RESUMO
PURPOSE: We hypothesized that contrast-enhanced ultrasound (CEUS) using a microbubble technique to quantify microvascular changes and Nakagami imaging for tissue characterization would provide a new approach for diagnosing and differentiating benign and malignant choroidal lesions. METHODS: Five patients with choroidal melanoma (CM) and five patients with choroidal hemangioma (CH) were selected. Definity®, which contains perflutren microbubbles, was administered as a slow IV bolus (1 ml). CEUS was performed for 1 min postinjection of the contrast agent with ultrasound radiofrequency data acquired from 10 s to 60 s. The contrast value was calculated for the whole tumor region. A gradient magnitude method was used for each postcontrast frames with 1-second interval, and the time-averaged value in pixel intensity gradient of postinjection frames was estimated and reported. Based on the Nakagami statistical distribution model, two Nakagami parameters, m and Ω, where m (shape parameter), representing tissue heterogeneity, and Ω (scale parameter), representing the average energy of backscattered signals, were studied. RESULTS: CEUS analysis showed that the time-averaged estimated contrast was significantly higher (p = 0.008) for CH compared to CM. Furthermore, the time-averaged contrast within the normal choroidal region was significantly higher than the choroidal tumor region for both CH and CM (p = 0.001 for CH cases and p < 0.0001 for CM cases). Nakagami analysis showed that the m estimates were significantly higher (p = 0.032) for CH (m = 0.61) than for CM (m = 0.28), indicating that CH is a more heterogeneous tumor than CM. The Ω estimates were significantly higher (p = 0.0019) for CH (Ω = 0.15) compared to CM (Ω = 0.03). These results may be due to the more vascular structures in CH compared to CM. CONCLUSIONS: Quantitative intensity-based perfusion analysis using CEUS and backscattering tissue analysis using Nakagami imaging can provide valuable insights to differentiate benign and malignant choroidal lesions.
RESUMO
Ultrasound elastography enables noninvasive characterization of the tissue mechanical properties. Phantoms are widely used in ultrasound elastography for developing, testing, and validating imaging techniques. Creating phantoms with a range of viscoelastic properties relevant to human organs and pathological conditions remains an active area of research. Poly(vinyl alcohol) (PVA) cryogel phantoms offer a long shelf life, robustness, and convenient handling and storage. The goal of this study was to develop tunable phantoms using PVA with a clinically relevant range of viscoelastic properties. We combined low- and high-viscosity PVA to tune the viscoelastic properties of the phantom. Further, phantoms were created with an ethylene glycol-based cryoprotectant to determine whether it reduces the variability in the viscoelastic properties. Scanning electron microscopy (SEM) was performed to evaluate the differences in microstructure between phantoms. The density, longitudinal sound speed, and acoustic attenuation spectra (5-20 MHz) of the phantoms were measured. The phantoms were characterized using a shear wave viscoelastography approach assuming the Kelvin-Voigt model. Microstructural differences were revealed by SEM between phantoms with and without a cryoprotectant and with different PVA mixtures. The longitudinal sound speed and attenuation power-law fit exponent of the phantoms were within the clinical range (1510-1571 m/s and 1.23-1.38, respectively). The measured shear modulus (G) ranged from 3.3 to 17.7 kPa, and the viscosity (η) ranged from 2.6 to 7.3 Pa·s. The phantoms with the cryoprotectant were more homogeneous and had lower shear modulus and viscosity (G = 2.17 ± 0.2 kPa; η = 2.0 ± 0.05 Pa·s) than those without a cryoprotectant (G = 3.93 ± 0.7 kPa; η = 2.6 ± 0.14 Pa·s). Notably, phantoms with relatively constant viscosities and varying shear moduli were achieved by this method. These findings advance the development of well-characterized viscoelastic phantoms for use in elastography.
