A pH-responsive T 1 -T 2 dual-modal MRI contrast agent for cancer imaging

Magnetic resonance imaging (MRI) is a non-invasive imaging technology to diagnose health conditions, showing the weakness of low sensitivity. Herein, we synthesize a contrast agent, SPIO@SiO @MnO , which shows decreased T and T contrast intensity in normal physiological conditions. In the acid environment of tumor or inflamed tissue, the manganese dioxide (MnO ) layer decomposes into magnetically active Mn (T -weighted), and the T and T signals are sequentially recovered. In addition, both constrast quenching-activation degrees of T and T images can be accurately regulated by the silicon dioxide (SiO ) intermediate layer between superparamagnetic iron oxide (SPIO) and MnO . Through the "dual-contrast enhanced subtraction" imaging processing technique, the contrast sensitivity of this MRI contrast agent is enhanced to a 12.3-time difference between diseased and normal tissue. Consequently, SPIO@SiO @MnO is successfully applied to trace the tiny liver metastases of approximately 0.5 mm and monitor tissue inflammation.