Vessel Depths Research Articles

Mapping the human parafoveal vascular network to understand flow variability in capillaries.

Capillary flow is known to be non-homogenous between vessels and variable over time, for reasons that are poorly understood. The local properties of individual vessels have been shown to have limited explanatory power in this regard. This exploratory study investigates the association of network-level properties such as vessel depth, branch order, and distance from the feeding arteriole with capillary flow. Detailed network connectivity analysis was undertaken in 3 healthy young subjects using flood-illuminated adaptive optics retinal imaging, with axial depth of vessels determined via optical coherence tomography angiography. Forty-one out of 70 vessels studied were of terminal capillary type, i.e. fed from an arterial junction and drained by a venous junction. Approximately half of vessel junctions were amenable to fitting with a model of relative branch diameters, with only a few adhering to Murray's Law. A key parameter of the model (the junction exponent) was found to be inversely related to the average velocity (r = -0.59, p = 0.015) and trough velocity (r = -0.67, p = 0.004) in downstream vessels. Aspects of cellular flow, such as the minimum velocity, were also moderately correlated (r = 0.46, p = 0.009) with distance to the upstream feeding arteriole. Overall, this study shows that capillary network topology contributes significantly to the flow variability in retinal capillaries in human eyes. Understanding the heterogeneity in capillary flow is an important first step before pathological flow states can be properly understood. These results show that flow within capillary vessels is not affected by vessel depths but significantly influenced by the upstream feeder distance as well as the downstream vessel junction exponents, but there remains much to be uncovered regarding healthy capillary flow.

Veins Depth Estimation Using Diffused Reflectance Parameter

In order to perform the standard Intravenous (IV) catheterization, subcutaneous veins must be localized. It is a difficult task, especially in the cases when veins are hard to localize. The factors which affect the veins localization process are the physiological characteristics of patients, mainly darker skin tone, scars, hair, dehydration and low blood pressure. With the help of Near Infrared imaging, subcutaneous veins can be envisioned. This is due to the higher absorption of NIR light energy by Hemoglobin (Hb) found in the veins. Besides a superficial view, the veins depth information is also important in order to avoid their rupture by piercing through the walls during IV catheterization process. Diffused reflectance, measured with a camera sensor, can be used for the depth estimation of blood vessels. In this paper, a method to measure the depth of veins using diffused reflectance parameter, is presented. The well-known Monte Carlo model of light propagation in human tissues is used for the mathematical representation. A four-layered skin model is presented with varying vessel depths to describe the diffused reflectance of light while propagating inside skin tissues. The results are validated with Monte Carlo simulations for light propagation in layered medium. A sensitivity analysis of proposed method is also performed with a 5% alteration in the optical parameters of skin due to the change in operating conditions. The results showed a marginal error of maximum value 6.23% in vessel depth estimation using the standard optical parameters, 1.6% for −5% and 10.74% for +5% change in optical parameters.

Adaptive transverse blood velocity estimation in medical ultrasound: A simulation study

Undoubtedly, highly valuable information about vascular anomalies is attained by the examination of the blood flow profile. The chief drawback of the conventional medical ultrasound in preparation of the blood periodogram is the measurement system shortcoming at the beam to flow angles near 90°. Recently, a method based on transverse oscillation (TO) approach, known as “Fourth-order estimation”, has been developed to directly estimate the transverse power spectral density (PSD) of the fully transverse blood flow. One of the basic requirements to accomplish acceptable PSDs by this technique is the sufficiently large observation window. In this paper, two adaptive approaches for efficient estimation of the velocity spectrum of a fully transverse flow by a limited observation window length are described. The first proposed adaptive approach is based on the minimum variance adaptive spectral estimation in combination with the well-known TO technique (TO-MV). Then, by exploiting the eigenspace separation of the observed data to eliminate the contribution of the undesired components, the second technique (TO-EIBMV) is developed. The approaches are validated using Field II simulations for pulsating flow. The proposed methods are tested and compared to the conventional TO transverse spectral estimator by metrics of relative standard deviation (RSD) and relative bias (RB). One of the main achievements is the decrement of the required data samples for spectrogram estimation, which leads to a better temporal resolution. Moreover, for the analyzed adaptive techniques, the robustness of the estimation results for the beam to flow angles of 60–90° and vessel depths ranging from 20 mm to 60 mm are investigated.

Investigating the influence of blood-vessel depth and sensor location on the light-tissue interactions using a Monte Carlo model

A three-dimensional Monte Carlo model of light tissue interactions with a slab of fat tissue having a cylindrical blood vessel is presented. The model has been explored at an optical wavelength of 660 nm and simulations have been carried out to investigate the influence of – 1) vessel depths and b) sensor location on the associated light-tissue interactions. Such investigation will be immensely useful to design a wearable sensing technology and predicting the sensor outcomes.

