Vessel Angle Research Articles

Quantitative retinal-blood flow measurement with three-dimensional vessel geometry determination using ultrahigh-resolution Doppler optical coherence angiography

Retinal blood flow quantification by retinal vessel segmentation with Doppler optical coherence angiography is presented. Vessel diameter, orientation, and position are determined in an en face vessel image and two representative cross-sectional flow images of the vessel. Absolute blood flow velocity is calculated with the help of the measured Doppler frequency shift and determined vessel angle. The volumetric flow rate is obtained with the position and the region of the vessel lumen. The volumetric blood flow rate of retinal arteries before and after a bifurcation is verified in a healthy human eye.

Safety and technical efficacy of over-the-wire balloons for the treatment of subarachnoid hemorrhage–induced cerebral vasospasm

Over the past decade, low-pressure, flow-directed balloons have been replaced by over-the-wire balloons in the treatment of vasospasm induced by subarachnoid hemorrhage (SAH). The authors assess the procedural safety and technical efficacy of these newer devices. Seventy-five patients who underwent 85 balloon angioplasty procedures for the treatment of SAH-induced vasospasm were identified from a prospective quality-assurance database. Medical records and angiographic reports were reviewed for evidence of procedural complications and technical efficacy. No vessel rupture or perforation occurred, but thromboembolic complications were noted in four (4.7%) of the 85 procedures. Balloon angioplasty was frequently attempted and successfully accomplished in the distal internal carotid (100%), proximal middle cerebral (94%), vertebral (73%), and basilar (88%) arteries. Severe narrowing was present in 89 proximal anterior cerebral arteries. Angioplasty was attempted in 41 of these vessels and was successful in only 14 (34%). In 19 of the 27 unsuccessful attempts, the balloon could not be advanced over the wire due to severe vasospasm or unfavorable vessel angle. Follow-up angiography in a subset of patients demonstrated that severe recurrent vasospasm occurred in 15 (13%) of 116 vessels studied after angioplasty. Over-the-wire balloons involve a low risk for vessel rupture. The anterior cerebral artery remains difficult to access and successfully treat with current devices. Further improvements in balloon design, such as smaller inflated diameters and better tracking, are necessary. Finally, thromboembolic complications remain an important concern, and severe vasospasm may recur after balloon angioplasty.

Design of Cerebellar and Nontegmental Rhombencephalic Microvascular Bed in the Sterlet,Acipenser ruthenus: A Scanning Electron Microscope and 3D Morphometry Study of Vascular Corrosion Casts

The design of the microvasculature of cerebellum and nontegmental rhombencephalic areas was studied in eight adult Acipenser ruthenus L. by scanning electron microscopy of vascular corrosion casts and three-dimensional morphometry. Gross vascularization was described and diameters and total branching angles of parent and daughter vessels of randomly selected arterial and capillary bifurcations (respectively, venous mergings) were measured. With diameters ranging from 15.9 +/- 1.9 microm (cerebellum; mean +/- S.D.) to 15.9 +/- 1.7 mm (nontegmental rhombencephalon; mean +/- S.D.) capillaries in Acipenser were significantly (p > or = .05) smaller than in cyclostomes (18-20 microm) but significantly thicker than in higher vertebrates and men (6-8 microm). With the exception of the area ratio beta (i.e., sum of squared daugther diameters divided by squared diameter of parent vessel) of the venular mergings in the nontegmental rhombencephalon, no significant differences (p > or = .05) existed between the two brain areas. Data showed that arteriolar and capillary bifurcations and venular mergings are optimally designed in respect to diameters of parent vessel to daughter vessels and to branching (merging) angles. Quantitative data are discussed both in respect to methodical pitfalls and the optimality principles possibly underlying the design of vascular bifurcations/mergings in selected brain areas of a nonteleost primitive actinopterygian fish.

