Royal Marsden NHS Foundation Trust and Institute of Cancer Research, MRI Unit, Downs Rd, Sutton SM2 5 PT, UK.
Eur Radiol. 2013 Jun;23(6):1537-45. doi: 10.1007/s00330-012-2735-4. Epub 2012 Dec 16.
To investigate the effect of magnetic field heterogeneity in breast dynamic contrast-enhanced examinations with fat saturation (DCE-FS).
The magnetic field was mapped over the breasts in ten patients. DCE-FS was undertaken at 1.5 T with fast spoiled gradient echoes and spectrally selective fat saturation. Signal intensity was calculated for T1 values 25-1,200 ms both on and off resonance, and results were verified with a test object. Clinical examinations were evaluated for the predicted effects of field heterogeneity.
Magnetic field was found to vary by 3.6 ± 1.2 ppm over the central transaxial slice and 5.1 ± 1.5 over the whole breast volume (mean ± standard deviation). Computer simulations predict a reduction in the dynamic range if field heterogeneity leads to unintended water suppression, and distortion to CA uptake curves due to fat suppression failure (for fat containing pixels). A compromise between dynamic range and fat saturation performance is required. Both water suppression and fat suppression failure are apparent in clinical examinations.
Magnetic field heterogeneity is likely to reduce the sensitivity of DCE-FS by distorting the CA uptake curves because of fat suppression failure (for fat containing pixels) and by reducing the dynamic range because of unintended water suppression.
• Magnetic field heterogeneity is significant in breast magnetic resonance. • Contrast-agent uptake curves are distorted by a non-uniform magnetic field. • Radiologist must be aware of possibility of distortion to interpret uptake curves correctly. • Compromise between fat suppression and dynamic range is required.
研究磁场不均匀性对带有脂肪饱和（DCE-FS）的乳腺动态对比增强检查的影响。
在十名患者的乳房上进行了磁场测绘。在 1.5T 下进行 DCE-FS，采用快速扰相梯度回波和光谱选择性脂肪饱和。在共振和非共振时，计算 T1 值为 25-1200ms 的信号强度，并使用测试对象进行验证。对临床检查进行评估，以预测磁场不均匀性的预期影响。
在中央横轴切片上，磁场变化为 3.6±1.2ppm，在整个乳房容积上变化为 5.1±1.5ppm（平均值±标准差）。计算机模拟预测，如果磁场不均匀性导致意外的水抑制，以及由于脂肪抑制失败（对于含脂肪像素）导致 CA 摄取曲线失真，动态范围将会减小。需要在动态范围和脂肪饱和性能之间取得平衡。在临床检查中，水抑制和脂肪抑制失败都很明显。
磁场不均匀性可能会通过脂肪抑制失败（对于含脂肪像素）扭曲 CA 摄取曲线，从而降低 DCE-FS 的灵敏度，并且由于意外的水抑制而降低动态范围。
磁场不均匀性在乳腺磁共振中很重要。
不均匀磁场会使对比剂摄取曲线变形。
放射科医生必须意识到这种扭曲的可能性，以正确解释摄取曲线。
需要在脂肪抑制和动态范围之间取得平衡。
