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Novel system for determining contrast agent concentration in mouse blood in vivo

A method for measuring contrast agent concentration in blood was developed using a switchable RF tail coil to obtain MR signal from the mouse tail vein. The switchable RF coil was used to obtain quantitative high‐resolution T1 maps of the tail in combination with a second coil used to obtain images from regions of interest in a mouse tumor model. The effect of flow rates on the T1 measurements was validated using a flow‐phantom. Reliable estimates of blood T1 were obtained for flow rates up to 0.5 cm/sec in SCID mice. There was no significant difference between the in vivo tail coil measurements and in vitro blood sample relaxation rates of blood. The ability to measure the concentration of contrast agents in mouse blood in vivo is useful for several applications, such as obtaining quantitative values of tumor vascular volume and permeability, determining the effectiveness of drug delivery to tumors, or for detecting lymphatic drain. Magn Reson Med 51:612–615, 2004. © 2004 Wiley‐Liss, Inc.