Georgios Menikou

MRI compatible head phantom for ultrasound surgery

OBJECTIVE Develop a magnetic resonance imaging (MRI) compatible head phantom with acoustic attenuation closely matched to the human attenuation, and suitable for testing focused ultrasound surgery protocols. MATERIALS AND METHODS Images from an adult brain CT scan were used to segment the skull bone from adjacent cerebral tissue. The segmented model was manufactured in a 3-D printer using (Acrylonitrile Butadiene Styrene) ABS plastic. The cerebral tissue was mimicked by an agar-evaporated milk-silica gel (2% w/v-25% v/v-1.2% w/v) which was molded inside a skull model. RESULTS The measured attenuation of the ABS skull was 16 dB/cm MHz. The estimated attenuation coefficient of the gel replicating brain tissue was 0.6 dB/cm MHz. The estimated agar-silica gels T1 and T2 relaxation times in a 1.5 Tesla magnetic field were 852 ms and 66 ms respectively. The effectiveness of the skull to reduce ultrasonic heating was demonstrated using MRI thermometry. CONCLUSION Due to growing interest in using MRI guided focused ultrasound (MRgFUS) for treating brain cancer and its application in sonothrombolysis, the proposed head phantom can be utilized as a very useful tool for evaluating ultrasonic protocols, thus minimizing the need for animal models and cadavers.

MRI-compatible bone phantom for evaluating ultrasonic thermal exposures.

OBJECTIVE The goal of the proposed study was the development of a magnetic resonance imaging (MRI) compatible bone phantom suitable for evaluating focused ultrasound protocols. MATERIALS AND METHODS High resolution CT images were used to segment femur bone. The segmented model was manufactured with (Acrylonitrile Butadiene Styrene) ABS plastic using a 3-D printer. The surrounding skeletal muscle tissue was mimicked using an agar-silica-evaporated milk gel (2% w/v-2% w/v-40% v/v). MR thermometry was used to evaluate the exposures of the bone phantom to focused ultrasound. RESULTS The estimated agar-silica-evaporated milk gels T1 and T2 relaxation times in a 1.5T magnetic field were 776ms and 66ms respectively. MR thermometry maps indicated increased temperature adjacent to the bone, which was also shown in situations of real bone/tissue interfaces. CONCLUSION Due to growing interest of using MRI guided Focused Ultrasound Surgery (MRgFUS) in palliating bone cancer patients at terminal stages of the disease, the proposed bone phantom can be utilized as a very useful tool for evaluating ultrasonic protocols, thus minimizing the need for animal models. The estimated temperature measured and its distribution near the bone phantom/agar interface which was similar to temperatures recorded in real bone ablation with FUS, confirmed the phantoms functionality.

MRI‐compatible breast/rib phantom for evaluating ultrasonic thermal exposures

The target of this study was the development of a magnetic resonance imaging (MRI) compatible breast phantom for focused ultrasound which includes plastic (ABS) ribs. The objective of the current study was the evaluation of a focused ultrasound procedure using the proposed phantom that eliminates rib heating.

MRI-guided frameless biopsy robotic system with the inclusion of unfocused ultrasound transducer for brain cancer ablation

A magnetic resonance image (MRI) guided robotic system dedicated for brain biopsy was developed. The robotic system carries a biopsy needle and a small rectangular unfocused, single element, planar ultrasonic transducer which can be potentially utilized to ablate small and localized brain cancer.

The role of three-dimensional printing in magnetic resonance imaging-guided focused ultrasound surgery

Objectives: This article describes novel magnetic resonance imaging (MRI)-compatible focused ultrasound robotic systems and agar-based MRI-compatible ultrasonic phantoms mimicking bone. Materials and Methods: All the robotic systems and phantoms were developed using three-dimensional (3D) printing technology using plastic material. The tissue surrounding the bone in the phantoms was mimicked using agar-based solutions. Results: The article presents MRI-guided focused ultrasound robotic systems for brain, prostate, and gynecological targets. It also reports on MRI-compatible ultrasonic phantoms for brain, breast, bone, and motion. Conclusions: The popular 3D printing technology serves a major role in MRI-guided focused ultrasound surgery because MRI-guided focused ultrasound robotic systems can be developed. In addition, 3D printing can be used to develop MR-compatible phantoms that include bone structures for testing the safety and efficacy of focused ultrasound applications. All the developed structures have been evaluated in MRI environment using either mimicking materials or animals.

