Estimation of renal extraction fraction based on postcontrast venous and arterial differential T1 values: An error analysis

✍ Scribed by Yakir S. Levin; Lawrence C. Chow; Norbert J. Pelc; F. Graham Sommer; Daniel M. Spielman

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 490 KB
• Volume: 54
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.20548

✦ Synopsis

Abstract

An error analysis for quantifying single kidney extraction fraction (EF) via differential T~1~ measurements in the renal vein (RV) and renal artery (RA) is presented. Sources of error include blood flow effects, the effect of a short repetition time (TR), and the impact of uncertainties in the T~1~ estimates on the final EF calculations. Blood flow effects were investigated via simulation. For a range of blood velocities in the renal vein that may be found in kidney disease, incomplete refreshment of blood between readouts results in significant errors in T~1~ estimation. For a .5‐cm slice, 110‐ms sampling interval, and T~1~ of 600 ms, T~1~ estimation to within 5% of true T~1~ requires an average through‐plane velocity of 6.75 cm/s for parabolic flow, and 3.5 cm/s for plug flow. Improvement can be achieved by accurately estimating the fraction of blood that has not refreshed between readouts (f~old~), while the quality of the T~1~ estimate varies with the accuracy of f~old~ estimation. Shortening of the TR was investigated using phantom and in vivo studies. T~1~ was estimated to within 3% of the true value on phantoms, and within 5% of the true value for flowing blood for TR = 2__T__~1~. The estimated EF is shown to be very sensitive to the difference between T~1RA~ and T~1RV~. To achieve 10% or 20% uncertainty in the EF estimate, T~1~ in the renal vein and renal artery must be estimated to within approximately 1% or 2%. Because of limitations on measurement accuracy and precision, this method appears to be impractical at this time. Magn Reson Med 54:309–316, 2005. © 2005 Wiley‐Liss, Inc.