宮下 進^{1, 2}, 室月 淳^{2, 3}, 室本 仁^{2, 3}, 小澤 克典^{2, 4}, 長谷川 英之⁵, 金井 浩⁶

Susumu MIYASHITA^{1, 2}, Jun MUROTSUKI^{2, 3}, Jin MUROMOTO^{2, 3}, Katsusuke OZAWA^{2, 4}, Hideyuki HASEGAWA⁵, Hiroshi KANAI⁶

¹獨協医科大学総合周産期母子医療センター産科部門, ²東北大学大学院先進成育医学講座胎児医学分野, ³宮城県立こども病院産科, ⁴国立成育医療研究センター胎児診療科, ⁵富山大学大学院理工学研究部, ⁶東北大学大学院工学研究科電子工学専攻

¹Department of Obstetrics, Perinatal Medical Center, Dokkyo Medical University, ²Department of Advanced Fetal and Developmental Medicine, Tohoku University Graduate School of Medicine, ³Department of Maternal and Fetal Medicine, Miyagi Children's Hospital, ⁴Division of Fetal Medicine, National Center for Child Health and Development, ⁵Graduate School of Science and Engineering for Research, University of Toyama, ⁶Department of Electronic Engineering, Tohoku University Graduate School of Engineering

キーワード : phased-tracking method, pulse wave velocity, fetal pulse pressure, fetal growth restriction

位相差トラッキング法（phased-tracking method）は，東北大学大学院工学研究科の金井らにより開発された，微細な運動計測を可能とする次世代の超音波計測モードである．超音波探触子からの送受信により，運動している関心点の変位を観測するためには，受信信号のフレーム間の受信遅延時間の変化を検出する必要がある．位相差トラッキング法では受信した超音波RF信号の直交検波信号に相関法を適用して受信信号の位相偏移を推定することで受信信号の遅延時間の変化を高精度に検出し，関心点の微細な運動計測と追跡が可能となる．この方法では波長の制限を受けないため，高精度での計測が可能である．非侵襲的な高精度計測という特性を活かして，成人領域では動脈壁の弾性特性の推定などに応用されており，今後は胎児の循環動態評価に応用が期待される．筆者らは正常および発育不全胎児における下行大動脈の血管内径変動と，脈波伝播速度計測に位相差トラッキング法を応用し，さらに脈圧推定を試みた．発育不全胎児では脈波伝播速度と推定脈圧は有意に大きく，胎児期からの血管壁構造リモデリングによる壁特性（コンプライアンス）の変化を観察している可能性が示唆された．

The ultrasonic ‘phased tracking method’ (PTM) is a newly developed technique in which we can observe the phase difference of adjoining received RF signals. We aim to apply PTM—which enables precise measurement of the target’s velocity with 0.1 mm/s accuracy without restriction of transmitting wave length—for noninvasive measurements of fetal arterial diameter change, pulse wave velocity (PWV), and estimated fetal pulse pressure. We analyzed normal and growth-restricted fetuses using PTM. The fetal descending aorta was identified in the long axis direction using conventional B-mode with a convex array probe. Raw radiofrequency signals were recorded from the vessel wall of the descending aorta. Offline analysis was attempted for wall motion velocity waves. We employed PTM for measurement of pulsatile fine movement of the fetal descending aorta. Changes in internal diameter and PWV were analyzed. Pulse pressure was estimated from the transformed formula of Moens-Korteweg. PWVs were revealed to be significantly higher in growth-restricted fetuses. We could also demonstrate elevated estimated fetal pulse pressure in growth restriction. Measurement of fetal aortic diameter changes and fetal PWV using PTM is a feasible, noninvasive approach to evaluate fetal hemodynamics. Elevated PWV and estimated pulse pressure in growth-restricted fetuses suggest altered arterial wall compliance by histological remodeling that has already originated in the fetal period. Fetal PWV and estimated pulse pressure possibly distinguish cases at high risk for hypertensive complications later in life, which substantiates Developmental Origins of Health and Disease (DOHaD) theory.