One dimensional photo-acoustic imaging using laser source

number: 
2738
English
Degree: 
Author: 
Luma Waleed Jameel
Supervisor: 
Dr. Mohammed A. Hussain
year: 
2012
Abstract:

The present work consists of a theoretical and experimental procedure of laser photoacoustic one dimensional imaging to detect a blood vessel or a tumor embedded within normal tissue.The key task in photoacoustic imaging is to have an acoustic signal that helps to determine the size and location of the target object inside normal tissue. The analytical simulation has been performed using the plane and cylindrical wave models. The plane wave model simulates the target object (blood vessel or tumor), while the cylindrical wave model simulates the normal tissue. The analytical simulation has utilized a spherical wave model representing target object. This model generates a time resolved acoustic wave signal that include both expansion and contraction parts. The photoacoustic signal from the target object is simulated for a range of laser pulse energy10-150mJ, laser pulse duration 10µs-10ns, depth of target object 0.3-6 cm, distance from the object to the detector 0.7-3 cm and diameter of target object 0.2-1.2cm. The experimental work is accomplished using phantoms (sandwiched of chicken breast and piece of liver) to simulate a real tissue using Nd:YAG laser with 1.064µm wavelength,10ns pulse duration, 500, 400 and 250 mJ laser pulse energy. The target object inside the phantom has a slab shape with different dimensions: thickness 0.3-1.3 cm, the depth of object is 0.2-1 cm and the distance to the detector is 0.3-1.2 cm. The diameter of the object from the simulation results of the spherical model is 75% of its real assumed value. The amplitude of the signal is directly proportional with the laser pulse energy and inversely proportional with the depth of target object and distance from the object to the detector. No direct correlation could be established between the acoustic wave duration and the target dimension (as it should be) in the experimental work for various reasons such as the use a slab sample not a spherical one which is difficult to build and coupling in the breast chicken tissue, the coupling of the liver piece with the surrounding tissue, the coupling of the piezoelectric detector with the phantom, noise from the surrounding tissue (breast chicken) and other noise from laser, detector and oscilloscope.