Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2013 Nov 27;13(12):16245-62.
doi: 10.3390/s131216245.

Software Defined Radio (SDR) and Direct Digital Synthesizer (DDS) for NMR/MRI instruments at low-field

Aktham Asfour  1 , Kosai Raoof, Jean-Paul Yonnet
Affiliations

Software Defined Radio (SDR) and Direct Digital Synthesizer (DDS) for NMR/MRI instruments at low-field

Aktham Asfour et al. Sensors (Basel). .

Abstract

A proof-of-concept of the use of a fully digital radiofrequency (RF) electronics for the design of dedicated Nuclear Magnetic Resonance (NMR) systems at low-field (0.1 T) is presented. This digital electronics is based on the use of three key elements: a Direct Digital Synthesizer (DDS) for pulse generation, a Software Defined Radio (SDR) for a digital receiving of NMR signals and a Digital Signal Processor (DSP) for system control and for the generation of the gradient signals (pulse programmer). The SDR includes a direct analog-to-digital conversion and a Digital Down Conversion (digital quadrature demodulation, decimation filtering, processing gain…). The various aspects of the concept and of the realization are addressed with some details. These include both hardware design and software considerations. One of the underlying ideas is to enable such NMR systems to "enjoy" from existing advanced technology that have been realized in other research areas, especially in telecommunication domain. Another goal is to make these systems easy to build and replicate so as to help research groups in realizing dedicated NMR desktops for a large palette of new applications. We also would like to give readers an idea of the current trends in this field. The performances of the developed electronics are discussed throughout the paper. First FID (Free Induction Decay) signals are also presented. Some development perspectives of our work in the area of low-field NMR/MRI will be finally addressed.

PubMed Disclaimer

Figures

Figure 1.
Figure 1.
A block diagram of the DDS and SDR based NMR system at 0.1 T.
Figure 2.
Figure 2.
A simplified diagram of the DDS and its interface with the DSP.
Figure 3.
Figure 3.
Block diagram of one receiving channel and its interface with the DSP. The second receiving channel is not shown.
Figure 4.
Figure 4.
Block diagram of the developed software.
Figure 5.
Figure 5.
(a) The impulse response of the first programmable filter. (b) The frequency response of the same filter. The filter has a fixed decimation factor of 2. In this example, the input and the output sample rates were 100 kHz and 50 kHz, respectively.
Figure 6.
Figure 6.
(a) The impulse response of the second programmable filter. (b) The frequency response of the same filter. The filter has a programmable decimation factor (2 or 4). In this example, the input and sample rate was 50 kHz. The decimation factor was programmed to 2. The output sample rate was 25 kHz.
Figure 7.
Figure 7.
The electrical circuit of the coil and the matching loop Ls together with the passive T/R switch. The inductance of the coil is Lp ≈ 0.7 μH and the tuning capacitor is C = 2,080 pF (9 × 220 pF + 100 pF chip capacitors from ACT Corp.), Ls is the inductance of the matching loop.
Figure 8.
Figure 8.
Base band I/Q signals of the free induction decay (FID) obtained with a hard 90° pulse of 100 μs of duration and 50 ms of repetition time.
See this image and copyright information in PMC

References

    1. Blumich B., Perlo J., Casanova F. Mobile single-sided NMR. Prog. Nucl. Magn. Reson. Spectros. 2008;52:197–269.
    1. Asfour A. A New DAQ-Based and Versatile Low-Cost NMR Spectrometer Working at Very-Low Magnetic Field (4.5 mT): A Palette of Potential Applications. Proceedings of the I2MTC 2008 IEEE International Instrumentation and Measurement Technology Conference; Vancouver, BC, Canada. 12–15 May 2008; pp. 697–701.
    1. Asfour A. A novel NMR instrument for the in situ monitoring of the absolute polarization of laser-polarized 129Xe. J. Biom. Sci. Eng. 2010;3:1099–1107.
    1. Asfour A. Practical Applications and Solutions Using Labview™ Software. INTECH; Rijeka, Croatia: 2011. Low-Field NMR/MRI Systems Using Labview and Advanced Data Acquisition Techniques; pp. 17–40.
    1. Wright S.M., McDougall M.P., Bosshard J.C. A Desktop Imaging System for Teaching MR Engineering. Proceedings of EMBC 2010 32nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC); Buenos Aires, Argentina. 31 August–4 September 2010; pp. 6653–6656. - PubMed

MeSH terms