Combining b2500 diffusion-weighted imaging with BI-RADS improves the specificity of breast MRI

Magnetic resonance imaging (MRI) of the breast has a high sensitivity, but offers moderate specificity for the characterization of breast lesions [1]. MRI accuracy increases when a combination of dynamic contrast-enhanced and diffusion-weighted images (DWI) is used compared to dynamic contrast-enhanced MRI used alone [2], [3], [4], [5], [6], [7]. DWI allows evaluating tissue diffusivity, which is routinely quantified using the apparent diffusion coefficient (ADC). However, ADC is not always measurable because of technical issues [8,9]. ADC assessment is also dependent on acquisition parameters, such as b values, echo time (TE), repetition time (TR) and region of interest selection for its measurement [10], [11], [12], [13]. To limit variability and standardize protocols, international societies have published guidelines on DW sequence parameters [14,15]. The use of a b value of 800 s/mm2 has been recommended because of T2 signal attenuation and noise reduction that might obscure diffusion information. Multi-shot echo-planar imaging (EPI) techniques, such as readout segmentation of long variable echo trains (RESOLVE) reconstruction is also recommended to increase spatial resolution and to limit distortions and blurring. However, diffusion at a b value of 800 s/mm2 correlates with “cellularity” and is too low to carry non-Gaussian diffusion effects [16]. Recent studies showed that the maximum contrast-to-noise ratio to discriminate between malignant and benign lesions seemed to range between b = 1200 s/mm2 and b = 1500 s/mm2 [17]. However, for young patients and patients with dense breasts, a greater b value showed better diagnostic performances in one study [18]. When the b value increases further, the diffusion signal is even less sensitive to the T2 signal and is amplified by diffusion kurtosis, which reflects diffusion at a smaller spatial scale, through tissue microstructural complexity and heterogeneity [16,19]. Thus, the generally increased diffusion kurtosis of malignant lesions intensifies the global diffusion signal [20,21]. As a consequence, high b-value DWI could increase the overall performance of breast MRI [22]. To reach a b value of 2500 s/mm2 with sufficient contrast-to-noise ratio in a clinically acceptable time, simultaneous multislice echo planar imaging can be used [23]. Simultaneous multislice is an emerging diffusion acceleration technique that deploys multiband pulses to excite multiple slices simultaneously [24]. At one b value of 2500 s/mm2, ADC map cannot be calculated accurately using monoexponential fit. However, visual assessment might be appropriate, as DWI obtained with a b value of 2500 s/mm2 (b2500DWI) is less sensitive to the T2 signal. Moreover, it avoids challenging ADC measurement and technical issues [8,9].

Therefore, the purpose of our study was to evaluate the diagnostic performance of visual assessment (VA) of b2500DWI in addition to a conventional MRI protocol for the characterization of breast lesions.

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