Nondestructive Tomographic Imaging of Rust with Rapid THz Time-Domain Spectroscopy

In this study, we developed a rapid nondestructive tool for testing rust spread in a metal covered by a paint layer by using a THz time-domain spectroscopy system at a speed of 100 Hz/pixel. Time-of-flight imaging helps identify rust formation by exclusively obtaining the reflection from the steel below the paint surface. The use of frequency-selective imaging allows us to manipulate the contrast in rust imaging. Higher contrast is generally obtained when monitoring using the higher frequency component. In addition, we monitored the spread of rust in a steel plate under the influence of two different chemical solutions: NaCl and acid. We found that in the early stages, the decrease in THz reflection was governed by the high-frequency components due to the formation of lepidocrocite, whereas the low-frequency component develops as the proportion of hematite increases with time.

Time-Resolved High-Resolution Angiography Combining Arterial Spin Labeling and Time-of-Flight Imaging

A strategy to combine two non-contrast-enhanced magnetic resonance angiography techniques is presented. It is based on arterial spin-labeled magnetic resonance imaging to visualize the arterial system at different time points to obtain information about hemodynamic properties in conjunction with a high-resolution time-of-flight angiography acquisition. The temporal information obtained by arterial spin labeling (ASL) is combined with the highly spatial resolved time-of-flight image to obtain information about blood flow. Extracting the information of ASL and time-of-flight-imaging leads to images with high spatial resolution which also give information about the temporal course of blood through the intracerebral vasculature. Furthermore, owing to the properties of ASL, visible venous flow in the time-of-flight images can be suppressed. The behavior of vascular filling (i.e. signal changes in the ASL) is investigated and used for further interpretation of the data. Furthermore, the ASL data were down-sampled to find a minimally needed spatial resolution to combine both image types. Up to 1.6 mm isotropic resolution still showed satisfying results rated by two independent readers. In conclusion, a combination of these two different vascular imaging modalities allows to obtain highly spatial and time-resolved images.