Station 10: Imaging
Magnetic Resonance Imaging (MRI) II
The aim of these experiments is to show how the spin echo technique can be used to generate 2D MR images of a slice of a well-defined thickness, orientation, and size (Localized Spin Echo 2D). These parameters determine the so-called „field of view“ (FOV) of the MR image. We will introduce a method that enables the recording of 3D MR images (Spin Echo 3D). For this purpose, an additional phase encoding will be performed in the third dimension. Both methods include the automatic calibration of the system frequency with regard to the Larmor frequency. As a result, the MR image is more stable over several averaging steps.
Basic methods in imaging of micro and nanostructures with AFM (Atomic Force Microscopy)
Approaching a sharp silicon tip mounted on a cantilever to a sample surface leads to an atomic scale interaction. The result is a bend of the cantilever which is detected by a laser. In static mode the resulting deflection is used to investigate the topography of the sample surface line by line using a feedback loop. In dynamic mode the cantilever is oscillated at fixed frequency resulting in a damped amplitude near the surface. The measurement parameters (setpoint, feedback gain) play a crucial role for image quality. Their effect on the imaging quality is investigated for different nano structured samples.
Ultrasonic echography (A-Scan)
An ultrasonic wave transmitted in a sample will be reflected at discontinuities (defects, cracks). From the relationship between the time of flight of the reflected wave and the sound velocity, the distance between ultrasonic transducer and defects (reflector) can be calculated. Position and size of these defects can be determined by measuring in different directions.
This set-up shows how blood flow studies are performed using Doppler ultrasound (Doppler sonograph). On a realistic arm dummy, the differences between continuous (venous) and pulsating (arterial) flow are shown as well as the difference in flow through a normal blood vessel and a stenosis.