In this work, an acoustic imaging method based on contrast source inversion and its feasibility in quantitatively reconstructing compressibility, attenuation, and density of human thorax is studied. In the acoustic wave equation, the inhomogeneity in density makes the relationship between the contrasts and the total pressure highly nonlinear. To reduce this nonlinearity, two contrast sources are introduced to ensure symmetry in the equation, such that the inverse problem can be solved efficiently by alternately updating two contrast sources and two contrasts. Moreover, to improve the stability of the algorithm, the multiplicative regularization scheme with two additive regularization factors is applied. Using this algorithm, acoustic parameters of human thorax from low frequency ultrasound measurement are reconstructed. Numerical results show that the acoustic parameters of human thorax can be properly reconstructed at frequency of tens of kHz using this algorithm.