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The purpose of this study was to investigate the effect of frame rate and probe frequency on the accuracy of speckle tracking echocardiography-derived strain measurements in infants. An infant-sized left ventricle phantom with sonomicrometer crystals was made from polyvinyl alcohol. The examined stroke rates were 60, 120 and 180 strokes per min (SPM). Longitudinal strain and circumferential strain measurements were analyzed from a total of 1860 cine loops. These cine loops were acquired using two pediatric probes of different frequencies at both fundamental and harmonic imaging modes. Both probes were examined at different settings (in total, 30 different frame rate-frequency combinations). At optimal settings, both longitudinal and circumferential strain displayed high accuracy. Frequency settings did not have a consistent effect on accuracy, while low frame rates led to less accurate measurements. We recommend a frame rate/heart ratio >1 frame per second/beats per min, especially for circumferential strain., (Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

With little data published on the accuracy of cardiac 3-D strain measurements, we investigated the agreement between 3-D echocardiography and sonomicrometry in an in vitro model with a polyvinyl alcohol phantom. A cardiac scanner with a 3-D probe was used to acquire recordings at 15 different stroke volumes at a heart rate of 60 beats/min, and eight different stroke volumes at a heart rate of 120 beats/min. Sonomicrometry was used as a reference, monitoring longitudinal, circumferential and radial lengths. Both single- and multi-beat acquisitions were recorded. Strain values were compared with sonomicrometer strain using linear correlation coefficients and Bland-Altman analysis. Multi-beat acquisition showed good agreement, whereas real-time images showed less agreement. The best correlation was obtained for a heart rate 60 of beats/min at a volume rate 36.6 volumes/s., (Copyright © 2013 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

We tested the effect of reducing the ultrasound output energy on obstetric measurements made from two-dimensional (2-D) grayscale images. We measured three fetal structures (femur, umbilical vein and lateral cerebral ventricle) in 113 pregnant women, commencing with an output energy that provided a thermal index for bone (TIB) of ≤1.0, and then repeated the measurements at TIB ≤ 0.5 and then TIB ≤ 0.1. There was a trend toward shorter femur measurements and larger umbilical vein diameter measurements with decreasing output energy. However, since these effects (which did not exceed 0.03 mm) were very small compared with the inter- and intraobserver variations, they were considered to be of no clinical significance. Furthermore, the residuals did not increase when the output energy decreased, indicating that the precision of the measurements was unaltered. We conclude that using a reduced output energy setting corresponding to a TIB of 0.1 does not compromise ultrasound biometry findings., (Copyright © 2013 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

Real-time elastography is a method for visualization of the elastic properties of soft tissue and may potentially enable differentiation between malignant and benign pathologic lesions. Our aim was to validate the method on a tissue-mimicking (TM) phantom and to evaluate the influence of different scanning parameters and investigator variability. A TM-phantom containing eight spherical inclusions with known storage modulus was examined using two different transducers on an ultrasound (US) scanner equipped with software for real-time elasticity imaging. The ultrasound transducers were moved vertically in a repetitive manner to induce strain. Two investigators performed series of standardized elastography scans applying a 0-4 categorical quality scale to evaluate the influence of seven parameters: dynamic range of elasticity, region-of-interest, frequency of transducer movement, rejection of elastogram noise, frame rate, persistence and smoothing. Subsequently, repeated examinations of four selected inclusions were performed using a visual analog scale (VAS) where investigators marked a 100 mm horizontal line representing the span in image quality based on experience from the first examination. The hardest and softest inclusions were imaged more clearly than the inclusions with elasticity more similar to the background material. Intraobserver agreement on elastogram quality was good (kappa: 0.67 - 0.75) and interobserver agreement average (kappa: 0.55 - 0.56) when using the categorical scale. The subsequent VAS evaluation gave intraclass-correlation coefficients for the two observers of 0.98 and 0.93, respectively, and an interclass-correlation coefficient of 0.93. Real-time elastography adequately visualized isoechoic inclusions with different elastic properties in a TM-phantom with acceptable intra- and interobserver agreement. Dynamic range of elasticity was the parameter with most impact on the elastographic visualization of inclusions.

