FUNCTIONAL OVERVIEW OF THE MRI SYSTEM





The MRI Magnet provides the external magnetic field(B0) which brings the intrinsic magnetic fields of certain nuclei into specific alignments, setting the conditions for NMR to occur. Spatial uniformity of the B0 field is maintained by the shim system.
The RF Transmitter produces shaped pulses of alternating current at appropriate frequencies which, when passing through the transmit coils, create a magnetic field rotating at the Larmor frequency (B1). This excitation field realigns and organises the intrinsic nuclear magnetic fields of tissues so they coherently rotate in the X-Y plane (Mxy). The rotating magnetic fields can induce an RF alternating current (MR signal) in the receive coils (detection). The receiver systems demodulates MR signal to extract information that is digitised to create the raw data.
The raw data is used by the array processor to calculate digital images.
Image contrast is manipulated by the method and timing of MR signal excitation and detection through the use of pulse sequences set up by scanning interface software in the host computer, and controlled by sequence control software in the host and distributed computers.
Spatial localisation is achieved by the Gradient System which alters the magnetic field strength in different locations for the period that the gradient field is applied, creating frequency shift, phase shifts and creating the precondition for frequency selective excitation.
The MR Radiographer handles the images and other equipment maintenance functions at an operating console or work-station via image manipulation software within a User Interface.
The Host Computer is used to manage image data display, storage, transmission, and transfer to hard copy devices.

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