Assessment of Diffusion of Contrast Agent
in Colorectal Liver Metastases Using DCE-MRI
Guang Jia
Purpose: Diffusion is the major factor in delayed MR signal enhancement in liver lesions with large extravascular diffusion space after intravenous injection of a nonspecific contrast agent. The diffusion of contrast agent in liver metastases is quantitatively investigated.
Materials and Methods: Eight patients with colorectal liver metastases were enrolled in a clinical therapy trial, and were imaged twice prior to treatment. Dynamic contrast-enhanced MRI was performed using a Gd-chelate contrast agent with a standardized fast saturation recovery sequence with the target volume covered in an oblique-coronal plane. The target lesion region of interest (ROI) was drawn in pre-enhanced dynamic images and sub-segmented into several layers using an onion-peeling approach. The contrast agent concentration gradient within the lesion ROI was plotted versus pixel coordinate, from which the area under the curve of concentration gradient (Icg) was calculated. Using the post-injection time points, a plot of Icg versus time gave a decaying exponential curve with the decay constant b, which can be related to the diffusion coefficient.
Results: The enhancement of the contrast agent in liver metastases was most prominent at the periphery, spreading centrally on delayed DCE-MR images, with early-enhancement in marginal layers (positive elimination factor kel) and delayed-enhancement in central regions (negative kel). The diffusion coefficient ranged from 0.01 to 0.55 mm2/s for different patients with coefficient of variance of 1.9% and 51.2% between studies.
Conclusion: This approach allows an objective assessment of contrast agent diffusion within liver metastases. The reproducibility of diffusion coefficient measurements suggests it is a potential biomarker of therapeutic effects.
A Comparative Study on MR Quantification Methods of
Hepatic Iron Concentration
Xiangyu Yang