Among different clinical applications of magnetic nanoparticles, contrast enhancing magnetic resonance mechanism is one of the major implementations of these nanoparticles. MRI sensitivity can be significantly enhanced by using contrast agent, typically in the form of T₁ and T₂ contrast agents. T₁ imaging, normally using paramagnetic particles as the contrast materials, increase MR signal intensity consequently lead to high resolution between tissues. However it has high contrast-to-noise ratio. SPIONs have been most widely used as dominant T₂ MRI contrast agent because of their strong magnetization and bio-compatibility. However, the main problem of the SPIO nanoparticles in MRI is the magnetic susceptibility artifacts which cause dark MR images.² Although SPIONs are T₂-weighted materials, Zhou et al. reported that very small iron oxide nanoparticles, approximately 3 nm in diameter, can provide T₁- weighted (positive contrast) effect in MRI.¹ In our presented study, we suggested a dual- modal contrast agent for MRI.³ The unique advantages of combing T₁ and T₂ imaging possibility into a single form of contrast agent is very useful for clinical applications. Accurate and entire diagnostic knowledge can be achieved by integration of various image modalities in both T₁-weighted imaging with excellent tissue resolution and T₂-weighted imaging with better possibility on lesion identification.⁴ We synthesized highly crystalline SPIO nanoparticles in cubic shape using thermal decomposition technique. The transmission microscopy (TEM) image indicates that monodisperse cubic shaped nanoparticles are achieved with a size of ~ 9.7 nm (Fig 1a). The field- dependent magnetization curve (M-H) shows that cubic-shape nanoparticles behave in both super- paramagnetic and paramagnetic regime simultaneously (Fig 1b). To investigate the dual-mode MR contrast enhancement effect of silica coated SPIO nanocubes, we obtained multiecho spinecho sequence T₁ and T₂-weighted images at different SPION concentrations. The following sequence parameters were considered: TR = 1000, TE = 12 ms (For T₁), TR = 10000, TE = 330 ms (For T₂), Flip angle = 90°, Flice thickness = 3 mm, FoV = 120 × 120 mm2, Acquisition matrix = 384 pixels × 384 pixels. By increasing the SPION concentration we observed increased signals in T₁-weighted MR images and decreased signals in T₂-weighted MR images (Fig 2a). The MRI relaxivity (r₁, r₂) values of cubic nanoparticles were calculated using equation (1) and the results are shown in Figure 2b,c. $$$ r_{1,2}=R_{pre1,2}-R_{post1,2} $$$. Which R_pre1,2 and R_post1,2 are the relaxation rates before and after contrast agent, respectively. We then demonstrated the T₁ and T₂ dual-mode in vivo MR imaging of SPIO nanocubes with a 3T MRI scanner. Using a Sprague Dawley (200-250 g) rat as a model, we obtained T₁ and T₂-weighted images before and after IV injection of SPION, with the dose of 1mg kg^-1. We focused on the kidney as interested region. The results demonstrated that T₁-weighted MR image represents a brighter signal, and obviously darker signal was achieved in T₂-weighted MR image at transverse plane, 1 hour after injection (Fig 3a, b). The investigation of MR signal variation in the kidney as a region of interest noticed that the signal intensity significantly changes on both T₁ and T₂ imaging. These results indicated that SPIO nanocubes show dual-mode MR contrast enhancement, which can provide more exhaustive clinical information and consequently more accurate diagnosis. In this study, we reported a dual-mode MR contrast agent which can be implemented in kidney imaging. The in vivo T₁ and T₂ MR images promise the great potential clinical application of SPIO nanocubes as dual-mode MR contrast agent.