammalian cells using a photoswitchable phytochrome reporter protein. In: Communication Physics (2018), DOI: 10.1038 / s42005-017-0003-2
  • A. Walther, L. Rippe, LV Wang, S. Andersson-Engels, S. Kröll: Analysis of the potential for non-invasive imaging of oxygenation at heart depth, using ultrasound optical tomography (UOT) or photo-acoustic tomography (PAT ). In: Biomedical optics express. Volume 8, number 10, October 2017, pp. 4523–4536, doi: 10.1364 / BOE.8.004523 , PMID 29082082 , PMC 5654797 (free full text).
  • LV Wang: Ultrasound-mediated biophotonic imaging: a review of acousto-optical tomography and photo-acoustic tomography. In: Disease markers. Volume 19, number 2-3, 2003-2004, pp. 123-138, doi: 10.1155 / 2004/478079 , PMID 15096709 , PMC 3851612 (free full text) (review).

Individual evidence

  1. ↑ J. Xia, J. Yao, LV Wang: Photoacoustic tomography: principles and advances. In: Electromagnetic waves. Volume 147, 2014, pp. 1–22, PMID 25642127 , PMC 4311576 (free full text).
  2. ↑ JY Sim, CG Ahn, EJ Jeong, BK Kim: In vivo Microscopic Photoacoustic Spectroscopy for Non-Invasive Glucose Monitoring Invulnerable to Skin Secretion Products. In: Scientific Reports . Volume 8, number 1, 01 2018, p. 1059, doi: 10.1038 / s41598-018-19340-y , PMID 29348411 , PMC 5773698 (free full text).
  3. ↑ Tumor cells produce their own contrast agent , press release, Charité, March 12, 2015. Accessed June 22, 2019.
  4. ↑ Sreyankar Nandy, Atahar Mostafa et al. a .: Evaluation of Ovarian Cancer: Initial Application of Coregistered Photoacoustic Tomography and US. In: Radiology. 289, 2018, p. 740, doi : 10.1148 / radiol.2018180666 .

Web links