- Oral presentation
- Open Access
Taui, A high-resolution metabolic imaging biomarker for myocardium
© Springer et al.; licensee BioMed Central Ltd. 2014
- Published: 16 January 2014
- Extracellular Volume Fraction
- Intravascular Contrast Agent
- Water Permeability Coefficient
- Myocardial Extracellular Volume
- Contrast Agent Extravasation
Contrast-enhanced 1H2O T1-weighted cardiovascular MRI is usually interpreted using tracer paradigms; e.g., the extra-/intravascular contrast agent (CA) partition coefficient. However, the signal molecule is water, not CA. Consequently, the myocardial extracellular volume fraction (ECV) is underestimated in proportion to its magnitude. Even more importantly, intercompartmental water exchange kinetics are inaccessible. The mean intracellular water molecule lifetime [taui] is assumed effectively 0; though it is a fraction of a second. For cylindrical myocytes with mean cytolemmal water permeability coefficient PW and diameter d: taui-1= 4(PW/d). taui-1 is linearly related to PW and to d-1. However, PW dominates and is itself dominated by active trans-membrane water cycling. Thus, taui-1 is proportional to the driving cytolemmal ATPase ion pump activity.
We acquired serial 1.5T T1-weighted 1H2O data from 6 normal human subjects before and after a single bolus 0.15 mmol/kg CA IV injection. The tissue and blood ROIs comprised ~300 LV wall and ~25 LV voxels [(2 × 2 × 8) mm3]. Hematocrit values allowed R1p estimation.
[n = 6]
0.26 (+/- 0.02)
0.33 (+/- 0.04)
0.20 (+/- 0.09) s
The first taui metabolic sensitivity hint came in a 2006 perfused ex vivo rat heart study (with other collaborators) finding that (no flow) ischemia increased taui by 56% - from 0.18 to 0.28 s. For control mice taui = 0.19 s, and for a hypertensive mouse model taui = 0.44 s, values have been reported. The very large (132%) taui increase is accompanied by an only 30% d increase; from 20 to 26 μm. These results demonstrate PW dominance of taui, and sensitivity to metabolic activity slowing caused by both ischemia and chronic hypertension.
NIH [RO1 NS40801].
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