| 1. |
- Bjarnegård, Niclas, et al.
(författare)
-
Age affects proximal brachial artery stiffness : differential behaviour within the length of the brachial artery?
- 2003
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 29:8, s. 1115-1121
-
Tidskriftsartikel (refereegranskat)abstract
- With increasing age, the diameter of central elastic arteries increases, whereas their distensibility decreases. The purpose of this study was to investigate the mechanical properties of the proximal brachial artery in relation to age and gender. Distensibility coefficient (DC), stiffness and compliance coefficient (CC) were calculated in 136 healthy males and females (range 9-82 y) using echo-tracking sonography. CC decreased with age in both genders, but CC was higher in males. Stiffness increased and DC decreased with age in an exponential manner, without any differences between genders. In conclusion, as in central elastic arteries, the distensibility of the proximal brachial artery decreases with age, in contrast to earlier reports on the muscular distal brachial artery. This may imply that the transition between elastic and muscular artery behavior is within the length of the brachial artery. In future studies using the brachial artery, the examination site needs to be defined.
|
|
| 2. |
- Edler, I, et al.
(författare)
-
The history of echocardiography
- 2004
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 30:12, s. 1565-1644
-
Forskningsöversikt (refereegranskat)abstract
- Following a brief review of the development of medical ultrasonics from the mid-1930s to the mid-1950s, the collaboration between Edler and Hertz that began in Lund in 1953 is described. Using an industrial ultrasonic flaw detector, they obtained time-varying echoes transcutaneously from within the heart. The first clinical applications of M-mode echocardiography were concerned with the assessment of the mitral valve from the shapes of the corresponding waveforms. Subsequently, the various M-mode recordings were related to their anatomical origins. The method then became established as a diagnostic tool and was taken up by investigators outside Lund, initially in China, Germany, Japan and the USA and, subsequently, world-wide. The diffusion of echocardiography into clinical practice depended on the timely commercial availability of suitable equipment. The discovery of contrast echocardiography in the late 1960s further validated the technique and extended the range of applications. Two-dimensional echocardiography was first demonstrated in the late 1950s, with real-time mechanical systems and, in the early 1960s, with intracardiac probes. Transesophageal echocardiography followed, in the late 1960s. Stop-action two-dimensional echocardiography enjoyed a brief vogue in the early 1970s. It was, however, the demonstration by Bom in Rotterdam of real-time two-dimensional echocardiography using a linear transducer array that revolutionized and popularized the subject. Then, the phased array sector scanner, which had been demonstrated in the late 1960s by Somer in Utrecht, was applied to cardiac studies from the mid-1970s onwards. Satomura had demonstrated the use of the ultrasonic Doppler effect to detect tissue motion in Osaka in the mid-1950s and the technique was soon afterwards applied in the heart, often in combination with M-mode recording. The development of the pulsed Doppler method in the late 1960s opened up new opportunities for clinical innovation. The review ends with a mention of color Doppler echocardiography. (E-mail: kjell.lindstrom@elmat.Ith.se) (C) 2004 World Federation for Ultrasound in Medicine Biology.
|
|
| 3. |
- Eriksson, A, et al.
(författare)
-
Arterial pulse wave velocity with tissue doppler imaging
- 2002
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 28:5, s. 571-580
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes a new noninvasive ultrasonic method for estimating pulse wave velocity (PWV), an important physical parameter for characterizing the elastic properties of the arterial walls. The method utilizes a relatively new color Doppler modality for measuring tissue motion (tissue Doppler imaging or TDI). In contrast to previously proposed methods, the TDI modality offers multiple recording sites along the artery that improve the PWV estimation considerably. The new PWV estimation method was evaluated through an in vitro setup consisting of an elastic vessel supplied with a pulsatile pump. The study concentrated on the effect of different system parameters controlling resolution, sensitivity and the amount of acquired data. It was shown that the system parameters have a significant effect on the PWV variance, whereas the PWV mean remains unchanged. It was also established that high temporal resolution is the most vital parameter for minimizing PWV variance. Finally, the new PWV estimation method was applied to a limited set of human carotid artery data sets, with good results. (E-mail:magnus.persson@elmat.lth.se)
|
|
| 4. |
- Gardiner, H, et al.
(författare)
-
Volume blood flow estimation in the normal and growth-restricted fetus
- 2002
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 28:9, s. 1107-1113
-
Tidskriftsartikel (refereegranskat)abstract
- The objective was to compare volume blood flow (VBF) in the descending aorta (DAo) of gestational age and weight-matched growth restricted (GR) and normal (N) fetuses. A longitudinal study of 20 N was compared with 11 GR in two analyses matched for weight and gestation. DAo dimensions and flow velocity were measured simultaneously using a new technique combining an ultrasonic phase-locked echo-tracking system synchronized with a pulsed Doppler velocimeter. Cardiac output was estimated using standard echocardiographic views. DAo and semilunar valve diameters increased linearly in N and indexed cardiac output was similar in N and GR, although GR showed reduced DAo relative pulse amplitude, mean flow velocity and VBF. This synchronized technique permits calculation of VBF in human fetuses. Growth restriction is associated with reduced aortic wall pulsations and lower mean blood flow velocities and VBF in DAo secondary to increased placental impedance. (C) 2002 World Federation for Ultrasound in Medicine Biology.
|
|
| 5. |
- Gudmundsson, Saemundur, et al.
(författare)
-
Factors affecting color Doppler energy ultrasound recordings in an in-vitro model
- 1998
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 24:6, s. 899-902
-
Tidskriftsartikel (refereegranskat)abstract
- Compared to conventional color Doppler ultrasound imaging, the new color Doppler modality "color Doppler energy" (CDE) has improved the possibility of visualizing blood vessels having low blood-flow velocities, but appears to be influenced by the settings of the ultrasound instrument and motion artefacts. The aim of this methodological study was to evaluate the effects of the different factors on the CDE signal. The CDE mode of a commercially available ultrasound system (Acuson 128 XP) was tested in an in vitro study. The effect of depth, angle of insonation, flow velocity, instrument power output, gain and other instrument settings were evaluated. The CDE signals obtained were stored on videotape and subsequently subjected to off-line computer analysis. The CDE signal intensity was found to be influenced mainly by fluid flow velocity, but was also affected by depth and instrument settings. Gain and power had, however, limited influence in this setting. Thus, the intensity of the CDE signal is influenced by several factors. Our results emphasize the need for optimum fixed preinstalled instrument settings when attempting to quantify organ perfusion by use of this new technique.
|
|
| 6. |
- Hansen, F, et al.