Investigation of Intrinsic Spectral Broadening on the Aixplorer ultrafast ultrasound system

For Doppler velocity measurements, Intrinsic Spectral Broadening (ISB) is a broadening of the Doppler spectrum due to the finite spacing between the transducer elements, leading to a range of insonation angles. This effect leads to overestimation in velocity and a decrease in quantification precision. There have been limited attempts to quantify the Intrinsic Spectral Broadening (ISB) of the Aixplorer system under a wide range of imaging conditions. This could be of clinical relevance as it remains unclear whether ultrafast Doppler suffers from the same degree of imprecision as conventional Doppler imaging. In this work, the Aixplorer system ISB was measured using a Doppler string phantom for a range of velocities (10–200 cm/s) and vessel depths (1–4 cm). The results of this analysis showed that, for all depths, the ISB could be modelled using a power law fit with respect to velocity, with a percentage ISB in the range of 3–10 ± 2%. With respect to depth, the ISB did not appear to change significantly, with a percentage ISB in the range of 3–4 ± 2% measured. When utilising ultrafast acquisitions, the percentage ISB was 0.44–0.63 ± 0.07%, affecting an ISB reduction of a factor of 6.5 ± 0.3. These results indicate that the velocity dependence of ISB is strong, with low velocities suffering a high degree of overestimation. Despite the expected result of a strong dependence of ISB on depth, none was observed. Finally, by utilising ultrafast acquisitions, the percentage of ISB can be dramatically reduced.

Ultra Long versus Standard Long Peripheral Intravenous Catheters: A Randomized Controlled Trial of Ultrasound-Guided Catheter Survival

Background: Ultrasound-guided intravenous (US-IV) peripheral catheters have dismal dwell time with most IVs failing prior to completion of therapy. Catheter length in vein is a variable directly related to catheter longevity. We investigate the survival of an ultra long (UL) US-IV compared to a standard long (SL) US-IV. Methods: We conducted a single site, 2-arm, nonblinded, randomized controlled trial of catheter survival. Adult patients presenting to the Emergency Department (ED) with difficult vascular access were recruited and randomized to receive either SL 4.78 cm 20 gauge US-IV or UL 6.35 cm 20 gauge US-IV. The primary outcome was catheter survival. Functional catheters removed with less than 24 hours dwell time were excluded per protocol analysis. Secondary outcomes included: first-stick success, time to insertion, number of attempts, thrombosis and infection. Findings: 270 patients were enrolled between October 2018 and March 2019.194 patients met study criteria, with 99 in the SL US-IV group and 95 in the UL US-IV group. Kaplan-Meier estimate of catheter median survival time was 135.88 hours (5.66 days) [95%CI 115-310] for the UL US-IVs compared to 77.67 hours (3.23 days) [95%CI 63-102] for the SL US-IVs(p = 0.008). IVs with greater than 2.75 cm of the catheter situated in the vein lumen had a median survival of 128.90 hours (5.37 days) [95%CI 102-210] compared to 75.05 hours (3.12days) [95%CI 52-116] for IVs with ≤ 2.75 cm in the vein(p=0.006). There were no cases of catheter-related bloodstream infection or thrombosis. Interpretation: This study demonstrates increased catheter survival when >2.75 cm is situated in the vessel. UL US-IV catheters facilitate establishing this cutoff length at commonly encountered vessel depths. Further, as UL catheters have similar insertion characteristics and no additional education/training is needed for insertion competency, adoption of these catheters can occur seamlessly. Trial Registration: The trial is registered on clinicaltrials.gov Identifier: NCT03655106 and is closed to recruitment. Funding Statement: B. Braun Medical, Inc. Declaration of Interests: Dr. Bahl reports grants from B Braun Medical, Inc, during the conduct of the study. All other authors declare none. Ethics Approval Statement: The study was approved by the home institution Internal Review Board.

Directional Transverse Oscillation Vector Flow Estimation.

