Biomedical subjects

H Torp

Publications and source records attributed to H Torp.

At least 19 recordsLinked to original sources

PubMed2006

Three-dimensional ultrasound volume calculations of human embryos and young fetuses: a study on the volumetry of compound structures and its reproducibility.

OBJECTIVE: To evaluate volumetry with three-dimensional (3D) ultrasonography in the assessment of the size of human embryos and fetuses. METHODS: Forty-four healthy embryos/fetuses with crown-rump length (CRL) ranging from 9 mm to 58 mm were studied using a 7.5-MHz annular array transvaginal 3D probe. EchoPAC 3D software was used to calculate the volumes of the head, body and limbs in the same data set by two observers working independently of each other. Regression analysis was used to assess the relationship between estimated volumes and CRL. RESULTS: The embryonic and fetal volume estimates of both observers ranged from a mean of 93 mm3 at 10 mm CRL to a mean of 11 169 mm3 at 55 mm CRL. The volume of the limbs as a proportion of the mean whole-body volume increased from 4.7% at a CRL of 15 mm to 9.3% at a CRL of 55 mm. Limits of agreement between the observers were calculated to be -0.12 +/- 9.2%. CONCLUSION: It is possible to reconstruct complex small anatomic structures and calculate the volumes of human embryos and fetuses in vivo by using dedicated 3D ultrasound equipment. The reproducibility of whole-body volume estimates seems to be high. The limbs represent a significant proportion of the size of the embryonic/fetal body.

Anthropometry↗

PubMed2003

Comparison of time-domain displacement estimators for two-dimensional RF tracking.

Techniques have been described in the literature to enable multidimensional strain rate estimation. They are based on multidimensional velocity estimation. One of the problems in obtaining robust lateral strain rate estimates is the fact that lateral velocity estimates are intrinsically noisier than axial ones. The aim of this study was to find the optimal estimator for tracking of the radiofrequency patterns both in axial and lateral directions. Performances of the following estimators were investigated using simulations: cross-correlation, normalized cross-correlation, sum of absolute differences and sum of squared differences. Two-dimensional (2-D) velocity estimation was not feasible using cross-correlation. However, normalized cross-correlation, sum of absolute differences and sum of squared differences showed accurate axial and lateral results. For smaller window lengths, sum of squared differences was found to be the preferred estimator for 2-D velocity estimation using a 1-D kernel.

Acoustics↗

PubMed2001

High frame rate strain rate imaging of the interventricular septum in healthy subjects.

OBJECTIVE: In the present study the feasibility was assessed of a new strain rate imaging method with a very high frame rate of around 300 frames per second. METHODS: Digital radio-frequency (RF) data were obtained in nine healthy subjects using a sector of 20-30 degrees in an apical four chamber view. The RF data were analysed using a dedicated software package that displays strain rate images and profiles and calculates strain rate values. With the new method, it is possible to study events and spatial-temporal differences in the heart cycle with duration down to 3.5-3 ms, including the pre-ejection period and the isovolumic relaxation period. Since the interventricular septum (IVS) is of crucial importance for the left and right ventricular function, we assessed changes through the heart cycle of the strain rate in the IVS. RESULTS: Mean peak systolic strain rate in the healthy subjects was -1.65+/-0.13 s(-1). Mean peak diastolic strain rate during early filling was 3.14+/-0.50 s(-1) and during atrial systole 0.99+/-0.09 s(-1). We found individual differences in the strain rate patterns, but in all subjects, the ventricular contraction started simultaneously in all parts of the septum. After the ejection period, the elongation started before aortic valve closure, in the midinferior septum and propagated towards the apex. CONCLUSION: High frame rate strain rate imaging makes it possible to study rapid deformation patterns in the heart walls.

Adult↗

PubMed2001

A semiautomated objective technique for applying the proximal isovelocity surface area method to quantitate mitral regurgitation: Clinical studies with the digital flow map.

