Investig Magn Reson Imaging.  2016 Dec;20(4):207-214. 10.13104/imri.2016.20.4.207.

Effect of Number of Measurement Points on Accuracy of Muscle T2 Calculations

• Tawara N
• Nishiyama

• KMID: 2366402
• DOI: http://doi.org/10.13104/imri.2016.20.4.207

Abstract

PURPOSE
The purpose of this study was to investigate the effect of the number of measurement points on the calculation of transverse relaxation time (T2) with a focus on muscle T2.
MATERIALS AND METHODS
This study assumed that muscle T2 was comprised of a single component. Two phantom types were measured, 1 each for long ("phantom") and short T2 ("polyvinyl alcohol gel"). Right calf muscle T2 measurements were conducted in 9 healthy male volunteers using multiple-spin-echo magnetic resonance imaging. For phantoms and muscle (medial gastrocnemius), 5 regions of interests were selected. All region of interest values were expressed as the mean ± standard deviation. The T2 effective signal-ratio characteristics were used as an index to evaluate the magnetic resonance image quality for the calculation of T2 from T2-weighted images. The T2 accuracy was evaluated to determine the T2 reproducibility and the goodness-of-fit from the probability Q.
RESULTS
For the phantom and polyvinyl alcohol gel, the standard deviation of the magnetic resonance image signal at each echo time was narrow and mono-exponential, which caused large variations in the muscle T2 decay curves. The T2 effective signal-ratio change varied with T2, with the greatest decreases apparent for a short T2. There were no significant differences in T2 reproducibility when > 3 measurement points were used. There were no significant differences in goodness-of-fit when > 6 measurement points were used. Although the measurement point evaluations were stable when > 3 measurement points were used, calculation of T2 using 4 measurement points had the highest accuracy according to the goodness-of-fit. Even if the number of measurement points was increased, there was little improvement in the probability Q.
CONCLUSION
Four measurement points gave excellent reproducibility and goodness-of-fit when muscle T2 was considered mono-exponential.

Keyword

Transverse relaxation time; Skeletal muscle; Number of measurement points; Goodness-of-fit; T2 effective signal-ratio

MeSH Terms

Humans
Magnetic Resonance Imaging
Male
Muscle, Skeletal
Polyvinyl Alcohol
Relaxation
Volunteers
Polyvinyl Alcohol

Figure

• 

  Fig. 1 Defining regions of interest (ROI). ROIs were placed in the (a) phantom (e.g., PVA-gel phantom), and (b) medial gastrocnemius (MG). In (a), the ROI in the phantom is represented by a gray circle. In (b), the MG is within the dashed line, and ROI is represented by a white circle.

• 

  Fig. 2 T2 relaxation curve and T2 effective signal ratio (T2SR) curve. (a) T2 relaxation curve and (b) T2SR for each material. Phantom (◇), PVA-gel (△), medial gastrocnemius muscle (MG) (□).

• 

  Fig. 3 Changes caused by number of measurement points in phantom. (a) Changes in T2 and (b) changes in the probability Q. There were no significant differences in the T2 when ≥ 3 measurement points were used. If the probability Q was > 0.9, the goodness-of-fit was high. The dashed line in (b) indicates that the probability Q was 0.9.

• 

  Fig. 4 Changes caused by number of measurement points in PVA-gel. (a) Changes in T2 and (b) changes in the probability Q. There were no significant differences in the T2 when ≥ 3 measurement points were used. If the probability Q was > 0.9, the goodness-of-fit was high. The dashed line in (b) indicates that the probability Q was 0.9.

• 

  Fig. 5 Changes caused by number of measurement points in medial gastrocnemius muscle (MG). (a) Changes in T2, (b) Changes in the probability Q.

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