Kuhnke M, Langner S, Khaw A V, Angermaier A, Hosten N, Kirsch M
Institut für Diagnostische Radiologie und Neuroradiologie, Universitätsmedizin Greifswald.
Rofo. 2012 Apr;184(4):303-10. doi: 10.1055/s-0031-1299103. Epub 2012 Jan 24.
Diffusion-weighted imaging (DWI) has become an important component in modern stroke imaging. This MR technique detects diffusion abnormalities, which can be quantified by computing apparent diffusion coefficient (ADC) maps. ADC values are typically calculated from a set of MR images obtained with varying degrees of diffusion weighting (b-values) using nonlinear regression. However, there is no agreement concerning the number of images needed for ADC calculation. The aim of our study was to determine how many b-values are necessary to reliably calculate ADC maps.
In 100 consecutive patients with clinical signs of acute ischemic stroke, 6 identically oriented and centered diffusion data sets with different b-values were acquired. ROI analysis was performed for DWI-positive lesions, normal-appearing gray and white matter, CSF, and background noise. ADC values for each ROI were calculated using a nonlinear regression model. Additionally, the CNR and SNR were calculated for each ROI.
Acquisition time was 0:39 min for 2 b-values and up to 2:49 min for a sequence with 7 b-values. The mean ADC (× 10(-3) mm2/s) for ischemic lesions was 58.29, 58.47, 57.83, 57.81, 57.58 and 54.51 using 2, 3, 4, 5, 6, and 7 b-values. Ischemic lesions had significantly different mean ADC values only for high b-values (b = 2000 s/mm2).
ADC values can be reliably calculated using 2 b-values. Radiologists may use the more time-efficient 2-point method for reliably estimating ADC values and detecting ischemic lesions in the daily clinical routine.
扩散加权成像（DWI）已成为现代卒中成像的重要组成部分。这种磁共振技术可检测扩散异常，通过计算表观扩散系数（ADC）图对其进行量化。ADC值通常使用非线性回归，从一组具有不同扩散加权程度（b值）的磁共振图像中计算得出。然而，关于计算ADC所需图像数量尚无定论。我们研究的目的是确定可靠计算ADC图需要多少个b值。
对100例有急性缺血性卒中临床症状的连续患者，采集6组具有相同方向且位于中心的不同b值扩散数据集。对DWI阳性病变、外观正常的灰质和白质、脑脊液及背景噪声进行感兴趣区（ROI）分析。使用非线性回归模型计算每个ROI的ADC值。此外，计算每个ROI的对比噪声比（CNR）和信噪比（SNR）。
2个b值时采集时间为0:39分钟，7个b值的序列采集时间长达2:49分钟。使用2、3、4、5、6和7个b值时，缺血性病变的平均ADC（×10⁻³mm²/s）分别为58.29、58.47、57.83、57.81、57.58和54.51。仅在高b值（b = 2000 s/mm²）时，缺血性病变的平均ADC值有显著差异。
使用2个b值即可可靠计算ADC值。放射科医生在日常临床工作中可采用更省时的两点法来可靠地估计ADC值并检测缺血性病变。
