Tim Idzenga - Academia.edu (original) (raw)

Papers by Tim Idzenga

World Journal of Urology, Jun 19, 2007

In patient studies the correlation between maximum urethral closure pressure (MUCP) and Valsalva ... more In patient studies the correlation between maximum urethral closure pressure (MUCP) and Valsalva leak point pressure (LPP) is meagre at best (r = 0.22-0.50). We therefore studied the relation between MUCP and LPP in a Xexible and extensible model urethra. We applied diVerently sized pressure zones and diVerent degrees of resistance to a biophysical model urethra by stepwise inXating three types of blood pressure cuV placed around the model. At each degree of resistance we measured detrusor LPP, an in vitro equivalent of Valsalva LPP. Subsequently, we recorded the Urethral Pressure ProWle using a water-perfused 5F end-hole catheter at four withdrawal rates and Wve perfusion rates and calculated MUCP. We tested the dependence of LPP on pressure zone length and MUCP on perfusion rate, withdrawal rate and pressure zone length using analysis of variance. We tested the correlation between LPP and MUCP using Pearson's correlation coeYcient and Linear Regression. LPP did not signiWcantly depend on the pressure zone length (P = 0.80) and increased linearly with increasing cuV pressure. MUCP also increased with increasing cuV pressure, however, MUCP signiWcantly depended (P < 0.01) on perfusion rate, withdrawal rate and pressure zone length. MUCP increased with increasing perfusion rate, and decreased with increasing withdrawal rate. In our model urethra MUCP only accurately reXected urethral resistance for a very limited number of combinations of perfusion rate and withdrawal rate. LPP reXected urethral resistance independent of the type of pressure zone.

Bioscience Hypotheses, 2009

Myocardial infarction and stroke are two of the leading causes of death and primarily triggered b... more Myocardial infarction and stroke are two of the leading causes of death and primarily triggered by destabilization of atherosclerotic plaques. Fatty streaks are known to develop at sites in the arterial wall where shear stress is low. These fatty streaks can develop into more advanced plaques that are prone to rupture. Rupture leads to thrombus formation, which may subsequently result

Phys Med Biol, 2010

Ultrasound strain imaging is used to measure local tissue deformations. Usually, only strains alo... more Ultrasound strain imaging is used to measure local tissue deformations. Usually, only strains along the ultrasound beam are estimated, because those estimates are most precise, due to the availability of phase information. For estimating strain in other directions we propose to steer the ultrasound beam at an angle, which allows estimating different projections of the 2D strain tensor, while phase information remains available. This study investigates beam steering at maximally three different angles to determine the full 2D strain tensor. The method was tested on simulated and experimental data of an inclusion phantom and a vessel phantom. The combination of data from a non-steered acquisition and acquisitions at a large positive and an equally large but negative steering angle enabled the most precise estimation of the strain components. The method outperforms conventional methods that do not use beam steering.

The Journal of urology, Jan 3, 2016

To develop a non-invasive method for diagnosing Bladder Outlet Obstruction (BOO), an ultrasound b... more To develop a non-invasive method for diagnosing Bladder Outlet Obstruction (BOO), an ultrasound based decorrelation method was applied in male patients with Lower Urinary Tract Symptoms (LUTS). In 60 patients ultrasound data were acquired transperineally while they were voiding in sitting position. Each patient also underwent a standard invasive pressure-flow study (PFS). High frequent sequential ultrasound images were successfully recorded during voiding in 45 patients. The decorrelation (decrease in correlation) between subsequent ultrasound images was higher in patients with BOO than in unobstructed patients and healthy volunteers. Receiver Operating Characteristic (ROC) analysis resulted in an area under the curve (AUC) of 0.96, a 95% specificity and 88% sensitivity. A linear relationship was fitted to the decorrelation values as a function of the degree of obstruction represented by the Bladder Outlet Obstruction Index (BOOI), measured in the separate PFS. It is possible to non...

Artery Research, 2010

50e00 mg daily for one year. Endothelial function (Salbutamol-induced vasodilation), wave reflect... more 50e00 mg daily for one year. Endothelial function (Salbutamol-induced vasodilation), wave reflection (Augmentation index (AI x )), carotid-femoral pulse wave velocity (PWV), carotid artery intima-media thickness (IMT) and left ventricular wall thickness were measured at baseline, 6 months, and 12 months of treatment. Results: NEB and MET decreased equally brachial blood pressure (BP), whereas reduction in central pulse pressure and left ventricular wall thickness was significant only in the NEB group. Left ventricular wall thickness change was significantly related to central systolic BP change (r Z 0.41; P Z 0.001) and central pulse pressure change (r Z 0.32; P Z 0.01). No significant changes in AIx, PWV and IMT were detected in either treatment group. Endothelial function improved significantly after 6 months in the NEB treatment group. Conclusion: Our study expands earlier observations with vasodilating BB and shows that nebivolol has a stronger impact on central blood pressure and left ventricular wall thickness reduction than metoprolol. Thus, b-blockers with vasodilating properties may offer a clear advantage over a conventional bblocker in antihypertensive therapy.

