<title>Study of the effects of quantization noise on magnetic resonance image quality</title>

Abstract

The affects of quantization noise in magnetic resonance images (MRI) were studied, and simple modifications are shown to give significant improvement in subjective image quality and in some quantitative measurements. A liver phantom based on a MR liver image was created to simulate the effects of quantizing the MR signal. The MR signal which would be generated by this phantom was characterized and used to study quantization effects as well as to help in developing a more efficient quantization scheme. Uniform quantization of the signal was simulated to determine the effects of quantization noise on the liver phantom. Quantitative measurements using SNR and detectability were made and used as a basis of comparison for similar measurements utilizing other quantizers including uniform quantization with quantizer overload and logarithmic quantization. Quantitative measurements were again made and compared to the full range uniform quantizer. Simulations were performed without additive noise, and results are given in the form of graphs, tables, and actual images. Simulations were also performed with noisy data but are not reported in detail in this paper. Q uantitative measurements were consistent in most cases and agreed well with subjective evaluations. It was found that uniform quantization noise can significantly affect image quality. It was also determined, by using a logarithmic quantizer or by simple overloading of the uniform quantizer, that significant improvements in image quality can be achieved. The results are extensible to other image collection systems, particularly those with high dynamic range.