On-site construction of a point-of-care low-field MRI system in Africa

Abstract

Purpose: To describe the construction and testing of a portable point-of-care low-field MRI system on site in Africa.

Methods: All of the components to assemble a 50 mT Halbach magnet-based system, together with the necessary tools, were air-freighted from the Netherlands to Uganda. The construction steps included individual magnet sorting, filling of each ring of the magnet assembly, fine-tuning the inter-ring separations of the 23-ring magnet assembly, gradient coil construction, integration of gradient coils and magnet assembly, construction of the portable aluminum trolley and finally testing of the entire system with an open source MR spectrometer.

Results: With four instructors and six untrained personnel, the complete project from delivery to first image took approximately 11 days.

Conclusions: An important step in translating scientific developments in the western world from high-income industrialized countries to low- and middle-income countries (LMICs) is to produce technology that can be assembled and ultimately constructed locally. Local assembly and construction are associated with skill development, low costs and jobs. Point-of-care systems have a large potential to increase the accessibility and sustainability of MRI in LMICs, and this work demonstrates that technology and knowledge transfer can be performed relatively seamlessly.

Keywords: Accessibility; halbach magnets; low field MRI; open-source spectrometer; point-of-care MRI; sustainable design.

Figure 1.

Photographs of the major components of the system. (a) Plastic rings in which the individual magnet elements are placed, (b) lids for each side of the rings, (c) 12 × 12 × 12 mm³ NdBFe magnets, (d) 3D printed gradient coils with grooves for wire insertion, (e) 3D printed supports for the finished magnet assembly, (f) aluminium used for the trolley, (g) small parts – brass rods, nuts/bolts/wire/superglue/PMMA glue, (h) simple wire-wound solenoid coil, (i) custom-built spectrometer based on a Red Pittaya.

Figure 2.

(left) Crate containing all components including assembly tools, overall size 1.2 × 1.0 × 0.8 m and weight 325 kg. (center) Final delivery after two weeks en route via taxi from the closest airport 5 hours away. (right) Illustration of individual plastic rings for the magnet.

Figure 3.

Individual steps in preparing the magnet components. (upper left) cubic magnets are (lower left) coloured to indicate north/south poles, and (center) magnets are inserted manually into the holes in each ring.

Figure 4.

An example of B-field measurements performed on each ring to check the orientation of each of the hundreds of magnets in each ring. The robot scans around the red line. The top plot on the right shows the expected sinusoidal variation in B_y and Bx fields as a function of azimuthal angle. In the bottom plot, one magnet has the incorrect polarity, which is shown by the green arrow.

Figure 5.

Magnet assembly. (left) Brass rods are used to align each of the rings of the magnets. Nuts are used as spacers between each ring. The forces between each ring are significant but not dangerous. (center) After each ring is threaded onto the rods, the position of each nut is carefully adjusted so that there is equal spacing between each of the rings, and they are precisely aligned parallel to each other. (right) The completed magnet consisting of 25 rings, the central 17 containing two layers of magnets, and the front/back three rings having three layers.

Figure 6.

Stages involved in gradient coil assembly from 3D printed formers. (left) Residual plastic from the 3D printing is removed to clear the grooves. Insulated wire is placed into the grooves and superglued into place after each turn, (right) photograph showing one completed section: four sections are used for the two outer gradient sets, and two sections for the inner set.

Figure 7.

Installation of gradient set and system characterization. (left) The design consists of interlocking components which click into place. (center) Before the final gradient set is inserted the wiring that connects the two halves and the gradient amplifier is installed. (right) After installation of the gradients a 3D robot is used to map the magnetic field.

Figure 8.

Construction of the portable trolley used for the system. Components consist of aluminium subunits screwed together.

Figure 9.

Completed system, with 10 cm diameter RF solenoidal coil placed in the center and a bell pepper used as the sample. A Marcos open-source spectrometer is used to acquire the data, with a small low-power minicircuits amplifier used for the RF. The first image, showing a zipper artifact to illustrate that the data are real!

Figure 10.

Approximate time-line for the build in Uganda, with four instructors and six students – work days were ~10 hours per day with 1–2 hours per day taken up by instruction. At each stage the approximate number of people working in parallel is indicated. On the right we outline the overall topics of lectures presented in parallel to the build.