在体乳腺组织非线性变形特征及其在静态超声弹性成像中的影响

Effects of nonlinear elasticity on ultrasound elastography of normal breast tissues

目的通过剪切波弹性成像定量研究在体乳腺组织非线性变形特征,评价非线性变形特征对乳腺组织静态超声弹性成像测量的影响,以指导和规范乳腺超声弹性成像操作方法。方法前瞻性选取自2014年1月至2014年5月于北京友谊医院超声科进行体检的女性26例。其中14例女性(8例双侧乳腺,6例单侧乳腺)纳入乳腺组织非线性变形特征的研究,12例女性(8例双侧乳腺,4例单侧乳腺)纳入乳腺组织非线性变形特征在静态超声弹性成像中的影响相关研究。采用超声剪切波弹性成像功能对乳腺组织非线性变形特征进行研究,采用超声静态弹性成像功能对乳腺组织非线性变形特征在静态超声弹性成像中的影响进行研究。计算乳腺组织的非线性参数硬化系数(b)、初始未受压状态下的剪切模量(μ0)及伸长比(λ),并绘制乳腺非线性变形特征曲线。在体乳腺组织非线性变形特征研究中,将8例受试者双侧乳腺的b及μ0按照左右两侧分组,并进行比较;将14例受试者所有乳腺的b及μ0按照相对位置不同分为乳头上方组、乳头内侧组、乳头下方组、乳头外侧组、外上象限组,并进行比较。结果14例受试者的乳腺非线性参数b=6.36±1.74,μ0=(3.01±0.47)kPa,据此绘制出反映乳腺非线性特征的曲线图,其反映乳腺组织形变与剪切模量的关系为伸长比λ值越小(乳腺的形变越大),剪切模量μ值变化越显著。8例受试者左右两侧乳腺的非线性参数b及μ0比较,差异均无统计学意义(t=0.520、0.437,P均>0.05)。14例受试者乳腺不同相对位置的非线性参数b及μ0比较,差异均无统计学意义(F=1.339、1.916,P均>0.05)。静态超声弹性成像中12例受试者,计算得出乳腺组织的最小伸长比λ=0.75±0.05,绘制反映乳腺组织形变和弹性模量增加倍数之间关系的曲线图,其反映在乳腺非线性变形达到25%时,剪切模量达到初始剪切模量的5.72倍,在变形程度达到5%时,剪切模量为未受压状态的1.10倍。结论乳腺组织的弹性模量随变形程度的增大而呈非线性增加。乳腺两侧及不同相对位置非线性弹性性质无明显差异。应用乳腺静态超声弹性成像时,需将超声探头加压导致的压缩变形控制在5%以内。

Objective To quantify the nonlinear elasticity of breast tissue to guide the manipulating mode of ultrasound elastography.Methods In this prospective study,26 women who underwent physical examination at the Department of Ultrasound of Beijing Friendship Hospital from January 2014 to May 2014 were included.Among them,14 women (8 cases of bilateral breasts and 6 cases of unilateral breast) participated in the study of non-linear breast deformation.Twelve women (8 cases of bilateral breasts and 4 cases of unilateral breast) participated in the study of non-linear deformation of breast tissue in static ultrasound elastography.We used ultrasound shear wave elastography to study the nonlinear elasticity of breast tissues in vivo (group A),and static ultrasound elastography to study effects of nonlinear elasticity on static ultrasound elastography (group B).The non-linear parameters [coefficient of hardening (b),initial shear modulus (μ0),and stretch ratio (λ)] of the breast were calculated and the non-linear deformation characteristic curve of the breast was drawn.In group A,b and μ0 of 8 subjects (bilateral breasts) were grouped according to the side of the breast and compared,while b and μ0 of 14 subjects were divided into five groups according to their positions,which were upper (relative to the nipple),medial,lower,lateral,and upper lateral quadrant groups, and compared.Results The equations for b and μ0 were:b=6.36±1.74 and μ0=(3.01±0.47) kPa.No significant difference was found in the nonlinearity of bilateral breast (bleft=6.12±1.56,bright=6.53±2.21,P=0.428). Also,F was 1.339 and 1.916 and P was 0.260 and 0.113,respectively,there was no significant difference among different relative locations (F=1.339 and 1.916,P=0.260 and 0.113,respectively).The minimum λ of the breast in static ultrasound elastography was 0.75±0.05,and the shear modulus was 5.72 times the initial value.Conclusion The elastic modulus of the breast increases nonlinearly with the decrease in the stretch ratio,implying that deformation should be controlled while applying static ultrasound elastography.