BACKGROUND: Clinical application of the color Doppler proximal isovelocity surface area (PISA) method to quantify mitral regurgitation (MR) has been limited by the often inaccurate assumption that isovelocity surfaces are hemispheric. This study applied an objective method for selecting the region where the hemispheric geometry holds best on the basis of mathematic analysis of results at different distances from the orifice. We aimed to demonstrate this approach can be applied accurately in the clinical setting and can be semiautomated to promote routine use by extracting velocities from the digital Doppler output and then performing all the calculations automatically. METHODS: In 75 patients with isolated MR, centerline velocities (V(r)) at each distance (r) from the orifice in the proximal flow field were extracted digitally. The automated analysis calculated peak MR flow rates as 2pir(2)V(r) and plotted these against their respective velocities. The optimal value for peak flow rate was obtained mathematically at the site where the slope of this curve was minimal (least inaccuracy). This value was combined with continuous wave Doppler data to provide regurgitant stroke volume (RSV) and orifice area (ROA), which were compared with quantitative Doppler in 75 patients and angiography in 42. RESULTS: RSV and ROA by this optimized, semiautomated PISA method correlated and agreed well with values from quantitative Doppler (y = 0.9x + 1.9, r = 0.90, standard error of the estimate [SEE] = 8.1 mL, mean difference = -0.7 +/- 8.5 mL for RSV; y = 0.9x + 0.02, r = 0.90, SEE = 0.048 cm(2), mean difference = -0.005 +/- 0.1 cm(2) for ROA) and correlated well with angiography (rho = 0.90 for both RSV and ROA). CONCLUSIONS: This objective PISA method for quantifying MR is accurate in the clinical setting and has been semiautomated by use of analysis of digital velocity data to provide a rapid and practical technique suitable to facilitate more extensive application in routine practice.

Algorithms↗

PubMed2001

A new method describing cross-sectional blood flow velocity profiles in the left ventricular outflow tract of patients with atrial fibrillation with the use of high-frame rate 2-dimensional color flow imaging.

A new Doppler method was developed to evaluate the instantaneous cross-sectional velocity profile variability in the left ventricular outlet tract in patients with atrial fibrillation. Blood flow velocities acquired at a high frame rate (>90 frames/s) from a single heart cycle were used to display the velocity profile. In 9 patients, 2 heart cycles with different R-R interval lengths were recorded in color flow mode in a transthoracic apical 5-chamber and long-axis view. Raw digital ultrasound data were analyzed with an external personal computer. The data indicated a variable skew in the profiles with the highest velocities and velocity-time integral (VTI) most often located in the center and toward the septum. The maximum VTI overestimated the mean VTI by approximately 40%. No significant difference existed between the two heartbeats. Thus the VTI can be averaged from heartbeats of different R-R lengths in atrial fibrillation.

Adult↗

PubMed2001

Three-stage approach to ultrasound contrast detection.

A new method for detecting ultrasound contrast agents using a three-stage pulsing sequence is proposed. The method is based on observations showing that the scattering properties of contrast agents are modified by ultrasonic insonation at high power, but remain unchanged at low power. The objective of the first stage of the pulsing sequence is to use low power pulses to obtain a high resolution reference image without altering the agent. Higher power pulses in the second stage modify the contrast agent. The third stage detects the changes imposed to the contrast agent using low power pulses. A temporal filter is proposed to discriminate contrast response from clutter signal. The method is similar to power Doppler methods in that it uses several pulses to survey the target while destroying the agent. The new idea is to separate detection and destruction to circumvent a trade-off between sensitivity and resolution. Results from in vitro experiments with three different contrast agents are presented. The results are compared with harmonic power Doppler processed from the same data and show that an improvement in sensitivity is achievable by including the high power burst in the pulsing sequence. The results also show that the proposed filter reduces clutter artifacts from moving tissue.

Biomedical Engineering↗

PubMed2000

Myocardial strain by Doppler echocardiography. Validation of a new method to quantify regional myocardial function.

BACKGROUND: Myocardial strain is a measure of regional deformation, and by definition, negative strain means shortening and positive strain, elongation. This study investigates whether myocardial strain can be measured by Doppler echocardiography as the time integral of regional velocity gradients, using sonomicrometry as reference method. METHODS AND RESULTS: In 13 anesthetized dogs, myocardial longitudinal strain was measured on apical images as the time integral of regional Doppler velocity gradients. Ultrasonic segment-length crystals were placed near the left ventricular (LV) apex and near the base. Apical ischemia was induced by occluding the left anterior descending coronary artery (LAD), and preload was increased by saline. Percentage systolic strain by Doppler correlated well with strain by sonomicrometry (y=0.82x-1.79, r=0.92, P<0.01). During LAD occlusion, apical myocardium became dyskinetic, as indicated by positive strain values and negative Doppler velocities. At the LV base, myocardial strain by Doppler, strain by sonomicrometry, and velocity of shortening by sonomicrometry (dL/dt) were unchanged during apical ischemia. However, myocardial Doppler velocities at the base decreased from 4.2+/-0.7 (+/-SEM) to 2.7+/-0. 4 cm/s (P<0.05), probably reflecting loss of motion caused by tethering to apical segments. Volume loading increased myocardial Doppler velocities from 2.2+/-0.3 to 4.1+/-0.8 cm/s (P<0.05) and Doppler-derived strain from -12+/-1% to -22+/-2% (P<0.05), whereas peak LV elastance remained unchanged. CONCLUSIONS: Myocardial strain by Doppler echocardiography may represent a new, powerful method for quantifying regional myocardial function and is less influenced by tethering effects than Doppler tissue imaging. Like myocardial Doppler velocities, strain is markedly load-dependent.

