A Novel Microflow Phantom Dedicated to Ultrasound Microvascular Measurements

Superficial Bifurcated Microflow Phantom for High-Frequency Ultrasound Applications

OBJECTIVE

To evaluate and optimize high-frequency ultrasound (HFUS) imaging techniques that visualize the morphology of microscale vasculatures, many studies have used flow phantoms with straight channels. However, the previous phantoms lack the complexity of microvessels to simulate a realistic vascular environment in a shallow depth. This study was aimed at devising a new protocol for fabrication of a microflow phantom with bifurcated geometry at a superficial region.

METHODS

The proposed protocol involved the following features: (i) a bifurcated flow tract model 300 µm in diameter was debossed on the surface of a tissue slab made of polyvinyl alcohol cryogel, and (ii) a wall-less lumen was created via bonding tissue slabs to put a lid on the debossed flow tract. The structure of the created microflow phantom was evaluated using 2-D and 3-D power Doppler imaging with a 30 MHz HFUS modality.

RESULTS

Ultrasound imaging revealed that the desired flow tract with bifurcation was successfully created in the phantom at a depth of 2-5 mm from the ultrasound probe. The diameters of the flow tract measured in the axial direction were 307 ± 3.7 µm in the parent branch and 232 ± 18.2 and 256 ± 23.3 µm in the two daughter branches, respectively.

CONCLUSION

The experiments revealed that the proposed protocol for creating a microscale intricate flow tract with desired dimensions and depth is valid. This new phantom will facilitate further improvement in the ultrasound technologies for the precise visualization of superficial complex vasculatures such as those in skin layers.

Custom-made flow phantoms for quantitative ultrasound microvessel imaging

Morphologically realistic flow phantoms are essential experimental tools for quantitative ultrasound-based microvessel imaging. As new quantitative flow imaging tools are developed, the need for more complex vessel-mimicking phantoms is indisputable. In this article, we propose a method for fabricating phantoms with sub-millimeter channels consisting of branches and curvatures in various shapes and sizes suitable for quantifying vessel morphological features. We used different tissue-mimicking materials (TMMs) compatible with ultrasound imaging as the base and metal wires of different diameters (0.15-1.25 mm) to create wall-less channels. The TMMs used are silicone rubber, plastisol, conventional gelatin, and medical gelatin. Mother channels in these phantoms were made in diameters of 1.25 mm or 0.3 mm and the daughter channels in diameters 0.3 mm or 0.15 mm. Bifurcations were created by soldering wires together at branch points. Quantitative parameters were assessed, and accuracy of measurements from the ground truth were determined. Channel diameters were seen to have increased (76-270%) compared to the initial state in the power Doppler images, partly due to blood mimicking fluid pressure. Amongst the microflow phantoms made from the different TMMs, the medical gelatin phantom was selected as the best option for microflow imaging, fulfilling the objective of being easy to fabricate with high transmittance while having a speed of sound and acoustic attenuation close to human tissue. A flow velocity of 0.85 ± 0.01 mm/s, comparable to physiological flow velocity was observed in the smallest diameter phantom (medical gelatin branch) presented here. We successfully constructed more complex geometries, including tortuous and multibranch channels using the medical gelatin as the TMM. We anticipate this will create new avenues for validating quantitative ultrasound microvessel imaging techniques.

A Review of Blood-mimicking Fluid Properties Using Doppler Ultrasound Applications

Doppler imaging ultrasound characterization and standardization requires blood that is called blood mimicking fluid for the exam. With recognized internal properties, acoustic and physical features of this artificial blood. Both acoustical and physical merits set in the International Electrotechnical Commission (IEC) scale are determined as regular values, where the components utilized in the artificial blood preparation must have values identical to the IEC values. An artificial blood is commercially available in the medical application and may not be suitable in the mode of ultrasonic device or for rate of new imaging technique. It is sometimes qualified to have the strength to produce sound features and simulate blood configuration for particular implementations. In the current review article, appropriate artificial blood components, fluids, and measurements are described that have been created using varied materials and processes that have modified for medical applications.

