乳腺弥散加权成像的原理和临床应用.ppt

Diffusion-weighted Imaging of the Breast:Principles and Clinical Applications,何杰 2013年12月25日,乳腺弥散加权成像：原理和临床应用,Diffusion-weighted imaging is a modality that makes use of magnetic resonance(MR)imaging to depict the diffusivity of water molecules in a defined voxel by means of the application of motion-probing gradients.This imaging property is unique and provides a different contrast mechanism than that observed on conventional T1-and T2-weighted MR images.Evaluation of breast images acquired with sensitization to the diffusion of water molecules has the potential to play an adjunct role in the assessment of breast tissue.DWI是一种通过运动-探测梯度磁场的应用的方式，在一个有限的像素内，利用磁共振来检测水分子弥散的方法。这种成像方式是唯一，并且与常规的T1和T2加权MR图像相比，提供一个不同的对比机制。乳腺图像的获取来源于对水分子的扩散敏感，其拥有在乳腺组织的评估中发挥辅助作用的潜力。,Introduction,Diffusion-weighted imaging was initially applied in the clinical setting in the mid-1990s for the diagnosis of acute stroke.At that time,diffusion-weighted imaging demonstrated a high diagnostic utility,not only in the investigation of acute stroke,but also in developing the differential diagnosis for other brain abnormalities,including tumors and abscesses.弥散加权成像在临床上最初的应用是90年代中期对急性脑卒中的诊断，不仅用于检测急性脑卒中，而且发展到别的脑部异常病变的鉴别诊断，包括肿瘤和脓肿。,Introduction,Subsequent technical advances in MR imaging,including the development of ultrafast imaging sequences and the proliferation of array coils and of imagers with higher magnetic field strength(which increase signal-to-noise ratio SNR per unit time)have led to a reduction in the impact of motion artifacts and the investigation of organs other than the brain.在MR成像随后的技术进步，包括超快成像序列的发展和较高磁场强度阵列线圈和成像器的发展（这提高了每单位时间的信噪比），导致了运动伪影的影响的减少,Introduction,Diffusion-weighted imaging has subsequently been used in the evaluation of disease processes in various anatomic locations(eg,chest,liver,pancreas,prostate gland)that had previously not been studied due to difficulties resulting from movement during patient respiration,peristalsis,and low inherent SNR.弥散加权成像随后被用于不同的解剖部位疾病过程的评价（如胸部，肝脏，胰腺，前列腺），这些以前从未研究过，因为病人呼吸，蠕动所导致的困难和低的信噪比。,Introduction,In 1997,Englander et al addressed the possibility of applying diffusion-weighted imaging to the human breast.Since that time,clinical studies have been undertaken,and several studies have shown diffusion-weighted imaging to be highly sensitive for the evaluation of breast cancer and a possible means of differentiating between benign and malignant tumors 在1997年，Englander等人探讨了DWI应用于人体乳腺的可能性。从那时起，一些临床研究开始进行，并且一些研究表明DWI在评估乳腺癌上有高的敏感性，是一种鉴别诊断良恶性肿瘤的可能的方法。,Introduction,As a result of these findings,diffusion-weighted breast imaging has attracted greater interest among breast imagers,with many clinicians advocating applications beyond just clinical research.However,the incorporation into clinical decision making of information gleaned from diffusion-weighted breast imaging has been slow compared to the use of information obtained from diffusion-weighted imaging of other organs.由于这些发现，乳腺弥散加权成像吸引了乳腺影像学家越来越多的注意，许多医生主张应用不仅仅是临床研究。然而，与其他器官的弥散加权图像的使用相比，应用在乳腺上比较缓慢。,Introduction,One reason is that the diagnostic role of diffusion-weighted imaging in breast imaging has not been incorporated into the already established Breast Imaging and Reporting Data System lexicon(11).Contrast materialenhanced breast MR imaging is currently accepted as the most sensitive imaging technique for the diagnosis and staging of breast cancer.However,several studies have noted that conventional breast MR imaging,including T2-weighted imaging and contrast-enhanced T1-weighted imaging,is limited in terms of specificity in the assessment of breast tumors原因之一是弥散加权成像在乳腺成像上的诊断作用还没有纳入到已经确定的BI-RADS系统中。对比增强乳腺磁共振是目前公认是最敏感的用于乳腺癌诊断和分级的成像技术。然而，然而，一些研究表明常规乳腺磁共振成像，包括T2加权像和T1对比增强磁共振在评价乳腺肿瘤的特异性方面作用有限。