Numerical investigation of the intravascular coronary stent flexibility

Nowadays stent therapy is widely adopted to treat atherosclerotic vessel diseases. The high commercial value of these devices and the high prototypation costs require the use of finite element analyses, instead of classical trial and error technique, to design and verify new models. In this paper, we explore the advantages of the finite element method (FEM) in order to investigate new generation stent performance in terms of flexibility. Indeed, the ability of the stent to bend in order to accommodate curvatures and angles of vessels during delivery is one of the most significant prerequisites for optimal stent performance. Two different FEM models, resembling two new generation intravascular stents, were developed. The main model dimensions were obtained by means of a stereo microscope, analyzing one Cordis BX-Velocity and one Carbostent Sirius coronary stent. Bending tests under displacement control in the unexpanded and expanded configuration were carried out. The curvature index, defined as the ratio between the sum of rotation angles at the extremes and the length of the stent, yielded comparative information about the capability of the device to be delivered into tortuous vessels and to conform to their contours. Results, expressed in terms of the bending moment-curvature index, demonstrated a different response for the two models. In particular the Cordis model showed a higher flexibility. Lower flexibility in the expanded configurations for both models was detected. However this flexibility depends on how the contact takes place between the different parts of the struts.

MRI visualization of the female pelvis in the plane of the tension-free vaginal tape (TVT) procedure.

We evaluated the distances and angles of the major blood vessels from various pelvic structures in the plane of the tension-free vaginal tape (TVT) procedure in 19 pelvic MR imagies. The major blood vessels were the iliofemoral vessels. The mean distance of the left iliofemoral vessels from the midline was 5.7+/-0.4 cm, and 5.7+/-0.3 cm for the right vessels. The mean distance of the left sacral tuberosities from the midline was 5.5+/-0.4 cm, and 5.6+/-0.3 cm for the right vessels. The angle between the midurethra and the left iliofemoral vessels was 50.6+/-4.4 cm, and 49.6+/-4.0 cm for the right. A significant correlation was found between the distance of the right and left iliofemoral vessels from the midline and the distance of right and left sacral tuberosities from the midline ( P<0.01, P<0.007). We suggest that palpation of the sacral tuberosities might indicate the location of the iliofemoral blood vessels.

The baboon (Papio anubis) extracranial carotid artery: an anatomical guide for endovascular experimentation.

BackgroundAs novel endovascular strategies are developed for treating neurological disease, there is an increasing need to evaluate these techniques in relevant preclinical models. The use of non-human primates is especially critical given their structural and physiological homology with humans. In order to conduct primate endovascular studies, a comprehensive understanding of the carotid anatomy is necessary. We therefore performed a detailed examination of the vessel lengths, lumen diameters and angles of origin of the baboon extracranial carotid system.MethodsWe characterized the extracranial carotid system often male baboons (Papio anubis, range 15.1–28.4 kg) by early post-mortem dissection. Photographic documentation of vessel lengths, lumen diameters, and angles of origin were measured for each segment of the carotid bilaterally.ResultsThe common carotid arteries averaged 94.7 ± 1.7 mm (left) and 87.1 ± 1.6 mm (right) in length. The average minimal common carotid lumen diameters were 3.0 ± 0.3 mm (left) and 2.9 ± 0.2 mm (right). Each animal had a common brachiocephalic artery arising from the aorta which bifurcated into the left common carotid artery and right braciocephalic artery after 21.5 ± 1.6 mm. The vascular anatomy was found to be consistent among animals despite a wide range of animal weights.ConclusionsThe consistency in the Papio anubis extracranial carotid system may promote the use of this species in the preclinical investigation of neuro-interventional therapies.

