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All-Optical Photoacoustic Imaging with Fiber-Optic Mach-Zehnder Interferometers / submitted by Johannes Bauer-Marschallinger
AutorInnenBauer-Marschallinger, Johannes
Beurteiler / BeurteilerinJakoby, Bernhard ; Paltauf, Günther
Betreuer / BetreuerinJakoby, Bernhard
ErschienenLinz, 2019
Umfangiv, 71 Blätter : Illustrationen
HochschulschriftUniversität Linz, Dissertation, 2019
Schlagwörter (EN)photoacoustic imaging / fiber optics imaging / ultrasound / interferometry / photoacoustic macroscopy / optical ultrasound detection / photoacoustic projection imaging
URNurn:nbn:at:at-ubl:1-26476 Persistent Identifier (URN)
 Das Werk ist gemäß den "Hinweisen für BenützerInnen" verfügbar
All-Optical Photoacoustic Imaging with Fiber-Optic Mach-Zehnder Interferometers [8.76 mb]
Zusammenfassung (Englisch)

Photoacoustic imaging (PAI) is an emerging method for biomedical and medical applications. In PAI, images of living tissue and biological samples are reconstructed from ultrasonic waves generated by optical absorption and detected on the outside. Thus, PAI denotes hybrid methods benefiting from the diverse optical contrast and the relative low scattering of ultrasound in biomaterials. Different types of tissue properties (e.g. anatomical, metabolic, histological, and functional properties) show endogenous optical absorption contrast and can therefore be examined with PAI. By using contrast agents, also molecular and cellular information can be gained. Object sizes ranging from cellular to organ level are covered by different implementations of PAI. In photoacoustic (PA) computed tomography (PACT), an array of ultrasound transducers is used to quickly acquire the necessary ultrasound information to reconstruct a 3D image of a volume. In PA microscopy (PAM), a 2D or 3D image is obtained by raster scanning a sample with focused ultrasound generation and detection. Optical methods are a promising alternative to commonly used piezoelectric transducers (PET). They offer e.g. a wide acceptance angle, high sensitivity, low-cross talk, and remote detection. Ultrasound sensors based on fiber-optic Mach-Zehnder interferometers were developed and investigated in the course of this thesis. In such a detector, one arm of the interferometer (i.e. the measurement fiber) is exposed to the ultrasonic field. The pressure along the measurement fiber affects its optical path length due to the elasto-optic effect. By suppressing other influences on the optical path length (e.g. thermal drifts), the output power of the interferometer varies according to the integrated ultrasonic pressure along the measurement fiber. These so-called integrating line detectors can be brought into different geometric shapes due to the mechanical flexibility of the fibers. Depending on the respective shape, these sensors allow special implementations of PAI. For example, the large depth-of-field offered by annular integrating line detectors makes PA scanning macroscopy (PASMac) feasible. In PASMac images are acquired with a scanning approach like in PAM but with imaging depths and resolutions comparable to PACT. For this thesis, a demonstrator for PASMac with annular fiber-optic detectors was developed and characterized. Another PAI implementation developed for this thesis features 64 fiber-optic parallel straight line detectors arranged along a circle. It facilitates PA projection imaging (PAPI) of objects with several centimeters in size. An imaging resolution in the range of 100 m to 260 m was achieved. The 3D problem of monitoring of large volumes can be reduced two a 2D problem by PAPI. This brings the major advantage of reducing the number of necessary sensor positions by two orders of magnitude. The demonstrators developed for PAPI and PASMac achieve respectable imaging resolutions and sensitivities. The occurrence of imaging artifacts should be reduced by increasing the number of sensors. Furthermore, the imaging speed should be increased by using a faster laser, by parallel readout of all measurement channels and by a modification of the scanning process in the PASMac system. In conclusion, PAI systems based on fiber-optic integrating line detectors can be a promising alternative and extension to existing PAI methods.

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