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Growing inventories of cord blood units have facilitated access to umbilical cord cell transplantation for many patients lacking conventional stem cell donors. They are in principle 'off-the-shelf', 'fit-for-use', as well as safe and effective therapy products. Cellular enumeration is used as a surrogate of graft potency, and users rely on the rigorous assessment carried out in banks to avoid poor engraftment after thawing (loss of cells or poor function), when the patient's situation is critical. However, in practice, when units are selected, initially on the basis of HLA matching and cell dose assessment, their absolute quality remains uncertain. Unfortunately, quality-related issues (particularly related to viability) are not uncommon in cord blood transplantation. The reasons for potency failures are diverse, but a lack of thorough validation during critical steps of the process and of appropriate use of quality-control tools for timely detection of problematic units are significant contributors. Moreover, incongruence between different sets of standards and regulations, and lack of common quality systems between banks result in a highly heterogeneous international inventory. Therefore, this complicates the matter for the end user of the product. To ameliorate this situation, it is essential to improve quality at each of the critical manufacturing steps wherein potency can be threatened, thereby creating homogeneous inventories of units with excellent quality and quantity.

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Migration-based traveltime (MBTT) formulation provides algorithms for automatically determining background velocities from full-waveform surface seismic reflection data using local optimization methods. In particular, it addresses the difficulty of the nonconvexity of the least-squares data misfit function. The method consists of parameterizing the reflectivity in the time domain through a migration step and providing a multiscale representation for the smooth background velocity. We present an implementation of the MBTT approach for a 2-D finite-difference (FD) full-wave acoustic model. Numerical analysis on a 2-D synthetic example shows the ability of the method to find much more reliable estimates of both long and short wavelengths of the velocity than the classical least-squares approach, even when starting from very poor initial guesses. This enlargement of the domain of attraction for the global minima of the least-squares misfit has a price: each evaluation of the new objective function requires, besides the usual FD full-wave forward modeling, an additional full-wave prestack migration. Hence, the FD implementation of the MBTT approach presented in this paper is expected to provide a useful tool for the inversion of data sets of moderate size.

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