[MRI and MRS in the diagnosis of cancer]

Characteristics and advantages of MRI (magnetic resonance imaging) in the diagnosis of cancer are represented using hepatic diseases as examples. MRI can detect as small as 10 mm lesion of hepatic tumor (less than 5 mm in favorite conditions) despite far longer acquisition time compared with CT. Although the prolongation of T1 (longitudinal relaxation time) and T2 (transverse relaxation time) is generally noted in cancer, the liver is the sole organ where in vivo measurement of T2 makes it possible to differentiate primary malignant tumor (hepatocellular carcinoma) from the most common benign tumor (cavernous hemangioma). Gd-DTPA, the clinically used contrast material on MRI, is as useful as iodine contrast material on dynamic CT for differentiation among hepatic tumors, and is safely administered in larger dose. Proton spectroscopic imaging can distinguish the signals of proton from water and fat, and can detect the presence of fat more specifically. Intravoxel incoherent motion imaging is a new technique to demonstrate diffusion (Brownish movement) and perfusion (blood flow in capillary) in the voxel as image, and has possibility to reveal the vascularity of tumor without contrast material. MRS (magnetic resonance spectroscopy) has been obtainable in vivo under the guidance of proton MRI. The pattern of 31P-MRS is essentially nonspecific but phosphorous compounds rapidly change in proportion after effective treatment against cancer. Therefore, 31P-MRS is useful in the early and noninvasive evaluation of anticancer treatment. Finally the so-called Fossel effect (widths of methyl and methylene of lipoprotein on 1H-MRS of plasma becomes narrow in patients with cancer) and critical paper against Fossel are discussed.