Measurements of MTF and SNR( f ) using a subtraction method in MRI

Abstract

A method was developed for accurate measurement of the modulation transfer function (MTF) and signal-to-noise ratio in the spatial frequency domain (SNR(f)) of magnetic resonance images (MRI). The MTF was calculated from the complex images of a line object which were obtained by the subtraction of two separately acquired data sets of a specially designed phantom with a sliding sheet. Moreover, the SNR(f) was calculated from the MTF and Wiener spectrum, both of which were determined using the same phantom configuration. The MTFs and SNR(f)s in the conventional spin-echo (SE) and turbo SE, in which the effective echo time was set to the first echo, were evaluated by changing the T2 of the phantom and the echo train length. The MTFs in the positive and negative frequencies indicated the effect of the k-space trajectory for each pulse sequence. SNR(f)s gave spatial frequency information that was not obtained with conventional methods. In this method, the influence of image nonuniformity and unwanted artefacts (edge and ghost) could be eliminated. An analysis of the MTF and the SNR in the spatial frequency domain provides additional information for the assessment of image quality in MRI.

Iterative image reconstruction that includes a total variation regularization for radial MRI

“…When the MTF is measured in MRI, there are problems such as loss of linearity due to the modulus operation [30,31]. For overcoming these problems, various measurement techniques have been proposed [30,31].…”

“…For overcoming these problems, various measurement techniques have been proposed [30,31]. In the case of a performance evaluation of an MRI device, these techniques should be employed.…”

Anatomical brain imaging at 7T using two‐dimensional GRASE

“…For comparing the PSF, the modulation transfer function (MTF) was determined using a phantom containing a thin removable polyethylene terephthalate sheet, similar to the method of Miyati et al . One axial slice was acquired using GRASE with different EPI factors: 1 (corresponding to TSE), 3, 5, and 7.…”

“…Intensity profiles were obtained perpendicular to the polyethylene terephthalate sheet and averaged. The PSF was then assessed by calculating the MTF as described previously . Additionally, a second phantom containing sharp edges was imaged (Fig.…”

“…The signal‐to‐noise ratio (SNR) per unit time was determined for both sequences using a phantom. Furthermore, the point spread functions (PSF) of TSE and GRASE were analyzed by a method described elsewhere . Both sequences were also compared in vivo.…”