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The dwell time (td) is the interval between digitized samples. This, in turn, is defined by the sampling time ( t s ) and the number of complex samples ( n s ) measured. Continuing the above example, if 256 samples were acquired in 5.12 ms, the dwell time ( t d ) would be 5.12 ms/256 = 20 μs.
Dwell Time is the primary determinant of noise in the MR image, the time between samplings (sampling interval). Noise is proportional to the square root of the bandwidth and the bandwidth is inversely proportional to the dwell time .
The duration required for the ADC to measure and record the amplitude of the echo signal is known as the dwell time (D). For a 256×256 matrix, the ADC samples the signal 256 times. Total sampling time (Ts) = matrix in read (N) x dwell time (D)
This time is called the dwell time D. For a 256 base matrix this process has to be repeated 256 times. The whole sample period Ts will be in this example (Fig. 3): Ts = 256 x 30 μs = 7.680 ms. The parameter ‘Bandwidth’ is found on the Sequence parameter card, part 1 (Fig. 4). lower left pixel 130-260 Hz and so forth.
The bandwidth depends on the readout (or frequency encoding) gradient strength and the data sampling rate (or dwell time). Bandwidth is defined by BW = Sampling Rate/Number of Samples. A smaller bandwidth improves SNR, but can cause spatial distortions, also increases the chemical shift.
Dwell Time is the primary determinant of noise in the MR image, the time between samplings (sampling interval). Noise is proportional to the square root of the bandwidth and the bandwidth is inversely proportional to the dwell time.
18 lip 2023 · We'll then review how receiver bandwidth determines the Nyquist limit and how we can use this to know the required sampling rate.
