With the rise of cluster architectures, high-performance parallel computing is available to more users than ever before. The programming of such systems, however, has not yet improved beyond the cumbersome programming style used in message passing libraries like PVM and MPI. In order to open clusters to a broader audience, higher level programming environments have to be designed with the goal of giving the end user an easier access to parallel computing. Such an environment is currently being developed within the NEPHEW project allowing the graphical specification of global dependencies. This work presents the NEPHEW approach and discusses its applicability using an example application from the area of nuclear medical imaging, the reconstruction of PET (Positron Emission Tomography) images.