Citations

Ultrasonic contrast agents consisting of microbubbles are used to assess tissue perfusion. The microbubbles are highly reflective and nonlinear and thus produce harmonics that are stronger than those from tissues. However, the magnitude of harmonic signals resulting from a region with microbubbles also depends on the acoustic pressure of incident ultrasound and the attenuation of intervening tissues in the ultrasound path. Therefore, the harmonic magnitude, as used in traditional harmonic imaging, may not be a reliable indicator of the presence or absence of microbubbles, and hence, tissue perfusion. To compensate for these effects, we present two parameters defined as the ratio of the harmonic to the fundamental component ( HFR) and the ratio of the harmonic to squared fundamental ( HSFR). A simplified model is used to illustrate the usefulness of these two parameters. Experiments show that both parameters improve detection of microbubbles and that HSFR performs better than HFR.

In this work, we study linear array beamforming for vibro-acoustography systems. The goal of this research is to assess the feasibility of vibro-acoustography imaging systems based on linear arrays for clinical applications. The vibro-acoustography transducer is designed with two arrays driven by two continuous-wave or tone-burst signals at slightly different frequencies. The system beamforming is modeled in a homogeneous and lossless fluid. In this model, the point-spread function (psf) of the system is obtained as the product of the spatial impulse function of each linear array. Three linear array configurations are analyzed for vibro-acoustography systems. Simulations considering 64 elements in each array are performed. Aspects related to clinical applications of vibro-acoustography, such as system spatial resolution, sidelobes, grating lobes and image frame-rate are discussed. It is concluded that linear array transducers can produce acceptable spatial resolution for clinical applications.

The intersection of two ultrasound beams with slightly different frequencies results in generation of a localized radiation force and stimulates emission of audio signals from targeted objects. Vibro-acoustography uses this phenomenon to probe elastic properties of objects. Vibro-acoustography of contrast microbubbles in degassed water produced quantitative flow measurements from analysis of their acoustic emission. We used a dual-beam transducer generating bursts of 40-kHz vibrations. The vibrations resulted from interference of 3.48-MHz and 3.52-MHz confocal beams intersecting at the center of a thin plastic conduit. We tested flows of 13, 48, 85, and 120 mL/min of contrast microbubbles at concentrations from 1.2 times 10 5 to 6 times 10 5 bubbles/mL. The amplitude of the acoustic emission was linear with microbubble concentrations up to a value of 3.6 times 10 5 bubbles/mL. A replenishment method for microbubble contrast and flow rate analysis was used with radiation force bursts deployed at 0.05, 0.1, 0.2, 0.5, 1, and 2-second pulsing intervals. The relation between the pulsing intervals and the peak amplitude was fitted by an exponential curve and a rate constant calculated for each tested flow rate. The rate constant values were linearly correlated with the tested flows. The vibro-acoustography method provides objective, quantitative, and highly-localized assessment of flow using contrast microbubbles.

This study deals with the relationship between the magnitude of acoustic nonlinearity, sound speed of tissues and the amount of fat present in them. A two-component model, i.e., nonfat and fat, has been assumed and equations that relate the nonlinear parameter (B/A) of a medium to the properties of its components have been derived for two cases. In the first case, the density and sound speed are the same for the two components; B/A is a linear function of fat concentration. To represent this case, mixtures of egg white and yolk were studied. Even though the differences in density and sound speed of the two egg components were within 1 percent of each other, B/A showed a deviation from linearity. In the second case, i.e., when the density and sound speed of the two components are not equal, a quadratic equation has been derived using mixture laws. Livers, fats, egg mixtures, and oil data were used to represent this case. B/A increased quadratically with fat concentration. The presence of proteins on the binary aqueous/fat mixtures modified the quadratic rule.

The geometric distortion due to the neglect of refraction in existing ultrasound scanners is demonstrated. An iterative technique to correct for refraction errors in B-mode ultrasound, denoted Second Order Refraction Transposition (SORT), is presented. In vitro experiments were performed that confirm the calculated results.

Global and local attenuation coefficient estimates were calculated using three methods: the envelope peak method, the central-frequency-downshift method, and the zero-crossing method. The results show that for each method the error of the local estimate with respect to the global estimate is increased as the sample volume is decreased. While the performances of the latter two methods are comparable, the performance of the envelope peak method is significantly superior.

Scattering of ultrasound by biological tissues (continuous-inhomogeneous media) is discussed. An analytical expression for the attenuation due to scattering (α T SC ) and backscatter coefficients (σ T ) of tissues are obtained. The results explain the variation of (α T SC ) and σ T with frequency for a number of tissues. The study also provides two statistical parameters, velocity fluctuation coefficient and correlation length, in terms of which the scattering of tissues can be defined quantitatively.