Ultrasonographic Detection of Vascularity of Focal Breast Lesions: Microvascular Imaging Versus Conventional Color and Power Doppler Imaging

To compare microvascular flow imaging (MVFI) to conventional Color-Doppler (CDI) and Power-Doppler (PDI) imaging in the detection of vascularity of Focal Breast Lesions (FBLs). A total of 180 solid FBLs (size: 3.5-45.2 mm) detected in 180 women (age: 21-87 years) were evaluated by means of CDI, PDI, and MVFI. Two blinded reviewers categorized lesion vascularity in absent or present, and vascularity pattern as (a) internal; (b) vessels in rim; (c) combined. The presence of a "penetrating vessel" was assessed separately. Differences in vascularization patterns (chi² test) and intra- and inter-observer agreement (Fleiss method) were calculated. ROC analysis was performed to assess performance of each technique in differentiating benign from malignant lesions. About 103/180 (57.2%) FBLs were benign and 77/180 (42.8%) were malignant. A statistically significant (p < .001) increase in blood flow detection was observed for both readers with MVFI in comparison to either CDI or PDI. Benign FBLs showed mainly absence of vascularity (p = .02 and p = .01 for each reader, respectively), rim pattern (p < .001 for both readers) or combined pattern (p = .01 and p = .04). Malignant lesions showed a statistically significant higher prevalence of internal flow pattern (p < .001 for both readers). The prevalence of penetrating vessels was significantly higher with MVFI in comparison to either CDI or PDI (p < .001 for both readers) and in the malignant FBLs (p < .001). ROC analysis showed MVFI (AUC = 0.70, 95%CI = [0.64-0.77]) more accurate than CDI (AUC = 0.67, 95%CI = [0.60-0.74]) and PDI (AUC = 0.67, 95%CI = [0.60-0.74]) though not significantly (p = .5436). Sensitivity/Specificity values for MVFI, PDI, and CDI were 76.6%/64.1%, 59.7%/73.8% and 58.4%/74.8%, respectively. Inter-reader agreement with MVFI was always very good (k-score 0.85-0.96), whereas with CDI and PDI evaluation ranged from good to very good. No differences in intra-observer agreement were noted. MVFI showed a statistically significant increase in the detection of the vascularization of FBLs in comparison to Color and Power-Doppler.

Compatibility and Validation of a Recent Developed Artificial Blood through the Vascular Phantom Using Doppler Ultrasound Color- and Motion-mode Techniques

Background:

Doppler technique is a technology that can raise the predictive, diagnostic, and monitoring abilities in blood flow and suitable for researchers. The application depends on Doppler shift (shift frequencies), wherein the movement of red blood cells away from the probe is determined by the decrease or increase in the ultrasound (US) frequency.

Methods:

In this experiment, the clinical US (Hitachi Avious [HI] model) system was used as a primary instrument for data acquisition and test the compatibility, efficacy, and validation of artificial blood (blood-mimicking fluid [BMF]) by color- and motion-mode. This BMF was prepared for use in the Doppler flow phantom.

Results:

The motion of BMF through the vessel-mimicking material (VMM) was parallel and the flow was laminar and in the straight form (regular flow of BMF inside the VMM). Moreover, the scale of color velocity in the normal range at that flow rate was in the normal range.

Conclusion:

The new BMF that is being valid and effective in utilizing for US in vitro research applications. In addition, the clinical US ([HI] model) system can be used as a suitable instrument for data acquisition and test the compatibility, efficacy, and validation at in vitro applications (BMF, flow phantom components).

A Brief Review for Common Doppler Ultrasound Flow Phantoms

In this review, the flow phantoms and the wall-less flow phantoms with recognized acoustic features (attenuation and speed of sound), interior properties, and dimensions of tissue were prepared, calibrated, and characterized by Doppler ultrasound (US) scanning which demands tissue-mimicking materials (TMMs). TMM phantoms are commercially available and readymade for medical US applications. Furthermore, the commercial TMM phantoms are proper for US purpose or estimation of diagnostic imaging techniques according to the chemical materials used for its preparation.

