Li Yi, Casula Victor, Karjalainen Jouni, Nissi Mikko J, Liimatainen Timo
Research Unit of Health Sciences and Technology, University of Oulu, Oulu, Finland.
Department of Technical Physics, University of Eastern Finland, Kuopio, Finland.
Heart Rhythm. 2025 Jun 26. doi: 10.1016/j.hrthm.2025.06.040.
Noninvasive visualization and characterization of the atrioventricular conduction axis (AVCA) can help avoid iatrogenic injury and improve the accuracy of heart rhythm therapy guidance.
This study aimed to identify the AVCA structure using noninvasive rotating-frame relaxation-time mappings (relaxation along a fictitious field in the second rotating-frame relaxation time [T] and longitudinal rotating-frame relaxation time [T]) in ex vivo swine hearts.
Ex vivo swine heart tissue blocks were scanned on a 3T clinical magnetic resonance imaging system. The contrast among AVCA, central fibrous body, and remote myocardium was evaluated using T and T compared with T and T relaxation-time mappings and magnetization transfer imaging. Histologic sections at 4 levels were stained with Masson's trichrome. The blue channel of histology images was used for analysis. Regions of interest in the myocardium, AVCA, and central fibrous body were selected slice-wise and sample-wise using multi-Otsu thresholding. Relative relaxation-time difference and magnetization transfer contrast were calculated between AVCA and remote myocardial areas.
In the AVCA region, all quantitative magnetic resonance imaging (qMRI) parameters were significantly higher than in remote myocardium. T, T, and T showed the highest contrast between AVCA and myocardium. All qMRI parameters correlated with the blue channel of Masson's trichrome-stained histology images. Three-dimensional reconstruction of 2-dimensional T maps revealed the AVCA structure with increased relaxation time compared with the surrounding myocardium.
This research demonstrates the potential of T, T, and T for visualizing the AVCA quantitatively in the swine heart without contrast agents. The contrast provided by the qMRI parameters is based on the fibrous content of the tissue.
房室传导轴（AVCA）的无创可视化和特征描述有助于避免医源性损伤，并提高心律治疗指导的准确性。
本研究旨在利用离体猪心脏的无创旋转框架弛豫时间映射（在第二个旋转框架弛豫时间[T]和纵向旋转框架弛豫时间[T]中沿虚拟场的弛豫）来识别AVCA结构。
在3T临床磁共振成像系统上对离体猪心脏组织块进行扫描。与T和T弛豫时间映射及磁化传递成像相比，使用T和T评估AVCA、中央纤维体和远端心肌之间的对比度。对4个层面的组织切片进行Masson三色染色。组织学图像的蓝色通道用于分析。使用多Otsu阈值分割逐片和逐样本选择心肌、AVCA和中央纤维体中的感兴趣区域。计算AVCA与远端心肌区域之间的相对弛豫时间差和磁化传递对比度。
在AVCA区域，所有定量磁共振成像（qMRI）参数均显著高于远端心肌。T、T和T在AVCA与心肌之间显示出最高的对比度。所有qMRI参数均与Masson三色染色组织学图像的蓝色通道相关。二维T图的三维重建显示AVCA结构的弛豫时间比周围心肌增加。
本研究证明了T、T和T在无需造影剂的情况下对猪心脏中AVCA进行定量可视化的潜力。qMRI参数提供的对比度基于组织的纤维含量。
