Suraj D Serai1, Jonathan R Dillman1, Hui Wang2, and Andrew T Trout1
1Radiology, Cincinnati Children's Hospital, Cincinnati, OH, United States, 2Philips Healthcare, Cincinnati, OH, United States
Synopsis
MR elastography (MRE) allows
non-invasive evaluation of hepatic stiffness and samples a larger area of the
liver than liver biopsy. The high accuracy of MRE for liver fibrosis staging
suggests that MRE could potentially replace liver biopsy. MRE
has traditionally been performed using a GRE sequence. GRE, however, has SNR
limitations at higher field strengths that can result in under-sampling potentially
leading to erroneous stiffness values. SE-EPI is an alternative means of
performing MRE that has higher SNR, lower susceptibility related signal loss
and increased speed. In this work, we compared GRE and SE-EPI MRE across two
vendor platforms. Purpose
As MRE gains acceptance, it is important to confirm that
liver stiffness values obtained by different sequences and on different vendor
platforms are reproducible. The aim of this study was to
compare GRE and SE-EPI MRE on volunteers on two different vendor platform 3T
MRI scanners performed on the same day.
Methods
16 volunteers (6
hours fasting status) were recruited under an approved IRB for liver MRE scans.
All subjects were imaged in one session using both GRE and SE-EPI MRE on two 3T
MRI scanners (750W, GE Healthcare, Waukesha, WI, USA and Philips Ingenia, Best,
Netherlands). All scan parameters
were identical on the two platforms to the best extent possible (Representative
image in Figure 1). The subjects did
not eat or drink between the two MRE exams in order to avoid postprandial
hepatic blood flow. MRE
scans were done using a 16-channel torso coil and identical active
driver amplitudes and frequency (60 Hz). The initiation and cessation of the
vibrations were controlled by the MR pulse sequence programmed and embedded as
part of the scanner software. GRE MRE was acquired in 4 breath holds of 15 seconds
each and SE-EPI MRE was acquired in a single breath hold of 15 seconds. Four axial
slices through the liver were obtained for each sequence. MR elastogram maps
were generated using a multimodal direct inversion (MMDI) algorithm (Mayo Clinic, Rochester, MN) with liver
stiffness calculated as a mean of mean stiffness measured on each slice (kPa),
measured by a single observer. Mean
liver stiffness values across the two platforms and between GRE versus SE-EPI
MRE sequences were compared using Bland-Altman difference plots. Pearson’s
correlation coefficient was used to assess correlation between stiffness values
obtained within and across scanners. Mean liver stiffness values between the two platforms were
compared using interclass correlation
coefficients (ICC). Area of the sampled regions of interest was also
recorded and compared with a paired t-test.
Results
Mean subject age was 39.2 years (range: 22.7-55.3 years) and 69%
were female. Mean liver stiffness values measured on the GE scanner were 1.98 ±
0.4 kPa by GRE MRE and 2.06 ± 0.3 kPa by SE-EPI MRE and were highly correlated (R
= 0.9). Similarly mean liver stiffness values on the Philips scanner were 1.83 ±
0.3 kPa by GRE MRE and 1.85 ± 0.3 kPa by SE-EPI MRE and were highly correlated
(R = 0.9). Sampled areas were 6174 ± 2197 mm2 for GRE MRE and 9915 ±
2721 mm2 for SE-EPI MRE on the GE MRI scanner and were 8392 ± 4666 mm2
for GRE MRE and 14540 ± 4490 mm2 for SE-EPI MRE on the Philips MRI
scanner. For both scanners, SE-EPI allowed sampling of significantly larger areas
(p<0.001). Stiffness measurements
by both GRE MRE and SE-EPI MRE were highly reproducible across the two scanner
platforms. ICC was 0.85 (95% confidence interval: 0.58 – 0.95) for GRE MRE and 0.84
(95% confidence interval: 0.52 – 0.94) for SE-EPI MRE. For both sequences, Bland-Altman
analysis shows all values falling within two standard deviations (Figure 2A and
2B). Bland-Altman analysis of GRE MRE versus SE-EPI MRE, independent of vendor,
demonstrates a bias of 0.06 kPa (standard deviation = 0.41 kPa) between
techniques with all values falling within 95% prediction limits (Figure 3) with
the exception of a single outlier. Scatter plots show stiffness values and
across scanners (GE and Philips) (Figure 4) and within scanners (GRE and
SE-EPI) (Figure 5); all stiffness values fell within 95% agreement with the line
of equality.
Conclusion
Liver MRE is a promising non-invasive quantitative
imaging tool used to determine liver stiffness in the assessment of patients
with chronic liver disease. As
MRE becomes more widespread in its availability and usage, and as more vendor
platforms become approved for routine clinical determination of liver stiffness,
it is imperative that cross vendor validation studies be performed to ensure that
liver stiffness values are consistent across different platforms. This
consistency will ensure that surveillance exams can be performed on individual
patients with chronic liver disease at different facilities, with different MR
platforms, but without concern for variation in liver stiffness results
secondary to purely technical factors. In this pilot investigation, we demonstrate that
there is strong agreement in measured hepatic stiffness
among two vendor scanners at 3T and between GRE and SE-EPI MRE sequences with minimal
bias (0.06 kPa) between techniques. SE-EPI MRE has the advantage of sampling a
larger area of the liver and can be performed in a single breath hold.
Acknowledgements
No acknowledgement found.References
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