Emerging Technique Reveals Higher Spatial Resolution for DWI with Breast MRI


Three-way comparison shows alternative protocols to standard echo-planar imaging can produce higher quality images with breast cancer screening.

Interest in the expanded use of diffusion-weighted imaging (DWI) with breast MRI continues to grow, but concerns about spatial resolution and image quality have kept it from widespread use. In a new study, investigators have identified a protocol that could make this technique more effective with breast imaging.

In a proof-of-concept study published in Radiology, researchers from the University of Minnesota determined that the axially reformatted simultaneous multi-slice protocol (AR-SMS) produced higher image quality than either standard SE echo-planar imaging DWI or RS echo-planar imaging.

“With growing interest in DWI for breast cancer, it is vital to improve the image quality and spatial resolution of DWI methods,” said the team led by Jessica A. McKay, Ph.D., from Minnesota’s biomedical engineering department.

Making improvements in these areas is critical to extend the use of DWI for identifying breast malignancies because even though the technique does a great job in detecting changes in cell density, organization, and membrane integrity – all characteristics common to breast malignancies – its limited spatial resolution reduces its ability to identify small breast lesions or to accurately assess lesion shape or intratumoral heterogeneity.

Screenshot of a picture archiving and communication system setup in a 70-year-old participant with large biopsy-proven cancer. Readers were provided with clinical images, including, G, a noncontrast-enhanced image, H, a single contrast-enhanced image, I, a contrast-enhanced subtraction T1-weighted image, and, J, a T2- weighted image, with the lesion indicated (arrow). Diffusion data included axial images with, A–C, b value of 800 sec/mm2 and, D–F, apparent diffusion coefficient (ADC) maps for all three methods, randomly ordered as methods A, B, and C, which are labeled here for illustration purposes. The metal needle of the contrast injection port caused the artifact on the right breast. AR-SMS = axially reformatted–simultaneous multislice, RS-EPI = readout-segmented echo-planar imaging. Courtesy: Radiology

Even by strictly adhering to protocol recommendations, said Savannah C. Partridge, Ph.D., professor of breast imaging at the University of Washington, in an accompanying editorial, DWI’s technical limitations result in images that are of too low quality for breast applications.

Consequently, to determine whether any particular protocol rose above others and offered better images for breast screening, McKay’s team tested three 5-minute DWI protocols that were acquired on a 3T scanner. They looked at standard SE echo-planar imaging, RS echo-planar imaging with five segments, and AR-SMS imaging with four-time slice acceleration and evaluated 30 lesions from 28 women with an average age of 51 who had contrast-enhanced lesions on contrast-enhanced subtraction images. They, then, compared the findings from these protocols to a resolution phantom that included a 1-mm feature that was detectable on the axial plane on AR-SMS and T2-weighted images and a 2-mm feature detectable on the axial plane for all protocols.

Small lesion example. Shown are, A, a contrast-enhanced subtraction image, E, a T2-weighted image, B–D, images with b value of 800 sec/mm2, and, F–H, apparent diffusion coefficient (ADC) maps, focused on an example of a small contrast-enhanced lesion (arrow). Radiologists were asked to measure the longest dimen- sion on images with b value of 800 sec/mm2 (B–D) and a lesion-average ADC by drawing a freehand two-dimensional region of interest on each ADC map (F–H). The longest lesion diameter was 4.7 mm, measured on the contrast-enhanced subtraction image (A) and averaged across all readers. Average measurements on images with b value of 800 sec/mm2 were as follows: B, standard, 5.8 mm; C, readout-segmented (RS) echo-planar imaging (EPI), 4.6 mm; and D, axially reformatted (AR)–simultaneous multislice (SMS) image, 5.5 mm. Average ADC measurements were as follows: F, standard, 1.45 3 10−3 mm2/sec; G, RS echo-planar image, 1.59 310−3 mm2/sec; and H, R-SMS image, 1.34 310−3 mm2/sec. The average quality scores on a five-point LIkert scale were as follows: standard, 2.3; RS echo-planar imaging, 2.7; and AR-SMS imaging, 3.7. Courtesy: Radiology

According to their analysis, AR-SMS outperformed RS echo-planar imaging, followed by standard SE echo-planar imaging, in both image quality and rank. Using the Likert scale to judge image quality, AR-SMS scored 0.74 points higher than RS echo-planar imaging and 1.31 points higher than standard SE echo-planar imaging.

Additionally, McKay’s team said, AR-SMS and RS echo-planar imaging measured lesion size with higher confidence than standard SE echo-planar imaging, but there was no statistically significant difference between the two former protocols. The team also discovered AR-SMS achieves larger anatomic coverage and better image quality than RS echo-planar imaging.

But, these protocols also have challenges, the team pointed out. AR-SMS can encode a large imaging volume quickly, allowing for full coverage and a large number of averages and directions, but it needs significant distortion correction. Plus, it is not commercially available yet. Conversely, RS echo-planar imaging, they said, is more commonly available on clinical systems, but it has reduced geometric distortion at the cost of imaging time. It also has limited anterior-posterior coverage that prevents the inclusion of most lymph nodes. To these problems, the team offered a possible solution.

“Combining the encoding speed of AR-SMS with the reduced distortion of RS echo-planar imaging may be a promising strategy for future work,” they suggested.

Even with these limitations, Partridge pointed out, these developing techniques are improving DWI’s potential for higher quality image acquisitions. She called it a “game-changer” for augmenting the clinical role DWI plays in breast imaging. And, the unique sagittal acquisition strategy that McKay’s team developed that takes advantage of greater slice acceleration potential, she said, allows for more time savings and higher spatial resolution with less in-plane blurring and artifacts.

Overall, she said, these advancements are a push in the right direction to increase DWI integration into breast imaging.

“Widespread clinical use of breast DWI requires tailored approaches for breast application, such as that proposed by McKay, et.al., to raise image quality and reliability closer to the levels of conventional contrast-enhanced MRI,” Partridge said. “Such technical advancements, across all vendor platforms, will be critical to maximize breast DWI performance and support its expanded role for breast imaging.”

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