Soft tissue vascular tumor-like lesions in adults: imaging and pathological analysis pitfalls per ISSVA classification.

OBJECTIVES: To compare the magnetic resonance imaging (MRI) and Doppler ultrasound (DUS) findings with the pathological findings of soft tissue vascular tumors (STVTs) according to the 2018 ISSVA (International Society for the Study of Vascular Anomalies) classification to differentiate vascular tumors from vascular malformations. METHODS: This retrospective study included patients with STVTs who underwent contrast-enhanced MRI and pathological analysis at our hospital between 2010 and 2020. The presumptive diagnosis based on the on-site imaging and histological analysis was compared with imaging and histological analysis conducted off-site utilizing the ISSVA criteria. RESULTS: This study included 31 patients with 31 vascular tumors located in the head and neck (n = 3), trunk (n = 2), and extremities (n = 26). The off-site pathological analysis confirmed benign vascular tumors in 54.8% of cases (non-involuting congenital hemangioma: 35.5%; epithelioid hemangioma: 13%; pyogenic granuloma: 3%; and spindle cell hemangioma: 3%). Based on the off-site histological analysis, 25.8% were reclassified as having a vascular malformation whereas three had other benign lesions. Only phleboliths were associated with a vascular malformation (p = 0.03). The concordance between off-site MRI and pathological findings was fair (k = 0.3902 (0.0531-0.7274)), whereas that between on-site and off-site pathological analyses was poor (k = -0.0949 (-0.4661 to 0.2763)). CONCLUSION: Benign vascular tumors have non-specific imaging features on imaging with some overlap with atypical vascular malformations. Therefore, histological analysis is recommended. Imaging and pathological analyses should be performed in accordance with the ISSVA classification to minimize inter-observer discrepancies. CRITICAL RELEVANCE STATEMENT: Imaging features of benign vascular tumors on MRI are non-specific, leading to discrepancies with pathological findings and potential overlap with atypical vascular malformations. Imaging and histological analyses should be performed in accordance with ISSVA guidelines to improve patient management. KEY POINTS: The imaging features of benign vascular tumors are non-specific. Histological analysis is recommended for soft tissue vascular tumors in adults. Analyses of soft tissue vascular tumors should be performed in accordance with ISSVA guidelines.

In Vivo Feasibility of Arterial Embolization with Permanent and Absorbable Suture: The FAIR-Embo Concept.

PURPOSE: Arterial embolization has been shown to be effective and safe for the management of bleeding, especially for postpartum and pelvic traumatic bleeding. We propose to evaluate the proof of concept of feasibility and effectiveness of arterial embolization with absorbable and non-absorbable sutures in a porcine model. MATERIALS AND METHODS: In the acute setting (n = 1), several different arteries (mesenteric, splenic, pharyngeal, kidney) were embolized using non-absorbable sutures (NAS): Mersutures™ braided sutures (polyethylene terephthalate). In the chronic setting (n = 3), only lower pole renal arteries were embolized. On the right side, NAS was used, whereas on the left side embolization was realized with absorbable suture (AS): Vicryl® braided suture (polyglactin 910). The chronic group was followed for 3 months. The pigs received contrast-enhanced CT the day before embolization (D-1), after the embolization (D0), at 1 month and 3 months after embolization (M1 and M3); digital subtraction angiography (DSA) was done at D0 and M3 and histological analysis at M3. RESULTS: All vascular targets were effectively embolized without any pre- or postoperative complications. Both DSAs and CTs at M3 showed a 100% recanalization rate for the AS embolization and a partial reversal rate for the NAS embolization. A renal hypotrophy in the embolized region was observed during both the M1 and M3 scans for both sutures (AS and NAS) with a clear hypotrophy for the NAS embolized kidney. CONCLUSION: Embolization by AS and NAS (FAIR-Embo) is a feasible and effective treatment which opens up the possibility of global use of this inexpensive and widely available embolization agent.

Incidental findings in CT imaging of coronary artery bypass grafts: results from a Canadian multicenter prospective cohort.