Ultrasound in medicine & biology, Jan 21, 2015

A feasibility study on the applicability of an ultrasound decorrelation method to urinary flow im... more A feasibility study on the applicability of an ultrasound decorrelation method to urinary flow imaging was carried out in 20 healthy male volunteers, to provide a basis for a non-invasive approach to diagnose bladder outlet obstruction. Each volunteer voided five times in a flow meter in standing position. During each voiding, ultrasound radiofrequency frames were acquired transperineally at different flow rates. The results indicated that the decrease in correlation (decorrelation) of ultrasound radiofrequency signals had no unique relation with flow rate, but decreased distinctively with urinary flow velocity. In most of the healthy volunteers, the decorrelation was small because of the low flow velocity. However, because of the different flow velocities in volunteers, the variation in slope between volunteers was statistically significant. Therefore, it is probably possible to use the decorrelation method to differentiate between healthy persons and patients with obstruction.

Ultrasound in Medicine & Biology, 2015

A feasibility study on the applicability of an ultrasound decorrelation method to urinary flow im... more A feasibility study on the applicability of an ultrasound decorrelation method to urinary flow imaging was carried out in 20 healthy male volunteers, to provide a basis for a non-invasive approach to diagnose bladder outlet obstruction. Each volunteer voided five times in a flow meter in standing position. During each voiding, ultrasound radiofrequency frames were acquired transperineally at different flow rates. The results indicated that the decrease in correlation (decorrelation) of ultrasound radiofrequency signals had no unique relation with flow rate, but decreased distinctively with urinary flow velocity. In most of the healthy volunteers, the decorrelation was small because of the low flow velocity. However, because of the different flow velocities in volunteers, the variation in slope between volunteers was statistically significant. Therefore, it is probably possible to use the decorrelation method to differentiate between healthy persons and patients with obstruction.

Atherosclerosis Disease Management, 2010

The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic pl... more The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic plaques. The chance of a plaque to rupture is related to its composition and geometry. Ultrasound (shear) strain imaging allows assessment of local tissue mechanics and possible risk assessment of vulnerable plaques. Intravascularly, in coronary arteries using a catheter, strain imaging has been demonstrated to be successful. At

2009 IEEE International Ultrasonics Symposium, 2009

The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic pl... more The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic plaques. It has been hypothesized that the shear strain, induced in the adventitial layer by the pulsating pressure wave and blood flow, initiates and/or stimulates the development of such a plaque into a rupture-prone, vulnerable plaque. The aim of this paper was to experimentally test and validate methods

Bioscience Hypotheses, 2009

Myocardial infarction and stroke are two of the leading causes of death and primarily triggered b... more Myocardial infarction and stroke are two of the leading causes of death and primarily triggered by destabilization of atherosclerotic plaques. Fatty streaks are known to develop at sites in the arterial wall where shear stress is low. These fatty streaks can develop into more advanced plaques that are prone to rupture. Rupture leads to thrombus formation, which may subsequently result

2010 IEEE International Ultrasonics Symposium, 2010

ABSTRACT Ultrasound strain imaging can be used to assess local mechanical properties of tissue. F... more ABSTRACT Ultrasound strain imaging can be used to assess local mechanical properties of tissue. From conventional non-steered 2D ultrasound data, the axial (along the beam) displacements and strains can be estimated precisely, whereas lateral (perpendicular to the ultrasound beam) displacements and corresponding strains are more complicated to estimate. The lateral displacements/ strains can be estimated more precisely by adding data from acquisitions at various large beam steering angles, although frame rates are reduced. Plane wave ultrasound transmission enables ultrasound acquisition at high frame rates. This study investigates beam steered plane wave ultrasound transmission for full strain tensor estimation at high frame rates. Using finite element modeling (FEM) and Field II, ultrasound radio frequency data of a vessel with a vulnerable plaque were generated before and after the vessel underwent an intraluminal pressure increase of 4 mmHg. RF data were simulated for a linear array transducer (3-11 MHz, fs = 39 MHz, pitch = 135 μm) that either transmitted focused pulses or plane waves at beam steering angles of -30°, 0° and 30°. In receive dynamic focusing was applied. Band limited noise was added to obtain a signal-to- noise ratio of 20 dB. Displacements were iteratively estimated using 2D cross-correlation. Next, principal strains were derived using 1D least squares strain estimators. The absolute differences between the estimated principal strains and the FEM principal strains were determined to compare the transmission methods. It was found that plane wave beam steering enabled a fast and more precise estimation (Wilcoxon, P

