A uniplanar three-axis gradient set for in vivo magnetic resonance microscopy

We present an optimized uniplanar magnetic resonance gradient design specifically tailored for MR imaging applications in developmental biology and histology. Uniplanar gradient designs sacrifice gradient uniformity for high gradient efficiency and slew rate, and are attractive for surface imaging applications where open access from one side of the sample is required. However, decreasing the size of the uniplanar gradient set presents several unique engineering challenges, particularly for heat dissipation and thermal insulation of the sample from gradient heating. We demonstrate a new three-axis, target-field optimized uniplanar gradient coil design that combines efficient cooling and insulation to significantly reduce sample heating at sample-gradient distances of less than 5 mm. The instrument is designed for microscopy in horizontal bore magnets. Empirical gradient current efficiencies in the prototype coils lie between 3.75 G/cm/A and 4.5 G/cm/A with current and heating-limited maximum gradient strengths between 235 G/cm and 450 G/cm at a 2% duty cycle. The uniplanar gradient prototype is demonstrated with non-linearity corrections for both high-resolution structural imaging of tissue slices and for long time-course imaging of live, developing amphibian embryos in a horizontal bore 7 T magnet.     

Predictions of stress jump by a transient network model

A model proposed by De Kee and Carreau predicts a stress jump and we compare the model predictions with the experimental data of Liang and Mackay. The values of the model parameters are determined from the steady viscosity data. Using the same values of the parameters, the stress jump as a function of the shear rate is calculated. The agreement between the calculated and experimental values of the stress jump is excellent.