,Introduction,Consequently,there has been considerable interest in the development of adjunct MR imaging methods to improve the specificity of dynamic contrast-enhanced breast MR imaging,and diffusion-weighted breast imaging is being investigated for its potential to improve breast disease diagnosis at the cost of a small increase in examination time.因此，在发展辅助磁共振成像方法用来提高动态对比增强乳腺磁共振的特异性上，引起了研究者很大的兴趣，研究者正在研究DWI乳腺成像，探讨其耗费最小的检查时间增加乳腺疾病诊断率的潜力。,Introduction,In this PPT we discuss the principles of diffusion-weighted imaging,offer suggestions for optimizing diffusion-weighted breast imaging technique,and discuss the clinical implementation of diffusion-weighted breast imaging.在这个PPT里，我们讨论DWI的原理，提出优化DWI乳腺成像技术的建议，并且讨论DWI乳腺成像的临床应用,Introduction,Principles of Diffusion-weighted Imaging,DWI的原理,Proton Diffusion in Biologic Tissue,Diffusion is the random and thermal(Brownian)motion of water molecules(or any other type of molecule).This motion is affected by the local tissue environment and the presence of barriers(eg,cell membranes and semipermeable membranes).The motion of water molecules is more restricted in tissues with a high cellular density 弥散是水分子（或其他分子类型）的无规则的热运动（布朗运动）。这种运动受局部组织环境和障碍的影响（如细胞膜和半透膜）。组织中的水分子的运动在细胞外和细胞内空间中更受限，如果细胞密度较高或者有亲脂性细胞膜作为障碍。,Proton Diffusion in Biologic Tissue,In contrast,the motion of water molecules is less restricted in areas of low cellularity or where cell membranes have been destroyed.A less cellular environment provides a larger extracellular space for the diffusion of water molecules,which may also freely transgress defective cell membranes to move from the extracellular into the intracellular compartment.Therefore,the degree of water diffusion in tissue is inversely correlated with tissue cellularity and the integrity of cell membranes.相比之下，水分子的运动在低的细胞密度或者细胞膜被破坏的区域受限较少。一个不完整的细胞环境为水分子的弥散提供一个大的细胞外空间，这也方面水分子从细胞外进入细胞内隔室。因此，水分子在组织中弥散的程度与组织的细胞密度和细胞膜的完整性呈负相关。,Proton Diffusion in Biologic Tissue,Diffusion-weighted imaging is used to visualize the degree of water molecule diffusion at in vivo MR imaging.Signal intensity at diffusion-weighted imaging is inversely proportional to the degree of water molecule diffusion,which will be influenced by the histologic structure;in other words,the signal intensity will imply the histologic structure.弥散加权成像用于在体磁共振中监测水分子扩散的程度。DWI里信号强度与水分子弥散的程度呈反比，其受组织学结构的影响；换句话说，信号强度将反映组织学结构。,Proton Diffusion in Biologic Tissue,Diffusion is quantified by measuring what is known as the apparent diffusion coefficient(ADC)value in square millimeters per second,which defines the average area covered by a molecule per unit time.The ADC value can be calculated by assessing the signal attenuation that occurs at diffusion-weighted imaging performed at different b values.扩散通过测量众所周知的表观扩散系数值（平方毫米每秒）来进行定量，这被定义为每单位时间一个分子覆盖的平均面积。ADC值通过评估施加不同b值弥散加权成像的信号强度来计算。,Technical Considerations,Spin-echo echoplanar diffusion-weighted imaging is the most popular clinical technique for generating diffusion-weighted images.To introduce diffusion weighting into a spin-echo echoplanar imaging sequence,two diffusion-sensitizing gradients are“sandwiched”around a 180 radiofrequency(RF)refocusing pulse before echoplanar imaging data collection(Fig 1).自旋回波平面扩散加权成像是目前最流行的产生弥散加权图像的临床技术。为了把弥散加权引入自旋回波平面成像序列，在回波平面图像数据收集之前，两个弥散致敏梯度夹在180度射频（RF）聚焦脉冲周围,Figure 1.Graph illustrates the pulse sequence of single-shot spin-echo echoplanar diffusion-weighted imaging.G=gradient,MPG=motion-probing gradient.该图说明了单次自旋回波平面弥散加权成像的脉冲序列。