Olivier H.J. Koning

Roentgen Stereophotogrammetric Analysis: An Accurate Tool to Assess Stent-Graft Migration

Purpose: To evaluate in an in vitro model the feasibility and accuracy of Roentgen stereophotogrammetric analysis (RSA) versus computed tomography (CT) for the ability to detect stent-graft migration. Methods: An aortic model was constructed from a 22-mm-diameter Plexiglas tube with 6-mm polytetrafluoroethylene inlays to mimic the renal arteries. Six tantalum markers were placed in the wall of the aortic tube proximal to the renal arteries. Another 6 markers were added to a Gianturco stent, which was cast in Plexiglas and placed inside the aorta and fixed to a micromanipulator to precisely control displacement of the stent along the longitudinal axis. Sixteen migrations were analyzed with RSA software and compared to the micromanipulator. Thirty-two migrations were measured by 3 observers from CT images acquired with 16X0.5-mm beam collimation and reconstructed with a 0.5-mm slice thickness and a 0.4-mm reconstruction interval. Measurements were made with Vitrea postprocessing software using a standard clinical protocol and central lumen line reconstruction. Results of CT were also compared to the micromanipulator. Results: The mean RSA measurement error compared to the micromanipulator was 0.002±0.044 mm, and the maximum error was 0.10 mm. There was no statistically significant interobserver variability for CT (p=0.17). The pooled mean (maximum) measurement error of CT was 0.14±0.29 (1.00) mm, which was significantly different from the RSA measurement error (p<0.0001). Conclusion: Detection of endograft migration by RSA is feasible and was significantly more accurate than CT in this nonpulsatile in vitro model.

Aneurysm sac pressure monitoring: effect of pulsatile motion of the pressure sensor on the interpretation of measurements.

Purpose: To determine the effect of pulsatile motion of graft-attached pressure sensors on the accuracy of aneurysm sac pressure measurement. Methods: Pressure inside a pressure box was measured with a sensor attached to a stent-graft (Sensorgraft) facing a sensor in fixed position (Sensorbox). Maximum inter-sensor variation of Sensorgraft and Sensorbox was determined in static experiments. Experiments with pulsatile circulation were performed with a compliant and a noncompliant stent-graft at 120/80 mmHg and 160/95 mmHg. Pressure measurements in the box were repeated after the box pressure was increased from 0 to 120 mmHg. Sensorgraft motion was measured by ultrasound. Measurements with Sensorgraft were compared to those with Sensorbox using Pearson correlation coefficients to determine the concordance between the sensors. Results: The maximum inter-sensor variation was 4 mmHg. Increased box pressure induced progressive pulsatile graft and sensor motion during all experiments. During the experiments with the compliant graft at systemic pressures of 120/80 and 160/95 mmHg, the maximum inter-sensor variation was exceeded at box pressures of 65 and 75 mmHg, respectively. The sensor motion at these box pressures was 214±2.70 μm and 210±0.93 μm, respectively. Measurements of Sensorgraft were higher than Sensorbox, up to 13 mmHg at a box pressure of 120 mmHg. The Pearson correlation coefficients during these experiments were 0.99 and 1.00 (p<0.001), respectively. In the experiments with the noncompliant graft, the maximum inter-sensor variation was not exceeded, and sensor motion was only 7±0.46 μm and 26±1.48 μm, respectively. The Pearson correlation coefficient during these experiments was 1.00 (p<0.001). Conclusion: Pulsatile sensor motion can influence the accuracy of pressure measurement. More compliant grafts are more susceptible to this phenomenon. Despite false high pressure measurements, stent-graft-attached pressure sensors seem appropriate to follow pressure trends in the aneurysm sac.

