|Year : 2018 | Volume
| Issue : 1 | Page : 22-26
The role of three-dimensional printing in magnetic resonance imaging-guided focused ultrasound surgery
Christakis Damianou1, Marinos Giannakou2, Christos Yiallouras3, Georgios Menikou4
1 Department of Electrical Engineering, Cyprus University of Technology, Limassol, Cyprus
2 Department of Electrical Engineering, Cyprus University of Technology; R and D, MEDSONIC LTD., Limassol, Cyprus
3 R and D, MEDSONIC LTD., Limassol, Cyprus
4 Department of Bioengineering, City University, London, UK
|Date of Web Publication||18-May-2018|
Department of Electrical Engineering, Cyprus University of Technology, 30 Arch. Kyprianou, 3036 Limassol
Source of Support: None, Conflict of Interest: None
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.
Keywords: Brain, breast, magnetic resonance imaging, motion, prostate, ultrasound
|How to cite this article:|
Damianou C, Giannakou M, Yiallouras C, Menikou G. The role of three-dimensional printing in magnetic resonance imaging-guided focused ultrasound surgery. Digit Med 2018;4:22-6
|How to cite this URL:|
Damianou C, Giannakou M, Yiallouras C, Menikou G. The role of three-dimensional printing in magnetic resonance imaging-guided focused ultrasound surgery. Digit Med [serial online] 2018 [cited 2018 Sep 19];4:22-6. Available from: http://www.digitmedicine.com/text.asp?2018/4/1/22/232710
| Introduction|| |
Focused ultrasound surgery (FUS) is becoming an important therapeutic modality due to its ability of noninvasively ablating diseased tissue, while sparing intervening healthy tissue. The procedure is usually monitored using magnetic resonance imaging (MRI), where morphological and temperature tissue changes can be observed accurately in real time. Diagnostic ultrasound imaging has also been tested for monitoring FUS, but up to date, there is no sufficient evidence that is capable of delivering the quantitative precision required for real-time control of temperature >50°C.,
The popular three-dimensional (3D) printing technology serves a major role in MRI-guided FUS. Primarily, this technology is used to manufacture robotic delivery FUS systems from nonmagnetic materials such as acrylonitrile butadiene styrene (ABS), to ensure compatibility with the MRI environment. In addition, 3D printing has been implemented in producing MR-compatible anthropomorphic phantoms replicating bone structures for testing the safety and efficacy of relevant FUS applications. The following article summarizes the contribution of 3D printing based on the experience gained by our group in designing MR-compatible robotic systems and phantoms for FUS.
| Materials and Methods|| |
All robotic systems were developed using the software Microstation (V8, Bentley Systems, Inc.). The individual parts were printed using an ABS 3D printer (FDM400, Stratasys, 7665 Commerce Way, Eden Prairie, Minnesota, 55344, USA) for production. This 3D printer produces parts made out ABS. The robotic stages were driven by piezoelectric ultrasonic motors (USR60-S3N, Shinsei Kogyo Corp., Tokyo, Japan).
Optical encoders were used (US Digital Corporation). For the linear axes, the EM1-0-500-I (US Digital Corporation) encoder was used. The EM1 optical encoders work in conjunction with polymer plastic strip materials, and it uses LED source and a monolithic detector. For the angular stages, the EM1-2-2500-I (US Digital Corporation) encoder was used. The encoder output is connected to the counter input of a data acquisition (DAQ) board USB 6251 (National Instruments, Austin, Texas, USA).
A DC supply (24 V, 2 A) drives the Shinsei driving electronics of the motors. Wires from the Shinsei drivers are connected to a USB 6251 DAQ interface card (NI) via a connecting block. The USB 6251 interface card includes timing and digital input/output modules.
An agar/silica dioxide/evaporated milk recipe was used to create soft-tissue mimicking phantoms. Agar of bacteriological grade type (HiMedia Laboratories, Mumbai, India) served as the gelling matrix and was doped with additives to control the acoustic properties of the phantom. The added crystalline silica dioxide powder (Merck Millipore, Darmstadt, Germany) enhanced acoustic scattering. Silica dioxide is ideal for hyperthermia applications since it is insoluble in water and possesses a high melting temperature (1750°C). Acoustic absorption was controlled by doping the gel with evaporated milk. Evaporated milk is a low acoustic scatter material which absorbs acoustic energy by denaturation of its rich content in proteins and fats. The use of the aforementioned additives allowed the independent control of each loss mechanism's contribution to the total attenuation coefficient by varying their concentrations appropriately to match the acoustic properties of the mimicked soft tissue.