As volume changes are a typical finding in the two-kidney, one-clip hypertensive rat model (2K1C), it is of interest to investigate within what time frame these volume changes occur and their relation to hypertension. Kidney volume changes in Wistar rats were measured by three-dimensional (3D) ultrasonography (USG). Clipped induced stenosis was applied to the left renal artery in 11-wk-old animals (n = 8), using age-matched nonclipped rats as controls (n = 7). Ultrasonographic recordings were made before clipping and, thereafter, weekly with corresponding systolic blood pressure and body weight measurements. The nonclipped kidney showed increased volume at week 2, 5 and 7. Three wk after clipping, clipped kidneys were smaller than the nonclipped kidneys (0.47 +/- 0.11 mL versus 1.28 +/- 0.07 mL). No difference was found between the left and right kidney in the control group at any week. Blood pressure was significantly higher in the 2K1C hypertensive group 4 weeks after clipping (201 +/- 16 versus 139 +/- 4 mm Hg) with stable blood pressure thereafter. Three-dimensional USG showed that clipping caused a decrease in kidney volume from week 3 in the clipped kidney and a volume increase in the nonclipped kidney at week 2. A significant increase in blood pressure appeared after week 4.

Strain rate imaging (SRI) enables study of deformation in soft tissues. The aim of this study was to evaluate the accuracy of SRI in measuring strain in the porcine antral wall in vitro. An experimental set-up enabled controlled distension of a porcine stomach in a saline reservoir. Radial strain obtained by SRI was compared with radial strain calculated from B-mode ultrasonography. Circumferential strain obtained by SRI was compared with circumferential strain calculated from sonomicrometry. The agreement between radial strain values measured by SRI and B-mode, along and across several ultrasound (US) beams, using US frequency 6.7 MHz and strain length (SL) = 1.9 mm was = -1.0 +/- 12.1% and 0.5 +/- 13.4%, respectively (mean difference +/- 2SD%) and it was better than with SL 1.2 mm. Compared with sonomicrometry, SRI-determined circumferential strain using 6.7 MHz and SL = 1.9 mm was less accurate, whether averaging along or across several US beams (-9.2 +/- 46.7% and 13.8 +/- 51.2%, respectively). In conclusion, SRI gave accurate measurement of radial strain of the antral wall, but seemed to be less accurate for measurement of circumferential strain for this in vitro set-up.

To evaluate the accuracy of small volume estimation, both in vivo and in vitro, measurements with a three-dimensional (3D) ultrasound (US) system were carried out. A position sensor was used and the transmitting frequency was 10 MHz. Balloons with known volumes were scanned while rat kidneys were scanned in vivo and in vitro. The Archimedes' principle was used to estimate the true volume. For balloons, the 3D US system gave very good agreement with true volumes in the volume range 0.1 to 10.0 mL (r = 0.999, n = 45, mean difference +/- 2SD = 0.245 +/- 0.370 mL). For rat kidneys in vivo (volume range 0.6 to 2.7 mL) the method was less accurate (r = 0.800, n = 10, mean difference +/- 2SD = -0.288 +/- 0.676 mL). For rat kidneys in vitro (volume range 0.3 to 2.7 mL) the results showed good agreement (r = 0.981, n = 23, mean difference +/- 2SD = 0.039 +/- 0.254 mL). For balloons, kidneys in vivo and in vitro, the mean percentage error was 9.3 +/- 4.8%, -17.1 +/- 17.4%, and 4.6 +/- 11.5%, respectively. This method can estimate the volume of small phantoms and rat kidneys and opens new possibilities for volume measurements of small objects and the study of organ function in small animals. (E-mail ).

Doppler strain rate imaging (SRI) was evaluated in vitro using a silicone strip phantom mimicking slowly moving tissue. A test apparatus was developed that enabled controlled strain experiments with variable strain and strain rate to be performed. SRI strain was measured at eight different calculated strains (range 5.7 to 63.4 %) at three different pump speeds with tissue velocity 0.1, 0.5 and 1.0 mm/s. The effect of varying tissue velocity and strain sample size on the measured SRI strain was elaborated. SRI strains agreed well with calculated values for strain when SRI strain was measured as the average over the whole strip cross-section and the strain sample size was 1.9 mm (mean difference = 2.78%, limits of agreement +/- 9.97% for tissue velocity 1.0 mm/s, n = 8). The variance was substantial if single central samples were used, especially for strain sample size of 0.8 mm (mean difference = -7.47%, limits of agreement +/- 20.90 for tissue velocity 0.5 mm/s, n = 24). Increasing the strain sample size to 1.9 mm removed some of the underestimation (giving mean difference of -4.46%, n = 24). We found low intra- and interobserver variation. This study indicates that, for the SRI method to give accurate estimates of strain, strain sample size should be in the region of 2 mm. Averaging over several ultrasound (US) beams increased the accuracy further.