Support value based stent-graft marker detection

With the development of the fluoroscopic roentgenographic stereophotogrammetric analysis (FRSA), it is possible to make the three-dimensional (3D) dynamics of stent-graft. The stent-graft markers, however, are identified manually. In this paper we present a robust solution for automatic detection of stent-graft marker projections in FRSA X-ray images. Several directional support value (dSV) filters and the directional support value transform (dSVT) method are studied. Based on the dSV of the dSVT, a support value matrix is constructed, and the determinant of this matrix is then defined as the markerness measure. The corresponding multi-scale correlations of the rescaled markerness measures are computed for enhancing the multi-scale marker response peaks while suppressing the effects of stent-grafts and Poisson noise. The marker spots are subsequently located by finding the local maximum of the correlated markerness measures. The conditional variance Stabilizer (CVS) is further integrated into this framework for removing Poisson noises. Performance comparisons are carried out among the proposed dSVT, the CVS+dSVT, local threshold operation (LTO) and the frequently adopted spot detectors, including the morphological grayscale opening top-hat filter (MTH), wavelet multiscale products (WMP), and multiscale variance-stabilizing transform (MSVST) methods. The results from experiments on synthetic as well as real FRSA X-ray image data show that the proposed CVS+dSVT method performs better than other detectors, in terms of the free-response receiver operation characteristic (FROC) curves.

Activation of the vitamin D receptor selectively interferes with calcineurin-mediated inflammation: a clinical evaluation in the abdominal aortic aneurysm

In vitro and in vivo studies attribute potent immune regulatory properties to the vitamin D receptor (VDR). Yet, it is unclear to what extend these observations translate to the clinical context of (vascular) inflammation. This clinical study evaluates the potential of a VDR agonist to quench vascular inflammation. Patients scheduled for open abdominal aneurysm repair received paricalcitol 1 μg daily during 2–4 weeks before repair. Results were compared with matched controls. Evaluation in a parallel group showed that AAA patients are vitamin D insufficient (median plasma vitamin D: 43 (30–62 (IQR)) nmol/l). Aneurysm wall samples were collected during surgery, and the inflammatory footprint was studied. The brief paricalcitol intervention resulted in a selective 73% reduction in CD4+ T-helper cell content (P<0.024) and a parallel 35% reduction in T-cell (CD3+) content (P<0.032). On the mRNA level, paricalcitol reduced expression of T-cell-associated cytokines IL-2, 4, and 10 (P<0.019). No effect was found on other inflammatory mediators. On the protease level, selective effects were found for cathepsin K (P<0.036) and L (P<0.005). Collectively, these effects converge at the level of calcineurin activity. An effect of the VDR agonist on calcineurin activity was confirmed in a mixed lymphocyte reaction. In conclusion, brief course of the VDR agonist paricalcitol has profound effects on local inflammation via reduced T-cell activation. The anti-inflammatory potential of VDR activation in vitamin D insufficient patients is highly selective and appears to be mediated by an effect on calcineurin-mediated responses.

SU‐FF‐I‐169: Endovascular Abdominal Aortic Aneurysm Repair: Patient Dose and Radiation Risks

Purpose: To assess cumulative patient dose and to calculate associated radiation risks for patients undergoing abdominal endovascular aortic aneurysm repair (EVAR). Method and Materials: A traditional protocol and a reduced dose scenario for medical imaging in EVAR planning, repair and surveillance was assumed and patient dose was assessed. The excess relative radiation risk was calculated using a model for age‐, gender‐ and site‐specific solid cancer mortality. Life tables were used to calculate risk related parameters for patients that underwent EVAR at 55, 65, 75 and 85 years of age. In addition to radiation risk, mortality rates that are typical for the EVAR population were taken into account, knowingly the probability of 30‐day mortality and the mortality rate from AAA‐related causes in general during follow‐up. Results: Effective dose for EVAR planning was 18 (8) mSv; for EVAR repair 10 (10) mSv; and during the first, second and subsequent years of surveillance 87.5 (35) mSv/y, 35 (17.5) mSv/y and 17.5 (17.5) mSv/y. The number of radiation induced deaths per 1000 EVAR patients was 12 (10), 8 (6), 4 (3) and 1 (1) for patients treated at ages 55, 65, 75 and 85 years (respectively traditional protocol and between brackets reduced dose scenario). The corresponding number of abdominal aortic aneurysm (AAA) related deaths per 1000 EVAR patients was: 126, 91, 67 and 47, respectively (for both the traditional protocol and the reduced dose scenario). The average radiation induced and AAA related reduction of life expectancy will be presented. Conclusion:Radiation exposure accumulates rapidly for patients undergoing surveillance after abdominal EVAR. However, associated radiation risks are modest, even for the traditional surveillance protocol that is associated with a relatively high patient dose. Radiation risks are much smaller compared to AAA‐related risks.