Gilles Soulez

Automatic navigation of an untethered device in the artery of a living animal using a conventional clinical magnetic resonance imaging system

The feasibility for in vivo navigation of untethered devices or robots is demonstrated with the control and tracking of a 1.5mm diameter ferromagnetic bead in the carotid artery of a living swine using a clinical magnetic resonance imaging (MRI) platform. Navigation is achieved by inducing displacement forces from the three orthogonal slice selection and signal encoding gradient coils of a standard MRI system. The proposed method performs automatic tracking, propulsion, and computer control sequences at a sufficient rate to allow navigation along preplanned paths in the blood circulatory system. This technique expands the range of applications in MRI-based interventions.The feasibility for in vivo navigation of untethered devices or robots is demonstrated with the control and tracking of a 1.5mm diameter ferromagnetic bead in the carotid artery of a living swine using a clinical magnetic resonance imaging (MRI) platform. Navigation is achieved by inducing displacement forces from the three orthogonal slice selection and signal encoding gradient coils of a standard MRI system. The proposed method performs automatic tracking, propulsion, and computer control sequences at a sufficient rate to allow navigation along preplanned paths in the blood circulatory system. This technique expands the range of applications in MRI-based interventions.

Noninvasive vascular elastography: theoretical framework

Changes in vessel wall elasticity may be indicative of vessel pathologies. It is known, for example, that the presence of plaque stiffens the vascular wall, and that the heterogeneity of its composition may lead to plaque rupture and thrombosis. Another domain of application where ultrasound elastography may be of interest is the study of vascular wall elasticity to predict the risk of aneurysmal tissue rupture. In this paper, this technology is introduced as an approach to noninvasively characterize superficial arteries. In such a case, a linear array ultrasound transducer is applied on the skin over the region of interest, and the arterial tissue is dilated by the normal cardiac pulsation. The elastograms, the equivalent elasticity images, are computed from the assessment of the vascular tissue motion. Investigating the forward problem, it is shown that motion parameters might be difficult to interpret; that is because tissue motion occurs radially within the vessel wall while the ultrasound beam propagates axially. As a consequence of that, the elastograms are subjected to hardening and softening artefacts, which are to be counteracted. In this paper, the Von Mises (VM) coefficient is proposed as a new parameter to circumvent such mechanical artefacts and to appropriately characterize the vessel wall. Regarding the motion assessment, the Lagrangian estimator was used; that is because it provides the full two-dimensional strain tensor necessary to compute the VM coefficient. The theoretical model was validated with biomechanical simulations of the vascular wall properties. The results allow believing in the potential of the method to differentiate hard plaques and lipid pools from normal vascular tissue. Potential in vivo implementation of noninvasive vascular elastography to characterize abdominal aneurysms and superficial arteries such as the femoral and the carotid is discussed.

Contrast-induced nephropathy in patients with chronic kidney disease undergoing computed tomography: a double-blind comparison of iodixanol and iopamidol.

