Objective
The minimization of treatment time, through varying the power deposited in space and time, can be accomplished through finding the optimal combination of scanning parameters that take advantage of described six basic, bio-thermal phenomena, namely: 1) Non-linear temperature thermal dose relationship, 2) superposition of temperatures, 3) thermal decay, 4) dose spreading by thermal diffusion, 5) superposition of thermal dose, and 6) tissue property changes (e.g. perfusion, absorptivity). The optimal combination of scanning parameters, specifically, the number of pulses (N), pulse heating time (ΔtQON,n), pulse power level (Qn(r,t)), and cooling time (Δt,QOFF,n) can be found for a given set of input parameters that minimize treatment time while guaranteeing treatment efficacy and safety.

Methods
The previous work of investigators which optimizes each of the above scanning parameters is evaluated, resulting in two different treatment paradigms, a minimum heating approach, which maximizes the non-linear thermal dose phenomena by decreasing the focal zone shape, resulting in high temperatures achieved in a relatively short time, and minimum cooling approach, which minimizes the cooling time, such that the power level is applied continuously at the maximum possible level without violating any near-field temperature constraints. These methods, as well as others, are simulated; using a simple ordinary differential equation model which combines both conduction and convective effects in an effective perfusion term. Parametric studies, varying the above scanning parameters, as well as effective perfusion, ratios of near-field to treatment region properties, and near-field upper and lower temperature limits are performed.

Results
The results of parametric studies show that depending on the input parameters, the minimum treatment time can be achieved through the minimum heating approach, minimum cooling approach, or a minimum total time approach, which minimizes the sum of both the heating and cooling times. Optimized values of the heating time, near-field lower tissue limit and power density are given for all treatment paradigms.

Conclusions
Treatment time can be minimized through the optimization of scanning parameters which manipulate six basic bio-thermal phenomena. The resulting optimal treatment paradigm, minimum heating, cooling or total time depends on the input parameters to the system.