Evaluation of a small flat rectangular therapeutic ultrasonic transducer intended for intravascular use.

HighlightsIntravascular transducer for atherosclerosis.Flat rectangular unfocused transducer.Intravascular transducer for thrombosis. Background: The aim of the proposed study was to evaluate the performance of a flat rectangular (2 × 10 mm2) transducer operating at 4 MHz. The intended application of this transducer is intravascular treatment of thrombosis and atherosclerosis. Methods: The transducers thermal capabilities were tested in two different gel phantoms. MR thermometry was used to demonstrate the thermal capabilities of this type of transducer. Results: Temperature measurements demonstrated that this simple and small transducer adequately produced high temperatures, which can be utilized for therapeutic purposes. These high temperatures were confirmed using thermocouple and MR measurements. Pulsed ultrasound in combination with thrombolytic drugs and microbubbles was utilized to eliminate porcine thrombi. Conclusions: The proposed transducer has the potentials to treat atherosclerotic lesions using the thermal properties of ultrasound, since high temperatures can be achieved in less than 5 s. The results revealed that the destruction of thrombi using pulsed ultrasound requires long exposure time and high microbubble dosage.

MRI guided focused ultrasound robotic system for animal experiments

In this paper an MRI‐guided focused ultrasound (MRgFUS) robotic system was developed that can be used for conducting experiments in small animals.The target for this robotic system regarding motion was to move a therapeutic ultrasound transducer in two Cartesian axes.

MRI‐guided focused ultrasound robotic system for the treatment of bone cancer

A novel MRI‐conditional robot was developed that navigates a focused ultrasound (FUS) transducer. With this robotic system the transducer can access bones. The intended application is pain palliation from bone cancer using thermal ablation using FUS.

Software that controls a magnetic resonance imaging compatible robotic system for guiding high-intensity focused ultrasound therapy

Background and Objectives: This study describes a software application for controlling a focused ultrasound system that was guided by magnetic resonance imaging (MRI). Materials and Methods: The softwares functionalities were tested using a custom-made electronic system, MRI compatible robotic systems, and a high-intensity focused ultrasound (HIFU) system. The experiments were conducted in gel phantoms to test the motion accuracy and functionality of the system. Results: The software includes the following functionalities: (a) patient database (patient identification number, age, weight, gender, etc.); (b) acquisition of MRI images; (c) transducer movement; (d) transducer coordinates; (e) ultrasound control; (f) MRI thermometry; (h) temperature measurement with thermocouple; (i) command history (command name, starting time, and remaining time); and (j) MRI compatible camera. Evaluation experiments were conducted to test the software for accuracy, functionality, and communication with MRI. Conclusions: User-friendly software was developed to control an MRI-guided HIFU system. The software was evaluated in phantom experiments and it was found to accomplish all the intended functions.

A multipurpose positioning device for magnetic resonance imaging-guided focused ultrasound surgery

Background and Objectives: An magnetic resonance imaging (MRI)-guided focused ultrasound (MRgFUS) positioning device was developed with 3 identical Cartesian stages. The robotic system can be utilized to move a focused ultrasound transducer for performing various MR-guided applications. Materials and Methods: A single element spherically focused transducer of 4 cm diameter, focusing at 10 cm, and operating at 1.14 MHz was used during the evaluation of the robotic system. The propagation of ultrasound was either lateral or superior to inferior. MRI thermometry algorithms were developed to assess the thermal effects of MRgFUS. The proposed robotic system was developed using a three-dimensional printer. Results: The system was tested successfully in a gel phantom for various tasks (robot motion, functionality, and MR compatibility). Controlled thermal lesions were created in the gel phantom. The lesion creation was monitored successfully using MRI thermometry. Conclusions: The system was tested successfully for its functionality and its MR compatibility. This system has the potential to be used for focused ultrasound applications in the brain, breast, abdominal, and thyroid.