(författare)
-
Diameter and compliance in the human common carotid artery--variations with age and sex
- 1995
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 21:1, s. 1-9
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, age and sex differences in diameter and compliance of the common carotid artery (CCA) were evaluated in 119 healthy subjects with a phase-locked echo-tracking system. The diameter and pulsatile diameter changes were measured, and pressure strain elastic modulus (Ep) and stiffness (beta) were calculated and used as the inverse estimate of compliance. The carotid diameter increased more rapidly in males and was larger than in females from 25 years of age. The relative diameter change was equal in both sexes, and decreased from 12% to 14% in younger subjects to approximately 5% in elderly subjects. Compliance decreased almost linearly and in parallel in males and females up to 45 years of age. Between 45 and 60 years the decrease was more marked in females than in males, whereas it was by far more marked in males between 60 and 70 years of age.
|
|
| 7. |
|
|
| 8. |
- Jansson, Tomas, et al.
(författare)
-
Movement artefact suppression in blood perfusion measurements using a multifrequency technique
- 2002
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 28:1, s. 69-79
-
Tidskriftsartikel (refereegranskat)abstract
- The standard way of suppressing movement artefacts in Doppler measurements is by means of a high-pass filter. This is because artefacts usually are of high amplitude, but have low frequencies. The immediate drawback is, then, that low-velocity blood flow is also filtered out. In this paper, a method to reduce movement artefacts in blood perfusion measurements is proposed, using simultaneous transmission and reception of multiple frequencies in a continuous-wave Doppler system. It is shown that Doppler signals originating from blood may be considered uncorrelated for a large enough frequency separation between channels, and tissue movements are more correlated. By subtracting perfusion estimates obtained by time-domain processing, correlated signals can be suppressed. The subtraction algorithm is shown to produce a linear perfusion estimate, but with twice the standard deviation compared to an estimate obtained by simply averaging channels. Movement artefacts in both in vitro and in vivo models are shown to be reduced by the algorithm. Imbalance between channels does, however, cause the artefacts to be only partly reduced. The problem can be alleviated by filtering the signals prior to subtraction, but this results in a nonlinear estimate, especially for large time constants in the filter. Some amount of filtering can still be desirable to suppress partly correlated artefacts, even if identical time-domain processing units are implemented, as could be done digitally. (E-mail: tomas.jansson@elmat.lth.se)
|
|
| 9. |
- Jansson, Tomas, et al.
(författare)
-
Ultrasound Doppler Vector Tomography - Measurements of Directional Blood Flow
- 1997
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 23:1, s. 47-57
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental system has been developed to verify the possibility of detecting flow activity using a technique called ultrasound Doppler vector tomography. A tomography algorithm is used to reconstruct blood flow vector fields using data from computer-controlled ultrasound continuous-wave Doppler scanning equipment. The result is a picture in which the brightness variations represent the reconstructed values of the curl of the velocity field (del x v). Continuous ultrasound is transmitted into a region with flow activity and the Doppler-shifted signals are received. To obtain measurement data suited for fan beam tomography, the scanning is performed in a plane from points encircling the region. Reconstructions have been achieved using measurement data from two different flow phantoms. A comparison between the experimental results and simulations shows good conformity. Copyright (C) 1997 World Federation for Ultrasound in Medicine & Biology.
|
|
| 10. |
- Länne, T, et al.
(författare)
-
Noninvasive measurement of diameter changes in the distal abdominal aorta in man
- 1992
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 18:5, s. 451-457
-
Tidskriftsartikel (refereegranskat)abstract
- An ultrasound phase-locked, echo-tracking system was used to determine the dynamic properties of the distal abdominal aorta in 10 Caucasian male subjects (mean age, 25 years). Recordings were made at rest and during the blood pressure increase resulting from isometric exercise. The pressure diameter curve was nonlinear with an inflection at about 90-110 mmHg. Above this pressure range, the vessel was stiffer (less compliant), but the pressure diameter relationship was roughly linear above as well as below the inflection. Individual pressure diameter curves showed hysteresis, i.e., the aorta had a smaller diameter during expansion than during retraction at corresponding pressures. The pressure strain elastic modulus (Ep) and stiffness (beta) were at rest [Mean Arterial Pressure (MAP), 81 mmHg] 0.70 10(5) N/m2 and 6.0, respectively. During isometric exercise (MAP, 122 mmHg), Ep increased significantly by 91% and stiffness (beta) nonsignificantly by 27%. The variability of the compliance determinations was 5% when the ultrasonic system was combined with intra-arterial blood pressure measurements and less than 7% when combined with auscultatory blood pressure measurements. It is concluded that the phase-locked, echo-tracking system fulfills clinical requirements for routine measurements of vascular compliance.
|
|
| 11. |
- Malcus, Peter, et al.
(författare)
-
Waveform Pattern Recognition – A New Semiquantitative Method for Analysis of Fetal Aortic and Umbilical Artery Blood Flow Velocity Recorded by Doppler Ultrasound
- 1991
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 17:5, s. 453-460
-
Tidskriftsartikel (refereegranskat)abstract
- A semiquantitative computerized waveform pattern recognition system for analysis of the fetal descending aortic and umbilical artery Doppler flow velocity waveforms is presented. Based on empirically and manually selected clinical recordings from both vessels, 11 computerized and normalized standard curves for the aorta (type curves A to K), and 10 curves for the umbilical artery (type curves a to j) were constructed. The best match between the normalized waveform and the standard curve was based on either the degree of absent diastolic flow or, in cases with positive diastolic flow, on the calculation of the least square sum of the difference. The pattern recognition was tested against conventional waveform indices and our older semiquantitative Blood Flow Class (BFC) system in 472 clinical consecutive Doppler recordings. A good correlation was found. This new relatively simple computer-based method for waveform analysis is now prospectively applied in clinical studies.
|
|
| 12. |
- Marsal, Karel
(författare)
-
Arterial Doppler flow in obstetrics.
- 2003
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 29:Suppl 1, s. 1-80
-
Tidskriftsartikel (refereegranskat)
|
|
| 13. |
- Persson, Johan K, et al.
(författare)
-
Ultrasound nucleolysis: an in vitro study.
- 2002
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 28:9, s. 1189-1197
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal intradiscal therapy for chronic low back pain, using a catheter inserted into the intervertebral disc, is becoming more popular in the treatment of low back pain. The aim of this study was to investigate the possibility of heating the nucleus pulposus of the intervertebral disc with high-intensity focused ultrasound (US) or HIFU. Two specific situations were considered, invasive transducers that would be in contact with the annulus fibrosus of the disc, and noninvasive transducers that could be used externally. Theoretical simulations were performed to find the optimal parameters of US transducers and then experimental studies were done using transducers made to these specifications. These experiments confirmed that it was possible to heat the discs with HIFU. Two orthogonal transducers resulted in a superior temperature distribution than using just one transducer. It is, therefore, feasible to consider thermal treatment of the nucleus pulposus of the disc using noninvasive US. (E-mail: Johan.Persson@ort.lu.se)
|
|
| 14. |
|
|
| 15. |
- Rydén Ahlgren, Åsa, et al.