Quantitative Musculoskeletal Ultrasound

Ultrasound (US) imaging plays a crucial role in the assessment of musculoskeletal (MSK) disorders. Several quantitative tools are offered by US systems and add information to conventional US imaging. This article reviews the quantitative US imaging tools currently available in MSK radiology, specifically focusing on the evaluation of elasticity with shear-wave elastography, perfusion with contrast-enhanced US and noncontrast superb microvascular imaging, and bone and muscle mass with quantitative US methods. Some of them are well established and already of clinical value, such as elasticity and contrast-enhanced perfusion assessment in muscles and tendons. MSK radiologists should be aware of the potential of quantitative US tools and take advantage of their use in everyday practice, both for clinical and research purposes.

Guidelines for ultrasound examination in ophthalmology. Part III: Color Doppler ultrasonography

The aim of this article was to present the possibilities of use and application of color-coded Doppler ultrasonography in the diagnosis of various diseases of the eyeball and orbit which result from vascular disorders. Color-coded Doppler ultrasonography is recommended for the assessment of blood flow velocity in the retrobulbar arteries. That is why the article contains current recommendations for Doppler imaging in ophthalmology. The paper provides detailed recommendations for patient's preparation for the examination, presents the scanning technique and safety of the examination, and lists ophthalmological diseases of vascular origin for which color-coded Doppler ultrasonography can be applied. Furthermore, the article also presents other techniques applied in clinical practice for the assessment of blood flow or imaging of vasculature of a given eyeball structure, inter alia: power Doppler ultrasonography, 3D and 4D ultrasonography, magnetic resonance angiography, spiral computer tomography, transcranial ultrasonography and modern microvascular imaging. The authors emphasize the usefulness of color-coded Doppler ultrasonography in the diagnosis of diseases which result from blood flow disorders within the eyeball, such as amaurosis fugax, ocular ischemic syndrome, insufficiency in vessels supplying the carotid and vertebral arteries, posterior ischemic optic neuropathy, glaucoma, age-related macular degeneration, vascular vision disorders, vascular malformations, such as arteriovenous fistula, orbital varices, systemic connective tissue diseases in retinopathy of prematurity, diabetes, thyroid disorders or strabismus. The application of color-coded Doppler ultrasonography is especially important in the assessment of the vasculature of intrabulbar tumorous lesions and in the differential diagnosis of intrabulbar tumors.

The aim of this article was to present the possibilities of use and application of color-coded Doppler ultrasonography in the diagnosis of various diseases of the eyeball and orbit which result from vascular disorders. Color-coded Doppler ultrasonography is recommended for the assessment of blood flow velocity in the retrobulbar arteries. That is why the article contains current recommendations for Doppler imaging in ophthalmology. The paper provides detailed recommendations for patient’s preparation for the examination, presents the scanning technique and safety of the examination, and lists ophthalmological diseases of vascular origin for which color-coded Doppler ultrasonography can be applied. Furthermore, the article also presents other techniques applied in clinical practice for the assessment of blood flow or imaging of vasculature of a given eyeball structure, inter alia: power Doppler ultrasonography, 3D and 4D ultrasonography, magnetic resonance angiography, spiral computer tomography, transcranial ultrasonography and modern microvascular imaging. The authors emphasize the usefulness of color-coded Doppler ultrasonography in the diagnosis of diseases which result from blood flow disorders within the eyeball, such as amaurosis fugax, ocular ischemic syndrome, insufficiency in vessels supplying the carotid and vertebral arteries, posterior ischemic optic neuropathy, glaucoma, age-related macular degeneration, vascular vision disorders, vascular malformations, such as arteriovenous fistula, orbital varices, systemic connective tissue diseases in retinopathy of prematurity, diabetes, thyroid disorders or strabismus. The application of color-coded Doppler ultrasonography is especially important in the assessment of the vasculature of intrabulbar tumorous lesions and in the differential diagnosis of intrabulbar tumors.