Eric Therasse

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.

Quality Initiatives: Guidelines for Use of Medical Imaging during Pregnancy and Lactation

The use of computed tomography (CT) and magnetic resonance (MR) imaging has increased tremendously in the past 2 decades. Hence, pregnant and breast-feeding women, although generally healthier than the population at large, are also more likely to require contrast material-enhanced imaging. When a contrast-enhanced CT or MR imaging study is being considered for a pregnant or lactating patient, the potential risks to the fetus related to exposure to radiation, high magnetic fields, or contrast agents must be considered and weighed carefully against the risks of potential misdiagnosis due to withholding contrast agents and imaging studies. Fetal radiation doses up to 1 mGy are considered acceptable; with larger doses, the risk of carcinogenesis approximately doubles, although it remains low in absolute terms. No damage to a developing human fetus caused by MR imaging exposure has been documented. However, caution is advised, and risks and benefits must always be considered before evaluating a pregnant patient with MR imaging. The use of iodinated contrast agents is generally safe during pregnancy; nevertheless, these agents should be used with caution due to the risk of fetal hypothyroidism and should be administered only when the clinical situation clearly requires doing so. The use of gadolinium-based contrast agents during pregnancy remains controversial due to lack of human clinical data and potential toxicity. Use of all contrast agents is considered safe during lactation. It is hoped that this knowledge will help radiologists develop a consensus with their clinical colleagues regarding case management of pregnant and lactating patients.

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.

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.

Preoperative embolization in the management of a mediastinal paraganglioma

Parangliomas are rare and highly vascular tumors of neuroendocrine cell origin which are treated by complete surgical resection. Preoperative embolization to reduce perioperative bleeding complications, although described in paragangliomas of the neck and carotid body, has never before been described in the case of a mediastinal paraganglioma. The following is a presentation of such a case of mediastinal paraganglioma, in which embolization was used successfully before surgical resection.

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.

The Erasme Study: A Multicenter Study on the Safety and Technical Results of the Palmaz Stent Used for the Treatment of Atherosclerotic Ostial Renal Artery Stenosis

AbstractPurpose: To assess, in a multicenter setting, safety, technical results, and restenosis rate of the Palmaz stent for treatment of atherosclerotic ostial renal artery stenosis. Methods: Ten centers enrolled 106 patients (120 treated renal artery stenoses) in the study. Patient selection was based on unsuccessful percutaneous transluminal renal angioplasty (residual stenosis ≥ 20%) performed for treatment of ostial stenosis ≥ 50%, in patients with hypertension and/or impaired renal function. Safety was assessed by means of the complication rate, and technical results by the number of successful stent placements and occurrence of restenosis (>50%) at intraarterial angiographic follow-up. Results: Stent placement was successful (n=112) or partially successful (n=5) in 117 (98%) arteries. Complications occurred in 19 procedures; seven were of serious clinical significance. Angiographic follow-up was performed in 89 of 117 (76%) cases, at a mean of 8 months (range 2.5–18 months). Fifteen stents (16.9%) showed restenosis (at a mean of 8.5 months), of which 10 were successfully redilated. Conclusion: Renal artery stenting has a high technical success rate, a complication rate comparable to percutaneous transluminal renal angioplasty, and a low rate of restenosis at 8 months angiographic follow-up.

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).

Clinical validation of a software for quantitative follow-up of abdominal aortic aneurysm maximal diameter and growth by CT angiography

PURPOSE To compare the reproducibility and accuracy of abdominal aortic aneurysm (AAA) maximal diameter (D-max) measurements using segmentation software, with manual measurement on double-oblique MPR as a reference standard. MATERIALS AND METHODS The local Ethics Committee approved this study and waived informed consent. Forty patients (33 men, 7 women; mean age, 72 years, range, 49-86 years) had previously undergone two CT angiography (CTA) studies within 16 ± 8 months for follow-up of AAA ≥ 35 mm without previous treatment. The 80 studies were segmented twice using the software to calculate reproducibility of automatic D-max calculation on 3D models. Three radiologists reviewed the 80 studies and manually measured D-max on double-oblique MPR projections. Intra-observer and inter-observer reproducibility were calculated by intraclass correlation coefficient (ICC). Systematic errors were evaluated by linear regression and Bland-Altman analyses. Differences in D-max growth were analyzed with a paired Students t-test. RESULTS The ICC for intra-observer reproducibility of D-max measurement was 0.992 (≥ 0.987) for the software and 0.985 (≥ 0.974) and 0.969 (≥ 0.948) for two radiologists. Inter-observer reproducibility was 0.979 (0.954-0.984) for the three radiologists. Mean absolute difference between semi-automated and manual D-max measurements was estimated at 1.1 ± 0.9 mm and never exceeded 5mm. CONCLUSION Semi-automated software measurement of AAA D-max is reproducible, accurate, and requires minimal operator intervention.