(författare)
-
Dynamic behaviour of the common femoral artery: age and gender of minor importance
- 2001
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629 .- 1879-291X. ; 27:2, s. 181-188
-
Tidskriftsartikel (refereegranskat)abstract
- The distensibility of elastic arteries has been extensively studied, while studies of muscular arteries are sparse. The influences of age and gender on the mechanical properties of the common femoral artery (CFA) were studied. The pulsatile diameter changes of the CFA were noninvasively measured using echo-tracking sonography in 173 healthy volunteers (95 females, 78 males, range 7-81 years). In combination with blood pressure measurements, stiffness (beta) and pressure strain elastic modulus (Ep) were calculated. Neither beta nor Ep was related to age or gender and a considerable interindividual variation was present. The CFA diameter increased with age. In conclusion, the distensibility of this muscular artery is not clearly affected by age or gender, although the diameter increases with age. This indicates remodelling of the arterial wall and an impact of vascular smooth muscles on long-term wall mechanics. Thus, there appear to be fundamental differences in the dynamic behaviour of the common femoral artery when compared to elastic arteries, such as the aorta and the common carotid artery.
|
|
| 16. |
- Rydén Ahlgren, Åsa, et al.
(författare)
-
Stiffness and diameter of the common carotid artery and abdominal aorta in women
- 1997
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 23:7, s. 983-988
-
Tidskriftsartikel (refereegranskat)abstract
- Vascular disease is differentiated throughout the vascular regions with aorta more prone to dilatation and with peripheral arteries more prone to occlusive disease. In this study, we investigated the diameter and distensibility in the common carotid artery (CCA) and abdominal aorta (AO) in healthy females of varying ages to assess potential differences in the aging process. The diameter and pulsatile diameter change of the CCA and AO in 66 healthy Caucasian females aged 8 to 79 y were examined using an ultrasound phase-locked echo-tracking technique. Blood pressure was obtained by the auscultatory method. Arterial stiffness (beta) was calculated. The diameter of both CCA and AO increases, not only in childhood, but also in adult women. The dilatation in adults (25 to 75 y) seems to be more pronounced in the AO (23%) than in the CCA (11%). Stiffness (beta) is higher in the CCA than AO before 20 y of age (p < 0.05). Stiffness increases with aging in both arterial regions, but the increase is initially somewhat higher in the AO, which means that no differences between the CCA and AO are seen from 25 y onward. In conclusion, this study demonstrates regional differences in diameter change and stiffness in the CCA and AO, and implies that the AO is more prone to age-related changes of the arterial wall than the CCA. These differences, however, are not as marked as previously reported in males.
|
|
| 17. |
- Sladkevicius, Povilas, et al.
(författare)
-
Reproducibility of Doppler measurements of blood flow velocity in the uterine and ovarian arteries in premenopausal women
- 1995
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 21:3, s. 313-319
-
Tidskriftsartikel (refereegranskat)abstract
- Intra- and interobserver reproducibility of Doppler measurements of the pulsatility index (PI) and time-averaged maximum velocity (TAMXV) in the uterine and ovarian arteries were evaluated in examinations of healthy premenopausal women. Each woman underwent reproducibility measurements once in the late follicular phase and once in the midluteal phase. Intraobserver repeatability was assessed in examinations of 12 women, three replicate Doppler measurements being made by one observer in the same vessel. Interobserver agreement was assessed by comparing the results of Doppler measurements made by two investigators in 11 women. The intraclass correlation coefficient (Intra-CC) was 0.78 for the TAMXV in the dominant uterine artery in the follicular phase and 0.82 for the PI in the wall of the dominant follicle. For all other measurements the Intra-CC was < 0.75, indicating poor reproducibility. The interclass correlation coefficient (Inter-CC) was > 0.75 (0.79 to 0.88) for the PI and TAMXV in the dominant uterine artery in the follicular phase and for the PI of both uterine arteries in the luteal phase. For all other measurements the Inter-CC was < 0.75.
|
|
| 18. |
|
|
| 19. |
- Brandberg, Joakim, et al.
(författare)
-
Increased accuracy of echocardiographic measurement of flow using automated spherical integration of multiple plane velocity vectors
- 1999
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629 .- 1879-291X. ; 25:2, s. 249-257
-
Tidskriftsartikel (refereegranskat)abstract
- The calculation of blood flow in the heart by surface integration of velocity vectors (SIVV) using Doppler ultrasound is independent of the angle. Flow is normally calculated from velocity in a spherical thick shell with its center located at the ultrasound transducer. In a numerical simulation, we have shown that the ratio between minor and major axes of an elliptic flow area substantially influences the accuracy of the estimation of flow in a single scan plane. The accuracy of flow measurements by SIVV can be improved by calculating the mean of the values from more than one scan plane. We have produced an automated computer program that includes an antialiasing procedure. We confirmed an improvement of flow measurements in a pulsatile hydraulic flow model, the 95% confidence interval for single estimations being reduced from 20% to 10% (p < 0.05) using the newly developed software. We think that the SIVV method has important implications for clinical transthoracic echocardiography.
|
|
| 20. |
- Chew, Michelle, et al.
(författare)
-
Doppler flow measurement using surface integration of velocity vectors (Sivv) : in vitro validation
- 2000
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629 .- 1879-291X. ; 26:2, s. 255-262
-
Tidskriftsartikel (refereegranskat)abstract
- Blood flow measurement using an improved surface integration of velocity vectors (SIVV) technique was tested in in vitro phantoms. SIVV was compared with true flow (12–116 mL/s) in a steady-state model using two angles of insonation (45° and 60°) and two vessel sizes (internal diameter = 11 and 19 mm). Repeatability of the method was tested at various flow rates for each angle of insonation and vessel. In a univentricular pulsatile model, SIVV flow measured at the mitral inlet was compared to true flow (29–61 mL/s). Correlation was excellent for the 19-mm vessel (r2= 0.99). There was a systematic bias but close limits of agreement (mean ± 2 SD = −24.1% ± 7.6% at 45 °; +16.4% ± 11.0% at 60 °). Using the 11-mm vessel, a quadratic relationship was demonstrated between between SIVV and true flow (r2 = 0.98–0.99), regardless of the angle of insonation. In the pulsatile system, good agreement and correlation were shown (r2 = 0.94, mean ± 2 SD = −4.7 ± 10.1%). The coefficients of variation for repeated SIVV measurements ranged from 0.9% to 10.3%. This method demonstrates precision and repeatability, and is potentially useful for clinical measurements.
|
|
| 21. |
|
|
| 22. |
- Janerot-Sjöberg, Birgitta, 1958-, et al.