Medical physics, 2015

Decreased prostatic compliance as a result of benign prostatic enlargement can result in bladder ... more Decreased prostatic compliance as a result of benign prostatic enlargement can result in bladder outlet obstruction. This changes the urethral pressure profile during voiding. In this study, the authors propose noninvasive estimation of this pressure profile. In four soft tissue mimicking models of the urethra with increasing degree of obstruction, the authors measured deformation of the wall during flow, using ultrasound imaging. Combined with estimates of the model compliance, the authors were able to estimate the pressure profile. First, the compliances (Young's moduli) of the four models were derived by applying static luminal pressure and measuring the resulting strain of the tissue using an ultrasound imaging system. Next, continuous flow was applied to the models and the strain in the urethral wall was measured similarly. The luminal pressure profile was estimated from the strain (measured under continuous flow conditions) and the derived compliance (measured under static...

Current opinion in urology, Jan 18, 2015

An imaging tool providing reliable prostate cancer (PCa) detection and localization is necessary ... more An imaging tool providing reliable prostate cancer (PCa) detection and localization is necessary to improve the diagnostic pathway with imaging targeted biopsies. This review presents the latest developments in existing and novel ultrasound modalities for the detection and localization of PCa. The ultrasound modalities that were very promising on introduction (HistoScanning and Doppler) have shown a wane in performance when tested in larger patient populations. In the meantime, novel ultrasound modalities have emerged in the field of PCa detection. Modalities, such as shear wave elastography (SWE) and contrast-enhanced ultrasound (CEUS) show very promising results. SWE produces an absolute elasticity measure and removes the need for manual compression of the tissue. The former allows comparison between scans and patients, the latter reduces the interoperator variability. Quantification of CEUS enables easily interpretable and accurate imaging of the microvascular changes associated ...

2011 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2011

ABSTRACT With ultrasound strain imaging, the function of tissue and organs can be identified. The... more ABSTRACT With ultrasound strain imaging, the function of tissue and organs can be identified. The technique uses multiple images, acquired from tissue under different degrees of deformation. We developed techniques for cardiovascular applications. The displacement of tissue can be determined at micrometer scale using the raw (i.e., radio frequency, RF-) ultrasound data, containing the amplitude as well as the phase information. A 2D/3D cross-correlation based coarse-to-fine strain estimation strategy is used to quantify the strain. The maximum value of the cross-correlation function is also used for automated segmentation. Furthermore, strain estimation is improved by strain compounding, a technique that combines data acquired at multiple beam-steered angles. Validation experiments in phantoms demonstrated that accurate strain images can be determined using the proposed technique and that strain compounding improves the strain estimate in directions perpendicular to the ultrasound beam. Evaluation using cardiac data in animals showed that automated segmentation provides accurate quantification of the cardiac output and that the strain in the heart walls can be estimated in three dimensions. Segmentation based on combining temporal correlation and filtered echo level outperforms segmentation based on echo level alone.

Urology, 2015

To develop an ultrasound (US)-based method for noninvasive diagnosing of bladder outlet obstructi... more To develop an ultrasound (US)-based method for noninvasive diagnosing of bladder outlet obstruction, and the relationship between decorrelation of sequential US images and the degree of obstruction in a urethra model was studied. A flexible model of a male urethra was constructed from 15% aqueous solution of polyvinyl alcohol cryogel. To create 4 different degrees of obstruction, polyvinyl alcohol rings representing the prostate were placed around the model. Each model was perfused at different flow rates (1-15 mL/s) with an aqueous solution containing scattering particles mimicking urine. At each flow rate, 10 sequential US images were acquired. The average correlation coefficients between the images were calculated and plotted as a function of the degree of obstruction and the flow rate. The average correlation decreased approximately linearly with an increase in the degree of obstruction. This decrease in correlation (decorrelation) might be due to turbulence caused by the obstru...

The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic pl... more The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic plaques. It is hypothesized that shear strain in the adventitia initiates and/or stimulates development of these plaques into rupture-prone, vulnerable plaques. Therefore, assessment of shear strain might yield a prognosis for the development of vulnerable plaques. In simulations and phantom experiments, longitudinal shear strain was estimated using RF and envelope-based methods and compared to the applied values. Additionally, longitudinal shear strain estimates in the adventitia of six healthy volunteers were determined. In both experiments, the variance of the RF-based estimates was significantly smaller than that of the envelope-based estimates (Wilcoxon, p &amp;amp;amp;amp;lt; 0.05). The periodicity of these estimates corresponded well with the cardiac cycle. The estimated values were found to be similar to previously published data. Furthermore, the signal-to-noise ratio of the shear strain estimate in the posterior wall based on RF-data was significantly higher (Wilcoxon, p 0 &amp;amp;amp;amp;lt; 0.05) than that based on envelope-data. In conclusion, noninvasive ultrasound strain imaging using radiofrequency signals appeared to allow adequate estimation of longitudinal shear strain in the adventitial layer of the carotid artery wall.

