Field dependent transverse relaxation rate increase may be a specific measure of tissue iron stores

Authors

  • George Bartzokis M.D.,

    Corresponding author
    1. Research Service, VA Medical Center West Los Angeles (Brentwood Division)
    2. Department of Psychiatry and Biobehavioral Sciences, UCLA School of Medicine
    3. Department of Radiology, Harbor-UCLA Medical Center
    • West Los Angeles VAMC (Brentwood Division), 11301 Wilshire Bld., Mail Code B-151H, Los Angeles, CA 90073
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  • Manickam Aravagiri,

    1. Department of Psychiatry and Biobehavioral Sciences, UCLA School of Medicine
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  • William H. Oldendorf,

    1. Research Service, VA Medical Center West Los Angeles (Brentwood Division)
    2. Department of Psychiatry and Biobehavioral Sciences, UCLA School of Medicine
    3. Department of Radiology, Harbor-UCLA Medical Center
    4. Department of Neurology and Radiology, UCLA School of Medicine
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    • Deceased.

  • Jim Mintz,

    1. Department of Psychiatry and Biobehavioral Sciences, UCLA School of Medicine
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  • Stephen R. Marder

    1. Department of Psychiatry and Biobehavioral Sciences, UCLA School of Medicine
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Abstract

The degree to which MRI magnet field strength affects measured transverse relaxation rates (R2) defines a measure termed the field dependent R2 increase (FDRI). We report here the results of in vivo and in vitro experiments that were conducted to evaluate whether FDRI is a potentially useful measure of tissue iron stores. T2 relaxation times were obtained using two clinical MRI instruments operating at 0.5 and 1.5 Tesla, and relaxation rates (R2) were calculated as the reciprocal of T2. The in vivo experiment measured R2 in human brain frontal white matter, caudate nucleus, putamen, and globus pallidus. The FDRI was very highly correlated with published brain iron levels for the four regions examined. The in vitro experiment measured R2 in agarose gel-based phantoms containing physiologic forms and amounts proteins involved in iron storage and transport (ferritin, apoferritin, transferrin, and apotransferrin). Significant field dependence was observed only for the ferritin phantoms. The differences in the R2 values obtained at the two field strengths were striking, and were proportional to the ferritin levels of the phantoms. These studies suggest that FDRI may be a specific measure of tissue ferritin. The quantitative significance of the results to imaging and possible applications to the clinical investigation of pathologic states are discussed.

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