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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 3  |  Issue : 3  |  Page : 123-132

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


1 Department of Electrical Engineering, Cyprus University of Technology; Research and Development, Medsonic Ltd., Limassol, Cyprus
2 Department of Biomedical Engineering, City University, London, UK
3 Department of Electrical Engineering, Cyprus University of Technology, Limassol, Cyprus

Date of Web Publication7-Dec-2017

Correspondence Address:
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/digm.digm_19_17

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  Abstract 

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 software's 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.

Keywords: Magnetic resonance imaging, robotics, software, ultrasound


How to cite this article:
Yiallouras C, Menikou G, Yiannakou M, Damianou C. Software that controls a magnetic resonance imaging compatible robotic system for guiding high-intensity focused ultrasound therapy. Digit Med 2017;3:123-32

How to cite this URL:
Yiallouras C, Menikou G, Yiannakou M, Damianou C. Software that controls a magnetic resonance imaging compatible robotic system for guiding high-intensity focused ultrasound therapy. Digit Med [serial online] 2017 [cited 2021 Dec 8];3:123-32. Available from: http://www.digitmedicine.com/text.asp?2017/3/3/123/220123


  Introduction Top


High-intensity focused ultrasound (HIFU) has the potential to induce thermal changes in tissue; and therefore, it is used extensively for medical applications. Nowadays, HIFU is utilized to selectively heat biological tissues for oncological applications with minimal invasiveness using magnetic resonance imaging (MRI) to provide, to the operator performing the procedure, images of a region within the subject being heated.

The idea of using HIFU was proposed by Lynn et al.[1] The first complete HIFU system was developed by Fry et al.[2] However, at that time, diagnostic imaging did not exist; and therefore, the previous systems were not guided effectively, and therefore had not survived in the clinical setting. HIFU was explored in almost every tissue that is accessible by ultrasound. The following literature represents some examples of some applications explored: Eye,[3] prostate,[4] liver,[5] brain, [2],[6],[7] and kidney.[8],[9]

In recent commercial systems,[4],[10],[11] HIFU was either guided by ultrasound or MRI. Ultrasonic imaging is the simplest and most inexpensive method that can guide HIFU; however, MRI offers superior tissue contrast than ultrasound, especially when imaging thermal effects.

The combination of ultrasound and MRI was first cited by Jolesz and Jakab [12] who demonstrated that an ultrasonic transducer can be used inside an MRI scanner. The concept of using MRI to monitor the necrosis produced by HIFU was demonstrated in the early nineties by Hynynen et al.[13] in the canine muscle. In the following years, additional studies have been conducted,[14],[15] showing that the contrast between necrotic tissue and normal tissue was superior. This was a great enhancement for the HIFU systems because the therapeutic protocols could be accurately monitored. Therefore the interest of using MRI as the diagnostic modality of guiding HIFU was increased.

The development of MRI compatible robotic systems to incorporate MRI for the guidance of therapeutic ultrasound was accelerated fast. The following studies [16],[17],[18],[19] developed several MRI compatible robotic systems for various purposes. The leading company in the area of MRI compatible robotics is the Insightec (Tirat Carmel, Israel). Insightec produced MRI compatible robotic systems for several applications: treatment of prostate cancer,[20] breast cancer,[21] liver,[22] pain palliation of bone metastases,[23] and treatment of essential tremor.[24] Philips Healthcare (Best, the Netherlands) produced a robotic system with 5 degrees of freedom for the treatment of fibroids and bone metastasis.[25]

Insightec developed a software application that controls the MRgFUS systems.[26],[27] The software communicates with GE MRI scanners (GE General Electric, Fairfield, CT, USA) to control the therapy. The software has the following features: (a) acquisition of MRI images, (b) manually segmentation of region of interest by the radiologist, (c) control of HIFU protocol by selecting a predefined treatment protocol (the user may change any parameter during the treatment), (d) MRI thermometry estimation during the sonication, and (e) MRI thermometry map after the sonication. Philips healthcare developed software that controls an MRI-HIFU system.[28] The software has very similar functionalities with the Insightec's application.

This article presents a software that controls an MRI-guided HIFU system developed by MEDSONIC (Limassol, Cyprus). The presented software includes the following features: (a) Patient database (patient identification (ID) number, age, weight, gender, etc.); (b) acquisition of MRI images; (c) transducer movement (the user may move the robot in single steps or in multiple steps by specifying the step distance and the number of steps for each stage); (d) transducer coordinates; (e) ultrasound control; (f) MR thermometry; (h) temperature measurement using thermocouples; (i) command history (command name, starting time, remaining time); and (j) MRI compatible camera (video and photograph acquisition).


