Using LabVIEW and PXI to Develop an Integrated MRI System Controller and Multichannel Spectrometer

"Our research spectrometer based on NI tools is a flexible research tool with capability in some cases that actually exceeds systems supplied by the major MR manufacturing companies, and we can further customize and adapt the system to meet new requirements through software modifications when necessary."

- Martyn Paley, University of Sheffield, InnerVision

The Challenge:

Developing a low-cost control and acquisition system to enable MRI research on clinical MRI systems without having to modify the standard hardware or software.

The Solution:

Using NI LabVIEW software and NI off-the-shelf hardware to develop a complete magnetic resonance (MR) control system and multichannel imaging spectrometer that MR research scientists can use independently from the standard scanner control system.

MRI is arguably the most powerful diagnostic imaging tool available today. MR systems typically cost more than $1 million USD and are supplied by some of the largest electronics companies such as GE, Siemens, and Philips. The systems use a large magnet, a radio frequency transceiver system, and a field gradient set based on powerful audio amplifiers and coils. The hardware is accurately programmed using sophisticated and expensive control systems. However, these systems are designed for clinical examinations and built using highly proprietary hardware and software, which often makes them difficult for research scientists to program independently. Many scientists around the world make major scientific technique developments in the MRI field using their own programming and hardware skills, but this often requires a massive learning curve and can interfere with proper operation of the clinical instruments.

 

Project Background

Professor Paley is a professor of biomedical imaging at the University of Sheffield and is also chief scientist of InnerVision MRI Ltd., a company founded in 1993 to pioneer the development of niche application MRI systems for orthopedic and neonatal imaging. InnerVision achieved FDA clearance for marketing the first neodymium boron iron-based (patented) niche MRI system in the U.S. in the late 1990s and has since sold several systems worldwide. A niche neonatal MRI system installed in Sheffield Neonatal Intensive Care Unit in 2001 has scanned more than 1,000 newborns safely and efficiently in the last 10 years. The company has since concentrated on developing independent spectrometers for MR scientists to perform novel research on standard clinical MR systems without interfering with the normal clinical operation of the system, which is vital in medical imaging departments. Researchers at Imperial College London and the Institute of Cancer Research in the United Kingdom have recently chosen the InnerVision spectrometer based on NI tools for ongoing MR research because the LabVIEW software platform is flexible and easy to extend and NI hardware is powerful and reliable.

 

Building a System Controller and MRI Spectrometer

MRI requires tight integration of simultaneous waveform output and input on multiple channels, as well as control of digital frequency synthesis with rapid phase-coherent frequency switching. The simultaneous sampling hardware and software provided by NI is ideal for building multichannel receiver systems with fast sampling rates for each channel. We can seamlessly increase channel count by purchasing additional modules that require only minor software changes. We built spectrometers with 32 receiver channels operating at 3.5 MS/s using NI S Series simultaneous sampling data acquisition (DAQ) modules because they operate extremely well and have low error rates.

 

Our previous designs used dedicated digital signal processor (DSP) modules, often from small manufacturers that used specialized low-level software drivers that quickly became obsolete as OSs and computer hardware interfaces evolved. This meant that we wasted significant time reinventing the wheel and duplicating our software. Initially, we coded our software in traditional ANSI C and then NI LabWindows™/CVI software. Even though we were skeptical that LabVIEW was suitable for spectrometer control, we converted a LabWindows/CVI version of the spectrometer software to LabVIEW in less than one month. It soon became apparent that LabVIEW was indeed a highly versatile and powerful development tool for this purpose. The intuitive graphical design software is ideal for creating the multiple looping control structures required for MRI. We can rapidly implement changes to the software architecture and easily make image reconstruction algorithms using the built-in signal and image processing tools.

 

Even though the initial investment in NI hardware and software seemed high for a small company, we concluded NI tools were the best choice for the project. NI regularly invests in product development to ensure its tools are up-to-date and backward compatible, which removed the need for us to continually redevelop our software and hardware platforms and helped us take advantage of the latest innovations in software and computer technology.

 

We realized additional benefits by using NI products such as the NI Analog Waveform Editor, a pre-engineered software tool that our customers can use to easily visualize and edit their own MRI waveforms. Producing an equivalent editor in house would have taken a major software effort and slowed down our development considerably.

 

NI sales, training, and support staff are very knowledgeable and efficient in answering our numerous questions and meeting our requests, and NI always dispatches equipment on time and it arrives in good condition. The NI Standard Service Program (SSP) keeps us up-to-date with new releases, which is essential in today’s fast-moving product environment.

 

 

 

Future System Upgrades

Our research spectrometer based on NI tools is a flexible research tool with capability in some cases that actually exceeds systems supplied by the major MR manufacturing companies, and we can further customize and adapt the system to meet new requirements through software modifications when necessary. We look forward to investigating reconfigurable field-programmable gate array (FPGA) hardware from NI, which we can also program with LabVIEW, for future designs. For example, NI FlexRIO hardware combines a high-performance FPGA back end with customizable I/O, which we may be able to use to acquire signals in the hundreds of megahertz and perform direct digital downconversion for even the most powerful MRI magnets. We can also investigate the process of implementing additional signal processing functions in the FPGA to increase imaging performance of the system.

 

The mark LabWindows is used under a license from Microsoft Corporation. Windows is a registered trademark of Microsoft Corporation in the United States and other countries.

 

Author Information:

Martyn Paley
University of Sheffield, InnerVision
United Kingdom
Tel: +44 1142713208

Figure 2. This dedicated InnerVision MRI niche system is operating at 0.2 Tesla field strength. The patient access is 750 mm (V) by 200 mm (H). The system weighs 500 kg and has a footprint of 500 by 500 mm.
Figure 3. This is a cross-sectional MRI acquired in the axial plane to show the bones and soft tissue of a hand. It was acquired using the MR spectrometer based on LabVIEW and an independent RF and gradient coil system on a 1.5 Tesla clinical MR scanner.