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Transstenotic Pressure Gradients: Measurement in Swine—Retrospectively ECG-gated 3D Phase-Contrast MR Angiography versus Endovascular Pressure-sensing Guidewires¹

¹ From the Department of Radiology, University of Wisconsin Hospital and Clinics, 600 Highland Ave, CSC E3/311, Madison, WI 53792. From the 2006 RSNA Annual Meeting. Received November 20, 2006; revision requested January 19, 2007; revision received January 31; accepted March 16; final version accepted May 11. Supported by National Institutes of Health grant R01HL072260-02 and a 2005-2006 Research Resident Grant from the RSNA Research and Education Foundation. Address correspondence to D.P.L. (e-mail: lum{at}wisc.edu).

Purpose: To prospectively evaluate the hypothesis that retrospectively electrocardiographically gated phase contrast with vastly undersampled isotropic projection reconstruction (VIPR) magnetic resonance (MR) angiography data sets can be used to measure transstenotic pressure gradients (TSPGs) in vivo.

Materials and Methods: TSPGs were calculated by using phase-contrast VIPR MR angiography data sets; measurements obtained with a pair of endovascular pressure-sensing guidewires served as a reference standard. With institutional animal care and use committee approval, 12 swine underwent surgical creation of stenoses at the left common carotid, right renal, and left external iliac arteries. The percentage stenosis and reference diameter of the lesions were calculated from conventional digital subtraction angiograms. A pair of 0.014-inch pressure-sensing guidewires was placed in tandem; sensors 1 cm distal and 1 cm proximal to the lesions measured the mean TSPG. Phase-contrast VIPR phase difference images were analyzed with an iterative technique based on the Navier-Stokes equations to determine the mean TSPG. Pearson product correlation was calculated, and Bland-Altman plots were generated to determine the degree of agreement between the two methods.

Results: Twenty-one lesions (12 carotid, nine iliac; mean percentage stenosis, 52.4%; range, 29.8%–64.9%; mean reference diameter, 3.4 mm; range, 2.4–5.6 mm) were analyzed. For carotid and iliac lesions, phase-contrast VIPR and guidewire TSPG measurements were highly correlated (r = 0.952, P < .001). Bland-Altman plots (bias, 0.86 mm Hg; limits of agreement: –6.17 to 7.88 mm Hg) showed good agreement. Measurements in renal lesions (n = 9) were poorly correlated (r = –0.081, P = .835) and were excluded because of image degradation secondary to respiratory motion.

Conclusion: Phase-contrast MR angiography with VIPR enables reliable measurements of TSPG in carotid and iliac lesions that are comparable to those obtained with endovascular pressure-sensing guidewires. However, further work to compensate for respiratory motion is required to extend this technique to the renal arteries.

© RSNA, 2007

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