  Materials and Methods Top


Electronic system

To control the robotic system, a data acquisition (DAQ) board (universal serial bus [USB] 6251, National Instruments, Austin, Texas, USA) was used. The DAQ device was connected with the computer through USB interface. The software communicates with the motor (USR60-S3N, Shinsei Kogyo Corp., Tokyo, Japan) through a digital input/output of the DAQ device. The motor drivers, DAQ card, and power supply (24 V) were enclosed in a custom-made enclosure.

Robotic system

The robotic system incorporates piezoelectric ultrasonic motors (Shinsei) for producing the motion of the transducer and optical encoders (EM1, US Digital Corporation, Vancouver, WA 98684, USA) for mechanical motion feedback. The robotic system developed by MEDSONIC was utilized successfully for various applications (for example, prostate,[29] brain,[30] gynecological tumors,[31] and bone [32]).

Gel phantoms

Agar gel phantoms were used for performing experiments with the proposed software. The agar gel was used to mimic the attenuation of the soft tissue. The agar gel phantoms were produced using the following recipe: 2% w/v agar, 2% w/v silica dioxide, and 40% v/v evaporated milk. Details of the recipe and the steps for the preparation of the silica/agar with evaporated milk phantom were described by Menikou et al.[33]. The agar gel phantoms were poured in a plastic case to be used in an MRI environment. The plastic enclosure was manufactured using acrylonitrile butadiene styrene (ABS) plastic and a three-dimensional (3D) printer (FDM400, Eden Prairie, Minnesota, USA).

High-intensity focused ultrasound system

The focused ultrasound system was used for the experiments consisted of signal generator (HP 33120A, Agilent Technologies, Englewood, CO, UA), RF amplifier (150 W AR, Souderton, PA, USA), and an MRI compatible spherical bowl transducer (HI96MRC-01, Sonic Concepts, Inc., Washington, USA). The transducer has a diameter of 40 mm, radius of curvature of 100 mm, and operates at 1 MHz.

The MRI compatible parts were placed inside the MRI room, and the noncompatible parts were placed outside of the room. The MRI compatible robotic device was placed on the patient's table of the MRI scanner. [Figure 1] shows the diagram of the complete MRI compatible HIFU system.
Figure 1: Schematic diagram of a magnetic resonance imaging-high-intensity focused ultrasound therapy system. PNC: Private network cable, USB: Universal serial bus, MRI: Magnetic resonance imaging, HIFU: High-intensity focused ultrasound, DICOM: Digital imaging and communication in medicine, DAQ: Data acquisition

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Magnetic resonance imaging

The software was tested in a 1.5 T MR system (Signa, General Electric, Fairfield, CT, USA) using a GPFLEX coil (USA instruments, Cleveland, OH, USA). To test the accuracy of the ablation the software the following sequence was used: T2-weighted fast spin echo (FSE): Repetition time (TR) = 2500 ms, echo time (TE) = 60 ms, slice thickness = 3 mm, matrix = 256 × 256, field of view (FOV) = 16 cm, number of excitations (NEX) = 3, echo train length = 8. To evaluate the MRI thermometry capabilities the following sequence was used T1-weighted spoiled gradient: TR = 38.5 ms, TE = 20 ms, FOV = 21 cm, matrix = 128 × 128, flip angle = 20°, NEX = 1.

Software functionality

The software controls a complete HIFU system guided by MRI. It was divided into eight main tasks during the development process. The software was tested in several conditions during experiments in gel phantoms. The software was developed in C sharp (Microsoft Corporation, Visual Studio Express Edition 2010, USA).

Patient information

This part of the software stores useful information about the patient. The patient's information was acquired from the digital imaging and communication in medicine (DICOM) files. The graphical user interface (GUI) has the following functionalities: (a) create-read-update-delete patient's information, (b) search for patient's information, (c) preview of all patients, (d) preview all operations for each particular patient, and (e) add new operation for a particular patient. [Figure 2] shows the GUI of the patient information form.
Figure 2: Graphical user interface of the patient's information form

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Robot control panel

This part of the software controls the transducer's motion by converting the rotational motion of the piezoelectric ultrasonic motor shaft into linear. Angular motion of the robot's stages was also possible. More detailed description of the mechanical design of one of the robotic systems can be found in Mylonas et al.[30] and Menikou et al.[33] The software exchanges message signals with the data acquisition device through USB interface port. The user may move the transducer manually in a single step or automatically in multiple steps by specifying the grid pattern (step distance and the number of steps for each axis). [Figure 3] shows the flowchart of a single-step motion.
Figure 3: Flowchart of a single motion step

