Biomedical Imaging Technology Center
Magnetic Resonance Imaging is a multi-disciplinary technique, which draws from NMR physics, optical imaging, and digital signal processing. During the MR scan various components of the system such as RF, gradients and data acquisition systems much work in concert to obtain MR images. Most modern MR imagers operate in a pulsed RF mode. A shaped RF pulse is sent to the RF amplifier and consequently down the analog RF chain to the coil. The shape of RF pulses and the timing of their operation is controlled by the pulse sequence timing diagram.
In an analogous way gradient coils are pulsed by the same timing diagram. MR systems are equipped with three gradient coils coinciding with the three cardinal spatial dimensions. The duration, amplitude and timing of these gradients is the process by which the image is formed. Gradients are programmed into the pulse sequence to perform various functions such as slice selection, phase encoding, and reading out lines of k-space. The readout gradient must be timed exactly to the data acquisition system, or ADC. The ADC is also controlled by the pulse sequence where important parameters of the acquisition are imposed such as image bandwidth and image resolution.
The pulse sequence is a development tool to find new applications of MR imaging. An example of a gradient echo imaging sequence is displayed below. In this sequence all the necessary components of the sequence are present which will generate an MR image. Pulse sequences often contain repeated elements, or blocks. In the diagram these blocks have been superimposed to generate a compact view of the sequence.
Here at the BITC our staff has been trained in pulse sequence development, and we have experience programming several commercial MR systems. The BITC works closely with Siemens and the IDEA sequence programming environment. Currently we have six personnel at the BITC trained in IDEA programming at the Siemens Training Center in Cary, NC. This concentration of experienced researchers will generate novel pulse sequences, which will be made available to the MR research community.
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