This study was undertaken to explore if strain of the muscle layers within the gastric wall could be measured by transabdominal strain rate imaging (SRI), a novel Doppler ultrasound (US) method. A total of 9 healthy fasting subjects (8 women, 1 man; ages 22 to 55 years) were studied and both grey-scale and Doppler US data were acquired with a 5- to 8-MHz linear transducer in cineloops of 97 to 256 frames. Rapid stepwise inflation (5 to 60 mL) of an intragastric bag was carried out and bag pressure and SRI were measured simultaneously. SRI enabled detailed studies of layers within the gastric wall in all subjects. Great variations in strain distribution of the muscle layers were found. Radial strain was much higher in the circular than in the longitudinal muscle layer. Strains derived from SRI correlated well with strains obtained with B-mode measurements (r = 0.98, p < 0.05). During balloon distension, we found an inverse correlation between pressure and radial strain (r = -0.87, p < 0.05). Intraobserver correlation of strain estimation was r = 0.98 (p < 0.05) and intraobserver agreement was 0.2% +/- 18.6% (mean difference +/- 2SD, % strain). Interobserver correlation was r = 0.84 (p < 0.05) and interobserver agreement was 6.9% +/- 56.8%. SRI enables detailed mapping of radial strain distribution of the gastric wall and correlates well with B-mode measurements and pressure increments.

The aim of this study was to compare blood flow determined by coloured microspheres vs. Doppler intravascular ultrasound (US) combined with angiography. A second endpoint was to assess cardiac troponin I (cTnI) as a marker of myocardial injury. Doppler and microspheres were compared in 11 closed chest pigs. Blood flow was measured by catheter-based percutaneous technique in the left circumflex artery (LCx) and compared with coloured microspheres injected in the left ventricle. cTnI was measured in all pigs (73). The mean blood flow (mL/min-1) was 23.3 +/- 8.7 vs. 21.9 +/- 12.1 by Doppler vs. microspheres (p = 0.156), correlation coefficient r = 0.90, p = 0.006. The mean coronary flow with Doppler technique and microspheres in the middle LCx was 22.9 +/- 7.6 vs. 21.2 +/- 6.2 (p = 0.077), and distal 23.9 +/- 10.9 vs. 23.1 +/- 12.1 (p = 0.698). Coronary blood flow measured by Doppler and angiography was comparable to myocardial blood flow measured by coloured microspheres injected in the left atrium or the left ventricle. cTnI was more sensitive to ischaemia than CK-MB mass.

The objective of this study was to evaluate the accuracy and precision of a magnetic position sensor system for acquisition of three-dimensional (3D) ultrasound images in volume estimation of phantoms in vitro. Installation of either 0.9% solution of saline at 37 degrees C or distilled water at 20 degrees C to a condom was performed. Scanning was performed either by a continuous or stepwise acquisition. This 3D ultrasound system demonstrated good correlation (r = 0.99-1.0, n = 8) between estimated (EV) and true volumes (TV). The errors were in the range 1.3%+/-0.3% (SEM) to 1.9%+/-0.6%, independent of sound velocity. Scanning through a porcine abdominal wall positioned at the fluid surface yielded a systematic underestimation of the volume: mean (EV - TV) = -7.2+/-0.8 ml. Eight repeated scans of the same volume yielded a coefficient of variation of 1.1%. Interobserver error of the tracing procedure was 2.6%+/-0.9%. This 3D ultrasound system gave high accuracy and precision in volume estimation in vitro, and yielded low interobserver error. A change in ultrasound velocity of approximately 60 m/s did not influence the accuracy significantly. Scanning through an abdominal wall underestimated volumes slightly.

