NIST engineer Kathryn Keenan opens an MRI system phantom used for calibrating MRI machines that is traceable to standardized values. The phantom is filled with small plastic containers of various salt solutions that mimic tissues of the human body.
Credit: R. Jacobson/NIST
Magnetic resonance imaging (MRI) has revolutionized medical diagnostics and research by providing a non-invasive way to investigate internal tissue structures and processes at millimeter scale, often with far better soft-tissue contrast than can be obtained by x-ray and other methods. MRI is unique in that contrast is dependent on many different tissue properties including water density, water motion, local chemical environment, blood oxygen levels, fat fraction, cellularity, and vascularization.
The value of MRI can be dramatically increased by making its output more quantitative so that images become maps of important tissue properties. Quantitative imaging further ensures that measurements are reproducible, data from one imaging system can be confidently compared to data from another, and performance stability can be monitored over time.
To help achieve those goals, the National Institute of Standards and Technology’s Physical Measurement Laboratory (PML) in collaboration with the National Institute of Biomedical Imaging and Bioengineering (NIBIB) at the National Institutes of Health (NIH) recently launched a unique service that provides MRI research centers and clinics with access to NIST-traceable reference standards.
Nearly all conventional MRI results are qualitative – that is, they show differences in contrast between adjacent areas but do not measure the specific signal properties or intensities that produced those differences. To generate that kind of reliable quantitative data, a scanner has to be calibrated by comparing its measurements of standard reference materials (whic ..
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