Assessment of volume flow rate in arteriovenous fistulas with a novel ultrasound Doppler device (earlybird): Trend analysis, comparison of methods, and inter- and intra-rater reliability.

BACKGROUND: An accessible tool is required to analyze volume flow trends in arteriovenous fistulas for hemodialysis. Earlybird, an easy-to-place ultrasound Doppler device, has shown comparable accuracy to duplex ultrasound. In this study, we compared volume flow measurements obtained with duplex ultrasound and the dilution technique to an enhanced earlybird device, featuring a dual Doppler probe system, eliminating the requirement for a known insonation angle. METHODS: Nine patients with a distal radiocephalic arteriovenous fistula were monitored for 12 months with regular volume flow measurements. Correlation and inter- and intra-class reliability analyses were conducted. RESULTS: An overall moderate correlation was observed between earlybird and duplex ultrasound or dilution technique (intraclass correlation coefficient = 0.606 (95% confidence interval 0.064, 0.721) and 0.581 (0.039, 0.739), respectively). Duplex ultrasound compared to dilution measurements, demonstrated an overall moderate correlation (0.725 (0.219, 0.843)). Correlation between earlybird and duplex ultrasound was stronger for the arteriovenous fistula (0.778 (0.016, 0.901)) than the brachial artery (0.381 (-0.062, 0.461)). For earlybird, inter-rater reliability was excellent for the arteriovenous fistula (0.907 (0.423, 0.930)) and poor for the brachial artery (0.430 (0.241, 0.716)). Duplex ultrasound showed a good inter-rater reliability (arteriovenous fistula: 0.843 (0.610, 0.871), brachial artery: 0.819 (0.477, 0.864)). The overall intra-rater reliability was good for duplex ultrasound (rater A: 0.893 (0.727, 0.911); rater B: 0.853 (0.710, 0.891)), while excellent for earlybird (rater A: 0.905 (0.819, 0.928); rater B: 0.921 (0.632, 0.969)). CONCLUSION: We observed a weaker correlation in the measurements of volume flow rates in arteriovenous fistulas when obtained using earlybird compared to dilution technique, unlike the comparison between duplex ultrasound and the dilution technique. However, inter-rater reliability for the arteriovenous fistula was excellent with earlybird and good with duplex ultrasound, indicating the potential of earlybird as a tool for frequent measurements, enabling trend surveillance and predicting adverse outcomes.

Combining Automatic Angle Correction and 3-D Tracking Doppler for the Assessment of Aortic Stenosis Severity.

Aortic valve stenosis (AS) is a narrowing of the aortic valve opening, which causes increased load on the left ventricle. Untreated, this condition can eventually lead to heart failure and death. According to current recommendations, an accurate diagnosis of AS mandates the use of multiple acoustic windows to determine the highest velocity. Furthermore, the optimal positioning of both patient and transducer to reduce the beam-to-flow angle is emphasized. Being operator dependent, the beam alignment is a potential source of uncertainty. In this work, we perform noncompounded 3-D plane wave imaging for retrospective estimation of maximum velocities in aortic jets with automatic angle correction. This is achieved by combining a hybrid 3-D speckle tracking method to estimate the jet direction and 3-D tracking Doppler to generate angle-corrected sonograms, using the direction from speckle tracking as input. Results from simulations of flow through an orifice show that 3-D speckle tracking can estimate the jet orientation with acceptable accuracy for signal-to-noise ratios above 10 dB. Results from 12 subjects show that sonograms recorded from a standard apical view using the proposed method yield a maximum velocity that matches continuous wave (CW) Doppler sonograms recorded from the acoustic window with the lowest angle within a ±10% margin, provided that a high enough pulse repetition frequency could be achieved. These results motivate further validation and optimization studies.

Realtime Automatic Assessment of Cardiac Function in Echocardiography.

