Thermoacoustic imaging is a new modality of generating ultrasonic waves with excitation of electromagnetic pulsed energy. Thermoacoustic imaging is based on the inverse soluion of thermoacoustic wave equation. Homogeneous assumption of tissue to be imaged results in degradation of image qualtiy. In this study, we obtain an analytical inverse solution of thermoacoustic wave equation for 3-dimensional concentric cylindrical multi layer structures. This solution can be applied for imaging of breast and brain. To test our solution, we use a 3-layer test phantom consisting of point sources in numerical simulations.