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Which of the following are true regarding MRI parameters? a. Increasing voxel size increases signal-to-noise ratio (SNR) b. Decreasing the receiver bandwidth helps reduce chemical-shift artefacts c. The degree of improvement in the SNR is directly proportional to the number of repetitions d. Increasing the field strength improves the SNR e. Image contrast is dependent only on the T1 and T2 values of tissues |
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Answer» a. True. The signal will increase at the expense of a reduction in spatial resolution. b. False. Decreasing the receiver bandwidth decreases the strength of the frequency-encoding gradient resulting in a larger chemical shift between water and fat. c. False. It is proportional to the square root of the number of repetitions. Thus, repeating the sequence four times would result in a twofold improvement in the SNR. d. True. As a first approximation, the SNR increases linearly with magnetic field strength. e. False. There are a number of methods to improve image contrast, including fat suppression, magnetization transfer and the use of contrast media. Image contrast will also depend on the chosen echo and repetition times, which will determine the image weighting. |
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