Unlabelled: The accuracy of cardiac output measurement by pulsed Doppler echocardiography can be affected by several factors, such as the velocity distribution, the measurement of diameter and the method of tracing the pulsed Doppler flow spectrum. This experimental study was designed to find the most accurate way of measuring cardiac output in consideration of all these factors. In 10 open-chest normal piglets (24 +/- 1 kg), the velocity distribution in the aortic annulus was evaluated using Doppler colour flow mapping. Cardiac output was measured by pulsed Doppler echocardiography in the aortic annulus by a number of different ways and compared to the simultaneous result of the thermodilution method. All measurements were made at baseline, after intravenous injection of esmolol and during infusion of dobutamine., Results: (1) the velocity distribution in the aortic annulus in the piglets was just slightly skewed during all three haemodynamic situations; (2) The in vivo measurements of the diameter of the aortic annulus varied throughout the ejection period, but the average of the three largest diameter measurements was almost identical with the diameter measured in vitro (18.5 +/- 0.3 mm vs. 18.6 +/- 0.2 mm; p = NS); (3) Tracing the maximal velocity of the pulsed Doppler flow spectrum produced a cardiac output that was 18%-21% higher than that measured by the thermodilution method, while tracing the brightest part (modal velocity) of the pulsed Doppler flow spectrum yielded a cardiac output very close to the thermodilution measurement., Conclusion: The velocity distribution in the aortic annulus in the piglet has little effect on cardiac output measurement by pulsed Doppler. Using the maximal measurable diameter of the aortic annulus and tracing the brightest part of the pulsed Doppler flow spectrum yielded the cardiac output closest to that measured by the thermodilution method.

The objective of this study was to evaluate the accuracy of a three-dimensional ultrasound system (3D-US) compared with Magnetic Resonance Imaging (MRI) in volume estimation of human kidneys in vivo. Twenty healthy volunteers were scanned fasting in supine position with MRI and with a 3D-US. An ultrasound sector scanner with a mechanical transducer coupled to a tilting motor provided images of multiple sections of kidneys. A 3.25-MHz transducer was tilted through 88 degrees yielding 81 frames, and volume estimation was performed on a Unix workstation after manual contour indication. Data acquisition with MRI was performed by using a 1-T magnet. Eighteen included kidneys [mean +/- standard deviation (SD)] measured 155.7 +/- 26.4 mL (range 110.0-205.0 mL) by 3D ultrasound and 171.8 +/- 24.6 mL (range 127.5-211.0 mL) by MRI, yielding a good correlation (r = 0.82, p < 0.001) between the two methods. The mean difference was -16.1 +/- 15.6 mL (SD) and the limits of agreement were -49.0 mL. We conclude that this 3D-US is accurate in volume estimation of human kidneys in vivo.

The purpose of this study was to evaluate the accuracy and precision of a three-dimensional (3D) ultrasound system in volume estimation of abdominal organs in vitro. A mechanical sector scanner coupled to a stepping motor recorded images of porcine stomach and kidneys. The transducer was tilted through 88 degrees yielding 81 frames, and volume estimation was performed digitally after interactive manual contour indication and organ reconstruction in 3 dimensions. This 3D system showed good correlation (r = 0.998) between estimated and true volumes. Volume estimation of stomach and kidneys using 3.25 MHz probe demonstrated limits of agreement of 0.877 to 1.146 and 1.007 to 1.125, respectively, depicting estimated volumes as a proportion of true volumes in 95% of the examinations. Intra- and interobserver variation of the tracing procedure revealed low values. We conclude that this 3D ultrasound system performs high accuracy and precision in volume estimation.

There is often a need for combining an ultrasound real-time scanner of one make with an ultrasound Doppler meter of a different make. This usually requires complicated and expensive adjustments of both apparatuses. This study describes how it is possible to identify the Doppler beam and locate the sample volume by adding a line to the video signal. The line ends at a point corresponding to the preselected depth of the pulsed Doppler showing the middle of the sample volume. The Doppler probe is mounted in a holder fixed to the scanner head. The holder allows rotation of the Doppler probe to form angles (35-90 degrees) with the scanner head surface. The sample volume indication corresponded well with actual sampling when tested on an in vitro flow rig and on different peripheral vessels. Modifications of neither scanner nor Doppler meter was necessary.