1. A method for determining a physiological parameter of a subject, the method comprising: providing a photonic signal to a first blood vessel site of the subject; detecting an acoustic pressure signal from the first blood vessel site using one or more acoustic detectors, wherein the acoustic pressure signal is caused by the absorption of at least some of the photonic signal by one or more constituents at the first blood vessel site, and wherein the acoustic pressure signal comprises a thermo-dilution response corresponding to an indicator provided to a second blood vessel site, wherein the indicator is provided at a temperature different than the temperature of the second blood vessel site; and determining cardiac output of the subject based on an initial indicator temperature, an initial blood temperature at a first time, and an adjusted blood temperature at a second time as indicated by the thermo-dilution response and based on an equation having the form: CO = K ⁡ ( T b , 0 - T i , 0 ) ⁢ V i ∫ ( T b , 0 - T b ⁡ ( t ) ) ⁢ ⅆ t , wherein K is a proportionality constant related to the effects of specific gravity and heat capacity of blood, the indicator, or both, T b,0 is the initial blood temperature, T i,0 is the initial indicator temperature, T b(t) is the adjusted blood temperature, and V is a volume of the indicator provided to the second blood vessel site.