G=梯度，MPG=运动探测梯度,CorrelationbetweenSignal Intensity,bValue,andADCValue,Signal Intensity and bValueSignal intensity at diffusion-weighted imaging is influenced by b value according to the following equation,which is modified from Equation 1:SDW=SSE(expb D)(1 expTR/T1)exp(TE/T2)exp(b D),(4)where D is the diffusion coefficient,SDW is the attenuated spin-echo signal,SSE is the full spin-echo signal without diffusion attenuation,and r is the spin density在弥散加权图像中，信号强度通过下面的公式受b值的影响，这个公式由公式1所改写：SDW=SSE(expb D)(1 expTR/T1)exp(TE/T2)exp(b D)，在这里D是弥散系数，SDW是衰减自旋回波信号，SSE是没有任何弥散衰减的完全性自旋回波信号，r是自旋密度。,CorrelationbetweenSignal Intensity,bValue,andADCValue,According to this equation,the signal intensity at diffusion-weighted imaging consists of T2-weighted signal and diffusion-weighted signal.The latter is emphasized with the application of higher motion-probing gradients.On the other hand,T2-weighted signal will be emphasized at lower b values(T2 shine-through effect).In addition,the signal intensity at diffusion-weighted imaging will decrease as b value increases;thus,an SNR that is sufficient for lesion detection must be provided while emphasizing the contribution from the diffusion coefficient alone because of their“trade-off”relationship(Fig 2)通过这个公式可知，弥散加权成像的信号强度包括T2加权信号和弥散加权信号。后者强调较高运动探测梯度的应用。另一方面，T2加权信号在低b值时比较明显（T2透射效应）。另外，弥散加权成像的信号强度将随着b值的提高而降低；因此，在提供一个足以检测出病灶的SNR的同时必须要着重弥散成分的贡献，因为它们之间的“矛盾关系”,Figure2.Diffusion-weighted images of a phantom,obtained at b values of 1000(a),1750(b),and 2000(c)sec/mm2,show how the signal intensity of water(W)and detergent(D)decreases as b value increases.The signal intensity of detergent remains high until b=1750 sec/mm2,whereas the signal intensity of water is close to the noise level at b=2000 sec/mm2.This is because detergent has a higher viscosity than water.水模的弥散加权图像，分别为1000(a),1750(b),and 2000(c)sec/mm2，显示了水模（W）和洗涤剂模型（D）的信号强度如何降低当b值提高。洗涤剂的信号强度直到b=1750 sec/mm2依旧保持很高，然而水的信号强度在b=2000 sec/mm2接近于噪声水平。这是因为洗涤剂比水有更高的粘度。,CorrelationbetweenSignal Intensity,bValue,andADCValue,Identification of a discrete breast lesion is mandatory for evaluating its ADC value,and doing so requires sufficient contrast resolution to differentiate the breast lesion from the adjacent breast parenchyma.Kuroki and Nasu compared the signal intensity of the normal mammary gland with that of breast cancer at various b values to establish the optimal b value.乳腺病变的鉴别是评估其ADC值，这样需要足够的对比度来鉴别诊断乳腺病变和邻近的乳腺实质。Kuroki 和 Nasu比较了不同b值下正常乳腺和乳腺癌的信号强度，以确定最佳的b值。,CorrelationbetweenSignal Intensity,bValue,andADCValue,In their study,a b value of 1000 sec/mm2 was considered optimal for diffusion-weighted breast imaging,since the signal of the normal mammary gland is suppressed and the signal of breast cancer is sufficiently high to allow detection and evaluation.On the other hand,the authors stated that the signal of the mammary gland might not be suppressed at b=1000 sec/mm2 in cases of severe fibrocystic disease(9),and recent studies have documented the usefulness of a b value of 1500 sec/mm2.在他们的研究中，b值为1000 sec/mm2被认为最适合于弥散加权乳腺成像，因为正常乳腺的信号被抑制及乳腺癌的信号足够高来用于检测和评价。另一方面，作者指出b值为1000 sec/mm2时，严重的纤维囊性疾病的乳腺组织的信号将不会被抑制，最近的研究已经证明b值等于1500 sec/mm2的有用性。,Figure 3 Ductal carcinoma in situ(DCIS)in the left breast.Diffusion-weighted images obtained at b values of 500(a),1000(b),and 1500(c)sec/mm2 show that the signal intensity of normal breast parenchyma decreases with increasing b value.The signal intensity of DCIS in the right breast(arrows)is conspicuous relative to the decreased signal intensity of normal breast parenchyma in b,and the signal intensity of normal breast parenchyma in the left breast is close to the noise level in c.左侧乳腺导管原位癌（DCIS）。b值分别为500,1000,1500 sec/mm2的弥散加权图显示正常乳腺实质的信号强度随着b值的升高而降低。b图中，相对于正常乳腺实质信号强度的降低，左乳导管原位癌的信号强度较显著。C图中左乳正常乳腺实质的信号强度接近于噪声水平,CorrelationbetweenSignal Intensity,bValue,andADCValue,Recent studies have documented that the signal decay fits the multiexponential model in vivo at higher b values,in which each compartment has different ADC values.The simplest model is the intracellular-extracellular compartments model,which is applied to the brain and prostate gland(Fig 4)最近的研究已经证明，高b值时，在体内信号衰减适合多指数模型，在多指数模型中，每个隔室具有不同的ADC值。