Algorithms↗

PubMed2000

Statistical evaluation of clutter filters in color flow imaging.

The filter used to separate blood signals from the tissue clutter signal is an important part of a color flow system. In this paper, statistical detection theory is used to evaluate the quality of the most commonly used clutter filters. The probability of falsely classifying a sample volume as containing blood is kept below a specified threshold. With this constraint, the probability of correctly detecting blood is calculated for all the filters. Using a measured clutter signal, we found that polynomial regression filters and projection-initialized IIR filters are best among the commonly used filters. The probability of correctly detecting blood with velocity 10.1 cm/s was 0.32 for both these filters. The corresponding value for the optimal detector was 0.81, whereas a regression filter that depends on the clutter signal statistics achieved a blood detection probability of 0.72.

Blood Flow Velocity↗

PubMed2000

Accuracy of in-vitro volume estimation of small structures using three-dimensional ultrasound.

We describe an ultrasound probe for three-dimensional transvaginal imaging. The transducer was an annular array with a center frequency of 7.5 MHz which was rotated with an internal stepper motor. The probe had no external moving parts, and the total volume covered by a full rotation defined a half sphere. The raw digital data from the scanner were transferred to an external PC for three-dimensional reconstruction. We evaluated the three-dimensional imaging system by measuring the volumes of phantoms (range 24.8-3362.5 mm(3)) in a water tank, and found good correlation with true volumes (two observers' measurements gave a linear regression with a slope of 1. 010 and R(2) = 0.993, and a slope of 0.956 and R(2) = 0.993, respectively). The size of the point-spread function was used in the calculations to eliminate the effect of under- or overestimation due to the limited ultrasound beam resolution. An example of data acquisition, volume estimation and imaging of an embryo less than 8 weeks old in vivo with the brain cavities and body is given. We conclude that the three-dimensional reconstruction and volume estimation were accurate and repeatable.

Embryo, Mammalian↗

PubMed2000

Volumetric blood flow measurement with the use of dynamic 3-dimensional ultrasound color flow imaging.

We describe a new method for measuring blood volume flow with the use of freehand dynamic 3-dimensional echocardiography. During 10 to 20 cardiac cycles, the ultrasonographic probe was slowly tilted while its spatial position was continuously recorded with a magnetic position sensor system. The ultrasonographic data were acquired in color flow imaging mode, and the separate raw digital tissue and Doppler data were transferred to an external personal computer for postprocessing. From each time step in the reconstructed 3-dimensional data, one cross-sectional slice was extracted with the measured and recorded velocity vector components perpendicular to the slice. The volume flow rate through these slices was found by integrating the velocity vector components, and was independent of the angle between the actual flow direction and the measured velocity vector. Allowing the extracted surface to move according to the movement of anatomic structures, an estimate of the flow through the cardiac valves was achieved. The temporal resolution was preserved in the 3-dimensional reconstruction, and with a frame rate of up to 104 frames/s, the reconstruction jitter artifacts were reduced. Examples of in vivo blood volume flow measurement are given, showing the possibilities of measuring the cardiac output and analyzing blood flow velocity profiles.

Aorta↗

PubMed2000

Velocity profiles in mitral blood flow based on three-dimensional freehand colour flow imaging acquired at high frame rate.

