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| Fig. 1: Example of a functional magnetic resonance image (FMRI). (Source: Wikimedia Commons.) |
Magnetic Resonance Imaging (MRI) has undoubtedly reshaped the medical landscape. They offer a means of diagnosing disease and elucidating brain function. Unfortunately, these machines have a cost. They necessitate the employment of a large and expensive cryogenic high-field magnet. [1] As a result, not only do they consume enormous amounts of energy, but they also deplete a finite resource: helium.
According to a report published in 2012, the United States performs 97.7 exams per population of 1000. [2] Given that the population of the US is 314,900,427 as of 2010, this means roughly 30,765,772 exams are performed in the US per year. [3] In a study done by PE International in 2012, the average exam takes about 15 kwh. [4] Given this, the US consumes roughly 461,486,576 khw a year. This accounts for roughly 0.01% of the U.S.'s energy use, given that the US uses 4,158 billion khw. [5] Because the standard of living is growing particularly in China and India, the energy costs globally will likely by increasing by a very large margin in the future.
Large amounts of helium are needed to cool the superconducting wire to temperatures as low as 4 degrees Kelvin. However, this cooling requires large amounts of helium. According to NEMA, MRI machines consume about 7000 tons of helium annually. [6] In 1996, it was estimated that the US used about 2.6 billion scf. [7] If one extrapolates the upward trend in helium consumption, then let's very roughly say that about 5 billion scf of helium are used annually. [7] That would mean 27% of the U.S.'s helium is being allocated towards the use of MRI's every year. Sources conflict on the exact amount of extractable helium left on the planet, but the amount is finite. [8]
MRI's are quite costly, and with a growing population, are not sustainable. However, the MRI has become such a staple of modern medicine that we cannot simply eliminate it. More energy efficient MRI's are needed. Shoujun Xu has developed a method to eliminate the need for cryogenics using a optical atomic magnetometers. [9] Such developments are promising for the future of medical imagining.
© Spencer Nam. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] C. Weiller et al., "Role of Functional Imaging in Neurological Disorders," J. Magn. Reson. Imaging. 23, 840 (2006).
[2] ""Health at a Glance 2009," Organization for Economic Co-Operation and Development (OECD), 2009.
[3] P. Mackun and S. Wilson, "Population Distribution and Change: 2000 to 2010," U.S. Census Bureau, March 2011.
[4] C. Herrmann and A. Rock, "Magnetic Resonance Equipment (MRI) - Study on the Potential For Environmental Improvement by the Aspect of Energy Efficiency," PE International, March 2012.
[5] "Electric Power Annual 2010," U.S. Energy Information Administration, November 2011.
[6] C. Updyke, "Nema Issue Brief," National Electrical Manufacturers Association, March 2012
[7] The Impact of Selling the Federal Helium Reserve (National Academy Press, 2000).
[8] M. Tilghman, "The Helium Crisis: Real and Avoidable," Physics 240, Stanford University, Fall 2011.
[9] S. Xu et el., "Magnetic Resonance Imaging With an Optical Atomic Magnetometer," Proc. Natl. Acad. Sci. 103 12668 (2006).
