Proton magnetic resonance spectroscopy of plasma from patients with dyslipoproteinemia: identification of factors governing methyl and methylene proton line widths.

The line width of the proton magnetic resonance spectrum (MRS) of the composite methylene and methyl resonances of plasma has been reported as a marker for the presence of malignancy. In this study, the contribution of very low density (VLDL), low density (LDL), and high density lipoproteins (HDL) to the MRS line width was determined. This was achieved by measuring the MRS line widths for the plasma from patients with primary disorders of lipoprotein metabolism and from normal individuals. A negative correlation between plasma trigylceride levels and the average line width was observed and this was confirmed in normal plasma to which pure VLDL was added. Also, computer simulations were employed to demonstrate how the line width varies in such complex mixtures of lipoproteins. We demonstrate that the line width is governed by the relative contribution of VLDL and HDL to the composite line shape. This is particularly important when the shoulder from the HDL line lies near the half-height of the VLDL line. As changes in VLDL/HDL ratio occur in patients with malignancy, we propose that this is the basis of the narrowed MRS lines observed in the proposed test for malignancy. However, any individual with elevated VLDL will be false positive in this test.