Longitudinal straightening effect of stents is an additional predictor for major adverse cardiac events

OBJECTIVESThe aim of this study was to perform an investigation of the effects of the longitudinal straightening of coronary arteries by stents and the possible association with major adverse cardiac events (MACE) (primary end point) and angiographic restenosis (secondary end point).BACKGROUNDStent deployment straightens a tortuous artery, and any consequent arterial longitudinal stretch may contribute to MACE and stent restenosis severity.METHODSClinical, qualitative and quantitative angiographic data on 404 patients with single stent implantation were subjected to multivariate nominal logistic regression analysis for the prediction of MACE. The predictive accuracy, sensitivity and specificity values and cut-off points of the continuous variables were determined via receiver operating characteristics curves. The longitudinal straightening effect of stents was characterized through the changes in vessel angle (defined by the tangents to the proximal and distal parts of the stenoses/stents).RESULTSFollow-up angiography on 354 patients revealed 73 cases of stent restenosis (≥50% diameter stenosis). Coronary bypass surgery was performed in 4 patients and repeated percutaneous transluminal coronary angioplasty in 56 patients; acute myocardial infarction (AMI) occurred in 2 patients, and 4 patients died during the follow-up. The overall incidence of MACE (death, AMI and revascularization) was 16.3% (66 patients). The best predictive accuracies and sensitivities/specificities of factors indicative of MACE were found for the minimal lumen diameter (MLD) at follow-up (predictive accuracy: 0.9305, sensitivity/specificity: 86.6%), the post-stent MLD (0.773, 77.2%), the percent diameter stenosis (%DS) at follow-up (0.9432, 87.1%), the prestent vessel angulation (0.6797, 68.2%) and the poststent changes in vessel angulation (0.6279, 62.2%). Multivariate nominal logistic regression analysis demonstrated that a poststent MLD ≤2.63 mm (p = 0.0017, odds ratio [OR] = 17.961, 95% confidence interval [CI] = 17.45–20.428), an MLD at follow-up ≤1.7 mm (p = 0.0059, OR = 11.880, 95% CI = 11.490–14.093), a %DS at follow-up ≥42.2% (p = 0.0000, OR = 49.553, 95% CI = 48.024–53.507), a prestent vessel angulation ≥33.5° (p = 0.0477, OR = 5.404, 95% CI = 5.382–7.142) and poststent changes in vessel angulation ≥9.1° (p = 0.0026, OR = 19.161, 95% CI = 18.562–21.750) were significant predictors for MACE. Multiple linear regression revealed that the poststent MLD (multivariate p = 0.0001), the MLD at follow-up (p = 0.0000), the prestent vessel angulation (p = 0.0431) and the changes in vessel angulation after stent implantation (p = 0.0316) were significant independent variables predicting angiographic stent restenosis severity.CONCLUSIONSThe longitudinal straightening effect of coronary artery stents contributes significantly to the occurrence of MACE and angiographic restenosis, and this finding may have an impact on future stent design.

Speckle tracking for multi-dimensional flow estimation

Speckle tracking methods overcome the major limitations of current Doppler methods for flow imaging and quantification: angle dependence and aliasing. In this paper, we review the development of speckle tracking, with particular attention to the advantages and limitations of two-dimensional algorithms that use a single transducer aperture. Ensemble tracking, a recent speckle tracking method based upon parallel receive processing, is described. Experimental results with ensemble tracking indicate the ability to measure laminar flow in a phantom at a beam–vessel angle of 60°, which had not been possible with previous 2D speckle tracking methods. Finally, important areas for future research in speckle tracking are briefly summarized.

Interobserver, interequipment and intersubject variability of echo-Doppler examination of the common carotid and vertebral arteries

Objective: We evaluated interobserver and interequipment variability in common carotid and vertebral flow measurements, using seven female members of nursing staff as subjects, four different ultrasound machines and three different radiologists as operators. Methods: The flow of the common carotid and vertebral arteries in each subject was examined at 0, 10, 20 and 30 min after lying down in a supine position. Peak velocity, end-diastolic velocity, mean velocity, systolic acceleration, cross-sectional area of the vessel, flow volume/min, resistance index and Doppler angle were measured. Results: A large proportion of the variance of peak velocity, cross-sectional area of the vessel and flow volume was patient-related. Significantly different values of end-diastolic velocity, mean velocity, resistance index, Doppler angle and systolic acceleration were obtained with different equipment. Significantly different values of systolic acceleration, vertebral peak velocity, common carotid artery flow and Doppler angle were obtained by different operators. However, part of the variability may be physiological due to the study protocol. Conclusion: The use of the same operator and equipment is recommended in follow-up examinations.

