Motion‐robust, blood‐suppressed, reduced‐distortion diffusion MRI of the liver

Abstract

Purpose To evaluate feasibility and reproducibility of liver diffusion‐weighted (DW) MRI using cardiac‐motion‐robust, blood‐suppressed, reduced‐distortion techniques. Methods DW‐MRI data were acquired at 3T in an anatomically accurate liver phantom including controlled pulsatile motion, in eight healthy volunteers and four patients with known or suspected liver metastases. Standard monopolar and motion‐robust (M1‐nulled, and M1‐optimized) DW gradient waveforms were each acquired with single‐shot echo‐planar imaging (ssEPI) and multishot EPI (msEPI). In the motion phantom, apparent diffusion coefficient (ADC) was measured in the motion‐affected volume. In healthy volunteers, ADC was measured in the left and right liver lobes separately to evaluate ADC reproducibility between the two lobes. Image distortions were quantified using the normalized cross‐correlation coefficient, with an undistorted T2‐weighted reference. Results In the motion phantom, ADC mean and SD in motion‐affected volumes substantially increased with increasing motion for monopolar waveforms. ADC remained stable in the presence of increasing motion when using motion‐robust waveforms. M1‐optimized waveforms suppressed slow flow signal present with M1‐nulled waveforms. In healthy volunteers, monopolar waveforms generated significantly different ADC measurements between left and right liver lobes (p=0.0078$$ p=0.0078 $$, reproducibility coefficients (RPC) = 470prefix×10prefix−6$$ 470\times 1{0}^{-6} $$ mm2$$ {}^2 $$/s for monopolar‐msEPI), while M1‐optimized waveforms showed more reproducible ADC values (p=0.29$$ p=0.29 $$, RPC=220prefix×10prefix−6$$ \mathrm{RPC}=220\times 1{0}^{-6} $$ mm2$$ {}^2 $$/s for M1‐optimized‐msEPI). In phantom and healthy volunteer studies, motion‐robust acquisitions with msEPI showed significantly reduced image distortion (p<0.001$$ p<0.001 $$) compared to ssEPI. Patient scans showed reduction of wormhole artifacts when combining M1‐optimized waveforms with msEPI. Conclusion Synergistic effects of combined M1‐optimized diffusion waveforms and msEPI acquisitions enable reproducible liver DWI with motion robustness, blood signal suppression, and reduced distortion.

Impact of velocity- and acceleration-compensated encodings on signal dropout and black-blood state in diffusion-weighted magnetic resonance liver imaging at clinical TEs

“…Geng et al [ 22 ] showed that gradient waveforms with small M 1 values combined with segmented echo planar readouts are well-suited to obtain low-distortion images without a large influence from motion artifacts in liver DWI. The application of small M 2 values may be an interesting further step in this regard.…”

“…In some studies, an aim was to minimize the echo time for each diffusion encoding separately [ 16 , 22 , 23 ]. For example, Aliotta et al proposed the CODE optimization algorithm to create asymmetric motion-compensated waveforms and demonstrated a significant reduction in the echo time [ 23 ].…”

“…However, blood vessels might appear bright [ 10 ] and confound lesion detection. Therefore, small velocity-weightings have been suggested instead of full motion-compensation [ 15 , 21 , 22 ].…”

Distortionless, free‐breathing, and respiratory resolved 3D diffusion weighted imaging of the abdomen

“…The benefits of M1-nulled diffusion encoding has been shown for cardiac triggering in the heart 19 and pancreas, 20 respiratory triggering in renal imaging, 21 and free-breathing, 22 and breath-holding in the liver. 23 The twice refocused preparation that satisfies the Carr-Purcell-Meiboom-Gill (CPMG) condition has reduced B1 sensitivity compared to single refocusing schemes, 24 and little echo time penalty compared to single refocused M1-nulled waveforms. A magnetization prepared approach was selected to achieve diffusion weighting over DW steady-state sequences which have an oscillating signal amplitude from motion and large gradient areas.…”

Robust multishot diffusion‐weighted imaging of the abdomen with region‐based shot rejection

“…The spleen moves relatively little during respiration, and will have fewer cycles of imparted phase from diffusion gradients compared to the pancreas, which is susceptible to cardiac motion. 6 velocity-or acceleration-compensated diffusion encoding [28][29][30][31][32][33] reduces the resolution of the imparted phase for a modest TE penalty. The imparted phase also depends on the method used for managing respiratory motion.…”