Evaluation of ultrasonic scattering in agar-based phantoms using 3D printed scattering molds

Purpose: Acoustic characterization of tissue mimicking materials in terms of attenuation, absorption, scattering and propagation velocity is essential for their utilisation in experiments, thus sparing the need for living tissues or cadavers. Although there is a vast literature regarding the acoustic characterization of such materials in terms of attenuation or propagation velocity, there is limited data regarding the quantification of the scattering coefficient. Herein stimulated the utilisation of four agar-based phantoms featuring different sizes of scattering agar-structures on one of their surfaces so as to provide experimental evaluation of the magnitude of scattering. Methods: The agar-based phantoms were developed with 6% w/v agar and 4% w/v silica and featured scatterers of sizes of 0–1 mm. The acoustic properties of propagation speed, impedance, insertion loss and attenuation were evaluated utilising the pulse-echo and through-transmission techniques. Scattering was deduced from the data. Results: The propagation speed measured at 2.7 MHz was in the range of 1531.23–1542.97 m/s. Respectively the attenuation as measured at 1.1 MHz was in the range of 1.216–1.546 dB/cm increasing with increased scatterer size. Respectively the scattering coefficient was in the range of 0.078–0.324 dB/cm. Moreover, the scattering coefficient was linearly dependent on frequency in the range of 0.8–2.1 MHz indicating a 6–23% effect of the total attenuation. Conclusions: The experimental results demonstrate the utilisation of the procedure for quantification of the scattering coefficient of tissue mimicking materials thus improving the diagnostic and therapeutic uses of ultrasound

Ultrasonic attenuation of canine mammary tumours

Canine mammary tumours (CMTs) are the most common neoplasm appearing in female dogs and are considered the equivalent animal model of human breast cancer. However, in the literature, there is a gap for ultrasonic characterisation of these tumours. In this study, experimental measurements for acoustic attenuation and propagation speed of three surgically excised malignant CMTs were implemented

Experimental evaluation of high intensity focused ultrasound for fat reduction of ex vivo porcine adipose tissue

The present study was stimulated by the continuous growth of commercially available high intensity focused ultrasound (HIFU) systems for fat reduction. Herein, HIFU was utilised for fat ablation using a single-element ultrasonic transducer operating in thermal mode

Robotic system for magnetic resonance imaging-guided focused ultrasound treatment of thyroid nodules

Background Herein, a robotic system offering Magnetic Resonance-guided Focused Ultrasound (MRgFUS) therapy of thyroid nodules was developed. Methods The robotic system offers linear motion in 2 PC-controlled axes that navigate a 3 MHz single-element focused transducer. The system, through a C-arm structure attaches to the table of Magnetic Resonance Imaging (MRI) scanners and couples to the neck of patients lying in the supine position. The MRI compatibility of the developed system was assessed inside a 3 T scanner. Benchtop and MRI feasibility studies evaluating the heating performance of the system were executed on excised pork tissue and on homogeneous and thyroid model agar-based phantoms. Results The MRI compatibility of the system was successfully established. Grid sonications executed using robotic motion inflicted discrete and overlapping lesions on the excised tissue, while magnetic resonance (MR) thermometry successfully monitored thermal heating in agar-based phantoms. Conclusions The developed system was found to be efficient with ex-vivo evaluation. The system can perform clinical MRgFUS therapy of thyroid nodules and other shallow targets after further in-vivo evaluation

Characterization of a fat tissue mimicking material for high intensity focused ultrasound applications

Tissue-mimicking materials (TMMs) have a prominent role in validating new high intensity focused ultrasound (HIFU) therapies. Agar-based TMMs are often developed mimicking the thermal properties of muscle tissue, while TMMs simulating fat tissue properties are rarely developed. Herein, twelve agar-based TMMs were iteratively developed with varied concentrations of agar, water, glycerol and propan-2-ol, and characterized for their suitability in emulating the thermal conductivity of human fat tissue

Advanced software for MRgFUS treatment planning

Herein, a user-friendly software platform for 3-dimensional Focused Ultrasound treatment planning based on Magnetic Resonance Imaging (MRI) images is presented

Experimental evaluation of the near-field and far-field heating of focused ultrasound using the thermal dose concept

Conventional motion algorithms utilized during High Intensity Focused Ultrasound (HIFU) procedures usually sonicate successive tissue cells, thereby inducing excess deposition of thermal dose in the pre-focal region. Long delays (~60 s) are used to reduce the heating around the focal region. In the present study the experimental evaluation of six motion algorithms so as to examine the required delay and algorithm for which the pre-focal (near-field) and post-focal (far-field) heating can be reduced using thermal dose estimations is presented

Phantom-based assessment of motion and needle targeting accuracy of robotic devices for magnetic resonance imaging-guided needle biopsy

Background:The current study proposessimple methodsfor assessingthe per-formance of robotic devices intended for Magnetic ResonanceImaging (MRI)‐guided needle biopsy. Methods:In‐housemade agar‐based breast phantoms containingbiopsy targetsservedasthemaintoolintheevaluationprocessofanMRIcompatiblepositioningdevice comprising a needle navigator. The motion accuracy of mechanical stages was assessed by calliper measurements. Laboratoryevaluationof needle targeting included a repeatability phantomtest and a laser‐based method. The accuracy andrepeatability of needle targeting was also assessed by MRI. Results: The maximum error of linear motion for steps up to 10 mm was 0.1 mm. Needle navigation relative to the phantomand alignment with the various biopsy targets were performed successfully in both the laboratory and MRI settings. The proposed biopsy phantoms offered tissue‐like signal in MRI and good haptic feed-back during needle insertion. Conclusions: The proposed methods could be valuable in the process of validating the accuracy of MRI‐guided biopsy robotic devices in both laboratory and real environments