Head multidetector-row CT angiography with low kV settings: Improved vessel enhancement and noise reduction in phantom studies

In order to improve the measurement accuracy of blood vessels, it was investigated how much contrast was improved and how much noise was increased, with low kV setting for Head multidetector-row computed tomography (CT, Aquilion64, Toshiba Medical Systems) angiography in phantom study. That is, using low (80or 100) kV instead of 120-140 kV should shift the mean photon energy closer to the K-edge of iodine and therefore improve the contrast between vessels filled with contrast medium and their surroundings. For the vascular models, we used urethane tube (47 Hounsfield unit (HU)) with two inner diameters (2and 4 mm) filled with contrast medium diluted to density (373 ± 14 HU). The urethane tube was fixed in a water-filled columnar acrylic container with a diameter of 20 cm. A Teflon resin pipe was inserted inside the acrylic container as a skull and two Teflon resin pipes with a diameter of 5 cm were placed near the center of the acrylic container as basis cranii. Then, the profile curve of the cross section of the vascular models, and physical image qualities characteristics such as modulation transfer function, S.D. and Wiener spectrum, were evaluated changing CT scan conditions. Furthermore, reducing the noise was tried, using mAs change, reconstruction functions or Quantum Denoising Filters (Toshiba Medical Systems). The maximum CT values of the profile of 80 kV increased from 1.5 to 1.7 times than that of 120 kV. The noise has increased evenly in all frequency band regions at the same time though the contrast rose in 2 and 4 mm vascular models. Quantum Denoising Filters were effective in noise reduction. Since there are the useful noise reduction methods, it can be said that vessel enhancement with low kV settings is realizable.