AIMS: To describe the mitral blood flow velocity distribution, we applied a freehand dynamic three-dimensional (3D) colour flow method using a moving sample surface that followed the mitral apparatus during diastole. METHODS: Nineteen healthy volunteers were studied. The ultrasound data were captured from 10-20 heartbeats at high frame rate (mean 46 frames/s) while freely tilting the transducer in an apical position. A magnetic position sensor system recorded the spatial position and orientation of the probe. Blood flow velocities were integrated across a spherical surface. In volumetric blood flow measurements this would yield angle independence of the Doppler beam. Raw digital data were analysed off-line with no loss of temporal resolution. RESULTS: The ratio of the maximum velocity time integral (VTI) to the mean VTI was mean 1.3 (range 1.1-1.6). At the time of peak flow the ratio of the maximum to the mean velocity was mean 1.5 (range 1.2-2.6). CONCLUSION: The blood flow velocity profile was non-uniform. By using a single sample volume in Doppler measurements of the maximum VTI errors ranging from 10 to 60% may be introduced in calculations of stroke volumes.

Adult↗

PubMed2000

Measurement of volumetric mitral and aortic blood flow based on a new freehand three-dimensional colour flow imaging method. An in vivo validation.

AIMS: To validate a new three-dimensional (3D) colour flow method used to calculate cardiac output (CO) in aortic and mitral blood flow. METHODS: The transducer was freely tilted transthoracically using a magnetic locating device recording its spatial position. Raw digital ultrasound data were recorded in healthy subjects during 10-20 heartbeats at a high frame rate ranging from 41 to 66 frames/s and analysed off-line with no loss in temporal resolution. Blood flow velocities aligned with the ultrasound beam were integrated across a moving spherical surface to calculate volumetric flow. RESULTS: The range of agreement between the 3D mitral and 3D aortic method was 0.04+/-1.32 l/min (mean+/-2 standard deviations). The range of agreement between 3D aortic flow and the two-dimensional (2D) pulsed wave Doppler method (2DPW) in the left ventricular outflow tract (LVOT) was 0.7+/-1.7 l/min, while the range of agreement between 3D mitral flow and the 2DPW method was 0.88+/-1.64 l/min. CONCLUSION: The 3D methods agreed well. The 3D volumetric flow overestimated the 2DPW method, as expected, and the range of agreement was wide. The common pitfalls in pulsed wave ultrasound methods to calculate CO were avoided, as the 3D method was angle-independent, no assumptions about the velocity profile were made, and a moving sample surface was applied. The acquisition of data was fast and easy and high temporal resolution was achieved.

Adult↗

PubMed2000

Strain rate imaging by ultrasonography in the diagnosis of coronary artery disease.

Regional strain rate in the left ventricle can be assessed in real time and color mapped. The method is termed strain rate imaging (SRI), and findings correspond well with 2-dimensional echocardiography. This study addresses SRI as a method for localizing coronary lesions, compared with standard echocardiography. Twenty patients with acute myocardial infarction who underwent coronary angiography for clinical reasons were examined with SRI and standard echocardiography. Wall motion was graded by SRI color and separately by wall thickening. Strain rate imaging and 2-dimensional echocardiography results agreed well. An infarct-related artery was identified from angiograms combined with electrocardiograms. Both methods identified an infarct-related artery in 19 possible cases and had equal sensitivity and specificity for wall segments affected by lesion. Combining the information from both methods did not change accuracy. The study validates SRI as a method for assessing regional wall function in coronary artery disease. The advantages of SRI are discussed and measurements of strain rates are given.

Adult↗

PubMed1999

Dynamic three-dimensional freehand echocardiography using raw digital ultrasound data.

In this paper, we present a new method for simple acquisition of dynamic three-dimensional (3-D) ultrasound data. We used a magnetic position sensor device attached to the ultrasound probe for spatial location of the probe, which was slowly tilted in the transthoracic scanning position. The 3-D data were recorded in 10-20 s, and the analysis was performed on an external PC within 2 min after transferring the raw digital ultrasound data directly from the scanner. The spatial and temporal resolutions of the reconstruction were evaluated, and were superior to video-based 3-D systems. Examples of volume reconstructions with better than 7 ms temporal resolution are given. The raw data with Doppler measurements were used to reconstruct both blood and tissue velocity volumes. The velocity estimates were available for optimal visualization and for quantitative analysis. The freehand data reconstruction accuracy was tested by volume estimation of balloon phantoms, giving high correlation with true volumes. Results show in vivo 3-D reconstruction and visualization of mitral and aortic valve morphology and blood flow, and myocardial tissue velocity. We conclude that it was possible to construct multimodality 3-D data in a limited region of the human heart within one respiration cycle, with reconstruction errors smaller than the resolution of the original ultrasound beam, and with a temporal resolution of up to 150 frames per second.