2011 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2011

Strain in the arterial wall can be estimated by crosscorrelation of radiofrequency ultrasound dat... more Strain in the arterial wall can be estimated by crosscorrelation of radiofrequency ultrasound data recorded at various blood pressure levels. Intravascular studies revealed a high correlation between high radial strain regions and plaque vulnerability in coronary arteries. A noninvasive variant of the technique is desired, since it will enable early screening for rupture prone plaques, also in asymptomatic populations. Recently, we have shown that it is possible to obtain more precise radial (and circumferential) strain estimates by combining data from multiple beam steered ultrasound acquisitions in phantoms. However, the multiangle method was tested using quasi-static data only, thus no motion artifacts were present. This study investigates the performance of the multi-angle method for pulsating vessels. Results are presented for a periodically pulsating vessel mimicking phantom and in vivo recordings of a healthy carotid artery. It is shown that the multi-angle technique also outperforms conventional single angle strain imaging for pulsating vessels. determined directly, but need to be derived from separately estimated axial (along the ultrasound beam) and lateral (perpendicular to the beam) data. From conventional linear array ultrasound acquisitions axial displacement and strain can be estimated accurately. However, the lateral counterpart is less accurate, due to the lower resolution and the lack of phase information in that direction. Recently we showed that more accurate lateral displacements can be obtained by combining axial information from acquisitions at two large beam steering angles [6]. In that study the beam steering approach was only tested for quasi-static experimental and simulated ultrasound data of simple phantoms. Quasi-static means that data were acquired for all beam steering angles in an initial state of deformation, after which the level of deformation was changed and another series of data was recorded. Thus, no tissue motion occurred during the change of steering angle and there was no misalignment of the angle information. In this study the performance of the beam steering method for more realistic cases is investigated. We apply the technique to simulations of a carotid artery with a vulnerable plaque, a periodically pulsating vessel phantom with a soft layer and a carotid artery of a healthy volunteer. The strain estimation performance of the multi-angle method is compared to that of conventional single-angle imaging. 2. MATERIALS & METHODS

2009 IEEE International Ultrasonics Symposium, 2009

ABSTRACT Strain imaging has been performed using 1D, 2D and 3D ultrasound data. Usually, strain i... more ABSTRACT Strain imaging has been performed using 1D, 2D and 3D ultrasound data. Usually, strain is only estimated in the beam direction, because of the availability of phase information. However, strain estimates in other directions are also desired, since most tissues are anisotropic. Beam steering enables measurement of different projections of the 2D displacement field while using phase information. The full 2D displacement field and strain tensor can be derived using multiple projections. This study aims at deriving the full 2D strain tensor by estimating only displacement along the beam while steering the beam at three angles, i.e. 0?, a positive, and a negative beam steering angle. Displacements were iteratively estimated using 2D cross-correlations. The 0? acquisition yielded the vertical displacement vector. Projection of the other measured displacements yielded the horizontal (lateral) vector. The full 2D strain tensor was derived using 1D least squares strain estimators. Since horizontal displacements and strains are usually the least accurate, these were first focused on. Horizontal displacements were estimated for simulated radiofrequency (rf) data of a block with a four times stiffer cylindrical inclusion before and after application of 2% vertical compression. Root mean squared error (RMSE) of the horizontal displacements were calculated for every symmetric pair of beam steering angles in the range of -30 to 30? with angular increments of 5?. The RMSE analysis was performed for signal-to-noise (SNR) levels of 5, 10, 20 and 50 dB. Beam steering combinations of about -25? and 25? were found to be most optimal. The technique&#39;s performance was maintained regardless of the SNR level. For an SNR of 5 dB a reduction in RMSE of up to 70% was observed. In analogy with the simulations, experiments were performed with a similar inclusion phantom made of polyvinyl alcohol. Using data from beam steering angles of -25?, 0? and 25? strain images were constructed for all stra- - in components and compared to strain images constructed without beam steering. The horizontal and shear strain images improved clearly with beam steering. Finally, the technique was also applied to derive radial and circumferential strain images for a homogeneous vessel phantom made of gelatin. Radially, SNRe and CNRe increased with 2.2 dB and 8 dB and circumferentially with 2.6 dB and 9.2 dB compared to non steered strain estimates. To conclude, the full 2D strain tensor can be accurately measured by using three beam steering angles.