A method for estimating vector velocities using transverse oscillation (TO) combined with directional beamforming is presented. In directional TO (DTO), a normal focused field is emitted and the received signals are beamformed in the lateral direction transverse to the ultrasound beam to increase the amount of data for vector velocity estimation. The approach is self-calibrating as the lateral oscillation period is estimated from the directional signal through a Fourier transform to yield quantitative velocity results over a large range of depths. The approach was extensively simulated using Field IIpro and implemented on the experimental Synthetic Aperture Real-time Ultrasound System (SARUS) scanner in connection with a BK Medical 8820e convex array transducer. Velocity estimates for DTO are found for beam-to-flow angles of 60°, 75°, and 90°, and vessel depths from 24 to 156 mm. Using 16 emissions, the standard deviation (SD) for angle estimation at depths ranging from 24 to 104 mm is between 6.01° and 0.93° with a mean SD of 2.8°. The mean relative SD for the lateral velocity component is 9.2% and the mean relative bias -3.4% or four times lower than for traditional TO. The approach also works for deeper lying vessels with a slight increase in SD to 15.7%, but a maintained bias of -3.5% from 126 to 156 mm. Data for a pulsating flow have also been acquired for 15 cardiac cycles using a CompuFlow 1000 pump. The relative SD was here 7.4% for a femoral artery waveform.

Validation of Endoscopic Ultrasound Measured Flow Rate in the Azygos Vein Using a Flow Phantom

Increase in flow rate within the azygos vein may be used as an indicator of the degree of liver cirrhosis. The aim of this study was to evaluate the error in measurement of flow rate using a commercial endoscopic ultrasound system, using a flow phantom that mimicked azygos vein depth, diameter and flow rate. Diameter was underestimated in all cases, with an average underestimation of 0.09 cm. Maximum velocity was overestimated, by 4 ± 4% at 50°, 11 ± 3% at 60° and 23 ± 7% at 70°. The increase in error with beam-vessel angle is consistent with the error as arising from geometric spectral broadening. Flow was underestimated by amounts up to 33%, and it is noted that the overestimation caused by geometric spectral broadening is in part compensated by underestimation of diameter. It was concluded that measurement of flow rate using a commercially available endoscopic ultrasound system is dependent on the beam-vessel angle, with errors up to 33% for typical vessel depths, diameter and beam-vessel angle. (E-mail: P.Hoskins@ed.ac.uk)

3D coronary motion tracking in swine models with MR tracking catheters

To develop MR-tracked catheters to delineate the three-dimensional motion of coronary arteries at high spatial and temporal resolution. Catheters with three tracking microcoils were placed into nine swine. During breath-holds, electrocardiographic (ECG)-synchronized 3D motion was measured at varying vessel depths. 3D motion was measured in American Heart Association left anterior descending (LAD) segments 6-7, left circumflex (LCX) segments 11-15, and right coronary artery (RCA) segments 2-3, at 60-115 beats/min heart rates. Similar-length cardiac cycles were averaged. Intercoil cross-correlation identified early systolic phase (ES) and determined segment motion delay. Translational and rotational motion, as a function of cardiac phase, is shown, with directionality and amplitude varying along the vessel length. Rotation (peak-to-peak solid-angle RCA approximately 0.10, LAD approximately 0.06, LCX approximately 0.18 radian) occurs primarily during fast translational motion and increases distally. LCX displacement increases with heart rate by 18%. Phantom simulations of motion effects on high-resolution images, using RCA results, show artifacts due to translation and rotation. Magnetic resonance imaging (MRI) tracking catheters quantify motion at 20 fps and 1 mm(3) resolution at multiple vessel depths, exceeding that available with other techniques. Imaging artifacts due to rotation are demonstrated. Motion-tracking catheters may provide physiological information during interventions and improve imaging spatial resolution.

Thermal depth profiling of vascular lesions: automated regularization of reconstruction algorithms

Pulsed photo-thermal radiometry (PPTR) is a non-invasive, non-contact diagnostic technique used to locate cutaneous chromophores such as melanin (epidermis) and hemoglobin (vascular structures). Clinical utility of PPTR is limited because it typically requires trained user intervention to regularize the inversion solution. Herein, the feasibility of automated regularization was studied. A second objective of this study was to depart from modeling port wine stain PWS, a vascular skin lesion frequently studied with PPTR, as strictly layered structures since this may influence conclusions regarding PPTR reconstruction quality. Average blood vessel depths, diameters and densities derived from histology of 30 PWS patients were used to generate 15 randomized lesion geometries for which we simulated PPTR signals. Reconstruction accuracy for subjective regularization was compared with that for automated regularization methods. The objective regularization approach performed better. However, the average difference was much smaller than the variation between the 15 simulated profiles. Reconstruction quality depended more on the actual profile to be reconstructed than on the reconstruction algorithm or regularization method. Similar, or better, accuracy reconstructions can be achieved with an automated regularization procedure which enhances prospects for user friendly implementation of PPTR to optimize laser therapy on an individual patient basis.

