MR imaging of tissue components with extremely fast transverse relaxation times require advanced MRI techniques such as continuous SWIFT (cSWIFT), Concurrent Excitation and Acquisition (CEA), and full duplex MRI. Frequency modulated pulses are used in these methods. A steady-state signal model with transverse relaxation term was formulated and solved for an arbitrary frequency and phase modulated RF pulse. An accurate expression for the optimal flip angle was derived. The performance of the new formulation was verified by a home-made Bloch equation simulator for T2 values between 10µs and 100ms.