World Journal of Urology, Jun 19, 2007

In patient studies the correlation between maximum urethral closure pressure (MUCP) and Valsalva ... more In patient studies the correlation between maximum urethral closure pressure (MUCP) and Valsalva leak point pressure (LPP) is meagre at best (r = 0.22-0.50). We therefore studied the relation between MUCP and LPP in a Xexible and extensible model urethra. We applied diVerently sized pressure zones and diVerent degrees of resistance to a biophysical model urethra by stepwise inXating three types of blood pressure cuV placed around the model. At each degree of resistance we measured detrusor LPP, an in vitro equivalent of Valsalva LPP. Subsequently, we recorded the Urethral Pressure ProWle using a water-perfused 5F end-hole catheter at four withdrawal rates and Wve perfusion rates and calculated MUCP. We tested the dependence of LPP on pressure zone length and MUCP on perfusion rate, withdrawal rate and pressure zone length using analysis of variance. We tested the correlation between LPP and MUCP using Pearson's correlation coeYcient and Linear Regression. LPP did not signiWcantly depend on the pressure zone length (P = 0.80) and increased linearly with increasing cuV pressure. MUCP also increased with increasing cuV pressure, however, MUCP signiWcantly depended (P < 0.01) on perfusion rate, withdrawal rate and pressure zone length. MUCP increased with increasing perfusion rate, and decreased with increasing withdrawal rate. In our model urethra MUCP only accurately reXected urethral resistance for a very limited number of combinations of perfusion rate and withdrawal rate. LPP reXected urethral resistance independent of the type of pressure zone.

Bioscience Hypotheses, 2009

Myocardial infarction and stroke are two of the leading causes of death and primarily triggered b... more Myocardial infarction and stroke are two of the leading causes of death and primarily triggered by destabilization of atherosclerotic plaques. Fatty streaks are known to develop at sites in the arterial wall where shear stress is low. These fatty streaks can develop into more advanced plaques that are prone to rupture. Rupture leads to thrombus formation, which may subsequently result

Phys Med Biol, 2010

Ultrasound strain imaging is used to measure local tissue deformations. Usually, only strains alo... more Ultrasound strain imaging is used to measure local tissue deformations. Usually, only strains along the ultrasound beam are estimated, because those estimates are most precise, due to the availability of phase information. For estimating strain in other directions we propose to steer the ultrasound beam at an angle, which allows estimating different projections of the 2D strain tensor, while phase information remains available. This study investigates beam steering at maximally three different angles to determine the full 2D strain tensor. The method was tested on simulated and experimental data of an inclusion phantom and a vessel phantom. The combination of data from a non-steered acquisition and acquisitions at a large positive and an equally large but negative steering angle enabled the most precise estimation of the strain components. The method outperforms conventional methods that do not use beam steering.

The Journal of urology, Jan 3, 2016

To develop a non-invasive method for diagnosing Bladder Outlet Obstruction (BOO), an ultrasound b... more To develop a non-invasive method for diagnosing Bladder Outlet Obstruction (BOO), an ultrasound based decorrelation method was applied in male patients with Lower Urinary Tract Symptoms (LUTS). In 60 patients ultrasound data were acquired transperineally while they were voiding in sitting position. Each patient also underwent a standard invasive pressure-flow study (PFS). High frequent sequential ultrasound images were successfully recorded during voiding in 45 patients. The decorrelation (decrease in correlation) between subsequent ultrasound images was higher in patients with BOO than in unobstructed patients and healthy volunteers. Receiver Operating Characteristic (ROC) analysis resulted in an area under the curve (AUC) of 0.96, a 95% specificity and 88% sensitivity. A linear relationship was fitted to the decorrelation values as a function of the degree of obstruction represented by the Bladder Outlet Obstruction Index (BOOI), measured in the separate PFS. It is possible to non...

Artery Research, 2010

50e00 mg daily for one year. Endothelial function (Salbutamol-induced vasodilation), wave reflect... more 50e00 mg daily for one year. Endothelial function (Salbutamol-induced vasodilation), wave reflection (Augmentation index (AI x )), carotid-femoral pulse wave velocity (PWV), carotid artery intima-media thickness (IMT) and left ventricular wall thickness were measured at baseline, 6 months, and 12 months of treatment. Results: NEB and MET decreased equally brachial blood pressure (BP), whereas reduction in central pulse pressure and left ventricular wall thickness was significant only in the NEB group. Left ventricular wall thickness change was significantly related to central systolic BP change (r Z 0.41; P Z 0.001) and central pulse pressure change (r Z 0.32; P Z 0.01). No significant changes in AIx, PWV and IMT were detected in either treatment group. Endothelial function improved significantly after 6 months in the NEB treatment group. Conclusion: Our study expands earlier observations with vasodilating BB and shows that nebivolol has a stronger impact on central blood pressure and left ventricular wall thickness reduction than metoprolol. Thus, b-blockers with vasodilating properties may offer a clear advantage over a conventional bblocker in antihypertensive therapy.

