Buying an MRI machine is a tough task for any hospital or diagnostic centre. The most important thing which need to be considered is technical evaluation of different machines. Should one buy a permanent magnet or superconducting magnet. In superconducting magnet whether one should go for 1.5 Tesla or 3 Tesla machine. Should one buy a refurbished machine or go for a new machine. These are some of the considerations which any hospital owner has to consider while evaluating different machines. When it comes for technical evaluation one has to consider things like Gradient Strength and Slew Rate.
One of the most important specification in an MRI Scanner is the SLEW Rate
Slew Rate = Peak Gradient Strength / Rise Time
Good MRI Scanner should have a higher gradient ( Peak Amplitude). Higher slew rate would mean higher gradient and low rise time (time to reach the peak amplitude). If the peak gradient is 40 mT/m and the time to reach the peak amplitude is 0.2 ms then the slew rate would be 40/0.2 meaning 200 mT/m/s
If cardiac or brain imaging is anticipated, then powerful gradients are mandatory. If the intended scanner use is for orthopedics, however, such demanding gradients may not be required.
3T versus 1.5T
3T has a higher signal to noise ratio which results in better image quality, spatial and temporal resolution and faster scanning time. The downside is that 3T machines have a higher specific absorption rate (SAR) which creates more image artefacts.
Gradient System - Gradient system encodes the MRI signal. This includes the gradient strength and the slew rate of the MRI system.
Radiofrequency System - The RF system is responsible for exciting the nuclei and detecting the nuclear magnetic resonance (NMR) signal. Higher the number of independent receiver channels in the coil, better will be the image and faster will be the acquisition. Use of dedicated RF coils with higher number of independent RF channels improves the SNR.
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