Assessment of cardiac function by echocardiography is challenging for nonexperts. In a patient with dyspnea, quantification of the mitral annular excursion (MAE) and velocities is important for the diagnosis of heart failure. The displacement of the atrioventricular (AV) plane is a good indicator of systolic left ventricular function, while the peak velocities give supplementary information about the systolic and diastolic function. By measuring these parameters automatically, a preliminary diagnosis can be given by the nonexpert. We propose an automatic algorithm to localize the mitral annular points in an apical four-chamber view and estimate the MAE, as well as the systolic, early diastolic, and late diastolic tissue peak velocities, by using a deformable ventricle model for orientation and tissue Doppler data for tracking. Automatic parameter estimates from 367 tissue Doppler recordings were compared to reference measurements by experienced cardiologists to assess the accuracy of the estimation, as well as the ability to correctly detect reduced MAE, which we defined as less than 10 mm. The dataset consisted of 200 recordings from a patient population and 167 healthy from a population study. When considering the average of the septal and lateral values, the estimation error for the MAE had a standard deviation of 2.1 mm, which was reduced to 1.9 mm when excluding recordings for which the automatic segmentation failed to locate the AV plane (41 recordings). The corresponding standard deviations for the peak velocities were around 1 cm/s. The classification of MAE was correct in 90% of the cases and had a sensitivity of 83% and a specificity of 92%. We conclude that the algorithm has good accuracy and note that the estimation error for the MAE was comparable to interobserver and methodology agreements reported in the literature.

Assessment of left ventricular function by GPs using pocket-sized ultrasound.

BACKGROUND: Assessment of left ventricular (LV) function with echocardiography is mandatory in patients with suspected heart failure (HF). OBJECTIVES: To investigate if GPs were able to evaluate the LV function in patients at risk of developing or with established HF by using pocket-sized ultrasound (pUS). METHODS: Feasibility study in general practice, seven GPs in three different Norwegian primary care centres participated. Ninety-two patients with reduced or at risk of developing reduced LV function were examined by their own GP using pUS. The scan (<5 minute) was done as part of a routine appointment. A cardiologist examined the patients <30 minutes afterwards with both a laptop scanner and pUS. Measurements of the septal mitral annular excursion (sMAE) were compared. RESULTS: In 87% of the patients, the GPs were able to obtain a standard view and measure the sMAE. There was a non-significant mean difference in sMAE between GP pUS and cardiologist laptop scanner of -0.15 mm 95% confidence interval (-0.60 to 0.30) mm. A comparison of the pUS recordings and measurements of sMAE made by GP versus cardiologist revealed a non-significant mean difference with acceptable 95% limits of agreement (-0.26 ± 3.02 mm). CONCLUSIONS: With tailored training, GPs were able to assess LV function with sMAE and pUS. pUS, as a supplement to the physical examination, may become an important tool in general practice.

Comparison of a new methodology for the assessment of 3D myocardial strain from volumetric ultrasound with 2D speckle tracking.

An alternative approach to extract 3D myocardial strain based on elastic registration of the ultrasound images (3DSE) was developed by our lab. The aim of the present study was to test its clinical performance by comparing strain values obtained by 3DSE with the ones obtained with 2D speckle tracking (2DST). Standard 2D B-mode and volumetric datasets were acquired in 12 patients with coronary heart disease (CHD) and in 12 control subjects. Longitudinal (ε(LL)), circumferential (ε(CC)) and radial (ε(RR)) strain values were obtained from 2D datasets using commercially available 2DST software and from volumetric datasets using the 3DSE approach. 3DSE provided lower strain values than 2DST. With both approaches global ε(LL) and ε(CC) were significantly lower in patients with CHD than in controls. Global ε(LL) and ε(CC) correlated well between both methods (R = 0.83, R = 0.86, respectively), while segmental correlations were moderate [R = 0.63 (ε(LL)), R = 0.41 (ε(CC))]. The highest differences in ε(LL) values obtained by the two methods and the highest number of erroneous ε(LL) with 3DSE were observed in the basal LV segments. This study shows that in real-life datasets our 3DSE method provides global and regional ε(LL) and ε(CC) values that are comparable with the ones obtained from 2DST, even though they are not interchangeable with each other. As only a single acquisition is required, 3D methods may offer advantages over the current 2D techniques. However, the accuracy of the 3DSE can still be improved by solving the problems that appear with deformation estimation in the basal segments.

