Acoustic streaming: a new technique for assessing adnexal cysts

Derivation of acoustical streaming equations for nonlinear and dispersive fluids

The equations of streaming generated by an acoustic mod propagating in a nonlinear dispersive medium (exhibiting absorption and dispersion of phase sound speed) are derived with an arbitrarily shaped incident acoustical field assumed. This field may be periodic or non-periodic. A general dispersion model represented by a convolution operator taking into account relaxation effects was taken into account. Making the assumption of a periodic acoustic field from the general streaming equation. The quasi-stationary flow is driven by a force given by the average value of the dispersion operator with respect to the velocity and acoustic pressure fields. In the spectral representation, it is given by the weighted spectral power density distribution of the acoustic field. The weight of the distribution is the dispersion coefficient - the eigenvalue of the dispersion operator. A new result also reveals the effect of the refractive index deviation on the driving force of streaming. The possibility of generalizing the description of streaming in the simplest case of a non-Newtonian fluid was analyzed. The Reiner-Revlin model of a simple liquid was assumed. It was also noted that the streaming model in the Maxwell liquid is analytically solvable. It was found that asymptotic states of streaming in this model and the Navier-Stokes model are identical. The derivations use new methods different from those used so far. They are based on the separation of nonlinear modes in the momentum transport equation and on the properties of the Gauss-Weierstrass function for the Fick diffusion operator. So far, the method of successive approximations has been used. The consistency of the obtained equations with the assumptions was checked. The obtained formulas generalize the known descriptions of the form of forces driving streaming and extend their application to the case of nonlinear propagation.

Acoustic streaming cannot discriminate reliably between endometriomas and other types of adnexal lesion: a multicenter study of 633 adnexal masses

OBJECTIVE

To determine the ability of acoustic streaming to discriminate between endometriomas and other adnexal masses.

METHODS

We used data from 1938 patients with an adnexal mass included in Phase 2 of the International Ovarian Tumor Analysis (IOTA) study. All patients had been examined by transvaginal gray-scale and Doppler ultrasound following a standardized research protocol. Assessment of acoustic streaming was voluntary and was carried out only in lesions containing echogenic cyst fluid. Acoustic streaming was defined as movement of particles inside the cyst fluid during gray-scale and/or color Doppler examination provided that the probe had been held still for two seconds to ensure that the movement of the particles was not caused by movement of the probe or the patient. Only centers where acoustic streaming had been evaluated in > 90% of cases were included. Sensitivity, specificity, positive and negative likelihood ratios (LR+, LR-), and positive and negative predictive values (PPV and NPV) of acoustic streaming with regard to endometrioma were calculated.

RESULTS

460 (24%) masses were excluded because they were examined in centers where </= 90% of the masses with echogenic cyst fluid had been evaluated for the presence of acoustic streaming. Acoustic streaming was evaluated in 633 of 646 lesions containing echogenic cyst fluid. It was present in 19 (9%) of 209 endometriomas and in 55 (13%) of 424 other lesions. This corresponds to a sensitivity of absent acoustic streaming with regard to endometrioma of 91% (190/209), a specificity of 13% (55/424), LR+ of 1.04, LR- of 0.69, PPV of 34% (190/559) and NPV of 74% (55/74).

CONCLUSIONS

Acoustic streaming cannot discriminate reliably between endometriomas and other adnexal lesions, and the presence of acoustic streaming does not exclude an endometrioma.

Ruptured corpus luteum with hemoperitoneum: case characteristics and demographic changes over time

OBJECTIVE

Women of reproductive age are at risk of ruptured corpus luteum with hemoperitoneum. We identified the clinical and demographic features of patients recently treated in our institution and compared the findings with those from an earlier series, to detect any changes in disease identity that have occurred over the past 20 years.

MATERIALS AND METHODS

Charts of patients treated between January 2001 and December 2003 at Changhua Christian Hospital were reviewed. Clinical parameters were compared with those from our previous study in the 1980s.

RESULTS

A total of 91 women were diagnosed with ruptured corpus luteum and hemoperitoneum (mean age, 26 years; range, 15-42 years). Most ruptures (60.4%) occurred during the secretory phase and most women (57.1%) reported recent sexual intercourse prior to the onset of pain. Most patients (81.3%) required laparoscopic intervention to achieve hemostasis. No obvious differences were found between the results of this study and those from the 1985 series, except that our patients were younger, were more often unmarried, chose laparoscopic interventions rather than laparotomy, and that there was an emerging trend towards conservative treatment.

CONCLUSION

The manifestations of corpus luteum hemorrhage in this study were similar to those observed in the 1980s at the same medical center. However, the demographic parameters (age, marital status) and the modalities of treatment (conservative treatment, mode of surgical interventions) had changed in line with the evolution of society, culture, and the progress of medical science over the past 20 years.

Magnetic resonance imaging of acoustic streaming: absorption coefficient and acoustic field shape estimation

In this study, magnetic resonance imaging (MRI) is used to visualize acoustic streaming in liquids. A single-shot spin echo sequence (HASTE) with a saturation band perpendicular to the acoustic beam permits the acquisition of an instantaneous image of the flow due to the application of ultrasound. An average acoustic streaming velocity can be estimated from the MR images, from which the ultrasonic absorption coefficient and the bulk viscosity of different glycerol-water mixtures can be deduced. In the same way, this MRI method could be used to assess the acoustic field and time-average power of ultrasonic transducers in water (or other liquids with known physical properties), after calibration of a geometrical parameter that is dependent on the experimental setup.

Acoustic streaming in two endometriomas: the exception to the rule?

The presence of acoustic streaming in ovarian cysts can be determined by ultrasound imaging and provides an indication of the viscosity of the cyst content. It has previously been demonstrated that the absence of acoustic streaming in endometriomas could be a pathognomonic feature of endometriomas. In this report we demonstrate the presence of acoustic streaming in two endometriomas.

Acoustic streaming: an in vitro study

The aims of this study were, first, to determine if cyst size and cyst-to-transducer distance have an impact upon acoustic streaming and, second, to investigate the effect of cyst content viscosity on acoustic streaming using an artificial ovarian cyst model. Artificial ovarian cysts were constructed and suspended in a tissue-mimicking bath. Although there was no subjective difference in acoustic streaming velocity between cyst sizes during B-mode insonation, with colour Doppler and pulsed Doppler examination, higher acoustic streaming scores were recorded for larger cysts. When the cyst-to-transducer distance was increased, the acoustic streaming velocity was noted to decrease in all scanning modalities. The second stage of the study demonstrated decreasing acoustic streaming velocity as the viscosity of the cyst content was increased. The finding of a clear association between cyst content viscosity and acoustic streaming velocity raises the exciting possibility that we may be able to make estimations of the viscosity of ovarian cyst contents, in the clinical setting, by sonographic means.