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Measuring right ventricular volume and ejection fraction with Simpson's method: which MRI axis is best? Comparison with a "gold standard"

Purpose

Because of its complex morphology, accurate and reliable quantification of right ventricular (RV) volume and function using MRI is challenging. This study had two aims: (1) to determine the interobserver reliability of RV volume and ejection fraction (EF%) calculated using Simpson's method of slice summation applied to data acquired in three different orientations: short axis (SA), transaxial (TA), and parallel to the horizontal long axis (pHLA); and (2) to determine how RV volume and EF% by each of the three orientations compared with values obtained using a validated "gold-standard" method with 3-D reconstructions (3DR).

Materials and methods

Twenty-three consecutive, consented patients referred for cardiac MRI were included in the study (10 males, 13 females; ave. age 43 ± 19 yrs; ave. ht: 66 ± 4 in; ave. wt: 177 ± 51 lbs). Steady-state free precession was used to generate stacked, bright-blood cine loops in 3 separate, randomly ordered orientations: SA, TA, and pHLA. Slice thickness was 8 mm and slice separation 2 mm. Using Simpson's method and pre-determined end-diastolic (ED) and end-systolic (ES) time points, three experienced reviewers independently measured RV ED and ES volumes and, in turn, EF% for each of the orientations. Volumes and EF% were also calculated using a 3DR technique based on the piecewise smooth subdivision surface method [1, 2], employing data from multiple orientations. Intraclass correlation was used to compare data from different observers. Paired t-test analysis was used to compare volumes and EF%.

Results

Interrater reliability (IRR) of RV ED and ES volumes and EF% was determined for each of the axes. For the SA, IRR for all readers was 0.92, 0.87, and 0.33, respectively; for TA, 0.95, 0.90, and 0.71; for pHLA, 0.83, 0.91, and 0.67. (A higher ratio indicates greater reliability). For comparison, the same parameters were also determined for LV ED and ES volumes, and EF% measured using the SA: 0.98, 0.96, and 0.84.

A wide range of RV volumes (37–323 cc) and EF%s (30–67%) were observed. Average EDV volumes for 3DR, SA, TA, & pHLA were: 161 ± 60 cc, 140 ± 45 cc, 136 ± 44 cc, 126 ± 37 cc. Average ESV volumes for 3DR, SA, TA, & pHLA were: 80 ± 44 cc, 76 ± 35, 65 ± 31 cc, 62 ± 30 cc. All ED and ES volumes were underestimated using Simpson's method (p < .01). SA, TA, and pHLA volumes were linearly correlated with 3DR volumes with R values 0.96, 0.96, and 0.93 (See Figures 1, 2, 3). Correlations for EDVs were slightly better than those for ESVs for SA and TA orientations. Average EF%s for 3DR, SA, TA, & pHLA were: 53 ± 9%, 47% ± 8% (p < .05), 53 ± 7% (P = NS), & 52 ± 9% (P = NS). SA, TA, and pHLA EF%s were linearly correlated with 3DR EF%s with R values 0.66, 0.57, and 0.65.

Figure 1
figure1

Short axis vs 3DR (ml).

Figure 2
figure2

Axial vs 3DR (ml).

Figure 3
figure3

pHLA vs 3DR (ml).

Conclusion

Reliability of RV ED and ES volume measurements is comparable for all three axes evaluated. However, the reliability of the EF% is best on TA imaging. Moreover, although TA offers slightly worse EF% correlation with 3DR, our data suggest that for consistency – if Simpson's method is used for RV volume and EF% quantification – the TA axis is preferred.

References

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    Hubka, et al : Int J Cardiovasc Imaging. 2002, 18: 111-118. 10.1023/A:1014616603301.

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    Legget, et al : IEEE Trans Biomed Eng. 1998, 45: 494-504. 10.1109/10.664205.

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Correspondence to Shawn Haji-Momenian.

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Haji-Momenian, S., Chang, K.J., Grand, D.J. et al. Measuring right ventricular volume and ejection fraction with Simpson's method: which MRI axis is best? Comparison with a "gold standard". J Cardiovasc Magn Reson 11, O98 (2009). https://doi.org/10.1186/1532-429X-11-S1-O98

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Keywords

  • Right Ventricular
  • Short Axis
  • Subdivision Surface
  • Right Ventricular Volume
  • Experienced Reviewer