Accuracy of internal mammary lymph node localization using lymphoscintigraphy, sonography and CT

Background and purpose: An accurate internal mammary (IM) lymph node localization technique is required for proper irradiation of the IM lymph nodes in breast cancer patients. In this study the measurement accuracy of three techniques for direct or indirect localization of the IM nodes was estimated. Materials and methods: In 40 patients the IM lymph node depth and lateral distance from the patient midline were measured with lymphoscintigraphy in intercostal spaces 2, 3 and 4. The corresponding position of an IM vessel was measured with sonography and CT in intercostal spaces 1–4. The sonography and CT vessel measurements in the four intercostal spaces were compared to determine the measurement accuracy of sonography. The node and vessel data in intercostal space 2 were inserted into a mathematical model to determine the measurement accuracy of lymphoscintigraphy and CT for node detection. Results: Vessel depths measured by sonography were systematically too shallow and the lateral vessel position could not be accurately determined. The mathematical model showed that the node depth and lateralization in one intercostal space can be measured directly by lymphoscintigraphy within an accuracy (1 SD) of 5 mm in depth and 6 mm in the lateral direction. The accuracy of CT for indirect node detection was 6 mm in depth and 7 mm in the lateral direction. Conclusions: Sonography is not a suitable technique for measuring the IM vessel or node position. Lymphoscintigraphy and CT have measurement accuracies for node detection that are acceptable for radiotherapy.

Optical Doppler velocimetry at various retinal vessel depths by variation of the source coherence length

We report on what we believe is a novel approach to measuring the velocity of red blood cells (RBC's) at different depths of retinal vessels by use of low-coherence sources. The technique, variable coherence optical Doppler velocimetry (VCODV), performs Doppler shift measurements through autodyne mixing between the light scattered by the RBC's and by the vessel front wall (reference). Only the light from RBC's moving at a depth less than half the coherence length (CL) mixes efficiently with the reference. Measurements of the Doppler shifts from RBC's with sources of four different CL's in a 152-microm vein of a volunteer confirmed the feasibility of VCODV. This approach has the potential to monitor in vivo retinal RBC velocity gradient at the vessel wall and the velocity profile within the blood vessel in the condition of symmetric blood flow profiles.

Optical low-coherence reflectometry to enhance monte Carlo modeling of skin

Optical low-coherence reflectometry and confocal microscopy images were taken of the rat dorsal skin flap window model. Blood vessel depths and diameters measured with the two techniques, and preparation thickness determined from reflectometry images, are in reasonable agreement with measurements from histologic sections. Blood vessels appear as areas of low signal when constant-depth reflectometry images are taken at a depth near the center of a vessel, whereas they appear bright when taken close to the blood–dermis boundary. Doppler shift plus increased light absorption in blood, and the blood–dermis index of refraction mismatch, are discussed as possible causes of the dark- and bright-appearing vessels, respectively. One reflectometry image was used to generate an input grid for a novel Monte Carlo analysis program that is capable of determining the light distribution and heat generation @J/m3# within complex blood vessel geometries. The feasibility of imaging skin blood vessel accurately with optical low-coherence tomography, and using the acquired knowledge of blood vessels structure to create more realistic Monte Carlo analyses is demonstrated by the results of the study.

Femoral vessel depth and the implications for groin node radiation

Purpose : To quantify, based on pretreatment computer tomographic measurements, potential groin node depths, which will aid in optimal treatment planning for patients requiring groin node radiation. Methods and Materials : The pretreatment computer tomographic scans of 50 gynecologic cancer patients were reviewed to determine the distance of each femoral vessel beneath the overlying skin surface, as an indicator of potential groin node depth. Correlative data regarding height and weight were obtained from patient medical records, and were used to calculate the Quetelet index, defined as (weight in kg)/(height in m)2. Treatment parameters of 5 patients who failed prophylactic groin radiation in a recently published study were assessed to determine if underdosage represented a possible cause of failure. Results : Individual femoral vessel depths ranged from 2.0 to 18.5 cm. When the depths of all four femoral vessels were averaged in each patient, the mean “4-vessel average” depth for this patient population was 6.1 cm. The median Quetelet index for the group was 25.6, and there was a strong correlation between femoral vessel depth and patient Quetelet index. Recalculation of doses provided to the 5 patients failing prophylactic groin radiation in the Gynecologic Oncology Group study showed that all had received potential tumor doses < 4700 cGy, with 3 patients being underdosed by >30%. Conclusion : While surgery is often indicated in the management of patients with potential groin node metastases, the role of prophylactic groin radiation should not be rejected. Data from this study may aid in the optimal design and implementation of groin node radiotherapy.