MRI hardware includes the electrical and mechanical components of a scanning device.
The main hardware components for the MRI machine are:
The magnet establishing the B0 field to align the spins.
Within the magnet are the gradient coils for producing variations in B0 in the X, Y, and Z directions to make a localization of the received data possible.
Within the gradient coil or directly on the object being imaged is the radio frequency (RF) coil.
This RF coil is used to establish the B1magnetic field necessary to excite the spinning nuclei.
The RF coil also detects the signal emitted from the spins within the object being imaged.
The RF amplifier increases the power of the pulses.
The analog to digital converter converts the received analograw data into digital values.
Depending on the design of the device and the body part being imaged the patient is positioned inside the magnet (e.g. on a movable table or standing upright).
The MRI scan room is surrounded by a RF shield (Faraday cage).
In addition, a computer console, a display, and a film printer belong to the MRI equipment.
An arrangement of reactive elements (inductors and capacitors) used to transform an input impedance of a given value to an output impedance of a second value. Such circuits are used in interfacing high impedance RF coils to low impedance (usually 50 ohms) transmission lines that feed RF energy to the coil or send the MR signal to an MR preamplifier.
A coil that produces an RF field with circular polarization. The RF power received from the RF power amplifier comes in two signals (quadrature detection), which have a phase difference of 90°. The RF transmit coil converts the power into a circularly polarized RF magnetic field.
Quadrature coils can be used as both, transmit and/or receive coil.
When used as a transmitter coil a factor of two power reduction over a linear coil results; as a receiver an increase in SNR of up to a factor of √2, can be achieved.
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Radio frequency quadrature artifacts occur when the detector channels of the quadrature detector are disturbed.
A DC offset of one amplifier output can e.g., produce a bright point in the center of the field of view (see also central point artifact), or a higher gain of one detector channel can generate diagonally ghosting.
Image Guidance
Radio frequency quadrature artifacts are technical faults and must be eliminated by the service.