BASIC PRINCIPLE OF MRI

This section will explain about proton, magnetic field in MRI, precession, and radiofrequency pulse.

This video briefly explain about basic principle of MRI

This video will explain the roles of proton in MRI

This video will explain about magnetic field in MRI

This video will explain about precession in MRI

This video will explain about radiofrequency pulse in MRI

SUMMARY

Alignment in Magnetic Field

When a patient is placed inside the MRI scanner, the protons in their body align with the strong magnetic field generated by the scanner.

Radiofrequency Pulse Excitation:

Short bursts of radiofrequency energy are then applied to the area of interest. These pulses cause the protons to absorb energy and temporarily deviate from their aligned position.

Relaxation

After the radiofrequency pulse is turned off, the protons release the absorbed energy and return to their aligned state. This process involves two relaxation times: T1 relaxation (longitudinal relaxation) and T2 relaxation (transverse relaxation).
T1 and T2 times are fundamental concepts in MRI imaging, describing the relaxation properties of protons in a magnetic field:

T1 Time (Longitudinal Relaxation):

T1 time, also known as longitudinal relaxation time, represents the time it takes for the protons to realign with the external magnetic field after being disturbed.
It influences the brightness of tissues in an MRI image, with shorter T1 times resulting in brighter signals and longer T1 times resulting in darker signals.
Tissues with short T1 times, like fat, appear bright on T1-weighted images, while tissues with longer T1 times, like fluid or water, appear darker.

T2 Time (Transverse Relaxation):

T2 time, also known as transverse relaxation time, represents when the protons lose phase coherence and stop emitting a detectable signal after the RF pulse is turned off.
It affects the contrast between different tissues in an MRI image, with shorter T2 times resulting in brighter signals and longer T2 times resulting in darker signals.
Tissues with short T2 times, like fluid or water, appear bright on T2-weighted images, while tissues with longer T2 times, like fat, appear darker.

Signal Detection:

As the protons return to their aligned state, they emit radiofrequency signals. These signals are detected by receiver coils in the MRI scanner.

Image Reconstruction:

A computer processes the detected signals to create detailed cross-sectional images of the scanned area. Different tissues within the body emit signals with varying intensity and timing, allowing for the differentiation of structures in the resulting images.