Gaarder Mario, Seierstad Therese
Department of Radiology and Nuclear Medicine, Oslo University Hospital, P,O, Box 4950, Nydalen 0424, Oslo, Norway.
Cardiovasc Ultrasound. 2015 Jan 27;13:5. doi: 10.1186/1476-7120-13-5.
Carotid intima media thickness (CIMT) measured with ultrasound (US) is widely used as biomarker for arteriosclerosis and as surrogate endpoint in interventional studies to assess efficacy of drug therapies. Strict US protocols are necessary to ensure reproducibility. The range of US signal intensities used for image formation, the dynamic range (DR), is rarely reported in studies and little is known about its effect on CIMT measurements in humans. The purpose of this study was to quantify the impact of DR on measurements of CIMT.
US was used to examine 313 carotid arteries in participants from two different clinical studies. For each artery, images with DR of 40, 55, 70 and 85 dB were captured from the same frozen US frame. Mean CIMT (CIMTmean), maximum CIMT (CIMTmax) and standard deviation of CIMT (CIMTsd) were obtained for all images. CIMT for different DRs were compared using student t-test.
CIMTmean for 40, 55, 70 and 85 dB were 0.529, 0.564, 0.590 and 0.605 mm respectively. For CIMTmax the corresponding values were 0.626, 0.667, 0.698, and 0.716 mm. CIMTmean and CIMTmax increased significantly for increasing DR steps (p < 0.01). The relative change in CIMTmean and CIMTmax were largest between 40 and 55 dB (6.7% and 7.0%) and smallest between 70 and 85 dB (2.6% and 2.7%) indicating a declining dependency for increasing DR.
DR significantly changes CIMT measurements and the changes are most prominent for lower DRs. The effect of changing DR is larger in human arteries than in phantoms. Reporting the DR will therefore increase the validity of CIMT data.
用超声（US）测量的颈动脉内膜中层厚度（CIMT）被广泛用作动脉硬化的生物标志物以及介入研究中评估药物治疗疗效的替代终点。严格的超声检查方案对于确保可重复性是必要的。用于图像形成的超声信号强度范围，即动态范围（DR），在研究中很少被报道，并且对于其对人体CIMT测量的影响知之甚少。本研究的目的是量化DR对CIMT测量的影响。
使用超声对来自两项不同临床研究的参与者的313条颈动脉进行检查。对于每条动脉，从同一冻结的超声图像帧中获取动态范围为40、55、70和85分贝的图像。获取所有图像的平均CIMT（CIMTmean）、最大CIMT（CIMTmax）和CIMT的标准差（CIMTsd）。使用学生t检验比较不同DR下的CIMT。
40、55、70和85分贝时的CIMTmean分别为0.529、0.564、0.590和0.605毫米。对于CIMTmax，相应的值分别为0.626、0.667、0.698和0.716毫米。随着DR步长增加，CIMTmean和CIMTmax显著增加（p < 0.01）。CIMTmean和CIMTmax的相对变化在40至55分贝之间最大（6.7%和7.0%），在70至85分贝之间最小（2.6%和2.7%），表明随着DR增加依赖性下降。
DR显著改变CIMT测量值，并且这种变化在较低DR时最为显著。改变DR的影响在人体动脉中比在体模中更大。因此，报告DR将提高CIMT数据的有效性。
