Knut Matre

In vitro evaluation of three-dimensional ultrasonography in volume estimation of abdominal organs

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.

Antroduodenal motility and movements of luminal contents studied by duplex sonography

The motility of the gastroduodenal wall, movement of gastric contents, and velocity curves of transpyloric flow can be synchronously visualized by duplex sonography. In eight healthy individuals, 18 +/- 6 (mean +/- SD) peristaltic cycles per person in response to the ingestion of 500 mL of meat soup were recorded. Coordinated antroduodenal contractions were seen in 67% of the cycles. Two types of duodenogastric reflux were observed. One type occurred in the middle of the peristaltic cycle (midcycle reflux), whereas the other followed immediately after antegrade flow at the end of the cycle (end-cycle reflux). End-cycle reflux was significantly more frequent in conjunction with coordinated (70%) than with uncoordinated (17%) antroduodenal contractions (P less than 0.005). Thus, in the fed state, a short gush of duodenogastric reflux normally precedes the peristaltic closure of the pylorus.

In vivo comparison of 3D ultrasonography and magnetic resonance imaging in volume estimation of human kidneys

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.

Freehand Real-Time Elastography: Impact of Scanning Parameters on Image Quality and In Vitro Intra- and Interobserver Validations

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.

Myocardial deformation in aortic valve stenosis: relation to left ventricular geometry.

Objective To assess left ventricular (LV) strain and displacement and their relations to LV geometry in patients with aortic stenosis (AS). Design Cross-sectional echocardiographic study in patients with AS. Peak circumferential, radial and longitudinal strain, and radial, longitudinal and transverse displacement were measured by 2D speckle tracking. Severity of AS was assessed from energy loss index (ELI). LV hypertrophy was present if LV mass/height2.7 ≥46.7/49.2 g/m2.7 in women/men and concentric LV geometry if relative wall thickness ≥0.43. LV geometry was assessed from LV mass/height2.7 and relative wall thickness in combination. Setting Department of Heart Disease, Haukeland University Hospital, Bergen, Norway. Patients 70 patients with AS (mean age 73±10 years, 54% women). Interventions None. Main outcome measures Association of regional and average LV myocardial strain and displacement with LV geometric pattern and degree of AS. Results Average longitudinal strain was lower in the hypertrophy groups and correlated with higher LV mass index and relative wall thickness, lower stress-corrected mid-wall shortening and smaller ELI (all p<0.05). Average strain and displacement in other directions did not differ between geometric groups. In multivariate regression analysis, lower average longitudinal strain was associated with higher relative wall thickness (β=0.15), lower ejection fraction (β=−0.16), systolic blood pressure (β=−0.16) and energy loss index (β=−0.20) (all p<0.05) (R2=0.72). When relative wall thickness was replaced with LV mass, lower longitudinal strain was also associated with higher LV mass (β=0.21, p<0.05) (R2=0.73). Conclusions In patients with AS, lower average longitudinal strain is related to higher LV mass, concentric geometry and more severe AS.

In vitro evaluation of three-dimensional ultrasonography based on magnetic scanhead tracking

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.

Strain during gastric contractions can be measured using Doppler ultrasonography

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.

In vitro volume estimation of kidneys using three-dimensional ultrasonography and a position sensor.

OBJECTIVE A new 3D ultrasound system using a position sensor based on magnetic scanhead tracking and new software utilising automatic contour tracing between manually traced contours was tested for volume estimation of kidneys in vitro. METHODS Kidneys from piglets and pigs were fixed in formaldehyde. A reservoir with 0.9% saline kept at 37 degrees C was used. The kidneys were scanned either by a linear translational movement along the organ or by a tilting movement. The outer contour of the kidneys was traced manually, by two independent investigators. The volume of each kidney was also measured using the Archimedes principle (true volumes). RESULTS Good agreement between 3D ultrasound volume estimates and true volumes was found for both probe movements. For translational movement of the transducer, the mean errors between the methods were 4.17 and 4.31 ml for the two independent investigators, and the volume range was 96-203 ml. The corresponding error values for tilting movement were 1.10 and 0.19 ml. The interobserver variation was also small, there was no difference in the volumes obtained by the two investigators, or by the two scanning movements. CONCLUSION Volume estimates using this 3D ultrasound method showed very good agreement with true volumes, both mean errors and interobserver variation were low.

A practical method for estimating enclosed volumes using 3D ultrasound

Abstract Objective : This paper describes an algorithm which resulted in a practical method for estimating an enclosed volume using three-dimensional ultrasound. It was tested in vitro on thin-walled phantoms. Method : Data was acquired with a standard mechanical sector transducer which was tilted through a given angle (26°, 51° or 88°) by a motorized mechanical holder. A total of 81 frames was captured, stored digitally on a Unix workstation, and scanned and converted into a three-dimensional volumetric data set. Planar contours were drawn manually to indicate an enclosing volume. From the given set of contours, a polyhedron was reconstructed and the volume calculated. Four different principles of manual contour indication; outside, inside, center, and leading edge to leading edge, were investigated. The volume estimation method was tested on a condom filled with water with varying volume. Results : The experiments demonstrated lowest error for the center edge contour indication, mean difference −0.47 ml ± 2.15 ml (mean ± 2 S.D.) in the volume range 1.15–45.90 ml. An inter-observer error of 0.6% ± 5.0% was found using the center edge contour indication. The error for leading edge contour identification was similar, 0.78 ml ± 2.65 ml. Both inside and outside contour identification gave much larger errors. Conclusion : It was concluded that this volume estimation method was accurate, contributed to low inter-observer error, and that the results from the different tracing indications demonstrated the necessity to standardize these procedures for thin-walled organs.

volume measurements of gastric antrum by 3-D ultrasonography and flow measurements through the pylorus by duplex technique

We present a method for estimating volumes of abdominal organs using 3-D ultrasonography.In vitro validation experiments demonstrated excellent agreement between estimated and true volumes.In vivo estimations after ingestion of 500 ml meat soup showed greater antral filling and poorer emptying of the gallbladder in patients with functional dyspepsia (FD) than in healthy controls. Abnormal antral filling was associated with dyspeptic symptoms. The relationship between motility and transpyloric movements of luminal contents after ingestion of 500 ml meat soup was studied in healthy subjects by duplex technique. Accurate timing of antegrade and retrograde flow were recorded using bidirectional velocity curves. Mid-cycle and end-cycle reflux were often observed; end-cycle reflux was more frequent in conjunction with coordinated than with uncoordinated antroduodenal contractions. The peristaltic closure of the pylorus was normally preceded by a short gush of duodenogastric reflux.