Spiral acquisition for diffusion-weighted imaging (DWI) has become possible with recent development of dynamic field monitoring and image reconstruction. In this work, we demonstrate high-quality in-vivo spiral DWI at high in-plane resolution (1mm) with minimal artifacts. In addition, we confirm the expected signal-to-noise ratio (SNR) gain of spiral- compared to echo-planar-imaging (EPI) readouts both theoretically and experimentally at varied resolutions and acceleration factors. An SNR gain up to 91% was measured in white matter. In conclusion, spiral acquisition provides improved SNR especially at high image resolutions.