Ultrasound in medicine & biology, Jan 21, 2015

A feasibility study on the applicability of an ultrasound decorrelation method to urinary flow im... more A feasibility study on the applicability of an ultrasound decorrelation method to urinary flow imaging was carried out in 20 healthy male volunteers, to provide a basis for a non-invasive approach to diagnose bladder outlet obstruction. Each volunteer voided five times in a flow meter in standing position. During each voiding, ultrasound radiofrequency frames were acquired transperineally at different flow rates. The results indicated that the decrease in correlation (decorrelation) of ultrasound radiofrequency signals had no unique relation with flow rate, but decreased distinctively with urinary flow velocity. In most of the healthy volunteers, the decorrelation was small because of the low flow velocity. However, because of the different flow velocities in volunteers, the variation in slope between volunteers was statistically significant. Therefore, it is probably possible to use the decorrelation method to differentiate between healthy persons and patients with obstruction.

Ultrasound in Medicine & Biology, 2015

A feasibility study on the applicability of an ultrasound decorrelation method to urinary flow im... more A feasibility study on the applicability of an ultrasound decorrelation method to urinary flow imaging was carried out in 20 healthy male volunteers, to provide a basis for a non-invasive approach to diagnose bladder outlet obstruction. Each volunteer voided five times in a flow meter in standing position. During each voiding, ultrasound radiofrequency frames were acquired transperineally at different flow rates. The results indicated that the decrease in correlation (decorrelation) of ultrasound radiofrequency signals had no unique relation with flow rate, but decreased distinctively with urinary flow velocity. In most of the healthy volunteers, the decorrelation was small because of the low flow velocity. However, because of the different flow velocities in volunteers, the variation in slope between volunteers was statistically significant. Therefore, it is probably possible to use the decorrelation method to differentiate between healthy persons and patients with obstruction.

Atherosclerosis Disease Management, 2010

The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic pl... more The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic plaques. The chance of a plaque to rupture is related to its composition and geometry. Ultrasound (shear) strain imaging allows assessment of local tissue mechanics and possible risk assessment of vulnerable plaques. Intravascularly, in coronary arteries using a catheter, strain imaging has been demonstrated to be successful. At

2009 IEEE International Ultrasonics Symposium, 2009

The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic pl... more The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic plaques. It has been hypothesized that the shear strain, induced in the adventitial layer by the pulsating pressure wave and blood flow, initiates and/or stimulates the development of such a plaque into a rupture-prone, vulnerable plaque. The aim of this paper was to experimentally test and validate methods

Bioscience Hypotheses, 2009

Myocardial infarction and stroke are two of the leading causes of death and primarily triggered b... more Myocardial infarction and stroke are two of the leading causes of death and primarily triggered by destabilization of atherosclerotic plaques. Fatty streaks are known to develop at sites in the arterial wall where shear stress is low. These fatty streaks can develop into more advanced plaques that are prone to rupture. Rupture leads to thrombus formation, which may subsequently result

2010 IEEE International Ultrasonics Symposium, 2010

ABSTRACT Ultrasound strain imaging can be used to assess local mechanical properties of tissue. F... more ABSTRACT Ultrasound strain imaging can be used to assess local mechanical properties of tissue. From conventional non-steered 2D ultrasound data, the axial (along the beam) displacements and strains can be estimated precisely, whereas lateral (perpendicular to the ultrasound beam) displacements and corresponding strains are more complicated to estimate. The lateral displacements/ strains can be estimated more precisely by adding data from acquisitions at various large beam steering angles, although frame rates are reduced. Plane wave ultrasound transmission enables ultrasound acquisition at high frame rates. This study investigates beam steered plane wave ultrasound transmission for full strain tensor estimation at high frame rates. Using finite element modeling (FEM) and Field II, ultrasound radio frequency data of a vessel with a vulnerable plaque were generated before and after the vessel underwent an intraluminal pressure increase of 4 mmHg. RF data were simulated for a linear array transducer (3-11 MHz, fs = 39 MHz, pitch = 135 μm) that either transmitted focused pulses or plane waves at beam steering angles of -30°, 0° and 30°. In receive dynamic focusing was applied. Band limited noise was added to obtain a signal-to- noise ratio of 20 dB. Displacements were iteratively estimated using 2D cross-correlation. Next, principal strains were derived using 1D least squares strain estimators. The absolute differences between the estimated principal strains and the FEM principal strains were determined to compare the transmission methods. It was found that plane wave beam steering enabled a fast and more precise estimation (Wilcoxon, P

