Compressed Sensing for Breast MRI: Resolving the Trade-Off Between Spatial and Temporal Resolution
Authors: Vreemann Suzan , Rodriguez-Ruiz Alejandro , Nickel Dominik , Heacock Laura , Appelman Linda , van Zelst Jan , Karssemeijer Nico , Weiland Elisabeth , Maas Marnix , Moy Linda , Kiefer Berthold , Mann Ritse M. 
Published: May 2017

Objective
Ultrafast dynamic contrast-enhanced magnetic resonance imaging of the breast enables assessment of the contrast inflow dynamics while providing images with diagnostic spatial resolution. However, the slice thickness of common ultrafast techniques still prevents multiplanar reconstruction. In addition, some temporal blurring of the enhancement characteristics occurs in case view-sharing is used. We evaluate a prototype compressed-sensing volume-interpolated breath-hold examination (CS-VIBE) sequence for ultrafast breast MRI that improves through plane spatial resolution and avoids temporal blurring while maintaining an ultrafast temporal resolution (less than 5 seconds per volume). Image quality (IQ) of the new sequence is compared with an ultrafast view-sharing sequence (time-resolved angiography with interleaved stochastic trajectories [TWIST]), and assessment of lesion morphology is compared with a regular T1-weighted 3D Dixon sequence (VIBE-DIXON) with an acquisition time of 91 seconds.

Materials and Methods
From April 2016 to October 2016, 30 women were scanned with the CS-VIBE sequence, replacing the routine ultrafast TWIST sequence in a hybrid breast MRI protocol. The need for informed consent was waived. All MRI scans were performed on a 3T MAGNETOM Skyra system (Siemens Healthcare, Erlangen, Germany) using a 16-channel bilateral breast coil. Two reader studies were conducted involving 5 readers. In the first study, overall IQ of CS-VIBE and TWIST in the axial plane was independently rated for 23 women for whom prior MRI examinations with TWIST were available. In addition, the presence of several types of artifacts was rated on a 5-point scale. The second study was conducted in women (n = 16) with lesions. In total, characteristics of 31 lesions (5 malignant and 26 benign) were described independently for CS-VIBE and VIBE-DIXON, according to the BI-RADS MRI-lexicon. In addition, a lesion conspicuity score was given.

Results
Using CS-VIBE, a much higher through-plane spatial resolution was achieved in the same acquisition time as with TWIST, without affecting in-plane IQ (P = 0.260). Time-resolved angiography with interleaved stochastic trajectories showed slightly more motion artifacts and infolding and ghosting artifacts compared with CS-VIBE, whereas CS-VIBE showed more breathing and pulsation artifacts. For morphologic assessment, intrareader agreement between CS-VIBE and the more time-consuming VIBE-DIXON was slight to almost perfect, and generally higher than interreader agreement. Mean sensitivity (84.0% and 92.0% for CS-VIBE and VIBE-DIXON, P = 0.500) and specificity (60.0% and 55.4% for CS-VIBE and VIBE-DIXON, P = 0.327) were comparable for both sequences.

Conclusions
Compressed-sensing volume-interpolated breath-hold examination allows an increase of the through-plane spatial resolution of ultrafast dynamic contrast-enhanced magnetic resonance imaging compared with TWIST at a comparable in-plane IQ. Morphological assessment of lesions using CS-VIBE is comparable to VIBE-DIXON, which takes 18 times longer. Consequently, CS-VIBE enables 3D evaluation of breast lesions in ultrafast breast MRI.