MRI image GUI: Final Project SIMG 726 Joseph Handfield February 19, 2004

Intro - Nuclear Magnetic Resonance: ‘NMR’ in unpaired spin nuclei (1H, 2H, 3He) Spin is just a small measure of angular momentum Nuclei can be aligned (low energy) or opposed to external magnetic fields (in high energy state). _ + _ +

NMR Signal How does the MRI hardware work? An additional RF coil causes specific nuclei in samples to resonate and return to normal when RF coil is turned off, making them quantifiable. RF coils individually can transmit frequencies, receive frequencies or both, dependent on hardware selection. Magnetic Resonance Images are spatially assessed more accurately with the help of spatially-sensitive coils. Gradient style coils generate 1-D gradients from the machine’s magnetic fields in x, y and z directions, which are then interpreted by RF coils.

MRI Machine Apparatus

Measuring t1, t2, spin density For T1, spin lattice relaxation time: For T2, spin spin relaxation time: Where TR is repetition time and TE is echo time

Depth-Tuning magnetic coils: Multiple RF frequencies for approximating density of spin nuclei requires switchable capacitor arrays.

MRI image characteristics Unsigned integer values (needs swap endian) Gray scale pixel values are the designated amount of signal concentrated at each pixel’s address (from spin nuclei) on a MRI image grid. Maximum pixel value depends on electronics, array processing power, and coils of the MRI used. Field strength of the magnet used is usually within health standards since high fields are dangerous. Since the number of gray levels n is always much greater than 256, how do we show minute detail?

MRI GUI rescale option A width and level selectable design for viewing detail in smaller selected areas of the histogram is needed. Width is the amount of histogram entries from the unsigned integer image to use in detail with the 254 distinct gray shades. Level sets the midpoint of the histogram region of interest (width). Pixels less than the selected area are set to 0 and pixels greater than are set to 255, then the look-up table that results is applied to the image pixel values directly.

Other MRI GUI options Mouse cursor can tell user the pixel location and value Region of interest widget finds mean and SD of select areas Plots define the histogram and the rescaling look-up table function for comparison purposes Quit button to exit program Save option (any image format) Temporary Image saves for comparisons (pointers) Image magnifier

Program Demo Any Questions?