OBJECTIVE: To assess the prevalence and clinical significance of incidental findings identified during computed tomography imaging of coronary artery bypass grafts. RESULTS: This prospective study includes 144 patients undergoing coronary graft patency assessment using computed tomography. Incidental findings were classified as significant if they were considered to need an immediate action or treatment, short-term work-up or follow-up, or minor. A total of 211 incidental findings were present in 109 (75.7%) patients. Seventy-one incidental findings (33.6%) were cardiac and 140 (66.4%) were extracardiac. Most common cardiac incidental findings were atrial dilatation [39 patients, 48 incidental findings (67.6%)] and aortic valve calcifications (7 patients, 9.9%). Among the 140 extracardiac incidental findings, the most common were lung nodules (51 patients, 54 nodules, 38.6%), and emphysema (21 patients, 15%). Thirty-six (25.7%) extracardiac incidental findings were significant and notably, 23 (63.9%) were lung nodules. Follow-up was recommended in 37 cases, among which all patients with significant lung nodules (23 patients, 62.2%). In conclusion, most common computed tomography incidental findings in patients with coronary grafts were lung nodules and emphysema.

Graft durability and fatigue after in situ fenestration of endovascular stent grafts using radiofrequency puncture and balloon dilatation.

OBJECTIVES: In situ fenestration of endovascular stent grafts is a technique that is becoming more common, as it has the advantages of decreased cost, increased availability, and more anatomic configuration than other methods of branch revascularization. However, a significant concern is the short- and long-term durability of the stent graft fabric during and after fenestration. METHODS: This study utilizes the textiles analysis techniques of macro- and microscopic imaging, tear strength testing, burst strength testing, and accelerated cyclic fatigue testing on the fabrics of the Cook Zenith, Medtronic Talent, and Medtronic Endurant stent grafts (three polyester grafts), as well as two different expanded polytetrafluoroethylene (ePTFE) membranes. Specimens were punctured using radiofrequency, and serially dilated with angioplasty balloons (3, 5, and 7 mm). For each type of fabric, three groups were analyzed: control, radiofrequency (RF) puncture only, and balloon dilated. RESULTS: A total of 110 specimens were analyzed, with 80 of them having been fenestrated. The Zenith fabric had the greatest strength after fenestration, but was limited by the inability to fully dilate the fenestration with the conventional balloons, which only achieved 26-29% of their nominal balloon diameter. While the Talent and Endurant grafts could be dilated with balloons, the orifices were markedly elliptical not circular. After accelerated fatigue testing, there was an increase in the size of fenestrations of the Talent fabric. There was no increase in fenestration size for the Endurant fabric, Zenith fabric, or the ePTFE fabrics, after fatigue testing. CONCLUSIONS: While the Zenith fabric was the strongest both before and after fenestration, it requires further study with cutting balloons to achieve full-sized fenestrations. All fenestrations remained stable during fatigue testing except for the Talent fabric. This study serves as the baseline for future studies that will include stent grafts, branch stents, and cutting balloons.

[Interventional angioradiology as a solution for microsurgical flap failure]. / La radioangiologie interventionnelle comme solution de sauvetage en microchirurgie.

The microsurgical failure rate is almost constant for several decades. We present two case reports describing a novel method of free flap salvage using angioradiological techniques. Our first case shows the potential utility of in situ thrombolysis, our second case describes the first use of stents within a microsurgical anastomosis. In boths cases, the flap would have been lost immediately, because flap revisions failed. Thus, before abandoning on a flap, one could perform a simple angiography to evaluate further angioradiological salvage possibilities and hereby contribute to improve long term microsurgical failure rate.

A new canine carotid artery bifurcation aneurysm model for the evaluation of neurovascular devices.

BACKGROUND AND PURPOSE: Stents are increasingly used for coiling of difficult aneurysms, to reduce the risk of recurrences, or to modify blood flow. Currently available bifurcation aneurysm models are ill-suited to assess stent performance before clinical use. We designed a new wide-neck canine T-type bifurcation aneurysm model. Its potential value as a training tool as well as in the evaluation of new techniques or embolic agents was assessed. Our first task was to verify that recurrences occurred after satisfactory coiling. A second aim of this preliminary work was to assess if the new model could recreate the technical challenges involved in bifurcation aneurysms. MATERIALS AND METHODS: We introduce a new canine wide-neck bifurcation aneurysm model, created by using a vein pouch at the apex of an end-to-side anastomosis of the carotid arteries, with flow reversal in the proximal RCA by ligation of the innominate artery. Three aneurysms were treated with coil embolization, 10 were treated with stents (7 self-expandable, 3 balloon-expandable), and 3 were left untreated. Aneurysms were followed by duplex ultrasonography and angiography, and studied with macroscopic photography after euthanasia 11.8 +/- 3.9 months after surgery. RESULTS: All aneurysms remained patent at 9.0 +/- 3.6 months' follow-up. Coiling led to recurrences by 3 months in all 3 cases. Stent placement was technically difficult in all cases and did not lead to aneurysm thrombosis or neointimal closure of the aneurysm neck at 3 months. CONCLUSIONS: This model may be suitable for studying the effects of endovascular treatment on aneurysm and branch occlusion rates, for preclinical testing of stents and other intravascular devices, and for training students of endovascular technique.