Beat-by-beat forearm blood flow with Doppler ultrasound and strain-gauge plethysmography

Simultaneous Doppler ultrasound estimates of brachial artery mean blood velocity (MBV) and venous occlusion strain-gauge plethysmography measures of forearm blood flow (FBF) were performed to determine the beat-by-beat relationship between the two methods and provide a method for flow calibration of Doppler MBV estimates. Such a calibration of Doppler MBV eliminates the need for knowledge of vessel cross-sectional area and angle of insonation while allowing for the quantification of limb blood flow. Six healthy subjects (5 men and 1 woman) performed 40 s of isometric forearm contraction at 35% maximal voluntary contraction with arterial inflow occluded. This resulted in elevated blood flow on relaxation and cuff deflation, and simultaneous beat-by-beat Doppler MBV and strain-gauge FBF measurements were then made over a period of 2-3 min as flow gradually decreased to resting levels. The r2 values for the fitted regression lines over a wide range of flows ranged from 0.87 to 0.98, and the mean square error terms ranged from 0.88 to 3.07 ml.100 ml-1.min-1. Significant day-to-day variation of the fitted regression parameters within subjects indicated that quantitative estimates of FBF from Doppler MBV require a calibration to be performed for each experiment. The finding of a strong linear relationship between Doppler MBV and venous occlusion strain-gauge plethysmography, as well as the marked beat-by-beat effect of cuff inflation on blood flow, confirms the importance of calibration on the same beats, not on adjacent segments of beats.

Simultaneous Measurements of Cerebral Circulation with Electromagnetic Flowmetry and Doppler Ultrasound Velocity in the Newborn Pig

Cerebral blood flow measurement has been an important investigative tool in newborns at risk for perinatal brain damage. The validity of Doppler cerebral blood flow velocity measurements depends on a constant vessel diameter. We have validated Doppler against the electromagnetic flowmeter (EM) using a modified common carotid artery model in the 1-d-old piglet. Two sets of continuous and simultaneous recordings were performed: 1) the Doppler and EM probe on the same common carotid artery (extracerebral branches were ligated), and 2) the EM probe on the common carotid artery and the Doppler probe recording from an intracerebral artery through an artificial fontanel. Arterial partial pressure of carbon dioxide (PaCO2) was manipulated (2.8-7.4 kPa), as was arterial blood pressure (3.7-9.3 kPa). Simultaneous EM flow and estimated Doppler flow were compared. Ninety-three recordings were obtained with both transducers on the modified carotid artery, and 49 were obtained with the Doppler insonicating an intracerebral artery. A multiple regression model was used for statistical analysis. The correlation between EM and both sets of Doppler measurements for individual animals was > 0.95 and was unaffected by changes in arterial blood pressure or PaCO2. Thus, the common carotid and the intracerebral artery investigated did not change their diameter significantly in response to PaCO2 or arterial blood pressure. The relationships between EM and Doppler in the individual animal were all linear but revealed great variability in the slopes due to the unknown vessel diameter and angle of insonication.(ABSTRACT TRUNCATED AT 250 WORDS)

A new approach to the noninvasive measurement of cardiac output using an annular array doppler technique—II. practical implementation and results

An experimental Doppler flowmeter system has been developed which can noninvasively measure blood flow volume rate in a vessel. It is based on the attenuation compensated technique and does not require knowledge of the vessel size or beam-vessel angle. In vitro results have shown that the measurement of volume flow rate is independent of vessel angle to within ±4%, and independent of vessel diameter to within ±5%. Flow rate linearity is better than ±3%. A good comparison has been obtained, in vivo, of aortic diameters measured by an imaging system and with this flowmeter; the r value was 0.98. The noninvasive measurement of cardiac output using this flowmeter has been compared with conventional dilution techniques in 54 patients, with a resulting correlation coefficient of r = 0.96.