Background:Based on a single clinical trial, it has been suggested that the contrast agent iodixanol, which is isotonic to human plasma, may be less nephrotoxic than other nonionic contrast agents in renally impaired patients after intra-arterial injection. We compared the effects on renal function of iopamidol-370 injection (796 mOsm/kg) and iodixanol-320 (290 mOsm/kg) in patients with chronic kidney disease undergoing contrast-enhanced multidetector computed tomography (CE-MDCT) examinations using a multicenter, double-blind, randomized, parallel-group design. Methods:A total of 166 patients with stable moderate-to-severe chronic kidney disease (screening and baseline serum creatinine, SCr, ≥1.5 mg/dL and/or creatinine clearance, CrCl, ≤60 mL/min) who were undergoing CE-MDCT of the liver or peripheral arteries were randomized to receive equi-iodine IV doses (40 gI) of either iopamidol-370 (370 mgI/mL) or iodixanol-320 (320 mgI/mL) at 4 mL/s. SCr and CrCl were obtained at screening, baseline, and at 48–72 ± 6 hours after dose (mean, 57.4 hours). Contrast-induced nephropathy (CIN) was defined as an absolute increase ≥0.5 mg/dL (44.2 &mgr;mol/L) and/or a relative increase in SCr ≥25% from baseline. Results:A total of 153 patients were included in the final analysis (13 patients excluded because of lack of follow-up, hemodialysis to remove contrast, average daily CrCl variation >1% at screening). The 2 study groups were comparable with regard to age, gender distribution, the presence of diabetes, concomitant medications, hydration, and contrast dose. Mean predose SCr was 1.6 ± 0.4 mg/dL in both groups (P = 0.9). An absolute increase ≥0.5 mg/dL (44.2 &mgr;mol/L) in SCr was observed in none of the patients receiving iopamidol-370 and in 2.6% (2/76) of patients receiving iodixanol-320 (95% confidence interval −6.2, 1.0, P = 0.2). A relative increase ≥25% in SCr occurred in 4% (3/77) of patients receiving iopamidol-370 and in 4% (3/76) of the patients receiving iodixanol-320 (95% confidence interval −6.2, 6.1, P = 1.0). Conclusion:The rate of CIN was similarly low in risk patients after intravenous administration of iopamidol-370 or iodixanol-320 for CE-MDCT.

Three-Dimensional C-arm Cone-beam CT: Applications in the Interventional Suite

C-arm cone-beam computed tomography (CT) with a flat-panel detector represents the next generation of imaging technology available in the interventional radiology suite and is predicted to be the platform for many of the three-dimensional (3D) roadmapping and navigational tools that will emerge in parallel with its integration. The combination of current and unappreciated capabilities may be the foundation on which improvements in both safety and effectiveness of complex vascular and nonvascular interventional procedures become possible. These improvements include multiplanar soft tissue imaging, enhanced pretreatment target lesion roadmapping and guidance, and the ability for immediate multiplanar posttreatment assessment. These key features alone may translate to a reduction in the use of iodinated contrast media, a decrease in the radiation dose to the patient and operator, and an increase in the therapeutic index (increase in safety-vs-benefit ratio). In routine practice, imaging information obtained with C-arm cone-beam CT provides a subjective level of confidence factor to the operator that has not yet been thoroughly quantified.

Co-encapsulation of magnetic nanoparticles and doxorubicin into biodegradable microcarriers for deep tissue targeting by vascular MRI navigation

Magnetic tumor targeting with external magnets is a promising method to increase the delivery of cytotoxic agents to tumor cells while reducing side effects. However, this approach suffers from intrinsic limitations, such as the inability to target areas within deep tissues, due mainly to a strong decrease of the magnetic field magnitude away from the magnets. Magnetic resonance navigation (MRN) involving the endovascular steering of therapeutic magnetic microcarriers (TMMC) represents a clinically viable alternative to reach deep tissues. MRN is achieved with an upgraded magnetic resonance imaging (MRI) scanner. In this proof-of-concept preclinical study, the preparation and steering of TMMC which were designed by taking into consideration the constraints of MRN and liver chemoembolization are reported. TMMC were biodegradable microparticles loaded with iron-cobalt nanoparticles and doxorubicin (DOX). These particles displayed high saturation magnetization (Ms = 72 emu g(-1)), MRI tracking compatibility (strong contrast on T2∗-weighted images), appropriate size for the blood vessel embolization (∼50 μm), and sustained release of DOX (over several days). The TMMC were successfully steered in vitro and in vivo in the rabbit model. In vivo targeting of the right or left liver lobes was achieved by MRN through the hepatic artery located 4 cm beneath the skin. Parameters such as flow velocity, TMMC release site in the artery, magnetic gradient and TMMC properties, affected the steering efficiency. These data illustrate the potential of MRN to improve drug targeting in deep tissues.