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The motors and optical encoders were connected to the digital input/output terminal of the board. The encoders ensured the accurate motion of the robot with an error of 20 μm on linear and 0.2° for angular stages. [Figure 4] shows the flowchart of the procedure of using multiple steps. The user provides the number of steps for each stage, the step distance in mm, the ultrasound OFF duration, and the sonication type. [Figure 5] shows the interface developed for performing motion using a linear sequential algorithm.
Figure 4: Flowchart of grid pattern operation. The user may specify the number of steps for each stage, the step distance in millimeters, the sonication type, and the OFF time between each sonication

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Figure 5: Graphical user interface of robot control panel

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Ultrasound control panel

This part of the software controls a signal generator that sends the required signal to the amplifier. The software interchanges messages in “string” format with the signal generator. The user has the option of two operation modes (continuous for thermal effects and pulsed for mechanical effects of ultrasound). The required parameters for continuous and pulsed mode are shown in [Table 1]. [Figure 6] shows the GUI of the ultrasound control panel during the execution of a pulsed ultrasound.
Table 1: List of variables

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Figure 6: Graphical user interface of the ultrasound control panel

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Digital imaging and communication in medicine client

The software communicates with the MRI scanner to transfer the DICOM files from the MRI system using DICOM protocol. To connect the system to the DICOM server of an MRI scanner, the following parameters are required: server name, application entity title, IP address, and the port type. The application can request files either using patient ID or study ID or series ID. The system stores the incoming files in a local database for further processing during the therapy or for later use. Therefore, the application executes the following command: Find, Move, and Store. There is a local store server that accepts the incoming DICOM files and stores them on local machine. [Figure 7] shows the schematic diagram of DICOM query/retrieve procedure. Client sends DICOM C-Find request to the DICOM server. The DICOM server will response based on the query criteria. To retrieve DICOM files from the server, the client sends C-Move request to the server, and the server responds with C-Store request to the client. The local store server class provider accepts and stores the incoming data.
Figure 7: Schematic diagram of digital imaging and communication in medicine query/retrieve procedure. SCP: Server class provider, C: Command, MRI: Magnetic resonance imaging, DICOM: Digital imaging and communication in medicine

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[Figure 8] shows the GUI of the DICOM client application. The software retrieves the DICOM files from the server and stores them on the local computer. The application separates the remote from local files in two different taps.
Figure 8: Graphical user interface application of digital imaging and communication in medicine client

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Magnetic resonance imaging data acquisition (digital imaging and communication in medicine viewer)

Images of a single series are loaded to a list box. The user has the following options: a) open the series of images using a horizontal scrollbar or mouse clicks, b) open a list of all DICOM tags, c) save the image as different format, d) zoom the image, and e) change of the image color level.

Transducer position

The software uses the MRI image coordination system and DICOM tags to calculate the position of the transducer accurately. In addition, the software can calculate the distance that is needed to move the transducer to reach a specific target. This is done using the left mouse click. The distance was calculated using the image coordination system and the pixel spacing tag of the DICOM file. The coordinates were sent to the robot control system to execute the treatment plan. [Figure 9] shows the GUI of the DICOM viewer. A specific area was targeted on the image as shown in [Figure 9]. The blue color indicates cells to be sonicated and the red color indicates cells that were not sonicated.
Figure 9: Image of the digital imaging and communication in medicine viewer application

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Magnetic resonance imaging thermometry

The temperature elevation was calculated based on the proton resonance frequency and MRI thermometry protocols. The MRI thermometry sequence produces series with three DICOM files. Each file represents different type of MRI signal: magnitude, real, and imaginary. Real and imaginary were used for the temperature estimation. The software merges real and imaginary, using a wrapping algorithm, and then, an image is produced. This image is unwrapped using an unwrapping algorithm to remove the noise.[34] [Figure 10] shows the MRI thermometry procedure.
Figure 10: Flowchart of the magnetic resonance imaging thermometry procedure

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[Figure 11] shows the GUI of MRI thermometry application. The software produced temperature maps and a temperature graph during the sonication. Initially, the software needs an image that can be used as a mask. The mask image represented the base temperature and was acquired before the sonication. Then, the user selects the region of interest (ROI) manually. The user sets the sonication time, and then, the software searches for new incoming series continuously. The new series passed from the wrapping and unwrapping procedures. Then, the new image was subtracted (pixel by pixel) from the mask image to calculate the difference in temperature. The temperature was calculated in degrees Celsius.
Figure 11: Example of magnetic resonance imaging thermometry during a high-intensity focused ultrasound exposure on a gel phantom

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Temperature acquisition system