(författare)
-
Influence of respiration on myocardial signal intensity
- 2001
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629 .- 1879-291X. ; 27:4, s. 473-479
-
Tidskriftsartikel (refereegranskat)abstract
- Echocardiographic quantification of myocardial perfusion after IV contrast is possible, based on the intensity of the received intermittent second harmonic signal. To investigate the influence of respiration on the intensity of myocardial signals, we examined nine patients with normal coronary angiograms. At baseline, end-expiratory and end-inspiratory images were obtained in broadband radiofrequency (RF) and intermittent second harmonic modes, the latter repeated during IV contrast at rest and at peak stress. In mid-septum at baseline, end-inspiratory integrated backscatter intensity was 4 dB higher (p < 0.05, both in second harmonic and fundamental domains) than end-expiratory intensity. In second harmonic imaging, contrast increased signal intensity by 4 dB (p < 0.05) in six examined segments, but the increase in the midseptal region (2 dB) was not significant. Contrast-enhanced intensity at end-inspiration was higher (3 dB, p < 0.01) than baseline intensity at end-expiration. We conclude that the increase in myocardial signal intensity during inspiration may resemble the contrast effect in intermittent second harmonic mode. The respiratory variation persists after contrast and may mask or exaggerate the effect of myocardial contrast.
|
|
| 23. |
- Olsson, Lennart, et al.
(författare)
-
Analysis and classification of secondary sounds from the disintegration of kidney-stones with acoustic shock waves
- 1991
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629 .- 1879-291X. ; 17:5, s. 491-495
-
Tidskriftsartikel (refereegranskat)abstract
- Secondary sound emission, partly in the audible frequency range, from shock wave disintegration of kidney stones has been recorded during the treatment of two patients. A skilled operator can determine by listening if the stone is hit by the shock-wave or not. Spectral analysis of these recordings show differences between sounds which can be used to evaluate the fragmenting effect on the stone. Results are presented of a preliminary discriminating method based on parameters in an autoregressive signal model.
|
|
| 24. |
- Pislaru, Cristina, et al.
(författare)
-
Is there a change in myocardial nonlinearity during the cardiac cycle?
- 2001
-
Ingår i: Ultrasound in Medicine and Biology. - 0301-5629 .- 1879-291X. ; 27:3, s. 389-398
-
Tidskriftsartikel (refereegranskat)abstract
- The distortion of a sound wave during propagation results in progressive transfer of the energy from fundamental to higher harmonics, and is dependent on the nonlinearity of the medium. We studied if relative changes in acoustical nonlinearity occur in healthy myocardium during the cardiac cycle. Radiofrequency data were acquired from transthoracic echocardiography (2.5 and 3.5 MHz), parasternal long axis view, from five dogs and nine healthy volunteers. Integrated backscatter was calculated after filtering for fundamental (FIB) and second harmonic frequencies (SHIB), from a region in the posterior myocardial wall. The results suggest that there is little difference between the SHIB and FIB, although there were large variations between individuals. The maximal changes in nonlinearity, as estimated by SHIB/FIB ratio, mostly occurred during systole. SHIB presented similar cyclic variation with FIB (p = NS). Further studies are necessary to separate the role of myocardial nonlinearity, attenuation, propagating distance, or acoustical properties of the blood. The results are important in further tissue characterization studies employing second harmonic data.
|
|
| 25. |
- Sundström, N., et al.
(författare)
-
Registration of surface structures using airborne focused ultrasound
- 1991
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629 .- 1879-291X. ; 17:5, s. 513-518
-
Tidskriftsartikel (refereegranskat)abstract
- A low-cost measuring system, based on a personal computer combined with standard equipment for complex measurements and signal processing, has been assembled. Such a system increases the possibilities for small hospitals and clinics to finance advanced measuring equipment. A description of equipment developed for airborne ultrasound together with a personal computer-based system for fast data acquisition and processing is given. Two air-adapted ultrasound transducers with high lateral resolution have been developed. Furthermore, a few results for fast and accurate estimation of signal arrival time are presented. The theoretical estimation models developed are applied to skin surface profile registrations
|
|
| 26. |
- Töyräs, Juha, et al.
(författare)
-
Speed of sound in normal and degenerated bovine articular cartilage.
- 2003
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier. - 0301-5629 .- 1879-291X. ; 29:3, s. 447-454
-
Tidskriftsartikel (refereegranskat)abstract
- The unknown and variable speed of sound may impair accuracy of the acoustic measurement of cartilage properties. In this study, relationships between the speed of sound and cartilage composition, mechanical properties and degenerative state were studied in bovine knee and ankle cartilage (n = 62). Further, the effect of speed variation on the determination of cartilage thickness and stiffness with ultrasound (US) indentation was numerically simulated. The speed of sound was significantly (n = 32, p < 0.05) dependent on the cartilage water content (r = -0.800), uronic acid content (per wet weight, r = 0.886) and hydroxyproline content (per wet weight, r = 0.887, n = 28), Young's modulus at equilibrium (r = 0.740), dynamic modulus (r = 0.905), and degenerative state (i.e., Mankin score) (r = -0.727). In addition to cartilage composition, mechanical and acoustic properties varied significantly between different anatomical locations. In US indentation, cartilage is indented with a US transducer. Deformation and thickness of tissue are calculated using a predefined speed of sound and used in determination of dynamic modulus. Based on the simulations, use of the mean speed of sound of 1627 m/s (whole material) induced a maximum error of 7.8% on cartilage thickness and of 6.2% on cartilage dynamic modulus, as determined with the US indentation technique (indenter diameter 3 mm). We believe that these errors are acceptable in clinical US indentation measurements.
|
|
| 27. |
- Byenfeldt, Marie, 1967-, et al.
(författare)
-
Influence of Probe Pressure on Ultrasound-Based Shear Wave Elastography of the Liver Using Comb-Push 2-D Technology
- 2019
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier. - 0301-5629 .- 1879-291X. ; 45:2, s. 411-428
-
Tidskriftsartikel (refereegranskat)abstract
- It has been postulated that in the liver, applying increased probe pressure during ultrasound-based shear wave elastography (SWE) might lead to a false increase in the SWE result. We aimed to determine the influence of increased intercostal probe pressure when performing SWE of the liver. We also investigated the number of measurements required to achieve technically successful and reliable SWE examinations. This prospective, clinical study included 112 patients and 2240 SWE measurements of the liver. We applied probe pressure intercostally, to reduce the skin-to-liver capsule distance (SCD), which could stabilize the SWE signal and thus increase the number of technically successful measurements. We performed 10 measurements with maximum probe pressure and 10 with normal pressure in each patient. Thus, two analysis groups were compared for differences. Compared with normal pressure, maximum probe pressure significantly reduced the SCD (p < 0.001) and significantly increased the number of technically successful measurements from 981 to 1098, respectively (p < 0.001). The SWE results with normal and maximum probe pressure were 5.96 kPa (interquartile range: 2.41) and 5.45 kPa (interquartile range: 1.96), respectively (p < 0.001). In obese patients, a large SCD poses a diagnostic challenge for ultrasound SWE. We found that maximum intercostal probe pressure could reduce the SCD and increase the number of technically successful measurements, without falsely increasing the SWE result. Only three measurements were required to achieve technically successful and reliable SWE examinations.
|
|
| 28. |
- Lötjönen, Pauno, et al.