最简单的模型是细胞内-细胞外隔室模型，其将适用于脑和前列腺,Figure 4.Simulations of single-compartment and two-compartment models with extracellular free diffusion and intracellular restricted diffusion.Graph illustrates the correlation between S/S0(S=signal intensity with diffusion,S0=signal intensity without diffusion)and b value,expressed as S/S0=f1(expb D1)+f2(expb D2),where D1=extracellular diffusion coefficient,D2=intracellular diffusion coefficient,f1=extracellular volume fraction,and f2=intracellular volume fraction.Parameters were as follows:D1=1.0 10-3 mm2/sec,D2=0.1 10-3 mm2/sec,f1=0.7,and f2=0.3.单室模型和双室模型（细胞外自由弥散和细胞内受限弥散）。图显示了S/S0（S是弥散的信号强度，S0是没有弥散的信号强度）与b值的关系，其公式以 S/S0=f1(expb D1)+f2(expb D2)表示，在这里D1是细胞外弥散系数，D2是细胞内弥散系数，f1是细胞外体积分数，f2是细胞内体积分数。参数如下：D1=1.0 10-3 mm2/sec,D2=0.1 10-3 mm2/sec,f1=0.7,and f2=0.3,CorrelationbetweenSignal Intensity,bValue,andADCValue,The important point is that ADC values can be influenced by which b values are applied,a fact that highlights the need for consistent and standardized protocols.Figure 5 illustrates the decrease in ADC value with a change in b value in various diseases.最重要的一点是，ADC值受b值的影响，这个事实强调了对扫描机器标准一致性和标准化的需要。图7显示在不同疾病随着b值的变化，ADC值的降低。,Figure5.Changes in ADC value versus changes in b value.Diffusion-weighted images were obtained at b values of 500,750,1000,and 1500 sec/mm2,and the ADC value at each b value was calculated from the signal intensity of diffusion-weighted images obtained at each b value and at b=0 sec/mm2.All cases show a decrease in ADC value with an increase in b value.ADC值的改变和b值的改变。b值分别为500,750,1000,and 1500 sec/mm2的弥散加权图，每个b值下的ADC值由b值为0及每个b值下的弥散加权图的信号强度计算。所有的病例显示随着b值的增加，ADC值降低。,Normal Breast Parenchyma,Variation in the signal intensity and ADC value of normal breast parenchyma is observed due to normal hormonal fluctuations throughout the menstrual cycle and differences in individual physiologic and biochemical makeup(52).In women with normal menstrual cycles,ADC values decrease in week 2 and increase during week 4,although these differences do not reach statistical significance.正常乳腺实质在信号强度和ADC值上的变化的原因是整个月经周期正常荷尔蒙波动和个体的差异。正常生理周期的女性，在第二周ADC值降低，在第四周ADC值升高，尽管这些差异没有达到统计学意义。,Normal Breast Parenchyma,This phenomenon is thought to be due to an increase in the water content of the breast during the second half of the menstrual cycle,with ADC values reaching a peak a few days before the onset of menstruation.The reduced ADC value in week 2 of the menstrual cycle is thought to correlate with reduced water content in the breast during this time 这种现象被认为是由于月经周期的第二阶段，乳腺含水量的增加，伴随着月经前几天ADC值达到高峰。月经周期的第二周时ADC值下降被认为与乳腺在这个时期含水量的降低有关。,Normal Breast Parenchyma,It has been found that there is an increased rate of false-positive findings at contrast-enhanced breast MR imaging during weeks 1 and 4 of the menstrual cycle(54).Therefore,it is recommended that contrast-enhanced breast MR imaging be performed during week 2 of the cycle.目前已经发现在对比增强乳腺磁共振上，月经周期的第一周和第四周假阳性结果的发生率会增加。因此，建议在月经周期的第二周施行对比增强乳腺磁共振,Normal Breast Parenchyma,In contrast,owing to the lower ADC value of normal breast parenchyma at this time,the difference in signal contrast and ADC value between the normal breast and breast tumor may be smaller in week 2 of the cycle;therefore,diffusion-weighted imaging of the breast may not be appropriate in week 2.Figure 6 shows changes in signal intensity and ADC value during the menstrual cycle.与此相反，由于正常乳腺组织在这个时期ADC值较低，所以在月经周期的第二周，正常乳腺和乳腺肿瘤之间信号对比和ADC值的不同将减小；因此，在第二周施行乳腺弥散加权成像也许并不合适。图8显示了在月经周期期间信号强度和ADC值的变化。,Figure 6.Changes in signal intensity and ADC value during the menstrual cycle in a 27-year-old woman.A focal asymmetric density was seen a