This part of the software acquires the temperature from the focal point using a thermocouple (SMCJ-T, OMEGA Engineering, INC, USA). The temperature samples are sent to the computer through a DAQ device for further processing. The software converts the voltage to temperature in degrees Celsius. The software has the following functionalities: (a) Real-time temperature, (b) average temperature, (c) interval time between samples, and (d) save temperature graph as image format. [Figure 12] shows the GUI of the temperature acquisition system.
Figure 12: Graphical user interface of the temperature acquisition system

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Command history List

This part of the software keeps temporarily in a list box all the commands that are executed by the user. The software keeps the following information: (a) name of the operation, (b) parameters of the operation, (c) the study ID, and (d) data/time. The user has the following options: a) save the history, b) retrieve the history for the future use, and (c) clear the temporal history.

Magnetic resonance imaging compatible camera

The utilization of MRI compatible camera (MRC, MRC Systems GmbH, Heidelberg, Germany) was needed to monitor the procedure within the MRI scanner. The software has the following options: (a) Preview of the camera content, (b) capture of images, and (c) video recording. It was demonstrated that the camera can be used inside the MRI scanner without causing artifacts on the images during the therapy procedure. [Figure 13] shows the GUI of the MRI compatible camera.
Figure 13: Magnetic resonance imaging compatible camera function showing a robotic system during an experiment

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  Results Top


Evaluation experiments

Experiment in gel phantoms

Experiments in gel phantoms were performed to evaluate the current software for (a) accurate control of the robotic systems, (b) functionality of the software, and (c) communication with the MRI scanner. [Figure 14] shows seven discrete thermal lesions created in the gel phantom using the single-step motion of the positioning device. The acoustic power used was 45 W for 60 s. The spacing between the lesions was 10 mm.
Figure 14: Discrete thermal lesions on gel phantom. The acoustic power used was 45 W for 60 s. The spacing between the lesions was 10 mm

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Experiments in magnetic resonance imaging

[Figure 15] shows nine discrete thermal lesions created in the gel phantom using the multiple steps function of the positioning device. The acoustical power used was 45 W for 60 s. The ablation grid was 3 × 3 with spacing between lesions of 10 mm. [Figure 15] shows a T2-W FSE MRI image using the DICOM query/retrieve function. This figure shows that the multiple steps function was utilized by moving the positioning device in an XY grid. This demonstrated the method to be used to ablate a large amount of tissues. [Figure 16] shows transducer motion with steps of 10 mm using the robotic system. The images were acquired using T2-W FSE. The transducer was moved exactly 10 mm in each step.
Figure 15: Discrete thermal lesions in gel phantom using multiple steps function of the robot control panel

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Figure 16: Transducer motion as imaged using magnetic resonance imaging

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During the development of the software, all the various modules were used by potential users (engineers and medical doctors). Therefore, several modifications were performed based on the feedback received from these users. The final version of the software was free of any bugs, and it was very user-friendly.


  Discussion Top


The presented software fulfills all the requirements that are needed to control an MRI-guided focus ultrasound therapy system. The current application software was designed and developed for controlling different positioning systems for various application of HIFU.

The software is friendly and comparable with other commercial software applications (Insightec, Philips healthcare)[27],[28] and it has the similar features as the software of commercially available systems (i.e., motion control, MR thermometry, and ultrasonic activation). A key difference of our software is that the user can select a number of algorithms that can reduce near-field substantially. Other systems have different motion trajectories (for example the Philips's product used a spiral trajectory). The software was tested successfully in various experiments using agar-based phantoms.


  Conclusion Top


The proposed system provides an application to the user that fulfills all the requirements of an MRI-guided HIFU therapy system. The system provides: (a) fast communication speed with the motor actuators (excellent motion accuracy), (b) precise control of the HIFU system, and (c) excellent control between all the devices of the system.

In the future, the software can be used on another platform instead of Windows using different GUI libraries. Another improvement of the software would be the 3D DICOM viewer (similar to what developed by Zangos et al.[17]). In addition, the DICOM query/retrieve operation can be improved. The current software retrieves the images from the DICOM database which is a time-consuming operation. Another approach would be the transferring of the images directly from their directories using file transfer protocol. This will significantly improve the time that is needed by the software to retrieve an image, and as a result, the software will calculate the temperature elevation faster providing immediate feedback.

The software drives robotic systems for focused ultrasound developed by our group. The main task of the software is to accurately move robotic systems. This key task (motion) was evaluated extensively and it was reported in several articles [29],[30],[31],[32],[35],[36] These studies also demonstrated the accurate activation of focused ultrasound and the proper acquisition of MRI data for performing MR thermometry.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16]
 
 
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