Objectives: The purpose of the present study was to compare periodically rotated overlapping parallel lines with enhanced reconstruction–type turbo spin echo diffusion-weighted imaging (pTSE-DWI) and readout-segmented echo planar imaging (rsEPI-DWI) with single-shot echo planar imaging (ssEPI-DWI) in a 7 T human MR system. We evaluated the signal-to-noise ratio (SNR), image distortion, and apparent diffusion coefficient values in the human brain.
Materials and Methods: Six healthy volunteers were included in this study. The study protocol was approved by our institutional review board. All measurements were performed at 7 T using pTSE-DWI, rsEPI-DWI, and ssEPI-DWI sequences. The spatial resolution was 1.2 × 1.2 mm2 in-plane with a 3-mm slice thickness. Signal-to-noise ratio was measured using 2 scans.
Results: The ssEPI-DWI sequence showed significant image blurring, whereas pTSE-DWI and rsEPI-DWI sequences demonstrated high image quality with low geometrical distortion compared with reference T2-weighted, turbo spin echo images. Signal loss in ventral regions near the air-filled paranasal sinus/nasal cavity was found in ssEPI-DWI and rsEPI-DWI but not pTSE-DWI. The apparent diffusion coefficient values for ssEPI-DWI were 824 ± 17 × 10−6 and 749 ± 25 × 10−6 mm2/s in the gray matter and white matter, respectively; the values obtained for pTSE-DWI were 798 ± 21 × 10−6 and 865 ± 40 × 10−6 mm2/s; and the values obtained for rsEPI-DWI were 730 ± 12 × 10−6 and 722 ± 25 × 10−6 mm2/s. The pTSE-DWI images showed no additional distortion comparison to the T2-weighted images, but had a lower SNR than ssEPI-DWI and rsEPI-DWI. The rsEPI-DWI sequence provided high-quality images with minor distortion and a similar SNR to ssEPI-DWI.
Conclusions: Our results suggest that the benefits of the rsEPI-DWI and pTSE-DWI sequences, in terms of SNR, image quality, and image distortion, appear to outweigh those of ssEPI-DWI. Thus, pTSE-DWI and rsEPI-DWI at 7 T have great potential use for clinical diagnoses. However, it is noteworthy that both sequences are limited by the scan time required. In addition, pTSE-DWI has limitations on the number of slices due to specific absorption rate. Overall, rsEPI-DWI is a favorable imaging sequence, taking into account the SNR and image quality at 7 T.
From the *Center for Information and Neural Networks, National Institute of Information and Communications Technology; †Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan; ‡Siemens Shenzhen Magnetic Resonance Ltd, Shenzhen, China; §Siemens Healthcare GmbH, Erlangen, Germany; and ∥Fraunhofer Institute for Medical Image Computing MEVIS, Bremen, Germany.
Received for publication August 26, 2015; and accepted for publication, after revision, November 27, 2015.
Conflicts of interest and sources of funding: K.Z. is an employee of Siemens Shenzhen Magnetic Resonance Ltd. A.S. is an employee of Siemens Healthcare GmbH. D.P. was an employee of Siemens AG, Healthcare sector until October 2014. D.P. receives ongoing financial remuneration for patents related to the submitted work, which he registered during his period of employment with Siemens and which are assigned to Siemens AG. The other authors report no conflicts of interest.
Correspondence to: Ikuhiro Kida, PhD, Center for Information and Neural Networks, National Institute of Information and Communications Technology, 1-4 Yamadaoka, Suita, Osaka 565-0871, Japan. E-mail: email@example.com.