Korean J Radiol.  2012 Dec;13(6):736-742. 10.3348/kjr.2012.13.6.736.

Experimental Evaluation of Accelerated T1rho Relaxation Quantification in Human Liver Using Limited Spin-Lock Times

• Zhao F
• Deng M
• Yuan J
• Teng GJ
• Ahuja AT
• Wang YX

• KMID: 1397504
• DOI: http://doi.org/10.3348/kjr.2012.13.6.736

Abstract

OBJECTIVE
It was reported lately that to obtain consistent liver T1rho measurement, at 3T MRI using six spin-lock times (SLTs), is feasible. In this study, the feasibility of using three or two SLT points to measure liver T1rho relaxation time was explored.
MATERIALS AND METHODS
Seventeen healthy volunteers underwent 36 examinations. Three representative axial slices were selected to cut through the upper, middle, and lower liver. A rotary echo spin-lock pulse was implemented in a 2D fast field echo sequence. Spin-lock frequency was 500 Hz and the spin-lock times of 1, 10, 20, 30, 40, and 50 milliseconds (ms) were used for T1rho mapping. T1rho maps were constructed by using all 6 SLT points, three SLT points of 1, 20, and 50 ms, or two SLTs of 1 and 50 ms, respectively. Intra-class correlation coefficient (ICC) and Bland and Altman plot were used to assess the measurement agreement.
RESULTS
Two examinations were excluded, due to motion artifact at the SLT of 50 ms. With the remaining 34 examinations, the ICC for 6-SLT vs. 3-SLT T1rho measurements was 0.922, while the ICC for 6-SLT vs. 2-SLT T1rho measurement was 0.756. The Bland and Altman analysis showed a mean difference of 0.19 (95% limits of agreement: -1.34, 1.73) for 6-SLT vs. 3-SLT T1rho measurement, and the mean difference of 0.89 (95% limits of agreement: -1.67, 3.45) for 6-SLT vs. 2-SLT T1rho measurement. The scan re-scan reproducibility ICC (n = 11 subjects) was 0.755, 0.727, and 0.528 for 6-SLT measurement, 3-SLT measurement, and 2-SLT measurement, respectively.
CONCLUSION
Adopting 3 SLTs of 1, 20, and 50 ms can be an acceptable alternative for the liver T1rho measurement, while 2 SLTs of 1 and 50 ms do not provide reliable measurement.

Keyword

Magnetic resonance imaging; Liver; T1rho; Spin-lock time

MeSH Terms

Adult
Eating
Echo-Planar Imaging/*methods
Fasting
Female
Humans
Liver/*anatomy & histology
Magnetic Resonance Imaging/*methods
Male
Young Adult

Figure

• 

  Fig. 1 Coronal (right) and sagittal (left) scout images. Three axial slices are selected to cut through upper, middle, and lower liver.

• 

  Fig. 2 T1rho map with coefficient of determination R2 > 0.8 evaluation. Five regions of interest are placed on liver parenchyma region, excluding observable artifacts and blood vessels.

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  Fig. 3 Example of one healthy volunteer's T1rho maps constructed with 6 SLTs, 3 SLTs or 2 SLTs. Left column: coefficient of determination (R2) maps, middle column: T1rho maps without R2 evaluation, right column: T1rho maps with R2 > 0.8 evaluation. Upper row: maps constructed with 6 SLTs, middle row: maps constructed with 3 SLTs, lower row: maps constructed with 2 SLTs. As SLT point decreases, R2 evaluation is less efficient to remove blood vessel contamination and artifact. Note that R2 is always equal to one, when SLT point = 2, so no pixels are excluded by criteria of R2 > 0.8. However, this does not seem to affect regions of interest placement, according to results in Table 1. Radiology trainee was able to identify and avoid regions with artifacts and blood vessels. SLT = spin-lock time

• 

  Fig. 4 Bland and Altman plots for comparison of 6 SLTs vs. 3 SLTs liver T1rho measurement (A) and 6 SLTs vs. 2 SLTs liver T1rho measurement (B). 3 SLTs measurement demonstrates good agreement with 6 SLTs measurement. SLT = spin-lock time

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