A nuclear magnetic resonance imaging (MRI) method is presented for quantitatively mapping the physical response of a material to harmonic mechanical excitation. The resulting images allow calculation of regional mechanical properties. Measurements of shear modulus obtained with the MRI technique in gel materials correlate with independent measurements of static shear modulus. The results indicate that displacement patterns corresponding to cyclic displacements smaller than 200 nanometers can be measured. The findings suggest the feasibility of a medical imaging technique for delineating elasticity and other mechanical properties of tissue.

Magnetic resonance imaging contrast agents are currently designed by modifying their structural and physiochemical properties to improve relaxivity and to enhance image contrast. Here, we show a general method for increasing relaxivity by confining contrast agents inside the nanoporous structure of silicon particles. Magnevist, gadofullerenes and gadonanotubes were loaded inside the pores of quasi-hemispherical and discoidal particles. For all combinations of nanoconstructs, a boost in longitudinal proton relaxivity r₁ was observed: Magnevist, r₁ ≈ 14 mM⁻¹ s⁻¹/Gd³⁺ ion (∼8.15 × 10⁺⁷ mM⁻¹ s⁻¹/construct); gadofullerenes, r₁ ≈ 200 mM⁻¹ s⁻¹/Gd³⁺ ion (∼7 × 10⁺⁹ mM⁻¹ s⁻¹/construct); gadonanotubes, r₁ ≈ 150 mM⁻¹ s⁻¹/Gd³⁺ ion (∼2 × 10⁺⁹ mM⁻¹ s⁻¹/construct). These relaxivity values are about 4 to 50 times larger than those of clinically available gadolinium-based agents (∼4 mM⁻¹ s⁻¹/Gd³⁺ ion). The enhancement in contrast is attributed to the geometrical confinement of the agents, which influences the paramagnetic behaviour of the Gd³⁺ ions. Thus, nanoscale confinement offers a new and general strategy for enhancing the contrast of gadolinium-based contrast agents.

The objective of this magnetic resonance imaging (MRI) study was to (1) test the validity of the ellipsoid formula for estimating kidney volume using ex vivo and in vivo models and (2) establish a normal range of values for kidney length and volume in patients with no known history of renal disease. The volumes of five excised porcine kidneys were measured by (1) disc-summation method, (2) ellipsoid formula, and (3) water displacement method. In a retrospective, consecutive group of clinically referred patients (n = 150; 300 kidneys), individual kidney volume and length were calculated by the disc-summation method and by multiplanar reformation of MRI data, respectively. For comparison, kidney volumes also were calculated using the ellipsoid formula in all patients. Renal volume that was obtained by MRI using the disc-summation method was within 5% of the volume that was determined by the water displacement method, independent of the spatial resolution of the MRI technique used. Data from both the in vivo and the ex vivo models revealed that the ellipsoid formula that commonly is used in ultrasonography underestimates renal volume by 17 to 29% compared with the disc-summation method (P < 0.05). As measured by MRI (mean ± SD), kidney lengths were 12.4 ± 0.9 cm for men and 11.6 ± 1.1 cm for women, and kidney volumes were 202 ± 36 ml for men and 154 ± 33 ml for women. The results from the ex vivo MRI study show that the kidney volume that was obtained using the disc-summation method is within 5% of the true kidney volume as measured by the water displacement method. The ellipsoid formula consistently and significantly underestimates the true kidney volume. The length and the volume of kidneys that are obtained by MRI in patients with no known history of intrinsic renal disease are greater than the commonly quoted reference values that are obtained by ultrasonography.

Background— Left ventricular ejection fraction is a powerful independent predictor of survival in cardiac patients, especially those with coronary artery disease. Delayed-enhancement magnetic resonance imaging (DE-MRI) can accurately identify irreversible myocardial injury with high spatial and contrast resolution. To date, relatively limited data are available on the prognostic value of DE-MRI, so we sought to determine whether DE-MRI findings independently predict survival. Methods and Results— The medical records of 857 consecutive patients who had complete cine and DE-MRI evaluation at a tertiary care center were reviewed regardless of whether the patients had coronary artery disease. The presence and extent of myocardial scar were evaluated qualitatively by a single experienced observer. The primary, composite end point was all-cause mortality or cardiac transplantation. Survival data were obtained from the Social Security Death Index. The median follow-up was 4.4 years; 252 patients (29%) reached one of the end points. Independent predictors of mortality or transplantation included congestive heart failure, ejection fraction, and age ( P <0.0001 for each), as well as scar index (hazard ratio, 1.26; 95% confidence interval, 1.02 to 1.55; P =0.033). Similarly, in subsets of patients with or without coronary artery disease, scar index also independently predicted mortality or transplantation (hazard ratio, 1.33; 95% confidence interval, 1.05 to 1.68; P =0.018; and hazard ratio, 5.65; 95% confidence interval, 1.74 to 18.3; P =0.004, respectively). Cox regression analysis showed worse outcome in patients with any DE in addition to depressed left ventricular ejection fraction (<50%). Conclusion— The degree of DE detected by DE-MRI appears to strongly predict all-cause mortality or cardiac transplantation after adjustment for traditional, well-known prognosticators.