Submitted on February 14, 2008
Accepted on May 30, 2008
Mapping and Quantifying Hyperpolarized 3He Magnetic Resonance Imaging Apparent Diffusion Coefficient Gradients
Andrea Evans1, David G. McCormack2, Giles E. Santyr3, and Grace Parraga4*
1 Imaging Research Laboratories, Robarts Research Institute, London, Canada; Department of Medical Biophysics, University of Western Ontario, London, Canada
2 Department of Medicine, University of Western Ontario, London, Canada; Lawson Health Research Institute, London, Canada
3 Imaging Research Laboratories, Robarts Research Institute, London, Canada; Department of Medical Biophysics, University of Western Ontario, London, Canada; Department of Radiology and Nuclear Medicine, University ofWestern Ontario, London, Canada
4 Imaging Research Laboratories, Robarts Research Institute, London, Canada; Department of Medical Biophysics, University of Western Ontario, London, Canada; Lawson Health Research Institute, London, Canada; Department of Radiology and Nuclear Medicine, University ofWestern Ontario, London, Canada
* To whom correspondence should be addressed. E-mail: gep{at}imaging.robarts.ca.
We measured hyperpolarized 3He magnetic resonance imaging (MRI) apparent diffusion coefficients (ADC) and quantified ADC gradients in each three by three voxel region of interest (ROI). Such local ADC gradients can be represented in vector maps showing the magnitude (|G3x3|) and direction of ADC gradients, providing a qualitative visualization tool and quantitative measurement of airway and airspace heterogeneity.
Twenty-four subjects (15 male, mean age 67 ±7 years) with GOLD stage II (n=9, mean age 68 ±6 years), GOLD stage III COPD (n=7, mean age 67 ±8 years) and age-matched healthy volunteers (n=8, mean age 67 ±6 years) were enrolled based on their age and spirometry results. Hyperpolarized 3He MRI was performed on a whole body 3.0 Tesla system. Mean 3He ADC and ADC standard deviation (SD) was calculated for the center coronal slice and the mean magnitude and direction of the ADC gradient vectors was calculated for each three by three voxel matrix (|G3x3|). While the 3He ADC SD was not significantly different, mean |G3x3| was significantly different between subjects with stage II (0.14 ±0.03 cm/s) and stage III COPD (0.19 ±0.03 cm/s) (p<.005) and between healthy subjects (0.12 ±0.03 cm/s) and those with stage II COPD (p<.02). The second order statistic, |G3x3|, may provide a sensitive measure of ADC heterogeneity for ROI representing 9.4mm x 9.4mm x 30mm, or 2.6 cm3 of lung tissue.