(författare)
-
Strain-dependent modulation of ultrasound speed in articular cartilage under dynamic compression.
- 2009
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier. - 1879-291X .- 0301-5629. ; 35:7, s. 1177-1184
-
Tidskriftsartikel (refereegranskat)abstract
- Mechanical properties of articular cartilage may be determined by means of mechano-acoustic indentation, a clinically feasible technique for cartilage diagnostics. Unfortunately, ultrasound speed varies in articular cartilage during mechanical compression. This can cause significant errors to the measured mechanical parameters. In this study, the strain-dependent variation in ultrasound speed was investigated during dynamic compression. In addition, we estimated errors that were induced by the variation in ultrasound speed on the mechano-acoustically measured elastic properties of the tissue. Further, we validated a computational method to correct these errors. Bovine patellar cartilage samples (n = 7) were tested under unconfined compression. Strain-dependence of ultrasound speed was determined under different compressive strains using an identical strain-rate. In addition, the modulation of ultrasound speed was simulated using the transient compositional and structural changes derived from fibril-reinforced poroviscoelastic (FRPVE) model. Experimentally, instantaneous compressive strain modulated the ultrasound speed (p < 0.05) significantly. The decrease of ultrasound speed was found to change nonlinearly as a function of strain. Immediately after the ramp loading ultrasound speed was found to be changed -0.94%, -1.49%, -1.84%, -1.87%, -1.89% and -2.15% at the strains of 2.4%, 4.9%, 7.3%, 9.7%, 12.1% and 14.4%, respectively. The numerical simulation revealed that the compression-related decrease in ultrasound speed induces significant errors in the mechano-acoustically determined strain (39.7%) and dynamic modulus (72.1%) at small strains, e.g., at 2.4%. However, at higher strains, e.g., at 14.4%, the errors were smaller, i.e., 12.6% for strain and 14.5% for modulus. After the proposed computational correction, errors related to ultrasound speed were decreased. By using the correction, with e.g., 2.4% strain, errors in strain and modulus were decreased from 39.7% to 7.2% and from 72.1% to 35.3%, respectively. The FRPVE model, addressing the changes in fibril orientation and void ratio during compression, showed discrepancy of less than 1% between the predicted and measured ultrasound speed during the ramp compression.
|
|
| 29. |
- Riekkinen, Ossi, et al.
(författare)
-
Acoustic properties of trabecular bone–relationships to tissue composition.
- 2007
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier. - 0301-5629 .- 1879-291X. ; 33:9, s. 1438-1444
-
Tidskriftsartikel (refereegranskat)abstract
- In osteoporosis, changes in tissue composition and structure reduce bone strength and expose it to fractures. The current primary diagnostic technique, i.e., dual energy X-ray absorptiometry, measures areal bone mineral density (BMD) but provides no direct information on trabecular structure or organic composition. Although still poorly characterized, ultrasound techniques may bring about information on bone composition and structure. In this study, relationships of 2.25-MHz ultrasound speed, attenuation, reflection and backscattering with composition of human trabecular bone (n=26) were characterized experimentally, as well as by using numerical analyses. We also determined composition of the trabecular sample (fat and water content, bone volume fraction) and that of the calcified matrix (mineral, proteoglycan and collagen content of trabeculae). In experimental analyses, bone volume fraction and mineral content of the calcified matrix were the only determinants of BMD. Further, bone volume fraction served as the strongest determinant of ultrasound parameters (r=0.51-0.87). In numerical simulations, density and mechanical properties of the calcified matrix systematically affected ultrasound speed, attenuation, reflection and backscattering. However, partial correlation coefficients revealed only low associations(|r|
|
|
| 30. |
- Sarvazyan, Armen, et al.
(författare)
-
Biomedical applications of radiation force of ultrasound : Historical roots and physical basis
- 2010
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier. - 0301-5629. ; 36:9, s. 1379-1394
-
Forskningsöversikt (refereegranskat)abstract
- Radiation force is a universal phenomenon in any wave motion, electromagnetic or acoustic. Although acoustic and electromagnetic waves are both characterized by time variation of basic quantities, they are also both capable of exerting a steady force called radiation force. In 1902, Lord Rayleigh published his classic work on the radiation force of sound, introducing the concept of acoustic radiation pressure, and some years later, further fundamental contributions to the radiation force phenomenon were made by L. Brillouin and P. Langevin. Many of the studies discussing radiation force published before 1990 were related to techniques for measuring acoustic power of therapeutic devices; also, radiation force was one of the factors considered in the search for noncavitational, nonthermal mechanisms of ultrasonic bioeffects. A major surge in various biomedical applications of acoustic radiation force started in the 1990s and continues today. Numerous new applications emerged including manipulation of cells in suspension, increasing the sensitivity of biosensors and immunochemical tests, assessing viscoelastic properties of fluids and biological tissues, elasticity imaging, monitoring ablation of lesions during ablation therapy, targeted drug and gene delivery, molecular imaging and acoustical tweezers. We briefly present in this review the major milestones in the history of radiation force and its biomedical applications. In discussing the physical basis of radiation force and its applications, we present basic equations describing the relationship of radiation stress with parameters of acoustical fields and with the induced motion in the biological media. Momentum and force associated with a plane-traveling wave, equations for nonlinear and nonsteady-state acoustic streams, radiation stress tensor for solids and biological tissues and radiation force acting on particles and microbubbles are considered.
|
|
| 31. |
- Virén, Tuomas, et al.
(författare)
-
Quantitative evaluation of spontaneously and surgically repaired rabbit articular cartilage using intra-articular ultrasound method in situ.
