46P/Wirtanen is a Jupiter Family comet with a short (5.4 year) orbital period. During its last apparition in 2018, it passed unusually close to the Earth (within 0.08 au), presenting an outstanding opportunity for close-up observations of its inner coma. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to obtain detailed, interferometric observations of 46P in the 243-366 GHz spectral range near the comet's closest approach in December 2018, resulting in an unprecedented sky-projected spatial resolution of up to 25 km. Spectral imaging of multiple molecules was performed, and these data were analyzed using our latest non-LTE radiative transfer code (SUBLIME), to determine the detailed physical and chemical structure of the coma. In this poster, we present images and spectra of the HCN, H13CN and HC15N molecules, from which the 12C/13C and 14N/15N ratios are derived.