Medical physics, 2015

Decreased prostatic compliance as a result of benign prostatic enlargement can result in bladder ... more Decreased prostatic compliance as a result of benign prostatic enlargement can result in bladder outlet obstruction. This changes the urethral pressure profile during voiding. In this study, the authors propose noninvasive estimation of this pressure profile. In four soft tissue mimicking models of the urethra with increasing degree of obstruction, the authors measured deformation of the wall during flow, using ultrasound imaging. Combined with estimates of the model compliance, the authors were able to estimate the pressure profile. First, the compliances (Young's moduli) of the four models were derived by applying static luminal pressure and measuring the resulting strain of the tissue using an ultrasound imaging system. Next, continuous flow was applied to the models and the strain in the urethral wall was measured similarly. The luminal pressure profile was estimated from the strain (measured under continuous flow conditions) and the derived compliance (measured under static...

Current opinion in urology, Jan 18, 2015

An imaging tool providing reliable prostate cancer (PCa) detection and localization is necessary ... more An imaging tool providing reliable prostate cancer (PCa) detection and localization is necessary to improve the diagnostic pathway with imaging targeted biopsies. This review presents the latest developments in existing and novel ultrasound modalities for the detection and localization of PCa. The ultrasound modalities that were very promising on introduction (HistoScanning and Doppler) have shown a wane in performance when tested in larger patient populations. In the meantime, novel ultrasound modalities have emerged in the field of PCa detection. Modalities, such as shear wave elastography (SWE) and contrast-enhanced ultrasound (CEUS) show very promising results. SWE produces an absolute elasticity measure and removes the need for manual compression of the tissue. The former allows comparison between scans and patients, the latter reduces the interoperator variability. Quantification of CEUS enables easily interpretable and accurate imaging of the microvascular changes associated ...

2011 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2011

ABSTRACT With ultrasound strain imaging, the function of tissue and organs can be identified. The... more ABSTRACT With ultrasound strain imaging, the function of tissue and organs can be identified. The technique uses multiple images, acquired from tissue under different degrees of deformation. We developed techniques for cardiovascular applications. The displacement of tissue can be determined at micrometer scale using the raw (i.e., radio frequency, RF-) ultrasound data, containing the amplitude as well as the phase information. A 2D/3D cross-correlation based coarse-to-fine strain estimation strategy is used to quantify the strain. The maximum value of the cross-correlation function is also used for automated segmentation. Furthermore, strain estimation is improved by strain compounding, a technique that combines data acquired at multiple beam-steered angles. Validation experiments in phantoms demonstrated that accurate strain images can be determined using the proposed technique and that strain compounding improves the strain estimate in directions perpendicular to the ultrasound beam. Evaluation using cardiac data in animals showed that automated segmentation provides accurate quantification of the cardiac output and that the strain in the heart walls can be estimated in three dimensions. Segmentation based on combining temporal correlation and filtered echo level outperforms segmentation based on echo level alone.

Urology, 2015

To develop an ultrasound (US)-based method for noninvasive diagnosing of bladder outlet obstructi... more To develop an ultrasound (US)-based method for noninvasive diagnosing of bladder outlet obstruction, and the relationship between decorrelation of sequential US images and the degree of obstruction in a urethra model was studied. A flexible model of a male urethra was constructed from 15% aqueous solution of polyvinyl alcohol cryogel. To create 4 different degrees of obstruction, polyvinyl alcohol rings representing the prostate were placed around the model. Each model was perfused at different flow rates (1-15 mL/s) with an aqueous solution containing scattering particles mimicking urine. At each flow rate, 10 sequential US images were acquired. The average correlation coefficients between the images were calculated and plotted as a function of the degree of obstruction and the flow rate. The average correlation decreased approximately linearly with an increase in the degree of obstruction. This decrease in correlation (decorrelation) might be due to turbulence caused by the obstru...

The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic pl... more The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic plaques. It is hypothesized that shear strain in the adventitia initiates and/or stimulates development of these plaques into rupture-prone, vulnerable plaques. Therefore, assessment of shear strain might yield a prognosis for the development of vulnerable plaques. In simulations and phantom experiments, longitudinal shear strain was estimated using RF and envelope-based methods and compared to the applied values. Additionally, longitudinal shear strain estimates in the adventitia of six healthy volunteers were determined. In both experiments, the variance of the RF-based estimates was significantly smaller than that of the envelope-based estimates (Wilcoxon, p &amp;amp;amp;amp;lt; 0.05). The periodicity of these estimates corresponded well with the cardiac cycle. The estimated values were found to be similar to previously published data. Furthermore, the signal-to-noise ratio of the shear strain estimate in the posterior wall based on RF-data was significantly higher (Wilcoxon, p 0 &amp;amp;amp;amp;lt; 0.05) than that based on envelope-data. In conclusion, noninvasive ultrasound strain imaging using radiofrequency signals appeared to allow adequate estimation of longitudinal shear strain in the adventitial layer of the carotid artery wall.