- 2010
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier. - 1879-291X .- 0301-5629. ; 36:5, s. 833-839
-
Tidskriftsartikel (refereegranskat)abstract
- During the last decade, a major effort has been devoted to developing surgical methods for repairing localized articular cartilage lesions. Despite some promising results no ultimate breakthrough in surgical cartilage repair has been achieved. Improvements in repair techniques would benefit from more sensitive and quantitative methods for long-term follow-up of cartilage healing. In this study, the potential of a new ultrasound technique for detecting the compositional and structural changes in articular cartilage after surgery, using recombinant human type II collagen gel and spontaneous repair was, investigated. Rabbit knee joints containing intact (n = 13) and surgically (n = 8) or spontaneously (n = 5) repaired tissue were imaged in situ at 6 months after the operation using a clinical intravascular high-frequency (40 MHz) ultrasound device. Based on the ultrasound raw data, ultrasound reflection coefficient (R), integrated ultrasound reflection coefficient (IRC), apparent integrated backscattering coefficient (AIB) and ultrasound roughness index (URI) were determined for each sample. URI was significantly higher in both repair groups than in intact cartilage (p < 0.05). The reflection parameters (R and IRC) were significantly lower in surgically repaired cartilage (p < 0.05) than in intact cartilage. Furthermore, AIB was significantly higher in surgically repaired cartilage than in intact tissue (p < 0.05). To conclude, the integrity of the rabbit articular cartilage repair could be quantitatively evaluated with the nondestructive ultrasound approach. In addition, clinically valuable qualitative information on the changes in cartilage integration, structure and composition could be extracted from the ultrasound images. In the present study, the structure and properties of repaired tissue were inferior to native tissue at 6 months after the operation. The applied ultrasound device and probes are FDA approved and, thus, applicable for the quantitative in vivo evaluation of human articular cartilage.
|
|
| 32. |
- Abramowicz, Jacques S., et al.
(författare)
-
Guidelines for Cleaning Transvaginal Ultrasound Transducers Between Patients
- 2017
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 43:5, s. 1076-1079
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this article is to provide guidance regarding the cleaning and disinfection of transvaginal ultrasound probes. These recommendations are also applicable to transrectal probes.
|
|
| 33. |
- Albinsson, John, et al.
(författare)
-
Improved tracking performance of lagrangian block-matching methodologies using block expansion in the time domain : In silico, phantom and invivo evaluations
- 2014
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier. - 0301-5629 .- 1879-291X. ; 40:10, s. 2508-2520
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to evaluate tracking performance when an extra reference block is added to a basic block-matching method, where the two reference blocks originate from two consecutive ultrasound frames. The use of an extra reference block was evaluated for two putative benefits: (i) an increase in tracking performance while maintaining the size of the reference blocks, evaluated using in silico and phantom cine loops; (ii) a reduction in the size of the reference blocks while maintaining the tracking performance, evaluated using in vivo cine loops of the common carotid artery where the longitudinal movement of the wall was estimated. The results indicated that tracking accuracy improved (mean - 48%, p<0.005 [in silico]; mean - 43%, p<0.01 [phantom]), and there was a reduction in size of the reference blocks while maintaining tracking performance (mean - 19%, p<0.01 [in vivo]). This novel method will facilitate further exploration of the longitudinal movement of the arterial wall. (C) 2014 World Federation for Ultrasound in Medicine & Biology.
|
|
| 34. |
|
|
| 35. |
|
|
| 36. |
|
|
| 37. |
- Byenfeldt, Marie, 1967-, et al.
(författare)
-
On patient related factors and their impact on ultrasound-based shear wave elastography of the liver
- 2018
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier. - 0301-5629 .- 1879-291X. ; 44:8, s. 1606-1615
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of the study was to investigate patient-related factors associated with either reliable or poorly reliable measurement results of ultrasound-based shear wave elastography (SWE) of the liver. A total of 188 patients were analyzed prospectively with binary logistic regression using the interquartile range/median as cutoff to define two groups based on reliable and poorly reliable SWE results. SWE results correlated significantly with liver biopsy. Factors associated with reliable SWE results (i.e., no negative impact on measurements) were age, sex, cirrhosis, antiviral and/or cardiovascular medication, smoking habits and body mass index. Factors associated with poorly reliable SWE results were increased skin-to-liver capsule distance (odds ratio = 3.08, 95% confidence interval: 1.70-5.60) and steatosis (odds ratio =2.89, 95% confidence interval: 1.33-6.28). These findings indicate that the interquartile range/median as a quality parameter is useful in avoiding poorly reliable SWE results. How best to examine patients with increased skin-to-liver capsule distance is a matter of some controversy, as the incidences of obesity, diabetes and metabolic syndrome are increasing worldwide; however, our results indicate that reliable SWE results can be obtained in this group of patients by using ultrasound-based SWE. (Email: marie.byenfeldt@umu.se, Marie.byenfeldt@aleris.se )
|
|
| 38. |
- Cinthio, Magnus, et al.
(författare)
-
A Method for Arterial Diameter Change Measurements Using Ultrasonic B-Mode Data.
- 2010
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 36:9, s. 1504-1512
-
Tidskriftsartikel (refereegranskat)abstract
- Arterial diameter change is related to distending blood pressure and is used in estimation of arterial stiffness parameters. A common technique to track the arterial walls is by integration of wall velocities estimated by different methods using cross correlation or tissue Doppler. However, because of the high pulse repetition frequency and the need for separate pulsing sequences, the B-mode image quality is affected. We have previously developed a fast algorithm for direct measurement of lumen diameter using B-mode images. In this study we have improved the technique to be more robust and also implemented measurements of diameter change, maximum differential wall velocity and relative diameter change of the common carotid artery noninvasively in vivo. The influence of the lateral width of the region of interest (ROI; 1 pixel, 0.1 mm, 0.5 mm, 1 mm, 2.5 mm and 5 mm) was evaluated. Using the optimal lateral width (2.5 mm), the systematic and random differences between two consecutive measurements were 21 mum and 105 mum, respectively, for lumen diameter measurement; -7 mum and 39 mum, respectively, for lumen diameter change measurements; -0.2 mm/s and 0.9 mm/s, respectively, for maximum relative wall velocity; and -0.2 % and 0.8 %, respectively, for measurements of the relative diameter change. The coefficient of variation (CV) was 1.9%, 5.2%, 7.9% and 6.0%, respectively. The study indicates that the reproducibility is sufficient for in vivo studies when the width of the ROI is 1.0 mm or wider. (E-mail: magnus.cinthio@elmat.lth.se).
|
|
| 39. |
- Cinthio, Magnus, et al.
