Dominant factor analysis of B-flow twinkling sign with phantom and simulation data

BACKGROUND AND PURPOSE

The twinkling sign in B-flow imaging (BFI-TS) has been reported in the literature to increase both specificity and sensitivity compared to the traditional gray-scale imaging. Unfortunately, there has been no conclusive study on the mechanism of this effect.

METHODS

In the study presented here, a comparative test on phantoms is introduced, where the variance of a phase estimator is used to quantify the motion amplitude. The statistical inference is employed later to find the dominate factor for the twinkling sign, which is proven by computer simulation.

RESULTS

Through the analysis, it is confirmed that the tissue viscoelasticity is closely coupled with the twinkling sign. Moreover, the acoustic radiation force caused by tissue attenuation is found to be the trigger of the twinkling sign.

CONCLUSION

Based on these findings, the BFI-TS is interpreted as a tissue movement triggering vibration of microcalcifications particle.

Microscopic observation of glass bead movement in soft tissue-mimicking phantom under ultrasound PW mode scanning

Previous studies have demonstrated that stones and calcification in soft tissue show special enhancement in response to color flow (CF) or pulse Doppler (PW) mode ultrasound scan. This phenomenon is known as the "twinkling sign (TS)". The authors conducted an in vitro experiment to investigate the mechanism of TS occurrence by observing a glass bead in a transparent PVA-H soft tissue-mimicking phantom. The TS in PW mode showed a low-power and slow-velocity spectrum. At the same time, analysis of images by high-speed camera showed that the glass bead in the phantom oscillated following the pulse repetition frequency (PRF) of the PW mode ultrasound scan. The harmonic oscillations were confirmed, as well. The ultrasound radiation force-driven micro-oscillation possibly affects the ultrasound propagation around the scatterer and triggers random signals in the received echo signals. The results indicate that TS is a phenomenon based on complicated acoustic-mechanical interaction of multiple mechanisms. Further investigation is required for gaining a full understanding of the mechanism of TS occurrence and its clinical application.

The role of the acoustic radiation force in color Doppler twinkling artifacts

PURPOSE

The aim of this experimental study was to evaluate whether the acoustic radiation force (ARF) is a potential source of twinkling artifacts in color Doppler images.

METHODS

Color Doppler images were obtained using a clinical ultrasonic scanner (Voluson e, GE Healthcare) for a high contrast (+15 dB) circular scattering phantom at pulse repetition frequencies (PRFs) ranging from 0.1 to 13 kHz. Ultrasound transmissions resulting in ARF were measured using a hydrophone at the various PRFs considered. The influence of ARF on the appearance of twinkling colors was examined via the common parameter PRF. This methodology is based on the fact that alternating positive and negative Doppler shifts induced by the ARF are centered at a PRF twice the maximum Doppler frequency on the color scale bar, whereas the twinkling color aliasing is expected to remain similar regardless of PRF.

RESULTS

Color twinkling artifacts were observed to be most conspicuous at the lowest PRF of 0.1 kHz. The extent of twinkling rapidly decreased as the PRF increased, eventually disappearing when the PRF ≥0.6 kHz. The measured ultrasound transmissions, however, were found to be insensitive to the PRF, and therefore it can be inferred that the PRF was insensitive to the ARF.

CONCLUSION

Based on our experimental observations, the ARF may not be a source of color Doppler twinkling artifacts.

In vitro study of ultrasound radiation force-driven twinkling sign using PVA-H gel and glass beads tissue-mimicking phantom

The twinkling sign observed in ultrasound coded-excitation imaging (e.g., GE B-Flow) has been reported in previous research as a potential phenomenon to detect micro calcification in soft tissue. However, the mechanism of the twinkling sign has not been clearly understood yet. We conducted an in vitro experiment to clarify the mechanism of the twinkling sign by measuring a soft tissue-mimicking phantom with ultrasonic and optical devices. A soft tissue-mimicking phantom was made of poly(vinyl alcohol) hydro (PVA-H) gel and 200-μm-diameter glass beads. We applied ultrasound to the phantom using medical ultrasound diagnostic equipment to observe the twinkling sign of glass beads. Optical imaging with a laser sheet and a high-speed camera was performed to capture the scatter lights of the glass beads with and without ultrasound radiation. The scatter lights from the glass beads were quantified and analyzed to evaluate their oscillations driven by the ultrasound radiation force. The twinkling sign from the glass beads embedded in the PVA-H gel soft tissue phantom was observed in ultrasound B-Flow color imaging. The intensity and oscillation of the scattered lights from the glass beads showed significant difference between the cases with and without ultrasound radiation. The results showed a close relationship between the occurrence of the twinkling sign and the variations of the scatter lights of glass beads, indicating that ultrasound radiation force-driven micro oscillation causes the twinkling sign of micro calcification in soft tissue.

Fundamental study on micro calcification detection using twinkling sign (TS): the effect of stiffness of surrounding tissue on the appearance of TS

The twinkling sign (TS) observed in ultrasound imaging (e.g., color flow mode and pulse Doppler mode) has been reported in previous researches as a potential phenomenon to detect micro calcification in soft tissue. However, the mechanism of the twinkling sign has not been clearly understood yet. The authors investigated the effect of stiffness of surrounding tissue on the appearance of TS using the soft tissue-mimicking phantoms and a medical ultrasound device. The author used Poly (vinyl alcohol) hydro (PVA-H) gel as the material of phantom and developed three phantoms with different PVA concentration; 8 %wt, 10 %wt and 15 %wt those correspond to Young's modulus (E) as 50 kPa, 100 kPa and 230 kPa, respectively. Micro glass and CaCO3 particles were embedded in the phantoms as pseudo micro calcification. The authors observed TS in each phantom and analyzed the temporal average of TS. The temporal average of TS was largest in the 8 %wt (E = 50 kPa) PVA-H gel phantom, and decreased with increasing the phantom stiffness. The result indicated that the micro oscillation of the particles had a close relationship with the occurrence of TS.

Correlation between twinkling artifact and color Doppler carrier frequency: preliminary observations in renal calculi

Color Doppler twinkling is a well-defined but not well-understood phenomenon that may assist in the detection of renal calculi. However, the relationship between the appearance of color Doppler twinkling and color Doppler carrier frequency has not been described systematically. To evaluate this relationship, a retrospective review was performed on 20 cases of renal calculi detected by twinkling on renal color Doppler sonography and confirmed with unenhanced computed tomography. The variable strength of twinkling at and behind renal calculi was observed with color Doppler carrier frequencies ranging from 1.75-4.0 MHz. All 20 calculi (100%) demonstrated twinkling when a low color Doppler carrier frequency, 1.75 or 2 MHz, was applied, whereas 12 of 20 cases (60%) were absent of twinkling when the highest carrier frequencies tested-3.5 or 4 MHz-were used. Quantitatively, there was a significant correlation between the amount of twinkling and carrier frequency (p = 0.002102). Hence, we conclude that the strength of the twinkling is color Doppler carrier frequency-dependent. The strength of the twinkling significantly increased when the color carrier frequency used for imaging decreased. Therefore, to improve renal calculi detection by enhancing the strength of the twinkling, the use of a lower color Doppler carrier frequency is recommended.