Signal-to-noise ratio measurement in parallel MRI with subtraction mapping and consecutive methods

Hiroshi Imai, Tosiaki Miyati, Akio Ogura, Tsukasa Doi, Toshio Tsuchihashi, Yoshio Machida, Masato Kobayashi, Kouzou Shimizu, Yoshihiro Kitou

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

Abstract

When measuring the signal-to-noise ratio (SNR) of an image the used parallel magnetic resonance imaging, it was confirmed that there was a problem in the application of past SNR measurement. With the method of measuring the noise from the background signal, SNR with parallel imaging was higher than that without parallel imaging. In the subtraction method (NEMA standard), which sets a wide region of interest, the white noise was not evaluated correctly although SNR was close to the theoretical value. We proposed two techniques because SNR in parallel imaging was not uniform according to inhomogeneity of the coil sensitivity distribution and geometry factor. Using the first method (subtraction mapping), two images were scanned with identical parameters. The SNR in each pixel divided the running mean (7 by 7 pixels in neighborhood) by standard deviation/radical2 in the same region of interest. Using the second (consecutive) method, more than fifty consecutive scans of the uniform phantom were obtained with identical scan parameters. Then the SNR was calculated from the ratio of mean signal intensity to the standard deviation in each pixel on a series of images. Moreover, geometry factors were calculated from SNRs with and without parallel imaging. The SNR and geometry factor using parallel imaging in the subtraction mapping method agreed with those of the consecutive method. Both methods make it possible to obtain a more detailed determination of SNR in parallel imaging and to calculate the geometry factor.

Original languageEnglish
Pages (from-to)930-936
Number of pages7
JournalNippon Hoshasen Gijutsu Gakkai zasshi
Volume64
Issue number8
DOIs
Publication statusPublished - 2008 Aug 20

ASJC Scopus subject areas

  • Medicine(all)

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