(författare)
-
Intra-Observer Variability of Longitudinal Movement and Intramural Shear Strain Measurements of the Arterial Wall using Ultrasound Non-Invasively in vivo
- 2010
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 36:5, s. 697-704
-
Tidskriftsartikel (refereegranskat)abstract
- Using a recently developed high-resolution noninvasive ultrasonic method, we recently demonstrated that the intima-media complex of the common carotid artery show a bidirectional multiphasic longitudinal displacement of the same magnitude as the diameter change during the cardiac cycle. The longitudinal movement of the adventitial region was smaller, thus, we identified shear strain and, thus, shear stress, within the arterial wall. The aim of this study was to evaluate the intra-observer variability of measurement of the longitudinal displacement of the intima-media complex and the intramural shear strain of the common carotid artery in vivo using the new ultrasonic method. The evaluation was carried out by comparing two consecutive measurements on the common carotid artery of 20 healthy human subjects. According to the method of Bland Altman, we show that the systematic and random differences for the different phases of movement are acceptable in comparison to the measured displacement and no significant differences between the two measurements could be detected (p > 0.05 for all measured parameters). The coefficient of variation (CV) for measurement of the different phases of movement was ≤16%, including short-term physiologic variations. The higher variability in the measurement of the intramural shear strain (CV = 24%) has several explanations, which are discussed. In conclusion, this study shows that the present first ultrasonic method for high-resolution measurement of the longitudinal movement of the arterial wall is reliable and satisfactory for the further research of the longitudinal movement of the arterial wall in vivo. Further studies on the longitudinal movement of the arterial wall are important for developing an improved understanding of the physiology and the pathophysiology of the cardiovascular system.
|
|
| 40. |
- Cinthio, Magnus, et al.
(författare)
-
Longitudinal Movement of the Common Carotid Artery Wall : New Information on Cardiovascular Aging
- 2018
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629 .- 1879-291X. ; 44:11, s. 2283-2295
-
Tidskriftsartikel (refereegranskat)abstract
- Putative changes in the multiphasic pattern of longitudinal movement of the common carotid artery wall in the normal aging process are unknown. The aim of this study was to explore the phases, and resulting patterns, of the longitudinal movement of the intima–media complex of the human common carotid artery with respect to age and gender. One hundred thirty-five healthy non-smoking patients of different ages were investigated using in-house-developed ultrasound methods. The patterns of longitudinal movement seen in middle-aged and older patients were markedly different from those commonly seen in young patients, including the appearance of two additional phases of motion and, thus, new complex patterns. The displacement and maximum velocity of one of the phases, occurring at the time of aortic valve closure, increased quadratically with age in both men and women.
|
|
| 41. |
- Dubiel, M, et al.
(författare)
-
Computer analysis of three-dimensional power angiography images of foetal cerebral, lung and placental circulation in normal and high-risk pregnancy
- 2005
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 31:3, s. 321-327
-
Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional (3-D) ultrasound (US) has greatly improved evaluation of organ circulation. The aim of this study was to explore the possible use of this new technique in normal and high-risk pregnancies. Fetal brain, lung and placenta 3-D power Doppler signal intensity were recorded in 115 normal singleton pregnancies (24 to 42 weeks gestation) and in 67 high-risk pregnancies. Mean image pixel signal intensity was calculated for each organ and a brain-lung ratio. In normal pregnancy, placental and lung signal intensity increased until 33, with a rapid decrease after 38, weeks of gestation. Fetal cerebral signal intensity increased with gestational age. Placental and fetal lung signal intensity was significantly lower in high-risk pregnancies than in the control group, with increased fetal brain and brain-lung ratios. The present results suggest a reduction of placental perfusion after 38 weeks of gestation in normal pregnancy, with redistribution of fetal circulation. Lung signal intensity increased abruptly at 32 weeks of gestation, which might reflect lung maturity. The new method showed signs of centralization of fetal circulation at the end of gestation. The results might suggest a possible clinical use for fetal surveillance in high-risk pregnancies.
|
|
| 42. |
|
|
| 43. |
- Erlöv, Tobias, et al.
(författare)
-
Automatic Measurements of Diameter, Distension and Intima Media Thickness of the Aorta in Premature Rabbit Pups Using B-Mode Images.
- 2014
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 40:2, s. 371-377
-
Tidskriftsartikel (refereegranskat)abstract
- To improve cardiovascular research, there is a growing need for arterial characterization in small animals. We developed a method, ARTIC (arterial characterization) for measuring lumen diameter, distension and intima media thickness (IMT). In this study ARTIC was used to automatically characterize the aorta of premature rabbit pups. Automatic measurements were compared with manual measurements, both performed by three observers. Diameter was 769 ± 140 μm (manual) and 766 ± 142 μm (automatic), distension was 35 ± 15 μm (manual) and 40 ± 12 μm (automatic) and IMT was 84 ± 11 μm (manual) and 88 ± 8 μm (automatic) (mean ± standard deviation). The variation in the measured diameter, distension and IMT ranged from 1.1% to 26.0% (manual) and from 1.0% to 9.0% (automatic). The intra-class correlation coefficient ranged from 33.0% to 99.3% (manual) and from 76.9% to 99.6% (automatic). The evaluation revealed that it is feasible to use ARTIC on B-mode images of arteries with small dimensions, which makes it a useful tool for arterial characterization in small animals.
|
|
| 44. |
- Espahbodi, S, et al.
(författare)
-
Colour Doppler ultrasound of the lumbar arteries: A novel application and reproducibility study in healthy subjects
- 2006
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 32:2, s. 171-182
-
Tidskriftsartikel (refereegranskat)abstract
- Lumbar arteries are important because they are the main source of blood supply to the lumbar spine structures. However, these vessels and their flow characteristics have received little attention and their role in conditions such as low back pain remains unclear. The present study 1. describes the application of duplex ultrasonography in the assessment of lumbar artery blood flow and 2. evaluates the interobserver and intraobserver reproducibility of lumbar artery Doppler velocimetry. A total of 13 healthy volunteers were evaluated by two different examiners successively on the same day and measurements repeated by the same examiners I week later. Peak systolic velocities of lumbar arteries were recorded at an optimal angle below 60 degrees. Overall mean peak systolic velocity (+/- SD) for lumbar arteries was 0.158 +/- 0.051 m/s, and mean Doppler angle (+/- SD) was 24.6 +/- 14.5 degrees. For interobserver variability, the coefficient of variation was 23.4% and SD of differences 0.037 m/s. Reliable results of lumbar artery Doppler velocimetry demonstrate its applicability in future clinical investigations in patients with low back disorders. (E-mail: shima.espahbodi@imperial.ac.uk) (C) 2006 World Federation for Ultrasound in Medicine & Biology.
|
|
| 45. |
- Grishenkov, Dmitry, 1983-, et al.
