Identification of the Most Important Subset of Doppler, Laboratory, and Clinical Parameters for Serial TIPS Evaluation.

OBJECTIVE. The purpose of the present study was to identify the subset of a wide range of serial Doppler, laboratory, and clinical parameters most predictive (both individually and in combination) of TIPS dysfunction in a large patient sample. MATERIALS AND METHODS. The medical records of 189 patients who had undergone TIPS procedures were analyzed. The patients (mean age, 52 years; 62% of whom were men) had undergone 1139 Doppler studies and 323 portovenograms. Laboratory parameters included model for end-stage liver disease (MELD) scores, serum albumin levels, presence of ascites, and time since last intervention. Doppler parameters included intrashunt velocities, temporal change in intrashunt velocities, main portal vein velocity, direction of flow in the left portal hepatic vein, and venous pulsatility index. Statistical analysis used ROC, univariate, and multivariate regression models to assess the parameters both individually and in combination. Shunt dysfunction was defined by a portosystemic gradient of more than 12 mm Hg. RESULTS. The laboratory and clinical parameters of greatest predictive value included the MELD score and the time since the last intervention. The Doppler parameters that were of greatest predictive value included the change in velocity at the hepatic venous end and the left portal vein flow direction. Multivariate models produced an AUC of 0.74. Differences between functional and dysfunctional shunts were also statistically significant for absolute velocity at the hepatic venous end, the change in velocity within the stent, and the temporal change in the mid shunt velocity. CONCLUSION. The subset of serial parameters most predictive of TIPS dysfunction are the temporal change in the velocity at the hepatic venous end, the absolute velocity at the hepatic venous end, the direction of flow in the left portal venous branch, and changes in the MELD score.

CT perfusion in the treatment of a swine model of unilateral renal artery stenosis: validation with microspheres.

PURPOSE: To assess the feasibility of using current computed tomography (CT) perfusion techniques for evaluating unilateral renal artery stenosis (RAS) with assessment of pre- and posttreatment perfusion and to compare those results against the standard of microsphere injection. MATERIALS AND METHODS: Six juvenile swine with surgically created right RAS were examined in a combined angiography-CT suite. CT perfusion, injection of fluorescent microspheres, and digital subtraction angiography were performed before and after release of the stenosis. Cortical horseshoe-shaped regions of interest were used to measure blood flow (in milliliters/[100 g min]). Two cortical samples (superior and inferior) from each kidney were excised and sent to a reference laboratory for microsphere analysis. The relative blood flow ratio (RBFR) and posttherapy increase in blood flow were determined. The Pearson product correlation was calculated to compare the absolute blood flow, pretherapy RBFR, and posttherapy increase in blood flow between the two techniques. Bland-Altman analysis of the absolute blood flow measurements was performed. RESULTS: Forty-eight blood flow measurements showed moderate correlation (r = 0.712, P < .001). However, Bland-Altman plots (bias, -19.21; limits of agreement, -156.1 to 117.7 mL/[100 g . min]) showed poor agreement. Measurements of RBFR with CT correlated well with microsphere data. Pretherapy RBFR showed moderate correlation with microsphere data (r = 0.859, P < .001, n = 12), whereas the posttherapy increase in blood flow was highly correlated (r = 0.898, P < .001, n = 12). CONCLUSIONS: CT perfusion and microspheres produce similar indexes of relative renal cortical perfusion when normalized to the unaffected kidney. Further work is needed to determine the clinical utility of CT perfusion for pre- and posttherapy decision making.

Transstenotic pressure gradients: measurement in swine--retrospectively ECG-gated 3D phase-contrast MR angiography versus endovascular pressure-sensing guidewires.

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.