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(2)@MnO(2), which shows decreased T(1) and T(2) contrast intensity in normal physiological conditions. In the acid environment of tumor or inflamed tissue, the manganese dioxide (MnO(2)) layer decomposes into magnetically active Mn(2+) (T(1)-weighted), and the T(1) and T(2) signals are sequentially recovered. In addition, both constrast quenching-activation degrees of T(1) and T(2) images can be accurately regulated by the silicon dioxide (SiO(2)) intermediate layer between superparamagnetic iron oxide (SPIO) and MnO(2). 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(2)@MnO(2) is successfully applied to trace the tiny liver metastases of approximately 0.5 mm and monitor tissue inflammation.