PURPOSE To investigate diagnostic performance of advanced modelled iterative reconstruction (ADMIRE) to filtered back projection (FBP) when using an ultra-low dose protocol for the detection of solid and sub-solid pulmonary-nodules. METHODS Single-energy CT was performed at 100kVp with tin-filtration in an anthropomorphic chest-phantom with solid and sub-solid pulmonary-nodules (2-10mm, attenuation, 20HU to -800HU at 120 kVp). CTDIvol of the standard chest protocol was 2.2 mGy. Subsequent scans were obtained at 1/8 (0.28 mGy), 1/20 (0.10 mGy), and 1/70 (0.03 mGy) dose levels by lowering tube-voltage and -current. Images were reconstructed with FBP and ADMIRE. One reader measured image noise; two readers determined image quality and assessed nodule localization. RESULTS Image noise was significantly reduced using ADMIRE compared to FBP (ADMIRE at a strength-level of 5: 70.4% for 1/20; 71.6% for 1/8;p<0.001). Inter-observer agreement for image-quality was excellent (k=0.88). Image-quality was considered diagnostic for all images at 1/20 dose using ADMIRE. Sensitivity of nodule detection was 97.14% (100% for solid, 93.8% for sub-solid nodules) at 1/20 dose and 100% for both nodule entities at 1/8 dose using ADMIRE5. Images obtained with 1/70 dose had moderate sensitivity (overall85.71%; solid 94%; sub-solid 73.3%). CONCLUSION Our study suggests that with a combination of tin-filtration and ADMIRE the mean volume CT dose index (CTDIvol) of chest CT can be lowered considerably, while sensitivity for nodule-detection remains high. For solid nodules CTDIvol was 0.10 mGy, while sub-solid nodules required a slightly higher CTDIvol of 0.28 mGy. Advances in knowledge: Detection of sub-solid nodules is feasible with ultralow-dose protocols.