Sub-diffraction imaging, also known as super-resolution (SR) imaging, is a novel method that can overcome the fundamental diffraction limit by localizing spatially isolated microbubbles (MBs). A low concentration of MBs is required to achieve isolated signals in microvasculature, which is especially challenging in cancerous tissue due to high vessel density and slow flow. This study proposes a frequency decomposition method that uses the polydisperse nature of commercial MB contrast agents to separate spatially non-isolated MBs with different acoustic signatures.