High resolution morphologic imaging and T2 mapping of cartilage at 7 Tesla: comparison of cartilage repair patients and healthy controls

Object

Our objective was to use 7 T MRI to compare cartilage morphology (thickness) and collagen composition (T2 values) in cartilage repair patients and healthy controls.

Materials and methods

We scanned the knees of 11 cartilage repair patients and 11 controls on a 7 T MRI scanner using a high-resolution, gradient-echo sequence to measure cartilage thickness and a multi-echo spin-echo sequence to measure cartilage T2 values. We used two-tailed t tests to compare cartilage thickness and T2 values in: repair tissue (RT) versus adjacent cartilage (AC); RT versus healthy control cartilage (HC); AC versus HC.

Results

Mean thickness in RT, AC, HC were: 2.2 ± 1.4, 3.6 ± 1.1, 3.3 ± 0.7 mm. Differences in thickness between RT–AC (p = 0.01) and RT–HC (p = 0.02) were significant, but not AC–HC (p = 0.45). Mean T2 values in RT, AC, HC were: 51.6 ± 7.6, 40.0 ± 4.7, 45.9 ± 3.7 ms. Differences in T2 values between RT–AC (p = 0.0005), RT-HC (p = 0.04), and AC–HC (p = 0.004) were significant.

Conclusion

7 T MRI allows detection of differences in morphology and collagen architecture in: (1) cartilage repair tissue compared to adjacent cartilage and (2) cartilage repair tissue compared to cartilage from healthy controls. Although cartilage adjacent to repair tissue may be normal in thickness, it can demonstrate altered collagen composition.     

Assessment of MRF for simultaneous T1 and T2 quantification and water–fat separation in the liver at 0.55 T

Magnetic Resonance Materials in Physics, Biology and Medicine - The goal of this work was to assess the feasibility of performing MRF in the liver on a 0.55 T scanner and to examine the...     

Reproducibility and regional variations of an improved gagCEST protocol for the in vivo evaluation of knee cartilage at 7 T

Objective

The objective was to establish a gagCEST protocol that would enable robust and reproducible assessment of the glycosaminoglycan (GAG) content in knee cartilage at 7 T within a clinically feasible measurement time.

Materials and methods

Ten young healthy volunteers (mean age 26 years, range 24–28, five males, five females) were examined on a 7 T MR system. Informed consent was obtained from all individual participants prior to enrollment into the study. Each volunteer was measured twice for reproducibility assessment. The examined knee was immobilized using a custom-made fixation device. For the gagCEST measurement, a prototype segmented 3-D RF-spoiled gradient-echo sequence with an improved saturation scheme employing adiabatic pulses was used in a scan time of 19 min. The asymmetry of the Z-spectra (MTR_asym) in selected regions of interest in knee cartilage was calculated. Differences in MTR_asym between different regions were evaluated using ANOVA and the Bonferroni corrected post hoc test.

Results

The improvement of the saturation scheme reduced the influence of field inhomogeneities, resulted in more uniform saturation, and allowed for good reproducibility in a reasonable measurement time (19 min), as demonstrated by an intraclass correlation coefficient of 0.77. Improved fixation helped to reduce motion artifacts. Whereas similar MTR_asym values were found for weight-bearing and non-weight-bearing femoral cartilage, lower values were observed in the trochlear groove (p = 0.028), patellar (p = 0.015) and tibial cartilage (p < 0.001) when compared to non-weight-bearing femoral cartilage.

Conclusion

Reasonable reproducibility and sensitivity to regional differences in GAG content suggests that the improved gagCEST protocol might be useful for assessing the biochemical changes in articular cartilage that are associated with early stages of cartilage degeneration.

     

Quantum transport of holes in 1D, 2D, and 3D devices: the?k?p?method

Quantum transport of holes in one-, two- and three-dimensional devices is simulated based on the 6-band k?p method. Detailed numerical aspects for an efficient development of a k?p-based simulator are provided. In particular, real-space and k-space discretization schemes for devices of different dimensionality are described and their effectiveness in numerical implementation is compared. The mode-space approach for drastic reduction of computation time is also described. The capability of the?k?p-based simulator is demonstrated by investigating various aspects of hole transport in devices of different dimensionality.     

Fabrication and Characterization of Gate-Connected 1T2C-Type Ferroelectric Memory with Paired Bi4 − xLaxTi3O12 Capacitors

A gate-connected 1T2C-type ferroelectric memory, in which the bottom electrodes of paired ferroelectric capacitors are connected to the gate electrode of an underlying FET (field effect transistor) on the field oxide region, was fabricated using a Bi_{4 ? x}La_xTi₃O₁₂ (BLT) film and its electrical properties were characterized. The I_D-V_G (drain current-gate voltage) characteristics of a FET combined with a single ferroelectric capacitor showed that the paired capacitors had almost the same ferroelectric property. It was found in the readout operation that there existed an optimum voltage to maximize the drain current on/off ratio between datum ‘1’ and datum ‘0,’ and that the maximum ratio was as large as 6 × 10⁴. It was also found that the drain current level remained constant, even if the readout operation was repeatedly conducted. It was concluded from these results that the 1T2C-type memory was successfully fabricated using the proposed process and operated properly.     

Calculation of phonon spectrum and thermal properties in suspended 〈100〉 In X Ga1?X As nanowires

The phonon spectra in zinc blende InAs, GaAs and their ternary alloy nanowires (NWs) are computed using an enhanced valence force field (EVFF) model. The physical and thermal properties of these nanowires such as sound velocity, elastic constants, specific heat (C _v ), phonon density of states, phonon modes, and the ballistic thermal conductance are explored. The calculated transverse and longitudinal sound velocities in these NWs are ∼25% and 20% smaller compared to the bulk velocities, respectively. The C _v for NWs are about twice as large as the bulk values due to higher surface to volume ratio (SVR) and strong phonon confinement in the nanostructures. The temperature dependent C _v for InAs and GaAs nanowires show a cross-over at 180°K due to higher phonon density in InAs nanowires at lower temperatures. With the phonon spectra and Landauer’s model the ballistic thermal conductance is reported for these III–V NWs. The results in this work demonstrate the potential to engineer the thermal behavior of III–V NWs.     

<Superscript>1</Superscript>H−MRS of hepatic fat using short TR at 3T: SNR optimization and fast T2 relaxometry

Object  

To increase the signal-to-noise ratio (SNR) efficiency of hepatic fat signals in proton magnetic resonance spectroscopy (¹H MRS) at 3 T, in order to improve the quantitation of hepatic fat and allow fast, single breath-hold T2 relaxometry of hepatic water and fat.