Intravascular ultrasound image segmentation: a three-dimensional fast-marching method based on gray level distributions

Intravascular ultrasound (IVUS) is a catheter based medical imaging technique particularly useful for studying atherosclerotic disease. It produces cross-sectional images of blood vessels that provide quantitative assessment of the vascular wall, information about the nature of atherosclerotic lesions as well as plaque shape and size. Automatic processing of large IVUS data sets represents an important challenge due to ultrasound speckle, catheter artifacts or calcification shadows. A new three-dimensional (3-D) IVUS segmentation model, that is based on the fast-marching method and uses gray level probability density functions (PDFs) of the vessel wall structures, was developed. The gray level distribution of the whole IVUS pullback was modeled with a mixture of Rayleigh PDFs. With multiple interface fast-marching segmentation, the lumen, intima plus plaque structure, and media layers of the vessel wall were computed simultaneously. The PDF-based fast-marching was applied to 9 in vivo IVUS pullbacks of superficial femoral arteries and to a simulated IVUS pullback. Accurate results were obtained on simulated data with average point to point distances between detected vessel wall borders and ground truth <0.072 mm. On in vivo IVUS, a good overall performance was obtained with average distance between segmentation results and manually traced contours <0.16 mm. Moreover, the worst point to point variation between detected and manually traced contours stayed low with Hausdorff distances <0.40 mm, indicating a good performance in regions lacking information or containing artifacts. In conclusion, segmentation results demonstrated the potential of gray level PDF and fast-marching methods in 3-D IVUS image processing.

Segmentation in Ultrasonic B -Mode Images of Healthy Carotid Arteries Using Mixtures of Nakagami Distributions and Stochastic Optimization

The goal of this work is to perform a segmentation of the intimamedia thickness (IMT) of carotid arteries in view of computing various dynamical properties of that tissue, such as the elasticity distribution (elastogram). The echogenicity of a region of interest comprising the intima-media layers, the lumen, and the adventitia in an ultrasonic B-mode image is modeled by a mixture of three Nakagami distributions. In a first step, we compute the maximum a posteriori estimator of the proposed model, using the expectation maximization (EM) algorithm. We then compute the optimal segmentation based on the estimated distributions as well as a statistical prior for disease-free IMT using a variant of the exploration/selection (ES) algorithm. Convergence of the ES algorithm to the optimal solution is assured asymptotically and is independent of the initial solution. In particular, our method is well suited to a semi-automatic context that requires minimal manual initialization. Tests of the proposed method on 30 sequences of ultrasonic B-mode images of presumably disease-free control subjects are reported. They suggest that the semi-automatic segmentations obtained by the proposed method are within the variability of the manual segmentations of two experts.

The Jonas Study: Evaluation of the Retrievability of the Cordis OptEase Inferior Vena Cava Filter

PURPOSE To evaluate the success, safety, and efficacy of the retrieval of the OptEase Permanent/Retrievable Vena Cava Filter (Cordis, Warren, NJ), when implanted for temporary protection against venous thromboembolism. MATERIALS AND METHODS This prospective, multicenter, non-randomized study enrolled 27 patients who needed temporary protection against pulmonary embolism in whom the intent at the time of filter insertion was retrieval of the OptEase filter. Patients presented with deep venous thrombosis (n = 17), pulmonary embolism (PE) (n = 6), and high risk for PE without thromboembolic disease (n = 4). Assessments included duplex sonography of the access site performed within 24 hours of device implantation and retrieval. All patients underwent cavography before and after filter placement and filter retrieval. Contrast-enhanced computed tomography (CT) of the abdomen and clinical follow-up was performed at 1 month after device retrieval. RESULTS Of the 27 enrolled patients, 21 patients (77.8%) met the criteria for retrieval and all 21 patients (100%) had filters successfully retrieved with no associated adverse events. Retrieval was not attempted in six patients as a result of ongoing contraindication to anticoagulation (n = 3), large trapped thrombi within the filter (n = 2), and poor patient prognosis (n = 1). Time to retrieval ranged from 5 to 14 days with a mean implantation time of 11.1 days +/- 1.82. No symptomatic pulmonary embolism, vena cava wall injury, vena cava stenosis, significant bleeding, filter fracture, or filter migration was observed. Nineteen of the 21 patients (90.5%) were followed for 1-month post-retrieval with no device-related adverse events or symptomatic PE. Caval patency was documented in 18 of these 19 patients with CT. Two patients were lost to follow-up, and one patient refused to undergo CT examination. CONCLUSION The OptEase permanent/retrievable vena cava filter can be safely and successfully retrieved up to 14 days in patients who no longer require inferior vena cava filter protection against pulmonary embolism.

