Application
The scanner design is a low-cost resource for demonstrating concepts like magnetic resonance, spatial encoding, and the Fourier transform in an educational setting. A significant part of the system design is open-source.
Contributors
Clarissa Z Cooley1,2, Jason P Stockmann3,4, Cris LaPierre2,4, Thomas Witzel2, Feng Jia5, Maxim Zaitsev5, Pascal Stang6,7, Greig Scott7, Yang Wenhui8, Wang Zheng8, and Lawrence L Wald2,9
Estimated cost
< $10K USD per system
Progress
Hardware: Prototype, partially open-source
Software: Stable Release
The scanner design is a low-cost resource for demonstrating concepts like magnetic resonance, spatial encoding, and the Fourier transform in an educational setting. The system was first used in an undergraduate course. Some parts of the system are open source designs.
System Components are:
- Magnet: A 0.19T B0 field with ~50ppm homogeneity in 1cm DSV is created by two 15cm NdFeB disks held 4cm apart. An iron yoke confines the magnetic field to the gap between the pole pieces. Total weight is 13kg.
- Console: The MEDUSA console [6] is low cost and easy to program in MatLab. It includes a controller board, RF TX/RX board, gradient waveform synthesizer, and digital-to-analog converter boards for each gradient axis.
- Gradients: Air-cooled shielded planar X, Y, Z, and Z2 gradient coils produce slopes of [13.7, 10.4, 12.3] mT/m/A for [x, y, z]. Coils are 8-layer boards (2 primary, 2 shielding) of 4 oz (140 μm) copper and are positioned ±1 cm (primary) and ±2 cm (shielding) from isocenter.
- RF Subsystem: A RF shielded solenoid coil is used for efficient RF transmission and reception (Fig. 1d). Samples are placed in a 10mm NMR tube and inserted into the solenoid. For RF transmit a Mini-Circuits 29.5 dBm amplifier is used. A PIN-diode activated quarter-wave T/R switch was built using a two-stage amplifier made of low-cost Mini-Circuits GALI-74+ ICs with 2.7dB noise figures in the receive path to achieve 50dB gain.
- Gradient power amplifiers: Two OPA549 power op-amps are used in a bridged configuration to supply up to 6 amps of current to the gradient coil. A current sensor compares the output current to the input voltage to ensure that the current itself is proportional to the desired signal.
- GUIs: User interfaces written in MatLab allow students to conduct experiments easily. Data can be saved for post-processing in MatLab. Each GUI covers a topic such as free induction decay, flip angle calibration, and spin echoes.
The following parts are available for download:
- Gradient coil circuit board files
- Gradient power amp and RF T/R switch circuit board files
- Parts list
- MatLab files:
- GUIs
- Pulse sequences
Affiliations
1Electrical Engineering, Massachusetts Institute of Technology, Cambridge, MA, United States;
2Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States;
3Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States;
4Department of Physics, Harvard University, Cambridge, MA, United States, 5Department of Radiology – Medical Physics, University Medical Centre Freiburg, Freiburg, Baden-Württemberg, Germany;
6Procyon Engineering, San Jose, CA, United States;
7Electrical Engineering, Stanford University, Stanford, CA, United States;
8Department of Electromagnetic Detection and Imaging Technology, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing, China;
9Harvard Medical School, Boston, MA, United States.