Intravoxel incoherent motion analysis of abdominal organs: computation of reference parameters in a large cohort of C57Bl/6 mice and correlation to microvessel density

Objective

Diffusion-weighted magnetic resonance imaging (DW-MRI) combined with intravoxel incoherent motion (IVIM) analysis may be applied for assessment of organ lesions, diffuse parenchymal pathologies, and therapy monitoring. The aim of this study was to determine IVIM reference parameters of abdominal organs for translational research in a large cohort of C57Bl/6 laboratory mice.

Materials and methods

Anesthetized mice (n = 29) were measured in a 4.7 T small-animal MR scanner with a diffusion-weighted echo-planar imaging sequence at the \(b\)-values 0, 13, 24, 55, 107, 260, 514, 767, 1020 s/mm². IVIM analysis was conducted on the liver, spleen, renal medulla and cortex, pancreas, and small bowel with computation of the true tissue diffusion coefficient \(D_{\text{t}}\), the perfusion fraction \(f_{\text{p}}\), and the pseudodiffusion coefficient \(D_{\text{p}}\). Microvessel density (MVD) was assessed by immunohistochemistry (IHC) against panendothelial cell antigen CD31.

Results

Mean values of the different organs [\(D_{\text{t}}\) (10^?3 mm²/s); \(f_{\text{p}}\) (%); \(D_{\text{p}}\) (10^?3 mm²/s); MVD (MV/mm²)]: liver 1.15 ± 0.14; 14.77 ± 6.15; 50.28 ± 33.21, 2008.48 ± 419.43, spleen 0.55 ± 0.12; 9.89 ± 5.69; 24.46 ± 17.31; n.d., renal medulla 1.50 ± 0.20; 14.63 ± 4.07; 35.50 ± 18.01; 1231.88 ± 290.61, renal cortex 1.34 ± 0.18; 10.83 ± 3.70; 16.74 ± 6.74; 810.09 ± 193.50, pancreas 1.23 ± 0.22; 20.12 ± 7.46; 29.35 ± 17.82, 591.15 ± 86.25 and small bowel 1.06 ± 0.13; 16.48 ± 3.63; 15.31 ± 7.00; 420.50 ± 168.42. Unlike \(D_{\text{t}}\) and \(f_{\text{p}}\), \(D_{\text{p}}\) correlates significantly with MVD (r = 0.90, p = 0.037).

Conclusion

This systematic evaluation of murine abdominal organs with IVIM and MVD analysis allowed to establish reference parameters for future DW-MRI translational research studies on small-animal disease models.

     

Specific purpose Monte Carlo code development for nuclear well logging applications

The authors have been developing specific purpose Monte Carlo simulation programs for the suite of nuclear well logging devices that are in present use. To date codes called McPNL and McDNL have been developed and tested for the pulsed neutron lifetime and dual-spaced or compensated neutron porosity logs, respectively. Another code called McLDL is presently under development for the gamma-ray litho-density logs. These codes are discussed and results are presented as to their construction, advantages, and uses as compared to the general purpose codes MCNP and McBEND. Computational benchmark problems are specified for all three logs for future quantitative comparisons.     

Transparent Thin Films of Multiwalled Carbon Nanotubes Self‐Assembled on Polyamide 11 Nanofibers

Electrospun polyamide 11 (PA11) nanofiber films are used as a guide for the deposition of two‐dimensional networks of multi‐walled carbon nanotubes (MWNTs). This method allows for the manufacturing of transparent and electrically conductive thin films. It is demonstrated that the sheet resistance (Rs) and transmittance (T) decrease, as the films become thicker due to longer electrospinning times or larger fibers. The transmittance could be improved by fusing (melting) the fibers at moderate temperatures or impregnating the film with a resin, showing that light scattering rather than absorption by the MWNTs or the polymer was responsible for a low transmittance. As the number of MWNT deposition cycles increases, the Rs decreases with a constant transmittance. A fused 100 nm film obtained after 10 min of electrospinning of the 2 wt % PA11 solution shows Rs = 154 kΩ sq^?1 and T = 83% after ten MWNT deposition cycles. A 95% transmittance was achieved after removing the polymer fibers by heating the glass plate in air (Rs = 440 kΩ sq^?1 after five MWNT deposition cycles).     

Fractional-order Fourier analysis for ultrashort pulse characterization

We report what we believe to be the first experimental demonstration of ultrashort pulse characterization using fractional-order Fourier analysis. The analysis is applied to the interpretation of spectral interferometry resolved in time (SPIRIT) traces [which are spectral phase interferometry for direct electric field reconstruction (SPIDER)-like interferograms]. First, the fractional-order Fourier transformation is shown to naturally allow the determination of the cubic spectral phase coefficient of pulses to be analyzed. A simultaneous determination of both cubic and quadratic spectral phase coefficients of the pulses using the fractional-order Fourier series expansion is further demonstrated. This latter technique consists of localizing relative maxima in a 2D cartography representing decomposition coefficients. It is further used to reconstruct or filter SPIRIT traces.     

On the effects of reflected waves in transient shear wave elastography

In recent years, novel quantitative techniques have been developed to provide noninvasive and quantitative stiffness images based on shear wave propagation. Using radiation force and ultrafast ultrasound imaging, the supersonic shear imaging technique allows one to remotely generate and follow a transient plane shear wave propagating in vivo in real time. The tissue shear modulus, i.e., its stiffness, can then be estimated from the shear wave local velocity. However, because the local shear wave velocity is estimated using a time-of- flight approach, reflected shear waves can cause artifacts in the estimated shear velocity because the incident and reflected waves propagate in opposite directions. Such effects have been reported in the literature as a potential drawback of elastography techniques based on shear wave speed, particularly in the case of high stiffness contrasts, such as in atherosclerotic plaque or stiff lesions. In this letter, we present our implementation of a simple directional filter, previously used for magnetic resonance elastography, which separates the forward- and backward-propagating waves to solve this problem. Such a directional filter could be applied to many elastography techniques based on the local estimation of shear wave speed propagation, such as acoustic radiation force imaging (ARFI), shearwave dispersion ultrasound vibrometry (SDUV), needle-based elastography, harmonic motion imaging, or crawling waves when the local propagation direction is known and high-resolution spatial and temporal data are acquired.