arXiv:2611.00472v2 Announce Type: replace Abstract: Gradient imperfections disrupt the encoding benefits of long-readout imaging applications on high-performance systems. Currently, external field monitoring hardware provides the only reliable solution for general spatial-temporal gradient characterization. We present FESTiVE, a data-driven alternative to higher-order field monitoring. FESTiVE leverages parallel imaging to both implicitly model and explicitly recover field imperfections. Using a fast k-t mapping calibration scan, FESTiVE formulates a time-varying GRAPPA problem which maps k-space data corrupted by a time-varying gradient imperfection against a clean reference. This mapping is represented compactly with an implicit neural representation, from which the spatial-temporal fields are recovered in image space using coil sensitivities. In phantom, FESTiVE produces comparable field measurements to a Skope field camera across multiple non-cartesian 2D acquisition strategies and gradient specifications. In vivo, FESTiVE achieves state-of-the-art image quality for a high-performance diffusion spiral protocol on the head-only MAGNUS 3T, where higher-order phase imperfections are significant. At 7T, on the head-only Siemens TerraX system, FESTiVE enables 300{\mu}m spiral imaging where conventional field camera-based approaches fall below probe dephasing limits. In conclusion, FESTiVE enables robust high-resolution non-cartesian imaging on high-performance gradients, characterizing gradient imperfections using parallel imaging rather than field monitoring hardware.