We report on technical improvements in experiments with a deformation-DIA (D-DIA) apparatus, which enable the study of the rheology of solid materials at P-T conditions of the Earth's mantle transition zone. Dimensions of the anvil truncation, pressure medium, and gasket were optimized to achieve deformation experiments above 1:3 GPa with a relatively low press load (<0.7 MN) to minimize the damage of the X-ray transparent second-stage anvils. The adoption of low X-ray absorbing material (e.g., cubic BN anvils, graphite window in a LaCrO3 heater) along the X-ray path enabled quantitative determination of stress and strain of a sample by means of simultaneous in situ X-ray radial diffraction and radiography using synchrotron radiation at SPring-8. Based on the new technique, a uniaxial deformation experiment with a strain rate of 3.88 x 10(-5) s strains up to 25.5% was carried out on wadsleyite at a pressure of 14.5 GPa and a temperature of 1700 K.