Importance of stenosis morphology in the estimation of restenosis risk after elective percutaneous transluminal coronary angioplasty

To determine the importance of predilatation stenosis morphology on the risk of restenosis after percutaneous transluminal coronary angioplasty (PTCA), 500 procedures were randomly chosen for analysis from 3,839 consecutive successful PTCA procedures. Angiographic follow-up was available for 308 patients (62%) at a mean of 7.3 ± 3.4 months after PTCA. One dilated site was randomly chosen per procedure. One hundred and one sites had documented restenosis (≥50% mean diameter stenosis from multiple projections) by quantitative angiography (33% of all sites restudied and 20% of all sites dilated). Twenty-eight morphologic variables and 20 other angiographic, clinical and procedural variables were analyzed by an observer blinded to clinical outcome. Univariate analysis found post-PTCA percent stenosis >30% (p = 0.005), bend point location (p = 0.01), post-PTCA gradient > 15 mm Hg (p = 0.02), angina class III to IV (p = 0.03), age (p = 0.04) and the absence of dissection (p = 0.04) to predict restenosis. Multivariate analysis found only 2 significant (p < 0.05) independent predictors of restenosis: post-PTCA percent stenosis > 30% and bend point location. Restenosis occurred in 41% of lesions located at an end-diastolic vessel angle ≥45 ° compared with 28% in lesions on lesser bends. Thus, only 1 predilatation morphologic characteristic, stenosis location at a bend point, was an important independent predictor of restenosis, and should be considered when assessing patients for PTCA.

Effect of the Trendelenburg Position on the Distribution of Arterial Air Emboli in Dogs

We examined the effects of buoyancy on the distribution of arterial gas bubbles using in vitro and in vivo techniques in dogs. A simulated carotid artery preparation was used to determine the effects of bubble size and vessel angle on the velocity and direction of bubble movement in flowing blood. Because buoyancy tends to float bubbles away from dependent areas, bubble velocity would be expected to decrease as the vessel angle increased. We found that larger bubbles increased in velocity in the same direction as the blood flow at 0-, 10-, and 30-degree vessel angles and decreased when the vessel was positioned at 90 degrees. Smaller bubbles did not change velocity from 0 to 30 degrees and increased in velocity in the same direction as blood flow at 90 degrees. In 10 anesthetized dogs, we studied the effects of 0-, 10-, 15-, and 30-degree Trendelenburg's position on carotid artery distribution of gas bubbles injected into the left ventricle or ascending aorta. Regardless of the degree of the Trendelenburg position, the bubbles passed into the carotid artery simultaneously with passage into the abdominal aorta. We conclude that the forces of buoyancy do not overcome the force of arterial blood flow and that the Trendelenburg position does not prevent arterial bubbles from reaching the brain.

Distribution of the geometric parameters of human aortic bifurcations: Bargeron CB, Hutchins GM, Moore GW, et al. Arteriosclerosis 1986;6:109–113

Careful measurements of 42 female and 28 male human aortas and their bifurcations were made. These included the angle of the axis of each iliac artery to the axis of the aorta; the branch angle, defined as the sum of the angles of the iliac vessels; the angular asymmetry, defined as the difference between the angles of the iliac vessels; and the amount of offset of the flow divider from the axis of the aorta. The arteries were obtained at autopsy and perfused with a 4% formaldehyde solution for 2 or 3 days with a hydrostatic pressure equivalent to the blood pressure recorded during life. After fixation, the vessels were filled with contrast medium and frontal plane radiographs were obtained. These radiographs were then used to digitize the configuration in two dimensions and the measurements described above were made. The mean values with standard deviations and ranges were (1) magnitude of flow divider offset = 1.4 ± 1.4 mm (range 0.04 to 8.1 mm); (2) branch angle = 35.0 ± 11.1 degrees (range 10.4 to 61.3 degrees); and (3) angular asymmetry = 15.3 ± 12.9 degrees (range 0.2 to 56.1 degrees). The male aortas had a statistically significant greater magnitude of offset and of angular asymmetry. The authors had previously noted a negative correlation between interfascial shear rate and intimal thickening; as a consequence they were interested in defining the range of relationships of the iliac arteries to the aorta. In this article, the authors did not report the degree of intimal thickening and offered no clues as to which anatomic configurations seemed to correlate with its presence or absence. Instead, their goal was to emphasize the concept of flow divider offset and angular asymmetry and to call attention to their variability as well as to establish mean values and ranges for these as well as for the branch angles.