2011 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2011

Strain in the arterial wall can be estimated by crosscorrelation of radiofrequency ultrasound dat... more Strain in the arterial wall can be estimated by crosscorrelation of radiofrequency ultrasound data recorded at various blood pressure levels. Intravascular studies revealed a high correlation between high radial strain regions and plaque vulnerability in coronary arteries. A noninvasive variant of the technique is desired, since it will enable early screening for rupture prone plaques, also in asymptomatic populations. Recently, we have shown that it is possible to obtain more precise radial (and circumferential) strain estimates by combining data from multiple beam steered ultrasound acquisitions in phantoms. However, the multiangle method was tested using quasi-static data only, thus no motion artifacts were present. This study investigates the performance of the multi-angle method for pulsating vessels. Results are presented for a periodically pulsating vessel mimicking phantom and in vivo recordings of a healthy carotid artery. It is shown that the multi-angle technique also outperforms conventional single angle strain imaging for pulsating vessels. determined directly, but need to be derived from separately estimated axial (along the ultrasound beam) and lateral (perpendicular to the beam) data. From conventional linear array ultrasound acquisitions axial displacement and strain can be estimated accurately. However, the lateral counterpart is less accurate, due to the lower resolution and the lack of phase information in that direction. Recently we showed that more accurate lateral displacements can be obtained by combining axial information from acquisitions at two large beam steering angles [6]. In that study the beam steering approach was only tested for quasi-static experimental and simulated ultrasound data of simple phantoms. Quasi-static means that data were acquired for all beam steering angles in an initial state of deformation, after which the level of deformation was changed and another series of data was recorded. Thus, no tissue motion occurred during the change of steering angle and there was no misalignment of the angle information. In this study the performance of the beam steering method for more realistic cases is investigated. We apply the technique to simulations of a carotid artery with a vulnerable plaque, a periodically pulsating vessel phantom with a soft layer and a carotid artery of a healthy volunteer. The strain estimation performance of the multi-angle method is compared to that of conventional single-angle imaging. 2. MATERIALS & METHODS

2009 IEEE International Ultrasonics Symposium, 2009

ABSTRACT Strain imaging has been performed using 1D, 2D and 3D ultrasound data. Usually, strain i... more ABSTRACT Strain imaging has been performed using 1D, 2D and 3D ultrasound data. Usually, strain is only estimated in the beam direction, because of the availability of phase information. However, strain estimates in other directions are also desired, since most tissues are anisotropic. Beam steering enables measurement of different projections of the 2D displacement field while using phase information. The full 2D displacement field and strain tensor can be derived using multiple projections. This study aims at deriving the full 2D strain tensor by estimating only displacement along the beam while steering the beam at three angles, i.e. 0?, a positive, and a negative beam steering angle. Displacements were iteratively estimated using 2D cross-correlations. The 0? acquisition yielded the vertical displacement vector. Projection of the other measured displacements yielded the horizontal (lateral) vector. The full 2D strain tensor was derived using 1D least squares strain estimators. Since horizontal displacements and strains are usually the least accurate, these were first focused on. Horizontal displacements were estimated for simulated radiofrequency (rf) data of a block with a four times stiffer cylindrical inclusion before and after application of 2% vertical compression. Root mean squared error (RMSE) of the horizontal displacements were calculated for every symmetric pair of beam steering angles in the range of -30 to 30? with angular increments of 5?. The RMSE analysis was performed for signal-to-noise (SNR) levels of 5, 10, 20 and 50 dB. Beam steering combinations of about -25? and 25? were found to be most optimal. The technique&#39;s performance was maintained regardless of the SNR level. For an SNR of 5 dB a reduction in RMSE of up to 70% was observed. In analogy with the simulations, experiments were performed with a similar inclusion phantom made of polyvinyl alcohol. Using data from beam steering angles of -25?, 0? and 25? strain images were constructed for all stra- - in components and compared to strain images constructed without beam steering. The horizontal and shear strain images improved clearly with beam steering. Finally, the technique was also applied to derive radial and circumferential strain images for a homogeneous vessel phantom made of gelatin. Radially, SNRe and CNRe increased with 2.2 dB and 8 dB and circumferentially with 2.6 dB and 9.2 dB compared to non steered strain estimates. To conclude, the full 2D strain tensor can be accurately measured by using three beam steering angles.