Marie-France Giroux

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.

Chemoembolization of Liver Metastasis from Breast Carcinoma

Chemoembolization was performed in eight patients with liver metastasis from breast carcinoma. Five of eight patients had some radiographic regression of the liver tumors, one had stable liver disease, and two had disease progression. Two of four patients with pain showed clinical improvement of their symptoms. Only one patient with radiographic response or disease stabilization subsequently had intrahepatic progression (at 3 months). Five patients developed other metastasis, particularly brain metastasis, at a mean of 4.6 months after first chemoembolization (range, 2-12 months). All patients died within 13 months of treatment, with a mean survival of 49 months from primary diagnosis, 20 months from liver metastasis diagnosis, and 6 months from first chemoembolization.

Segmentation of Plaques in Sequences of Ultrasonic B-Mode Images of Carotid Arteries Based on Motion Estimation and a Bayesian Model

The goal of this paper is to perform a segmentation of atherosclerotic plaques in view of evaluating their burden and to provide boundaries for computing properties such as the plaque deformation and elasticity distribution (elastogram and modulogram). The echogenicity of a region of interest comprising the plaque, the vessel lumen, and the adventitia of the artery wall in an ultrasonic B-mode image was modeled by mixtures of three Nakagami distributions, which yielded the likelihood of a Bayesian segmentation model. The main contribution of this paper is the estimation of the motion field and its integration into the prior of the Bayesian model that included a local geometrical smoothness constraint, as well as an original spatiotemporal cohesion constraint. The Maximum A Posteriori of the proposed model was computed with a variant of the exploration/selection algorithm. The starting point is a manual segmentation of the first frame. The proposed method was quantitatively compared with manual segmentations of all frames by an expert technician. Various measures were used for this evaluation, including the mean point-to-point distance and the Hausdorff distance. Results were evaluated on 94 sequences of 33 patients (for a total of 8988 images). We report a mean point-to-point distance of 0.24 ± 0.08 mm and a Hausdorff distance of 1.24 ± 0.40 mm. Our tests showed that the algorithm was not sensitive to the degree of stenosis or calcification.

Pain and Quality of Life Assessment after Endovascular Versus Open Repair of Abdominal Aortic Aneurysms in Patients at Low Risk

PURPOSE To compare functional autonomy, quality of life (QOL), and pain control after endovascular and open repair (OR) of abdominal aortic aneurysms. MATERIALS AND METHODS Forty patients with a low surgical risk profile and anatomic compatibility for stent-graft therapy were randomized to receive OR or endovascular aneurysm repair (EVAR). Technical and clinical success as well as mortality were assessed in both groups and compared by Kaplan-Meier analysis. Functional autonomy and QOL were assessed by Karnofsky score and Short Form 36 (SF-36) questionnaire. Pain control was assessed by a numeric rating scale and Brief Pain Inventory questionnaire. QOL outcomes by means of the SF-36 and pain questionnaires were compared with use of mixed-effects models for repeated-measures analysis. RESULTS All procedures were technically successful in both groups. Three late clinical failures requiring surgical conversion or repeated intervention were observed in the EVAR group and one was observed in the OR group. There was no significant difference between groups in terms of functional autonomy or QOL. No difference in pain level was evident during the early postoperative period, whereas the pain level was lower in the OR group after 1 month. Opioid analgesic drug consumption was significantly greater in the OR group during the postoperative period. Mean hospitalization duration was shorter in the EVAR group than in the OR group (4.5 days +/- 2.4 vs 11.5 days +/- 8.1; P= .001). CONCLUSION EVAR has no advantage over OR in patients at low risk in terms of functional autonomy, QOL, and pain control. However, EVAR was associated with shorter hospitalization durations compared with OR.