Multicenter evaluation of a self-expanding carotid stent system with distal protection in the treatment of carotid stenosis.

PURPOSE: Carotid artery stent placement may be limited by the embolization of atheromatous material. We evaluated the safety and feasibility of the Medtronic Self-Expanding Carotid Stent (Exponent) in combination with the Medtronic Interceptor Carotid Filter System for the treatment of carotid stenosis among patients at high risk for carotid endarterectomy. METHODS: Patients at high risk for carotid endarterectomy but amenable to percutaneous treatment with stent placement were enrolled. Clinical follow-up was performed at 30 days and 6 and 12 months postprocedure. The National Institutes of Health Stroke Scale was assessed before and within 3 days postprocedure and at 30 days and 6 months postprocedure. Angiography was performed pre- and postprocedure, and carotid duplex scans were performed at baseline and at 30 days and 6 months. RESULTS: Fifty-two carotid procedures were performed in 51 patients (mean age, 69 years; 84% of patients were men). The major adverse event (MAE) rate (death, stroke, and myocardial infarction [MI]) at 30 days was 5.9%: 2 strokes and a single death from periprocedural MI. MAE rates after 6 and 12 months were 5.9% and 11.8%, respectively. The delivery success rate was 94.2% (49/52) for the Interceptor Filter System and 95.9% (47/49) for the Exponent Stent. The mean diameter stenosis of the target lesion was reduced from 62.4% preprocedure to 21.2% postprocedure. CONCLUSION: High delivery success rates were achieved with a low rate of MAE (death, stroke, or MI) in a high-risk population. Treatment of carotid artery disease with the Exponent Carotid Stent combined with distal protection from the Interceptor Filter System is effective and safe.

Potential Applications of Untethered Microdevices in the Blood Vessels within the Constraints of an MRI System.

This paper presents potential medical applications that an untethered microdevice in the cardiovascular system could perform within an MRI system. Recent developments and continuing evolution in micro/nano fabrication and design techniques will enable the development of functional microdevices able to explore the cardiovascular system. The Magnetic Resonance Submarine (MR-Sub) project is a first step towards this goal. Magnetic force generated by the gradient coils of an MRI system provides a propulsion mechanism that simplifies miniaturization and bypasses energetic challenges. Untethered microdevices may play an important complementary role in the next generation of minimally invasive tools. A better efficiency and targetability of the treatments will be achieved when microsystems such as the MR-Sub will allow a more extensive access to smaller blood vessels.

Study of non stationary mode flow of an abdominal aortic aneurysm.

INTRODUCTION: Abdominal aortic aneurysm rupture is 95% lethal. Numerical simulation of Navier-Stokes equations allows seeing complex flow phenomenon in laminar state. METHOD: In this study, we work on a model using the finite element method with an actual 3D geometry. This geometry is from a point cloud obtained by a tomodensitometry scan of a typical patient. We consider rigid wall, homogeneous and Newtonian fluid. We impose four pulsative waveforms as entrance condition: two rest waveforms, two exercise waveforms. The four aver-age Reynolds numbers are 353 and 363 for the rest waveforms and 1058 and 1388 for the exercise waveforms. For the systolic peaks, the Reynolds numbers are 1639 and 1917 for the rest waveforms and 2800 and 2497 for the exercise waveforms. RESULTS: RESULTS show that during the systolic acceleration, vortices issued from the previous pulsation are pushed out and the flow reattached on the wall. During the systolic deceleration, a main vortex appears in the upper part of the aneurysm; it grows and moves to the center. During the diastole, the vortex sustains itself until the next pulsation for the exercise conditions. For the rest conditions, imposed oscillations during the diastole lead to secondary vortices. Pressure stays relatively constant in the aneurysm following the entrance conditions. DISCUSSION: These results on the flow and pressure repartition agreed with those found in the literature (1-6) validating in a first time our model. The next step of the study is the wall shear stress data exploitation.

