Halbach array (Netherlands)
LUMC is currently working on the second generation of this machine. The devices uses permanent magnets to establish the magnetic field. Magnets are carefully placed in the Halbach array to augment the field on one side of the array. This way the fields on the other side are cancelled to near zero, it therefore improves the quality of the created magnetic field.
Images created by the device are affected by unknown variations in the field cultivated by the (inexpensive) individual magnets. High precision manufacturing is required to ensure the exact location of the individual magnets. The lack of accuracy can lead to large errors and this makes it more difficult to compute a readable image.
As a result of using permanent magnets the machine is both lightweight and very power efficient.
Electromagnet (Uganda)
A prototype of this machine has been made at Penn State University and is currently being replicated in Uganda. The electromagnetic MRI consists of mainly copper coils to induce the required magnetic field. Creating the desired field strength requires enormous amounts of copper which directly increases both the costs and weight of the device.
Furthermore, due to the resistance in the copper wires, heat will be radiating from the coils which influences the magnetic field. To ensure a stable magnetic field the temperature needs to be controlled by an active cooling system. Less precision is required for this machine compared to regular MRIs, it will therefore be easier to produce this electromagnetic device.
MRI-Uganda 