Adult↗

PubMed1998

In-vivo three-dimensional ultrasound reconstructions of embryos and early fetuses.

BACKGROUND: Three-dimensional (3D) imaging of the living human embryo has become possible in the monitoring of embryological development, as described by classic human embryology. We aimed to create 3D images of organs in embryos on early pregnancy. METHODS: We used a specially developed 7.5 MHz annular array 3D transvaginal probe to examine embryos. We included 34 women at 7-10 weeks' gestation. We measured the crown-rump length (CRL) of the embryos and fetuses and transferred the 3D ultrasound data to an external computer for further processing to calculate volume. FINDINGS: The CRLs ranged from 9.3 mm to 39.0 mm. The quality of the images of the embryos and fetuses made it possible to outline in detail the outer contours and the contours of the brain cavities, and the calculated volumes corresponded well to the descriptions from classic human embryology. INTERPRETATION: Our 3D imaging system allowed visualisation of structures of less than 10 mm. Therefore, development and abnormal development of fetuses can be monitored.

Embryonic and Fetal Development↗

PubMed1998

Real-time strain rate imaging of the left ventricle by ultrasound.

The regional function of the left ventricle can be visualized in real-time using the new strain rate imaging method. Deformation or strain of a tissue segment occurs over time during the cardiac cycle. The rate of this deformation, the strain rate, is equivalent to the velocity gradient, and can be estimated using the tissue Doppler technique. We present the strain rate as color-coded 2-dimensional cine-loops and color M-modes showing the strain rate component along the ultrasound beam axis. We tested the method in 6 healthy subjects and 6 patients with myocardial infarction. In the healthy hearts, a spatially homogeneous distribution of the strain rate was found. In the infarcted hearts, all the infarcted areas in this study showed up as hypokinetic or akinetic, demonstrating that this method may be used for imaging of regional dysfunction. Shortcomings of the method are discussed, as are some possible future applications of the method.

Biomechanical Phenomena↗

PubMed1995

Velocity matched spectrum analysis: a new method for suppressing velocity ambiguity in pulsed-wave Doppler.

A new approach to spectrum analysis, which is capable of suppressing velocity ambiguity in pulsed-wave ultrasonic Doppler, is presented. By simultaneous processing of several data samples from a range in depth, the movement of the scatterers along the ultrasonic beam can be tracked from pulse to pulse for each velocity component in the spectrum. In this way the correlation length of the signal component arising from a specific velocity increases when that velocity matches the expected velocity. The resulting velocity/time spectral display shows a more clearly defined spectral envelope of the maximum velocity than with conventional methods based on the discrete Fourier transform of the Doppler signal. This makes it possible to delineate velocity waveforms with peak velocity up to several times the Nyquist limit. Experimental data from human subclavian and aortic arteries are presented, where the new method is compared to conventional spectrum analysis.

Blood Flow Velocity↗

PubMed1994

Abnormalities of left ventricular filling in patients with coronary artery disease: assessment by colour M-mode Doppler technique.

In 54 healthy individuals and 107 patients with coronary artery disease, intraventricular early filling velocities were recorded by colour M-mode Doppler. The time difference between the occurrence of peak velocity in the apical region and at the mitral tip was calculated, and normalized by dividing it by the mitral to apical distance. Transmitral velocities were determined by the single pulsed Doppler technique. The patients were divided into groups according to systolic function as assessed by left ventriculography. The normalized time difference was similar in the reference group (12 +/- 8 ms.cm-1) and the patient group with no electrocardiographical signs of previous infarction and normal ventriculography (16 +/- 16 ms.cm-1). It increased significantly in the group with infarction and/or regional systolic dysfunction (43 +/- 21 ms.cm-1), and a further increase was present in the group with severely impaired ventricles (53 +/- 14 ms.cm-1). The ratio between peak early and late transmitral velocity fell significantly in the group with infarction and/or regional systolic dysfunction, but was normalized in the group with severely impaired ventricles. Colour M-mode Doppler shows that apical filling is delayed in patients with injured left ventricles due to coronary artery disease. This delay increases with progression of ventricular injury. The technique may be an important addition to transmitral pulsed Doppler in assessing left ventricular filling.

Adult↗