Blood flow imaging: an angle-independent ultrasound modality for intraoperative assessment of flow dynamics in neurovascular surgery.

OBJECTIVE: The objective of this study was to investigate the clinical applicability of navigated blood flow imaging (BFI) in neurovascular applications. BFI is a new 2-dimensional ultrasound modality that offers angle-independent visualization of flow. When integrated with 3-dimensional (3D) navigation technology, BFI can be considered as a first step toward the ideal tool for surgical needs: a real-time, high-resolution, 3D visualization that properly portrays both vessel geometry and flow direction. METHODS: A 3D model of the vascular tree was extracted from preoperative magnetic resonance angiographic data and used as a reference for intraoperative any-plane guided ultrasound acquisitions. A high-end ultrasound scanner was interconnected, and synchronized recordings of BFI and 3D navigation scenes were acquired. The potential of BFI as an intraoperative tool for flow visualization was evaluated in 3 cerebral aneurysms and 3 arteriovenous malformations. RESULTS: The neurovascular flow direction was properly visualized in all cases using BFI. Navigation technology allowed for identification of the vessels of interest, despite the presence of brain shift. The surgeon found BFI to be very intuitive compared with conventional color Doppler methods. BFI allowed for quality control of sufficient flow in all distal arteries during aneurysm surgery and made it easier to discern between feeding arteries and draining veins during surgery for arteriovenous malformations. CONCLUSION: BFI seems to be a promising modality for neurovascular flow visualization that may provide the neurosurgeon with a valuable tool for safer surgical interventions. However, further work is needed to establish the clinical usefulness of the proposed imaging setup.

Assessment of numerical simulation strategies for ultrasonic color blood flow imaging, based on a computer and experimental model of the carotid artery.

Ultrasonic Doppler techniques are well established and allow qualitative and quantitative flow analysis. However, due to inherent limitations of the imaging process, the actual flow dynamics and the ultrasound (US) image do not always correspond. To investigate the performance of ultrasonic flow imaging methods, computational fluid dynamics (CFD) can play an important role. CFD simulations can be directly processed to mimic ultrasonic images or can be further coupled to ultrasound simulation models. We studied both approaches in the clinically relevant setting of a carotid artery using color flow images (CFI). The first order approach consisted of producing ultrasound images by color-coding CFD-simulations. For the second order approach, CFI was simulated using an ultrasound simulator, which models blood as a collection of point scatterers moving according to the CFD velocity fields. Color flow images were also measured in an experimental setup of the same carotid geometry for comparison. Results showed that during dynamic stages of the cardiac cycle, realistic ultrasound data can only be achieved when incorporating both the dynamic image formation and the measurement statistics into the simulations.

3-D speckle tracking for assessment of regional left ventricular function.

Speckle tracking in 2-D ultrasound images has become an established tool for assessment of left ventricular function. The recent development of ultrasound systems with capability to acquire real-time full volume data of the left ventricle makes it possible to perform speckle tracking in three dimensions, and thereby track the real motion of the myocardium. This paper presents a method for assessing local strain and rotation from 3-D speckle tracking in apical full-volume datasets. The method has been tested on simulated ultrasound data based on a computer model of the left ventricle, and on patients with myocardial infarction. When applied on simulated ultrasound data, the method showed good agreement with strain and rotation traces calculated from the reference motion, and the method was able to capture segmental differences in the deformation pattern, although the magnitudes of strains were systematically lower than the reference strains. When applied on patients, the method demonstrated reduced strain in the infarcted areas. Bulls-eye plots of regional strains showed good correspondence with wall motion scoring based on 2-D apical images, although the dyskinetic and hypokinetic regions were not apparent in all strain components.

