Simultaneous multislice accelerated diffusion-weighted imaging of the liver: comparison of different breathing schemes with standard sequences as reference

Christina Schraml¹, Jana Taron¹, Nina F Schwenzer¹, Holger Schmidt¹, Thomas Kuestner², Michael Erb³, Mike Notohamiprodjo¹, Konstantin Nikolaou¹, Fritz Schick⁴, and Petros Martirosian⁴

¹Diagnostic and Interventional Radiology, Department of Radiology, University Hospital Tuebingen, Tuebingen, Germany, ²Institute of Signal Processing and System Theory, University of Stuttgart, Stuttgart, Germany, ³Department of Biomedical Magnetic Resonance, University Hospital Tuebingen, Tuebingen, Germany, ⁴Section on Experimental Radiology, Department of Radiology, University Hospital Tuebingen, Tuebingen, Germany

Synopsis

SMS-acceleration allows for considerable scan time reduction in hepatic DWI without substantial drawbacks in image quality both using respiratory-triggering and free-breathing acquisitions. In the present study set-up, ADC measured in SMS-DWI were lower than in standard DWI which should be considered when using absolute ADC for clinical reading. The demonstrated high image quality of SMS-DWI obtained in FB indicates great potential for scan time reduction in DWI for abdominal and whole-body applications.

Purpose

Diffusion-weighted imaging (DWI) provides important diagnostic information in the evaluation of liver disease¹. However, the long scan time of DWI limits its acceptance in clinical routine. Thus, scan time reduction techniques and their validation are an essential issue in abdominal DWI. The so-called SMS (simultaneous multislice) technique^2-4 has recently been demonstrated as a promising method for scan time reduction in DWI of the liver⁵. The influence of the breathing scheme on image characteristics in SMS-DWI of the liver has not yet been systematically investigated. Thus, the aim of our study was to evaluate image characteristics obtained in SMS-accelerated DWI of the liver with both respiratory-triggering and free-breathing in comparison to standard (STD) sequences as reference.

Methods

The study was approved by the institutional review board. 10 healthy volunteers and 12 patients were included. All participants were scanned in a whole-body 1.5 T scanner (Aera, Siemens Healthcare). MR protocol included STD and SMS-accelerated EPI DWI sequences with respiratory-triggering and free breathing (STD-RT, STD-FB, SMS-RT, SMS-FB). Monopolar diffusion preparation according to the Stejskal-Tanner scheme⁶ was used with b-values of 50, 400, 800 s/mm². Sequence parameters are summarized in Table 1. Scan time of DWI sequences was measured. Images obtained by SMS-DWI and STD-DWI with both breathing schemes were analyzed quantitatively (ADC, SNR) and qualitatively with respect to overall image quality and detailed image criteria (5-point Likert scale, 5=excellent). Qualitative and quantitative parameters were compared using the Steel-Dwass test. P-values <0.05 were considered to indicate statistical significance.

Results

SMS-DWI provided diagnostic image quality in volunteers and patients with both breathing schemes with a reduction of scan time of 70 % (0:56 vs. 3:20 min in FB). Mean image quality did not significantly differ between breathing schemes in both STD and SMS sequences (STD-RT 4.1±0.7, STD-FB 4.0±0.8, SMS-RT: 4.0±0.7; SMS-FB: 4.0±0.7) (Figure 1-3). In the analysis of particular image quality criteria, discrepancies were observed between STD and SMS with slightly higher incidence of ghosting artifacts and interslice signal inhomogeneity in SMS-DWI. SNR did not significantly differ between DWI sequences. Slightly lower ADC where found in FB both in STD and SMS-DWI without statistical significance. In general, ADC were significantly lower in SMS-DWI compared to STD-DWI irrespective of the breathing scheme (1.2±0.1 x 10^-3 mm²/s vs. 1.0±0.1 x 10^-3 mm²/s; p<0.0001).

Discussion

SMS-accelerated DWI of the liver provided significant scan time reduction while maintaining equivalent image quality as compared to STD technique both using RT and FB acquisition. ADC values were within the range of values reported in the literature^1,7-10. The discrepancies in ADC between STD-DWI and SMS-DWI may possibly be explained by T1 saturation effects due to the relatively low repetition time chosen in SMS-DWI to optimize scan time reduction. As our study results indicate that the image quality in SMS with FB does not have substantial drawbacks compared to SMS with RT acquisition in both volunteers and patients, the FB technique will be preferable in clinical routine due to the markedly shorter scan time. Based on these results, prospective patient studies testing the diagnostic performance of FB SMS-DWI in the evaluation of liver pathologies should be encouraged.

Conclusion

SMS-acceleration allows for considerable scan time reduction in hepatic DWI with equivalent image quality compared to standard techniques both using respiratory-triggering and free-breathing. Potential discrepancies in ADC between STD-DWI and SMS-DWI need to be considered when transferring the SMS technique to clinical routine reading.

Acknowledgements

No acknowledgement found.

References

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2 Feinberg, D. A. et al. Multiplexed echo planar imaging for sub-second whole brain FMRI and fast diffusion imaging. PloS one 5, e15710, doi:10.1371/journal.pone.0015710 (2010).

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Figures

Figure 1 DWI of the liver obtained with different breathing schemes and sequences

Diffusion-weighted images and ADC maps are shown as obtained in standard (STD) and simultaneous multislice (SMS) technique with both breathing schemes. Overall image quality did not significantly differ between breathing schemes as well as sequence techniques.

Figure 2 STD-DWI and SMS-DWI acquired with respiratory-triggering in a 54 year old patient with liver cirrhosis who underwent follow-up after RFA of hepatocellular carcinoma

Diffusion-weighted images and ADC maps recorded with standard (STD, upper row) and simultaneous multislice (SMS, lower row) technique are shown. Overall image quality was rated high in SMS-DWI and STD-DWI.

Figure 3 STD-DWI and SMS-DWI acquired in free breathing in a 62-year-old female patient with hepatic metastases from uveal melanoma.

Hepatic metastases are visible in the right hepatic lobe. Image quality was rated moderately higher in STD without impact on the diagnostic significance. Image quality of ADC maps was rated equivalently high in both STD-DWI and SMS-DWI.

Table 1 Sequence parameters

Summary of sequence parameters for standard (STD) and simultaneous multislice (SMS) DWI sequences with respiratory-triggering (RT) and free-breathing (FB).

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

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