Adapting MRI systems to propel and guide microdevices in the human blood circulatory system.

Magnetic resonance imaging (MRI) systems are widely used to gather noninvasively images of the interior of the human body. This paper suggests that an MRI system can be seen beyond being just a tool for imaging purpose but one that can propel and guide special microdevices in the human body to perform specific medical tasks. More specifically, an MRI system can potentially be used to image the region of interest, propel a microdevice through the generation of magnetic gradients, determine the location of the device, compute the corrective actions through feedback control algorithms and adjust the generation of the magnetic gradients accordingly to navigate such a microdevice in a preplanned path. This paper presents an introductory description of the proposed techniques, the main issues to consider, and some preliminary data indicating the validity of this approach.

Soft-tissue venous malformations in adult patients: imaging and therapeutic issues.

Venous malformations are the most common vascular malformations. However, confusion with respect to terminology and imaging guidelines continues to result in improper diagnosis and treatment. An appropriate classification scheme for vascular anomalies is important to avoid the use of false generic terms. Adequate imaging in association with clinical findings is crucial to establishing the correct diagnosis. Doppler ultrasonography should be the initial imaging modality and demonstrates absence of flow or low-velocity venous flow. Computed tomography and magnetic resonance (MR) imaging are used primarily for pretreatment evaluation of lesion extension. These lesions are usually hypointense on T1-weighted MR images and markedly hyperintense on T2-weighted images with variable gadolinium enhancement. Direct phlebography helps confirm the diagnosis and exclude other soft-tissue tumors. Three distinct phlebographic patterns (cavitary, spongy, dysmorphic) have been identified. In most cases, conservative treatment is recommended. Sclerotherapy with or without surgery is useful in cases of functional impairment or significant aesthetic prejudice, even if recurrences are frequent. Direct phlebography is performed when a more detailed assessment of the vascular pattern is needed or as part of sclerotherapy. Use of the appropriate imaging technique is critical in establishing the diagnosis, evaluating extension, and planning appropriate treatment.

Detection of renal artery stenosis: prospective comparison of captopril-enhanced Doppler sonography, captopril-enhanced scintigraphy, and MR angiography.

OBJECTIVE: The objective of our study was to compare the value of captopril-enhanced Doppler sonography, captopril-enhanced renal scintigraphy, and gadolinium-enhanced MR angiography for detecting renal artery stenosis. SUBJECTS AND METHODS: Forty-one patients with suspected renovascular hypertension were prospectively examined with captopril-enhanced Doppler sonography, captopril-enhanced renal scintigraphy, gadolinium-enhanced MR angiography, and catheter angiography. The sensitivity and specificity of each technique for detecting renal artery stenosis measuring 50% or greater and 70% or greater were compared using the McNemar test. Positive and negative predictive values were estimated for populations with 5% and 30% prevalence of renal artery stenosis. Kappa values for interobserver agreement were assessed for both gadolinium-enhanced MR angiography and catheter angiography. RESULTS: For detecting renal artery stenosis measuring 50% or greater, the sensitivity of gadolinium-enhanced MR angiography (96.6%) was greater than that of captopril-enhanced Doppler sonography (69%, p = 0.005) and captopril-enhanced renal scintigraphy (41.4%, p = 0.001). No significant difference in specificity was observed among modalities. For renal artery stenosis measuring 50% or greater, positive and negative predictive values were respectively 62% and 86% for captopril-enhanced Doppler sonography, 49% and 76% for captopril-enhanced renal scintigraphy, and 53% and 98% for gadolinium-enhanced MR angiography. Interobserver agreement was high for both gadolinium-enhanced MR angiography (kappa = 0.829) and catheter angiography (kappa = 0.729). CONCLUSION: Gadolinium-enhanced MR angiography is the most accurate noninvasive modality for detecting renal artery stenosis greater than or equal to 50%. The use of captopril-enhanced Doppler sonography in combination with gadolinium-enhanced MR angiography for identifying renal artery stenosis needs to be evaluated with a cost-effectiveness analysis.

Infrarenal aortic stenosis: value of stent placement after percutaneous transluminal angioplasty failure.

