Background <p>Patients with early-stage node-negative oral cancer undergo a sentinel lymph node biopsy (SLNB) or elective neck dissection under general anesthesia. A noninvasive imaging alternative would be of great interest. Superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance imaging (MRI) can visualize draining lymph nodes and potentially metastases. We investigated the optimal combination of SPIO injection and T2*-weighted MRI settings to identify the sentinel lymph nodes (SLNs), the lymphatic drainage pattern, and possibly to detect metastatic SLNs.</p> Materials and methods <p>SPIO nanoparticles were injected submucosally around the primary tongue tumor in ten patients after routine SLNB imaging with indocyanine green-[^99mTc]Tc-nanocolloid, and MRI was performed 1 h after injection. SPIO dose was adjusted for every two patients based on the imaging quality. Drainage patterns were compared between single-photon emission computed tomography (SPECT)/computed tomography (CT) and MRI. MRI appearance of SLNs was compared to histopathology of resected nodes.</p> Results <p>One mg of iron was deemed a suitable dose after two dose alterations. All 25 SLNs observed on SPECT/CT in eight patients were also identified on MRI. Including higher echelons, 55 lymph nodes were seen on SPECT/CT, while 107 lymph nodes were seen on MRI. Eighteen lymph nodes showed a mixture of partial MRI signal attenuation and retention, which, when compared to histopathology, made discrimination between metastatic and nonmetastatic lymph nodes solely based on MRI impossible.</p> Conclusion <p>SPIO-enhanced T2*-weighted MRI is suitable for mapping SLNs and lymphatic drainage pattern, showing significantly more lymph nodes compared to SPECT/CT. Discriminating metastatic from nonmetastatic nodes does not seem feasible after SPIO injection.</p> Trial registration <p>Clinicaltrials.gov NCT04803331. Registered 4 March 2021; <a href="https://clinicaltrials.gov/study/NCT04803331">https://clinicaltrials.gov/study/NCT04803331</a>.</p> Relevance statement <p>SPIO-enhanced MRI seems noninferior to the current method of SLN detection with technetium, with better anatomical detail than SPECT/CT: if proven comparable, SPIO-enhanced MRI could be considered a nonradioactive alternative with higher spatial resolution to define lymphatic drainage of tumors.</p> Key Points <p><UnorderedList Mark="Bullet"> <ItemContent> <p>The use of superparamagnetic iron oxide (SPIO)-enhanced MRI in head and neck cancer is underassessed.</p> </ItemContent> <ItemContent> <p>SPIO-enhanced MRI detects nodal drainage patterns comparably to SPECT/CT.</p> </ItemContent> <ItemContent> <p>SPIO-enhanced MRI does not discriminate lymph node metastases from false positives.</p> </ItemContent> </UnorderedList></p> Graphical Abstract <p></p>