What is MRI frequency-encoding?
Frequency-encoding of spatial position is accomplished through the use of supplemental magnetic field gradients. Gradients mildly distort the main magnetic field in a predictable pattern, causing the resonance frequency to vary as a function of position.
What is MRI phase shift?
Image Quality – Functional MRI – Musculoskeletal and Joint MRI – Bioinformatics – Databases – Research Labs. Phase Shift. The phase shift is the loss of phase coherence in precessing spins. Vascular spins move at variable velocities; faster flow undergo a stronger phase shift than slower flowing spins.
What is MRI amplitude?
Amplitude. The signal height. The greater the amplitude of the signal, the larger the number of protons in the image and the brighter the signal will appear.
What is amplitude phase?
The Amplitude is the height from the center line to the peak (or to the trough). Or we can measure the height from highest to lowest points and divide that by 2. The Phase Shift is how far the function is shifted horizontally from the usual position.
What is the phase encoding direction?
The phase-encoding direction is associated with two major artifacts: wrap-around and flow/motion. Wrap-around (also called aliasing) occurs when the size of the body part imaged exceeds the defined field-of-view (FOV) in the phase-encode direction.
How can I tell what sequence my MRI is?
The best way to tell the two apart is to look at the grey-white matter. T1 sequences will have grey matter being darker than white matter. T2 weighted sequences, whether fluid attenuated or not, will have white matter being darker than grey matter.
What is Larmor frequency in MRI?
Magnetic fields used in MRI are typically in the range 1 to 4 T. The corresponding Larmor frequencies are about 43 to 170 MHz. These frequencies are in the radio frequency (RF) range, which are much lower than X-rays and do not disrupt living tissue.
What is the relationship between amplitude frequency period period and period?
Amplitude—distance between the resting position and the maximum displacement of the wave. Frequency—number of waves passing by a specific point per second. Period—time it takes for one wave cycle to complete. In addition to amplitude, frequency, and period, their wavelength and wave velocity also characterize waves.
What is amplitude period phase shift phase shift and frequency?
Amplitude, Period, Phase Shift and Frequency. and are called Periodic Functions. The Period goes from one peak to the next (or from any point to the next matching point): The Amplitude is the height from the center line to the peak (or to the trough). Or we can measure the height from highest to lowest points and divide that by 2.
What is the amplitude of a periodic motion?
Periodic motion is observed in mass on a spring, simple pendulum, molecular vibration etc. The maximum displacement from equilibrium is known as the amplitude (always positive as only magnitude is considered).
How do you calculate the frequency and phase of an MR image?
So frequency x time = (cycles/sec) x sec = # of cycles. Thus two sine waves differing in frequency by 200 Hz get progressively out of phase with each other by 200 cycles every second. To understand the more complex aspects of frequency and phase encoding of the MR image, it is necessary to review what happens when two sine waves are added together.