New noninvasive method for assessment of left ventricular rotation: speckle tracking echocardiography.

BACKGROUND: Left ventricular (LV) torsion is due to oppositely directed apical and basal rotation and has been proposed as a sensitive marker of LV function. In the present study, we introduce and validate speckle tracking echocardiography (STE) as a method for assessment of LV rotation and torsion. METHODS AND RESULTS: Apical and basal rotation by STE was measured from short-axis images by automatic frame-to-frame tracking of gray-scale speckle patterns. Rotation was calculated as the average angular displacement of 9 regions relative to the center of a best-fit circle through the same regions. As reference methods we used sonomicrometry in anesthetized dogs during baseline, dobutamine infusion, and apical ischemia, and magnetic resonance imaging (MRI) tagging in healthy humans. In dogs, the mean peak apical rotation was -3.7+/-1.2 degrees (+/-SD) and -4.1+/-1.2 degrees, and basal rotation was 1.9+/-1.5 degrees and 2.0+/-1.2 degrees by sonomicrometry and STE, respectively. Rotations by both methods increased (P<0.001) during dobutamine infusion. Apical rotation by both methods decreased during left anterior descending coronary artery occlusion (P<0.007), whereas basal rotation was unchanged. In healthy humans, apical rotation was -11.6+/-3.8 degrees and -10.9+/-3.3 degrees, and basal rotation was 4.8+/-1.7 degrees and 4.6+/-1.3 degrees by MRI tagging and STE, respectively. Torsion measurement by STE showed good correlation and agreement with sonomicrometry (r=0.94, P<0.001) and MRI (r=0.85, P<0.001). CONCLUSIONS: The present study demonstrates that regional LV rotation and torsion can be measured accurately by STE, suggesting a new echocardiographic approach for quantification of LV systolic function.

Intraoperative color Doppler ultrasound assessment of LIMA-to-LAD anastomoses in off-pump coronary artery bypass grafting.

BACKGROUND: Although techniques for off-pump coronary artery bypass grafting (CABG) are continually being refined, angiographic follow-up studies have indicated a higher rate of anastomoses-related stenoses than expected after traditional on-pump CABG. This study was performed to evaluate the use of intraoperative epicardial color Doppler ultrasound to quality-assess left internal mammary artery (LIMA) to left anterior descending coronary artery (LAD) anastomoses performed on the beating heart. METHODS: Twenty-four LIMA-to-LAD anastomoses were evaluated with real-time epicardial ultrasound imaging using an ultrasound transducer positioned between the paddles of the stabilizer during off-pump procedures. The length of the anastomosis (D(A)), diameters of LIMA (D(M)), LAD at the toe of the anastomosis (D1), and 5 mm distally to the anastomosis (D2) were measured, and the ratios between these variables were calculated. The flow velocity through the anastomoses was visualized by color Doppler coding, and flow was assessed with transit-time flowmetry. RESULTS: The epicardial color Doppler ultrasound allowed accurate assessment of the anastomoses. Twenty-three (96%) of the primary anastomoses were confirmed as patent. Mean ratios of D1/D2, D(A)/D2, and D(M)/D2 were 0.89 +/- 0.13, 3.01 +/- 1.04 and 1.32 +/- 0.32, respectively. One anastomosis had a stenosis more than 50% detected by color Doppler ultrasound. After surgical revision, transit-time flow increased from 22 to 40 ml/min. CONCLUSIONS: Intraoperative color Doppler ultrasound allowed adequate imaging for quality assessment of LIMA-to-LAD anastomoses performed on the beating heart. One anastomosis was revised due to a technical error detected by epicardial color Doppler imaging. Epicardial ultrasound scanning is a valuable tool for intraoperative assessment of LIMA-to-LAD anastomoses during off-pump coronary surgery.