Dynamic field-of-view imaging to increase temporal resolution in the early phase of contrast media uptake in breast DCE-MRI: A feasibility study.
Dynamic field-of-view imaging to increase temporal resolution in the early phase of contrast media uptake in breast DCE-MRI: A feasibility study.
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DOI：
10.1002/mp.12747
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发表时间：
2018-03
期刊：
影响因子：
3.8
通讯作者：
Karczmar GS
中科院分区：
文献类型：
--
作者：
Pineda FD;Easley TO;Karczmar GS
通过提高时间分辨率和更准确地采样造影剂摄取的早期动力学，提高乳腺MRI的诊断准确性。我们测试了通过减小FOV、允许混叠和展开结果图像来加速双侧乳腺DCE-MRI的可行性。先前双侧乳腺DCE-MRI（6s-10 s时间分辨率）的“超快”方案的经验表明，在造影剂注射后的前30至45秒内，显著增强的体素数量非常低。这表明在混叠图像中增强体素的重叠将非常罕见。因此，可以在造影剂注射后的前30-45秒期间采集混叠图像，并展开以产生几乎没有误差的全FOV图像。在原理验证测试中，从全FOV采集的前30秒模拟混叠图像。选择早期增强相对密集的病例，在最差情况下测试该方法。在初始测试中，模拟了全FOV大小的60%的FOV。为了减少由于混叠图像中的重叠体素而导致的错误概率，我们随后测试了动态FOV方法。FOV逐渐增加，以使增强体素在多个时间点不会重叠，并且在给定时间点处增强体素重叠的区域可以通过在之前和随后的时间点（用不同FOV采集）之间进行插值来展开。每个时间点的模拟FOV大小分别为全FOV的31%、44%和77%。为混叠图像生成减影图像（对比后减去对比前），并过滤以选择显著增强的体素。比较早期的，高度混叠的图像，与后来的，较少混叠的图像，然后帮助确定增强体素的真实位置。在初始混叠模拟中，胸壁上方平均2.9%的增强体素在混叠图像中重叠（范围0.1% - 6.7%）。使用CW-SSIM（复小波相似性指数）评价的模拟展开图像与正确全FOV图像之间的相似性在第一、第二和第三时间点分别为0.50 ± 0.26、0.76 ± 0.09和0.80 ± 0.10（数字越接近1表示图像越相似）。对于动态FOV测试，由于早期时间点的混叠较大，胸壁上方平均有11%的增强体素重叠（范围0% - 40%）。尽管有更多的体素重叠，但对于第一、第二和第三时间点，使用动态FOV采集的数据的CW-SSIM值分别为0.64 ± 0.25、0.93 ± 0.04和0.97 ± 0.02。动态FOV成像允许在早期造影剂吸收阶段加速双侧乳腺DCE-MRI。该方法依赖于乳腺DCE-MRI早期增强的稀疏性。模拟结果表明，动态FOV成像和展开产生的图像非常接近完全采样的图像，并允许时间分辨率高达2秒每图像。
To increase diagnostic accuracy of breast MRI by increasing temporal resolution and more accurately sampling the early kinetics of contrast media uptake. We tested the feasibility of accelerating bilateral breast DCE-MRI by reducing the FOV, allowing aliasing, and unfolding the resulting images. Previous experience with an ‘ultrafast’ protocol for bilateral breast DCE-MRI (6s-10s temporal resolution) showed that the number of significantly enhancing voxels is very low in the first 30 to 45 seconds after contrast media injection. This suggests that overlap of enhancing voxels in aliased images will be very infrequent. Therefore, aliased images can be acquired during the first 30-45 seconds after contrast media injection and unfolded to produce full FOV images with few errors. In a proof-of-principle test, aliased images were simulated from the first 30 seconds of full-FOV acquisitions. Cases with relatively dense early enhancement were selected to test this method in a worst-case scenario. In an initial test, an FOV of 60% the size of the full FOV was simulated. To reduce the probability of errors due to overlapping voxels in aliased images, we then tested a dynamic FOV approach. The FOV was progressively increased so that enhancing voxels could not overlap at multiple time-points, and areas where enhancing voxels overlapped at a given time-point could be unfolded by interpolating between the preceding and subsequent time-points (acquired with different FOVs). The simulated FOV sizes for each of the time-points were 31%, 44%, and 77% of the full FOV. Subtraction images (post minus pre-contrast) were generated for aliased images and filtered to select significantly enhancing voxels. Comparison of early, highly aliased images, with later, less aliased images then helped to identify the true locations of enhancing voxels. In the initial aliasing simulations, an average of 2.9% of the enhancing voxels above the chest wall overlapped in the aliased images (range 0.1% - 6.7%). The similarity between simulated unfolded images and the correct full FOV images, evaluated using CW-SSIM (complex-wavelet similarity index), was 0.50 ± 0.26, 0.76 ± 0.09, and 0.80 ± 0.10 for the first, second, and third time-point, respectively (numbers closer to 1 indicate more similar images). For the dynamic FOV tests an average of 11% of the enhancing voxels above the chest wall overlapped (range 0% - 40%) due to greater aliasing at early time points. Despite more voxels overlapping, the CW-SSIM values for the data acquired with dynamic FOV’s were 0.64 ± 0.25, 0.93 ± 0.04 and 0.97 ± 0.02 for the first, second, and third time points, respectively. Dynamic FOV imaging allows accelerated bilateral breast DCE-MRI during the early contrast media uptake phase. This method relies on the sparsity of enhancement at the early phases of DCE-MRI of the breast. The results of simulations suggest that dynamic FOV imaging and unfolding produces images that are very close to fully sampled images, and allows temporal resolution as high as 2 seconds per image.
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