NMR detection of cancer: Mechanism of contrast generation

One of the most effective ways today to detect cancer is using MRI (Magnetic Resonance Imaging). This technique is based on the nuclear magnetic resonance (NMR) measurement of water hydrogen signal inside the human body. In order to detect cancers using the NMR method, one needs to solve two technical problems: (1) How to produce a contrast between water molecules inside the cell and the extra-cellular water? (2) How to differentiate the water signals in cancer cells from the water signal in normal cells? These difficulties were resolved in the early 1970s through the discovery that the relaxation times of water protons inside the cells were very different from those of the extra-cellular water. Furthermore, we discovered that the relaxation times of water molecules undertake a progressive lengthening during the transformation from normal cells to cancer cells. In this presentation, I will give a concise review of the evidence for these discoveries. Finally, I will discuss the possible physical basis that may account for the relaxation time changes between normal cells and cancer cells.