Magnetic resonance imaging
The robotic systems and phantoms were tested in a 1.5 T superconductor MR system (Signa Excite, General Electric, Fairfield, CT, USA). A general-purpose flexible imaging coil was used to image the phantoms.
| Results|| |
Magnetic resonance imaging-compatible phantoms
Our group has gained significant experience in manufacturing FUS anthropomorphic phantoms. The first product developed was a composite head phantom. The skull part was mimicked with 3D-printed ABS. Based on the measurements conducted with acoustic pulse-echo immersion techniques, it was estimated that ABS possessed an attenuation coefficient within a range of values reported for human skull and a range of bony structures. The brain tissue was mimicked by acoustically matching to it an agar-based recipe. [Figure 1] shows the composite head phantom, where the agar-based brain phantom was molded inside the ABS skull part. The head phantom can be used mainly to evaluate the propagation of ultrasound through the high-attenuating skull. With this evaluation, it will be possible to find the optimum frequency to use through transkull transmission. A similar approach was also used for manufacturing a composite femur phantom, consisting of a femur bone part and the surrounding skeletal muscle agar-based gel. The muscle agar gel recipe was modified appropriately to match the reported acoustic properties of the replicated tissue. [Figure 2] illustrates the stereolithography (STL) mesh of a femur bone segmented from a patient's computed tomography (CT) images and which was used to 3D print the femur bone part with ABS. In this type of phantom, the main goal is to find the optimum frequency to use through the bone. Recently, the methodology described above was utilized to create a composite breast–rib phantom. The rib cage was 3D printed in ABS while the breast agar-based recipe was identical to the one used for modeling skeletal muscle in the femur phantom. [Figure 3] shows the STL mesh of a partial rib cage which was segmented for a patient's thoracic CT images and was used for the manufacturing the bony part of the breast/rib phantom. With this phantom, the goal was to evaluate the transmission of ultrasound through the breast/rib phantom. In one evaluation, the ultrasonic transducer is utilized by going through the ribs, and in another evaluation, ablation of ribs was avoided.
|Figure 1: Acrylonitrile butadiene styrene prototype of an adult skull filled with an agar-silica-evaporated milk gel|
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|Figure 2: Stereolithography file of a femur bone that was produced for the bone phantom|
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|Figure 3: Stereolithography file of a rib cage that was produced for the breast/rib phantom|
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Magnetic resonance imaging-compatible robotic systems
Mylonas and Damianou  developed a prototype robotic system for brain therapy using three linear stages. [Figure 4] shows the robotic system for brain ablation designed using 3D printing. This robotic system includes three Cartesian axes and access to the brain can be established. The motion of the axes was achieved using piezoelectric motors.
|Figure 4: Robotic system for brain ablation designed using three-dimensional printing|
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Yiallouras et al., 2014, produced a robotic system for endorectal use using focused ultrasound for prostate cancer. [Figure 5] shows the MRI-guided focused ultrasound robotic system for prostate therapy designed using 3D printing. The robotic system includes two PC-controlled axes and two manually driven axes. Moreover, our group developed a focused ultrasound system which is MRI compatible for endovaginal use for gynecological tumors (Epaminonda et al., 2016).
|Figure 5: Robotic system for prostate therapy designed using three-dimensional printing|
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[Figure 6] shows the prototype MRI-guided focused ultrasound robotic system for gynecological tumors designed using 3D printing. This robotic system includes one linear axis and one angular axis. The tumor can be ablated through endovaginal access. Finally, our group designed a robotic system that can be used as a motion phantom. The phantom includes a stationary ultrasonic transducer and two linear axes for moving a tissue in two axes (X, Y). [Figure 7] shows the robotic system for implementing a two-stage MRI-compatible focused ultrasound motion phantom. The robotic system includes two linear axes. The speed of the two axes is computer controlled.
|Figure 6: Robotic system for gynecological tumors designed using three-dimensional printing|
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| Discussion|| |
The article presents innovative robotic systems for brain, prostate, and gynecological targets. It also includes innovative phantoms for brain, breast, bone, and motion.
As it was shown by our group, 3D printing has two important contributions in MRI-guided FUS. The first contribution is the design of MRI-compatible robotic systems.,,,,, Due to the magnetic fields of MRI, all the parts of the robot had to be MRI compatible. Therefore, the 3D printers that produce plastic parts qualify for the design of such robots. In our case, we use an ABS printer. ABS has similar acoustical properties with bone, and therefore, 3D printers can be used for the design of MR-compatible phantoms which include bone.,, Thus, we developed successfully phantoms for skull, bone, and ribs. These phantoms were mostly used to evaluate the thermal protocols of focused ultrasound. The proposed robotic systems that we produced belong to the area of robotic systems for focused ultrasound. Recently, we have used 3D printing to create enclosure of ultrasonic transducers., It is very likely that additional tools can be developed for MRI-guided focused ultrasound technology.
The 3D printing technology is producing prototype very quickly. As a final product, robotic systems must be produced by sophisticated manufacturing technologies that provide improved appearance. However, recently, 3D printing technology offers improved appearance (see polyjet technology), and therefore, the issue of appearance can be overcome by 3D printing technology. In addition, 3D printing can be used only for low-volume production. Large-volume manufacturing has to be implemented by advanced manufacturing technology.
In the future, it will be possible to design robotic systems for other applications such as bone palliation, pancreas, and eye. Regarding phantoms, this technology could be used to mimic prostate and gynecological tumors and other targets accessible by focused ultrasound.
| Conclusions|| |
The technology of 3D printing plays a very important role in MRI-guided FUS because prototype robotic systems can be produced quickly, thus speeding the development process. In addition, MRI-compatible phantoms can be easily developed due to the 3D printing technology, thus offering an important tool for ultrasound scientists.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 6], [Figure 5], [Figure 7]