Muhammad Arif

Estimation of Urinary Flow Velocity in Models of Obstructed and Unobstructed Urethras by Decorrelation of Ultrasound Radiofrequency Signals

The feasibility of estimating urinary flow velocity from the decorrelation of radiofrequency (RF) signals was investigated in soft tissue-mimicking models of obstructed and unobstructed urethras. The decorrelation was studied in the near field, focal zone and far field of the ultrasound beam. Furthermore, the effect of beam width was investigated. The results of this study suggest that it is feasible to estimate flow velocity in models of the urethra by quantifying the decorrelation of RF ultrasound signals. The decorrelation slope increased more rapidly and more linearly with increasing velocity in the focal zone than in the near and far field. A preliminary example of an in vivo measurement in a healthy volunteer illustrated that this method has potential for clinical use in the future.

Dependence of ultrasound decorrelation on urine scatter particle concentration for a non-invasive diagnosis of bladder outlet obstruction

We investigated the influence of scattering particles concentration on the decorrelation of ultrasound signals for urinary flow imaging in a urethra model. A flexible urethra model made from PolyVinyl Alcohol (PVA) was perfused at flow rate of 10 ml/s with five diluted urine solutions prepared from morning urine samples of 4 healthy volunteers and seven aqueous solutions containing silica gel as scattering particles. During flow, ten ultrasound RadioFrequency (RF) data sets were acquired for each solution at a pulse repetition frequency of 5 kHz. Correlation coefficients between each two sequential RF-data sets were calculated as a function of particle concentration. The results depict that average correlation increases with an increase in particle concentration. The curves derived from the urine samples of the volunteers displayed a behavior similar to that of the silica particle aqueous solutions. Therefore, we conclude that urinary flow imaging using the decorrelation method in patients might be feasible.

Noninvasive Diagnosis of Bladder Outlet Obstruction in Patients with Lower Urinary Tract Symptoms Using Ultrasound Decorrelation Analysis

PURPOSE We developed a noninvasive method to diagnose bladder outlet obstruction. An ultrasound based decorrelation method was applied in male patients with lower urinary tract symptoms. MATERIALS AND METHODS In 60 patients ultrasound data were acquired transperineally while they were voiding while sitting. Each patient also underwent a standard invasive pressure flow study. RESULTS 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 bladder outlet obstruction than in unobstructed patients and healthy volunteers. ROC analysis resulted in an AUC of 0.96, 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, measured in the separate pressure flow studies. CONCLUSIONS It is possible to noninvasively diagnose bladder outlet obstruction using the ultrasound decorrelation technique.

Noninvasive estimation of the pressure profile in the male urethra using ultrasound imaging

PURPOSE 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. METHODS First, the compliances (Youngs 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 pressure conditions). The estimated pressures up- and downstream of the obstruction were compared with the corresponding measured pressures. In the obstructed region, the strain gradient was estimated using linear regression. RESULTS The luminal pressure values estimated from the ultrasound data up- and downstream of the obstruction were not significantly different from the corresponding measured pressures. The general pressure profile showed a decrease along the length of the obstruction followed by a small increase after the obstruction. The strain gradient in the obstructed region reflected the decrease in urethral pressure and increased with flow rate and degree of obstruction. CONCLUSIONS The results from this model study illustrate the feasibility of noninvasive estimation of the urethral pressure profile using ultrasound. This offers the prospect of a noninvasive, ultrasound based diagnostic tool for assessment of bladder outlet obstruction in men with lower urinary tract symptoms.

Diagnosing Bladder Outlet Obstruction Using Non-invasive Decorrelation-Based Ultrasound Imaging: A Feasibility Study in Healthy Male Volunteers

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.

Needle Tip Visibility in 3D Ultrasound Images

AimNeedle visibility is crucial for effective and safe ultrasound-guided interventional procedures. Several studies have investigated needle visibility in 2D ultrasound imaging, but less information is available for 3D ultrasound imaging, a modality that has great potential for image guidance interventions. We performed a prospective study, to quantitatively compare the echogenicity of various commercially available needles in 3D ultrasound images used in clinical practice under freehand needle introduction.Materials and MethodsA set of seven needles, containing biopsy needles, a TIPS needle, an ablation needle and a puncture needle, were included in the study. A liver-mimicking phantom and cow liver were punctured by each needle. 3D sweeps and real-time 3D data were acquired at three different angles (20°, 55° and 90°). Needle visibility was quantified by calculating contrast-to-noise ratio.ResultsIn the liver-mimicking phantom, all needles showed better visibility than in the cow liver. At large angles, contrast-to-noise ratio and needle visibility were almost similar in both cases, but at lower angles differences in visibility were observed with different types of needles.ConclusionThe contrast-to-noise ratio increased with the increase in angle of insonation. The difference in visibility of different needles is more pronounced at 20° angle. The echogenic properties of inhomogeneous cow liver tissues make the needles visibility worse as compared to a homogenous phantom. The needle visibility becomes worse in 3D real-time data as compared to 3D ultrasound sweeps.

Needle tip visibility in 3D ultrasound images

Needle visibility is of crucial importance for ultrasound guided interventional procedures. However, several factors, such as shadowing by bone or gas and tissue echogenic properties similar to needles, may compromise needle visibility. Additionally, small angle between the ultrasound beam and the needle, as well as small gauged needles may reduce visibility. Variety in needle tips design may also affect needle visibility. Whereas several studies have investigated needle visibility in 2D ultrasound imaging, no data is available for 3D ultrasound imaging, a modality that has great potential for image guidance interventions1. In this study, we evaluated needle visibility using a 3D ultrasound transducer. We examined different needles in a tissue mimicking liver phantom at three angles (200, 550 and 900) and quantify their visibility. The liver phantom was made by 5% polyvinyl alcohol solution containing 1% Silica gel particles to act as ultrasound scattering particles. We used four needles; two biopsy needles (Quick core 14G and 18G), one Ablation needle (Radiofrequency Ablation 17G), and Initial puncture needle (IP needle 17G). The needle visibility was quantified by calculating contrast to noise ratio. The results showed that the visibility for all needles were almost similar at large angles. However the difference in visibility at lower angles is more prominent. Furthermore, the visibility increases with the increase in angle of ultrasound beam with needles.

Dependence of ultrasound decorrelation on urine scatter particle concentration

We investigated the influence of scattering particles concentration on the decorrelation of ultrasound signals for urinary flow imaging in a urethra model. A flexible urethra model made from PolyVinyl Alcohol (PVA) was perfused at flow rate of 10 ml/s with five diluted urine solutions prepared from morning urine samples of 4 healthy volunteers and seven aqueous solutions containing silica gel as scattering particles. During flow, ten ultrasound RadioFrequency (RF) data sets were acquired for each solution at a pulse repetition frequency of 5 kHz. Correlation coefficients between each two sequential RF-data sets were calculated as a function of particle concentration. The results depict that average correlation increases with an increase in particle concentration. The curves derived from the urine samples of the volunteers displayed a behavior similar to that of the silica particle aqueous solutions. Therefore, we conclude that urinary flow imaging using the decorrelation method in patients might be feasible.