(författare)
-
Characterization of acoustic properties of PVA-shelled ultrasound contrast agents : linear properties (Part I)
- 2009
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629 .- 1879-291X. ; 35:7, s. 1127-1138
-
Tidskriftsartikel (refereegranskat)abstract
- This work examines the linear acoustic behavior of ultrasound contrast agents made of three types of poly (vinyl alcohol) (PVA) shelled microbubbles manufactured at different pH and temperature conditions. Back-scattered power, attenuation coefficient and phase velocity of ultrasonic waves propagating through suspensions of PVA contrast agents were measured at temperature values ranging between 24 degrees C and 37 degrees C in a frequency range from 3 MHz to 13 MHz. Enhancement of the backscattered power higher than 20 dB and displaying a weak dependence on temperature was observed. Attenuation and phase velocity, on the other hand, showed higher sensitivity to temperature variations. A modified version of the Church model, which accounts for the dispersion of the dynamic modulus of the PVA shells, was developed to simultaneously fit the attenuation and phase velocity data at 24 degrees C. The frequency dependence of the storage modulus was found to be that of semiflexible polymeric networks. On the other hand, the frequency dependence of the dynamic loss modulus suggests that additional mechanisms, which may be related to the finite dimensions of the shell and/or to its inhomogeneity, may play a significant role in the dissipation of the acoustic energy. For the microbubbles of interest, this model predicts frequency dependent resonance frequency higher than 100 MHz.
|
|
| 46. |
- Grishenkov, Dmitry, 1983-, et al.
(författare)
-
Characterization of acoustic properties of PVA-shelled ultrasound contrast agents : ultrasound-induced fracture (Part II)
- 2009
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629 .- 1879-291X. ; 35:7, s. 1139-1147
-
Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the magnitude of the peak negative pressure, P-thr, at which ultrasound contrast agents fracture is relevant for using these microbubbles both as devices for contrast enhancement purposes, as well as carriers of drugs to be delivered locally. In the second part of this communication, the acoustic properties of three types of microbubbles stabilized by poly (vinyl alcohol) (PVA) shells are further investigated. In particular, the dependence of P-thr on system parameters such as the number of cycles, frequency and exposure is examined. The effects of temperature, blood and, wherever data are available, of the dimension of the microbubbles on P-thr are also considered. The large shelf thickness notwithstanding, the results of this investigation show that at room temperature, PVA contrast agents fracture at negative peak pressure values within the recommended safety limit. Furthermore, P-thr decreases with increasing temperature, radius of the microbubbles and number of cycles of the incident wave. Fatigue seems to be a physical mechanism playing a dominant role in the fracture process. The effect of blood on P-thr varies according to condition under which the microbubbles have been synthesized, although stiffening of the shell is observed in most cases. In conclusion, these results suggest that PVA-shelled microbubbles may offer a potentially viable system to be employed for both imaging and therapeutic purposes.
|
|
| 47. |
- Grönlund, Christer, et al.
(författare)
-
Imaging two-dimensional mechanical waves of skeletal muscle contraction
- 2013
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629 .- 1879-291X. ; 39:2, s. 360-369
-
Tidskriftsartikel (refereegranskat)abstract
- Skeletal muscle contraction is related to rapid mechanical shortening and thickening. Recently, specialized ultrasound systems have been applied to demonstrate and quantify transient tissue velocities and one-dimensional (1-D) propagation of mechanical waves during muscle contraction. Such waves could potentially provide novel information on musculoskeletal characteristics, function and disorders. In this work, we demonstrate two-dimensional (2-D) mechanical wave imaging following the skeletal muscle contraction. B-mode image acquisition during multiple consecutive electrostimulations, speckle-tracking and a time-stamp sorting protocol were used to obtain 1.4 kHz frame rate 2-D tissue velocity imaging of the biceps brachii muscle contraction. The results present novel information on tissue velocity profiles and mechanical wave propagation. In particular, counter-propagating compressional and shear waves in the longitudinal direction were observed in the contracting tissue (speed 2.8-4.4 m/s) and a compressional wave in the transverse direction of the non-contracting muscle tissue (1.2-1.9 m/s). In conclusion, analysing transient 2-D tissue velocity allows simultaneous assessment of both active and passive muscle tissue properties. (E-mail: christer.gronlund@vll.se) (C) 2013 World Federation for Ultrasound in Medicine & Biology.
|
|
| 48. |
- Harling, Solweig, et al.
(författare)
-
Quantification of left to right shunt in patent ductus arteriosus by color doppler
- 2009
-
Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 35, s. 403-408
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrasound is a reliable tool to diagnose patent ductus arteriosus in premature infants but no reliable noninvasive method exists to quantify ductal flow. The aim of this study was to quantify the size of the shunt via persistent ductus arteriosus from pixel counts in color Doppler flow images. A cotton band was placed around the ductus arteriosus of newborn lambs to adjust the magnitude of flow. For flow measurements, ultrasonic transit time flow probes were applied around the ascending aorta and ductus arteriosus. Twenty-four different flow states were attained in four newborn lambs. An Acuson Sequoia scanner equipped with a 7 MHz transducer was used to register Doppler data and images with maximal color distribution during diastole in the pulmonary artery longitudinal sections (PALS). Each image-pixel was matched with the color velocity bar and the pixels were assigned to the corresponding flow velocity. The total area showing color relative to the area of the PALS correlated well with the amount of ductal flow (r = 0.87, r(2) = 0.75, p < 0.001). When Qp/Qs was >1.4:1, more than 40% of the area in PALS in diastole exhibited color information. Similarly, the color pixel velocities squared correlated with the size of the shunt. Quantification of the percentage of pixels in a color Doppler registration via a computer-based analysis shows a high correlation with the size of ductal shunting. (E-mail: solweig.harling@med.lu.se).
|
|
| 49. |
- Hedman, Kristofer, et al.
(författare)
-
ECHOCARDIOGRAPHIC CHARACTERIZATION OF THE INFERIOR VENA CAVA IN TRAINED AND UNTRAINED FEMALES
- 2016
-
Ingår i: Ultrasound in Medicine and Biology. - : ELSEVIER SCIENCE INC. - 0301-5629 .- 1879-291X. ; 42:12, s. 2794-2802
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of the study was to explore the long-and short-axis dimensions, shape and collapsibility of the inferior vena cava in 46 trained and 48 untrained females (mean age: 21 +/- 2 y). Echocardiography in the subcostal view revealed a larger expiratory long-axis diameter (mean: 24 +/- 3 vs. 20 +/- 3 mm, p amp;lt; 0.001) and short-axis area (mean: 5.5 +/- 1.5 vs. 4.7 +/- 1.4 cm(2), p = 0.014) in trained females. IVC shape (the ratio of short-axis major to minor diameters) and the relative decrease in IVC dimension with inspiration were similar for the two groups. The IVC long-axis diameter reflected short-axis minor diameter and was correlated to maximal oxygen uptake (r = 0.52, p amp;lt; 0.01). In summary, the results indicate that trained females have a larger IVC similar in shape and respiratory decrease in dimensions to that of untrained females. The long-axis diameter corresponded closely to short-axis minor diameter and, thus, underestimates maximal IVC diameter. (E-mail: kristofer.hedman@liu.se) (C) 2016 The Authors. Published by Elsevier Inc. on behalf of World Federation for Ultrasound in Medicine amp; Biology.
|
|
| 50. |
|
|