Three concepts are presented: 1) Extended kernels: The Ramachandran-Lakshminarayanan convolution kernel has one zero between each non-zero value in the spatial domain. By extending the kernel in Fourier space, it is shown that each extension leads to two additional zeros in the spatial domain of the convolution kernel, thus decreasing the required number of multiplications necessary for convolution. Any known kernel can be extended and in the limit of extension a simple backprojection reconstruction is obtained. 2) Binary kernels: A technique for generating binary approximations to any convolution kernel is described. Excluding the central element, all other elements of the kernel are approximated by an even power of two thus, multiplications are replaced by shift operations in the convolution procedure. 3) Recursive convolution: It is shown how additions can be saved by using a recursive formulation which generates new elements in the convolution procedure utilizing only a few summation steps. Results from both extended kernels and their binary approximations are described for simulated phantoms and ultrasound data obtained from breast scans of patients.

BackgroundPrucalopride is a selective, high‐affinity, 5‐hydroxytryptamine (serotonin) type 4 (5‐HT4) receptor agonist with gastrointestinal prokinetic activities. This integrated analysis of data from three double‐blind phase III trials (ClinicalTrials.gov: NCT00488137, NCT00483886, NCT00485940) compared the efficacy and safety of prucalopride 2 mg once daily in women with chronic constipation [≤2 spontaneous complete bowel movements (SCBM) per week] in whom laxatives had failed to provide adequate relief with that in the all‐patient (AP) population of men and women with chronic constipation who had or had not obtained relief from laxatives.MethodsPatients received prucalopride 2 mg or placebo once‐daily for 12 weeks. Efficacy endpoints included an average of ≥3 SCBM/week and average increases of ≥1 SCBM/week and ≥1 SBM/week over this period. A response on any of these three endpoints was considered to be clinically relevant, and an overall response rate was derived for patients satisfying any of these endpoints.ResultsOf the AP population (n = 1318), 936 were women in whom laxatives had failed to provide adequate relief (WLF). More patients on prucalopride 2 mg than placebo had an average of ≥3 SCBM/week (AP 24.4 vs 11.0%; WLF 24.7 vs 9.2%), an average increase of ≥1 SCBM/week (AP 43.5 vs 24.8%; WLF 44.2 vs 22.6%), and an average increase of ≥1 SBM/week (AP 66.7 vs 38.4%; WLF 68.3 vs 37.0%) (all p < 0.001). Significant differences from placebo were evident in week 1 and sustained thereafter. Overall response rates in the AP and WLF populations, respectively, were 69.7 and 71.0% with prucalopride 2 mg and 44.5 and 41.6% with placebo (p < 0.001). Early (weeks 1–4) response predicted ultimate response over time. Common (>10%) adverse events were abdominal pain, nausea, diarrhoea, and headache.ConclusionsPrucalopride 2 mg once daily is effective in WLF. The efficacy and safety profile observed in WLF was similar to that in the total evaluated population of patients with chronic constipation who had or had not obtained adequate relief from laxatives.

What's known on the subject? and What does the study add? Variations in the type of urinary diversion exist for patients undergoing radical cystectomy. Although its use has been increasing from 2001 to 2008, patients who are older, female, and primary insured by Medicaid are less likely to receive continent diversions. Furthermore, patients treated surgically at high‐volume and teaching hospitals are more likely to receive continent diversions. Objective To describe the contemporary trends in urinary diversion among patients undergoing radical cystectomy ( RC ) for bladder cancer; and elucidate whether socioeconomic disparities persist in the type of diversion performed in the USA from a population‐based cohort. Patients and Methods Using the Nationwide Inpatient Sample, we identified patients who underwent RC for bladder cancer between 2001 and 2008. Multivariable regression models were used to identify patient and hospital covariates associated with continent urinary diversion and enumerate predicted probabilities for statistically significant variables over time. Results Overall, 55 635 (92%) patients undergoing RC for bladder cancer received incontinent urinary diversion, while 4552 (8%) patients received continent diversion from 2001 to 2008. Receipt of continent urinary diversion increased from 6.6% in 2001–2002 to 9.4% in 2007–2008 ( P < 0.001 for trend). Patients who were older (odds ratio [ OR ] 0.93; P < 0.001), female ( OR 0.52; P < 0.001) and insured by Medicaid ( OR 0.54; P = 0.002) were less likely to receive continent urinary diversion. However, patients treated at teaching ( OR 2.14; P < 0.001) and high‐volume hospitals ( OR 2.39; P = 0.04) had higher odds of continent urinary diversion. Predicted probabilities of continent diversion remained lower for female patients, Medicaid insurance status, and non‐teaching and medium/low‐volume hospitals over time. Conclusions In this nationally representative sample of hospitals from 2001 to 2008, the use of continent diversion in RC gradually increased. Although variations in urinary diversion exist by hospital teaching status, case volume, patient gender and primary health insurance, increased attention in expanding the use of continent diversions may help reduce these disparities for patients undergoing RC for bladder cancer.