Noninvasive vascular elastography for carotid artery characterization on subjects without previous history of atherosclerosis

BACKGROUND Noninvasive vascular ultrasound elastography (NIVE) was recently introduced to assess mechanical properties (strain or elasticity) of peripheral vessel walls. The goal of this study was to determine strain values in subjects with normal carotid arteries and the reproducibility of these measurements. METHODS Sixteen individuals without previous history of carotid atherosclerosis were recruited in four age categories [40-49], [50-59], [60-69], and [70-79] years old. The left and right common and internal carotids (LCC, LIC, RCC, and RIC, respectively) were independently scanned by two radiologists (RAD-A and RAD-B). The axial strain elastograms were computed with the Lagrangian speckle model estimator. RESULTS Supported by Bland-Altman analyses, strain values between LCC and RCC were found similar with a Pearson correlation coefficient (r) of 0.83 (p < 0.0001). Equivalently, a good correlation was found between RAD-A and RAD-B for common carotids with r=0.80 (p < 0.0001). Lower strain values (p < 0.001) were measured for male common carotids (1.62 +/- 0.32%) than females (2.21 +/- 0.76%). Regarding the internal carotid strain measurements, the correlation was lower between RAD-A and RAD-B with r=0.52 (p=0.01), but drastically decreased between LIC and RIC (r=0.16, nonsignificant). Male internal carotid strain estimates (p=0.03) were lower (1.48 +/- 0.44%) than in females (1.84 +/- 0.64%). Additionally, male common and internal carotid mean elastic moduli varied from 33-106 kPa, whereas it covered a range of 25-67 kPa for females. Female carotids were more elastic (44 +/- 17 kPa) than males (58 +/- 17 kPa, p <0.001). CONCLUSION Strain measurements in common carotids were found reproducible. However, less consistency was observed for the deeper internal carotids. The NIVE imaging method still remains to be validated with pathological cases, but it might provide a unique approach for stroke prevention and characterization of vascular stiffness.

Embolization of Pulmonary Arteriovenous Malformations with Amplatzer Vascular Plugs: Safety and Midterm Effectiveness

PURPOSE To evaluate the safety and effectiveness of Amplatzer vascular plugs (AVPs) for percutaneous closure of arteries feeding pulmonary arteriovenous malformations (PAVMs). MATERIALS AND METHODS Over a 45-month period, 24 consecutive patients with at least one PAVM treated with an AVP were selected from a database on patients with a PAVM who received embolotherapy. Immediate technical success was defined as the complete absence of flow through the PAVM after embolization without the need for additional embolization material. Success on follow-up imaging was defined as a reduction in size of at least 70% of the aneurysm or draining vein on follow-up computed tomography or the absence of flow through the PAVM on a subsequent pulmonary angiogram. RESULTS Thirty-seven AVPs were used to close 36 feeding arteries in 35 PAVMs in seven male and 17 female patients aged 11-86 years (mean age, 50 y). Technical success was achieved in 35 feeding arteries (97%). One feeding artery required two AVPs for closure. There were no immediate procedure-related complications. At a mean clinical follow-up of 322 days (range, 1-1,126 d), all patients were alive without new PAVM-related complications. Imaging follow-up was available for 29 embolized vessels (81%) with a mean follow-up of 418 days (range, 40-937 d), and recanalization occurred in two treated vessels (7%). CONCLUSIONS AVPs are safe and effective for closure of PAVMs feeding vessels that can be reached with a guiding catheter, with an acceptable rate of recanalization.