PURPOSE: To evaluate the long-term clinical and hemodynamic effectiveness of aortic stent placement in cases of failure of intended infrarenal percutaneous transluminal aortic angioplasty (PTAA). MATERIALS AND METHODS: Fifty-three patients who underwent technically successful PTAA were compared with 24 patients who underwent aortic stent placement because of PTAA failure (19 patients) or ulcerated lesions (five patients) that otherwise would have been treated surgically because of the embolization hazard associated with PTAA alone. Clinical patency was defined as the absence or improvement of symptoms after the intervention. Hemodynamic patency was defined as a normal Doppler waveform in the common femoral arteries, an ankle-brachial index greater than 0.95, or the absence of a thigh-brachial pressure gradient. RESULTS: Three-year clinical and hemodynamic patency rates, respectively, were 85% and 79% for PTAA and 69% and 43% for aortic stent placement. No morbidity was encountered. With use of the Cox proportional hazards model, two significant risk factors were retained for restenosis: unchanged smoking habit (P =.04) and small dilatation diameter (P =.001). Aortic stent placement, performed in patients with a smaller aortic diameter (10.3 vs. 12.7 mm for PTAA), appeared to be a predictive factor for restenosis by using univariate analysis. By using the Cox proportional hazards model, however, the restenosis rates after PTAA and aortic stent placement were not significantly different. CONCLUSION: When aortic diameter is taken into consideration, there is no evidence that clinical outcome after secondary aortic stent placement would be poorer than technically successful PTAA.

Arterial embolotherapy for upper gastrointestinal hemorrhage: outcome assessment.

PURPOSE: To identify predictors of clinical outcome after arterial embolotherapy for upper gastrointestinal (UGI) hemorrhage. MATERIALS AND METHODS: Seventy-five consecutive patients (mean age, 62.5 y) underwent arterial embolization for acute UGI hemorrhage. Bleeding was detected at endoscopy and angiography in 22 patients, at endoscopy alone in 29 patients, and at angiography alone in 24 patients. As such, embolization was directed by angiography in 46 patients (61.3%) and by endoscopy (referred to as "blind" embolization) in 29 patients (38.7%). The embolic agents used were metallic coils, polyvinyl alcohol particles (size range, 355-710 microm), gelatin sponge, and tissue adhesive. Predictors of bleeding recurrence and mortality were analyzed with logistic regression and Cox models, respectively. RESULTS: The technical success rate of embolization was 98.7%. Primary clinical success was achieved in 57 patients (76%). Secondary clinical success occurred in five additional patients (82.5%) after repeat embolization. There were four (5.3%) complications: two cases of self-resolving duodenal ischemia, one hepatic infarct, and one inguinal hematoma. The periprocedural mortality rate was 34.6% (26 of 75), mostly related to underlying illness. Early recurrence of bleeding (within 30 days of embolization) was associated with coagulation disorders (international normalized ratio >1.5, partial thromboplastin time >45 seconds, or platelet count <80,000/microL; odds ratio, 19.46; P = .001) and with the use of coils as the only embolic agent (odds ratio, 7.73; P = .01). Cirrhosis and cancer shortened the overall survival of patients after embolic therapy. The mean patient follow-up time was 34.5 months. CONCLUSION: Arterial embolotherapy for UGI hemorrhage is safe, effective, and durable. Coagulopathy and the use of coils as the only embolic agent were associated with a higher risk of early bleeding recurrence.

Imaging of renovascular hypertension: respective values of renal scintigraphy, renal Doppler US, and MR angiography.

Renovascular hypertension affects 15%-30% of patients who have clinical criteria suggestive of renovascular disease. Noninvasive screening is crucial for patient selection prior to conventional angiography and renal revascularization. Renal scintigraphy has been reported to be sensitive for detection of renovascular hypertension, but some of its limitations (eg, in the setting of bilateral renal artery stenosis and renal failure) should be considered. Doppler ultrasonography (US) allows direct evaluation of the renal arteries as well as transrenal Doppler waveform analysis, but it remains operator dependent. Gadolinium-enhanced magnetic resonance (MR) angiography is becoming an excellent alternative to conventional angiography. The main limiting factors of this technique are inadequate visualization of segmental and accessory renal arteries as well as a tendency toward overestimation of stenoses. Given the high cost and low availability of MR angiography, scintigraphy and Doppler US should be considered the primary studies in screening for renovascular hypertension. MR angiography could be reserved for patients with inconclusive scintigraphic and Doppler US results, patients with high clinical suspicion of renovascular hypertension, and patients with a contraindication to conventional angiography.

