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.

Preliminary in vivo evaluation of a novel intrasaccular cerebral aneurysm occlusion device.

OBJECTIVE: Current endovascular technology does not offer a perfect solution for all cerebral aneurysms. Our group has built two versions of a novel aneurysm intrasaccular occlusion device (AIOD) to address the drawbacks associated with current occlusion devices. The objective of the present study was to perform pilot proof of concept in vivo testing of this new AIOD in swine and canines. METHODS: Two configurations of the AIOD, termed 'coil-in-shell' and 'gel-in-shell', were implanted in surgically created sidewall aneurysms (n=4) in swine for acute occlusion studies, as well as sidewall (n=8) and bifurcation aneurysms (n=3) in canines to assess long term occlusion efficacy. Occlusion at all time points (immediate, 6 weeks, and 12 weeks) was evaluated by angiography. Neointimal healing at 12 weeks post-implantation in canines was examined histologically. RESULTS: Angiographic analysis showed that both the coil-in-shell and gel-in-shell devices achieved complete aneurysm occlusion immediately following device delivery in sidewall aneurysms in swine. In longer term canine studies, initial occlusion ranged from 71.3% to 100%, which was stable with no recurrence in any of the sidewall aneurysms at 6 or 12 weeks. Histological analysis at 12 weeks showed mature fibromuscular tissue at the neck of all aneurysms and no significant inflammatory response. CONCLUSIONS: The AIOD tested in this study showed promise in terms of acute and chronic occlusion of aneurysms. Our findings suggest that these devices have the potential to promote robust tissue healing at the aneurysm neck, which may minimize aneurysm recurrence. Although proof of principle has been shown, further work is needed to deliver this device through an endovascular route.