Recovery G2 Inferior Vena Cava Filter: Technical Success and Safety of Retrieval

PURPOSE To assess the safety and technical success of the retrieval of the Recovery G2 filter when implanted for temporary protection against pulmonary embolism. MATERIALS AND METHODS The Recovery G2 inferior vena cava (IVC) filter was placed in 120 consecutive patients between September 2005 and September 2006 in a single center. Patients had deep venous thrombosis (DVT) (n = 63), pulmonary embolism and DVT (n = 55), and high risk for pulmonary embolism without recent thromboembolic disease (n = 2). Indications for filter placement included contraindication to anticoagulation (n = 106), failure of anticoagulation (n = 11), and prophylaxis in addition to anticoagulation (n = 3). In patients eligible for filter removal, the authors measured the mean implantation time, filter retrieval success rate, and retrieval procedure time. In addition, they assessed filter tilting, migration, caval penetration, thrombus within the filter, fracture, and caval injury or stenosis. RESULTS In the 51 patients who met the criteria for filter removal, filter tilting (>15 degrees ) was seen in six patients (12%), small thrombi were seen in filters of 15 patients (29%), presumed caval penetration was seen in nine patients (18%), and caudal filter migration was seen in two patients (3.9%). There were no fractures or cephalic migrations. Removal attempts were successful in all 51 patients (100%). The mean implantation time was 53.4 days (range, 7-242 days), and the retrieval procedure time averaged 16.8 minutes (range, 5-60 minutes). CONCLUSIONS Retrieval of the Recovery G2 filter is safe and can be performed successfully in patients who no longer need IVC filtration.

Measurements and detection of abdominal aortic aneurysm growth: Accuracy and reproducibility of a segmentation software

PURPOSE To validate the reproducibility and accuracy of a software dedicated to measure abdominal aortic aneurysm (AAA) diameter, volume and growth over time. MATERIALS AND METHODS A software enabling AAA segmentation, diameter and volume measurement on computed tomography angiography (CTA) was tested. Validation was conducted in 28 patients with an AAA having 2 consecutive CTA examinations. The segmentation was performed twice by a senior radiologist and once by 3 medical students on all 56 CTAs. Intra and inter-observer reproducibility of D-max and volumes values were calculated by intraclass correlation coefficient (ICC). Systematic errors were evaluated by Bland-Altman analysis. Differences in D-max and volume growth were compared with paired Students t-tests. RESULTS Mean D-max and volume were 49.6±6.2mm and 117.2±36.2ml for baseline and 53.6±7.9mm and 139.6±56.3ml for follow-up studies. Volume growth (17.3%) was higher than D-max progression (8.0%) between baseline and follow-up examinations (p<.0001). For the senior radiologist, intra-observer ICC of D-max and volume measurements were respectively estimated at 0.997 (≥0.991) and 1.000 (≥0.999). Overall inter-observer ICC of D-max and volume measurements were respectively estimated at 0.995 (0.990-0.997) and 0.999 (>0.999). Bland-Altman analysis showed excellent inter-reader agreement with a repeatability coefficient <3mm for D-max, <7% for relative D-max growth, <6ml for volume and <6% for relative volume growth. CONCLUSION Software AAA volume measurements were more sensitive than AAA D-max to detect AAA growth while providing an equivalent and high reproducibility.

CT and MR Imaging of Nitinol Stents with Radiopaque Distal Markers

PURPOSE To evaluate imaging characteristics and artifacts of a nitinol stent with distal tantalum markers with computed tomography (CT) angiography and magnetic resonance (MR) angiography. MATERIALS AND METHODS A vascular phantom was built to simulate in-stent restenosis. A nitinol stent with tantalum markers (Luminexx stent) was evaluated with CT angiography in different orientations relative to the z-axis and with MR angiography in different positions relative to both B0 and the readout gradient. Stenosis measurements were compared with conventional digital subtraction angiography for both modalities. In-stent signal intensity obtained with different flip angles was assessed in two nitinol stents with distal markers (Luminexx stent and SMART stent) and one without markers (Memotherm-FLEXX stent). RESULTS Stenosis detection was not possible with CT angiography when the stent was perpendicular to the z-axis because of streak-like artifacts induced by tantalum markers. Stenosis evaluation with multiplanar reformation was accurate when the stent was in parallel and oblique orientations relative to the table axis. With MR angiography, metallic artifacts were mostly related to the stent orientation with B0, whereas orientation of the readout gradient had little influence. The mean error (overestimation) for stenosis measurements varied between 0.1% and 7.4% for CT imaging in parallel and oblique positions and 3.6% and 9.5% for MR imaging. Higher flip angles did not improve signal intensity inside the three stents tested. CONCLUSION CT and MR angiography can be used for evaluating the patency of stents with distal markers that are parallel or oblique relative to the table axis (iliac, carotid, or femoral stents). MR angiography is preferred if the stent is perpendicular to the table axis (renal stent).