A Doppler flowmeter for use in theatre

We have developed a Doppler flowmeter based on a 10 MHz pencil probe and mean frequency estimator which overcomes many of the limitations of existing electromagnetic and ultrasonic flowmeters. The output of the flowmeter, which is proportional to the first moment of the Doppler power spectrum and hence mean blood velocity is linear from 1.3 to over 50 cm s −1 for pulsatile flow. Variation in vessel diameter and angle of insonation, which are the common sources of error in Doppler flowmetry, are minimised by constraining the vessel in a plastic cuff which fixes the probe angle at 50°. A simple gauge is used to compress the vessel flat, before the cuff is applied, to measure the wall thickness to within 0.25 mm. The vessel internal diameter and hence blood flow can then be calculated using an experimentally determined calibration factor to compensate for non-even insonation. A range of sterilizable cuffs from 3–12 mm diameter have been built and the flowmeter is now being used routinely during all arterial reconstructive surgery. The accuracy and reproducibility of the system was tested for range of different sized silastic tubes on a hydraulic model and found to be <12% for vessels >2 mm internal diameter. Satisfactory signals were easily obtained from all prosthetic materials with the exception of PTFE. The instantaneous output was compared to an electromagnetic flowmeter using a fast Fourier transform algorithm; the moduli of the harmonics were virtually identical but the Doppler system produced a smaller phase shift with increasing harmonics. The Doppler flowmeter is easy to use because no electrical contact with the vessel or zeroing is required and there is no variation in sensitivity with different wall compositions or thicknesses. It can also be used on plastic tubing and is relatively inexpensive because only one transducer is required.

In vitro comparison of alternative methods for quantifying the severity of doppler spectral broadening for the diagnosis of carotid arterial occlusive disease

Quantitative analysis of continuous wave Doppler recordings is of clinical value in the noninvasive diagnosis of carotid arterial disease. Peak frequency measurements are useful and accurately detect severe stenoses but do not reliably diagnose minor or moderate stenoses because the measurement is dependent upon the probe to vessel angle, which cannot be measured accurately. Recent investigations have focused on efforts to overcome this limitation by quantifying the degree of spectral broadening that occurs as the result of flow disturbances downstream from a stenosis. In this study, an in vitro model was used to determine the optimum method for quantifying the instantaneous Doppler spectrum. The model generates blood flow velocity waveforms that are virtually identical to those found in the human internal carotid artery. Doppler recordings were made from normal tubes and distal to stenoses (39–87% cross-sectional area reduction). The spectra were quantified by the following angle-independent measurements: spectral broadening index and three standard statistical shape descriptors, namely the coefficients of variation, skewedness and kurtosis. Using this model, the results demonstrate an excellent relationship between the severity of the stenosis and each of spectral broadening index ( r = 0.99), coefficient of variation ( r = 0.96), and coefficient of skewedness ( r = 0.99). The calculation of each of the measurements can be implemented quite easily, and a prospective trial is warranted to evaluate their clinical diagnostic accuracy.

The role of shear forces in arterial branching.

A new optimality principle for the branching angles of blood vessels in the cardiovascular system is proposed: the principle of minimum drag. The results are examined in the light of general observations and compared with those obtained from the principles of minimum work and minimum volume. It is shown that in some aspects the new principle is equally consistent with observations, and, in other aspects, it is perhaps more plausible than the other two principles.