Transvenous coil embolization of an extrahepatic portosystemic shunt in a dog: a naturally occurring model of portosystemic malformations in humans.

Congenital patent ductus venosus (PDV) occurs far more commonly in dogs than in people; consequently, the natural course of the disease in dogs was studied as a model to understand the pathophysiology behind the vascular anomaly and its response to therapy better. In this report, the authors describe the results of percutaneous coil embolization as a single procedure in a dog with a single congenital extrahepatic portocaval shunt and compare portosystemic vascular anomalies (PSVA) seen in dogs with those seen in children.

Percutaneous revascularization of the renal arteries: predictors of outcome.

PURPOSE: To identify predictors of clinical outcome after percutaneous revascularization of the renal arteries. MATERIALS AND METHODS: In 63 patients, the therapeutic response was retrospectively assessed after percutaneous revascularization of the renal arteries indicated for hypertension (41.3%), renal failure (4.8%), or both (53.9%). All patients underwent percutaneous transluminal renal angioplasty, complemented by stent insertion in 30 patients. The authors analyzed the role of clinical and imaging factors, including scintigraphy, Doppler sonography, and angiography for predicting clinical success. RESULTS: In the hypertensive population, there were three cures (5.6%), 26 improvements (48.1%), and 25 failures (46.3%). Among patients with renal insufficiency, 12 were improved (37.5%), 11 were stabilized (34.4%), and nine deteriorated (28.1%). Predictors of favorable outcome for hypertension were shorter duration of hypertension, higher diastolic blood pressure, fibromuscular dysplasia, abnormal Doppler study, higher percentage of angiographic stenosis, and lower grade of aortic atheromatous disease. Predictors of favorable outcome for renal failure were nondiabetic status, abnormal Doppler study, and higher percentage of angiographic stenosis. Abnormal Doppler and scintigraphic examinations predicted successful treatment of hypertension in 60% and 53.8% of cases, respectively, and renal insufficiency in 85% and 60% of cases, respectively. CONCLUSION: Clinical and angiographic variables were the best predictors of therapeutic success for hypertension. Doppler sonography was useful in patients with renal failure.

Assessment of arterial stenosis in a flow model with power Doppler angiography: accuracy and observations on blood echogenicity.

The objective of the project was to study the influence of various hemodynamic and rheologic factors on the accuracy of 3-D power Doppler angiography (PDA) for quantifying the percentage of area reduction of a stenotic artery along its longitudinal axis. The study was performed with a 3-D power Doppler ultrasound (US) imaging system and an in vitro mock flow model containing a simulated artery with a stenosis of 80% area reduction. Measurements were performed under steady and pulsatile flow conditions by circulating, at different flow rates, four types of fluid (porcine whole blood, porcine whole blood with a US contrast agent, porcine blood cell suspension and porcine blood cell suspension with a US contrast agent). A total of 120 measurements were performed. Computational simulations of the fluid dynamics in the vicinity of the axisymmetrical stenosis were performed with finite-element modeling (FEM) to locate and identify the PDA signal loss due to the wall filter of the US instrument. The performance of three segmentation algorithms used to delineate the vessel lumen on the PDA images was assessed and compared. It is shown that the type of fluid flowing in the phantom affects the echoicity of PDA images and the accuracy of the segmentation algorithms. The type of flow (steady or pulsatile) and the flow rate can also influence the PDA image accuracy, whereas the use of US contrast agent has no significant effect. For the conditions that would correspond to a US scan of a common femoral artery (whole blood flowing at a mean pulsatile flow rate of 450 mL min(-1)), the errors in the percentages of area reduction were 4.3 +/- 1.2% before the stenosis, -2.0 +/- 1.0% in the stenosis, 11.5 +/- 3.1% in the recirculation zone, and 2.8 +/- 1.7% after the stenosis, respectively. Based on the simulated blood flow patterns obtained with FEM, the lower accuracy in the recirculation zone can be attributed to the effect of the wall filter that removes low flow velocities. In conclusion, the small errors reported in vitro may support the clinical use of this technique.