Low sensitivity of clinical MR imaging to small changes in the concentration of nonparamagnetic protein.

This study attempts to determine the magnitude of change in the concentration of a nonparamagnetic protein (human serum albumin) required to effect a detectable change in signal intensity on a clinical imaging unit. For a range of protein concentrations from 0-6100 mg/dl the concentration could not be predicted by inspecting the images. Measurement of displayed signal intensity failed to distinguish concentrations of 0.09-3700 mg/dl, while 6100 mg/dl gave slightly higher intensity signals. Although this low sensitivity represents expected behavior for low concentrations, the failure to differentiate the higher concentrations implies limitations imposed by clinical imaging techniques. Our results suggest that additional factors, such as paramagnetic material and motion as well as differences in protein concentration, may be involved in the MR signal intensities observed in pathologic CSF and cystic CNS collections.