氫原子核磁振造影在肺部微灌流影像之技術與應用

Abstract

肺部的微灌流狀況在肺功能中扮演著重要的角色，因為肺部的區域血流供應與氣體供應是否良好匹配決定了氧氣的交換效率。目前在臨床上是使用核子醫學來量測肺部區域血流供應，其測量原理是利用具有放射性的大型聚合物，對比劑粒子直徑略大於微血管，因此由靜脈注入後會卡在肺部微血管中，可以提供區域血流狀況。近年來由於磁振造影的技術進步，磁振影像亦可用來量測肺部微灌流。在本篇論文中，我們將介紹磁振造影的微灌流影像的兩種技術，一種是利用注射對比劑後快速取得的動態磁振影像，另一種方法則不需打入對比劑，而是標記流入的動脈磁矩，藉由標記前後的影像差距來量測微灌流。我們將這兩種方法應用在健康受試者上，證明在當影像切面是在冠狀切面的時候，有些切面的流入磁矩無法正確標記，造成動脈標記法對於血流的低估，量測的結果與對比劑顯影法不一致；因此，在肺部使用動脈標記法，必須小心使用，以免造成誤判。此外，在血流供應不正常的患者方面，譬如患有先天性心臟病的患者，我們發現基於造影原理的差異，磁振造影的對比劑顯影法與核子醫學可能會得到不一致的結果，我們對此則提出限制積分法來修正磁振造影的血流計算方法，並證明此方法量測到與核醫一致的結果。我們認為磁振造影有助於肺部微灌流的量測，未來在臨床上的應用將越來越廣闊。

Pulmonary perfusion is a fundamental parameter of lung function, since matched distribution of the regional pulmonary blood flow and ventilation is a prerequisite for gas exchange to occur efficiently. Radionuclide techniques using intravenous administration of radioactive macroaggregates have been used for the clinical assessment of regional lung perfusion. Recently, magnetic resonance imaging has become feasible using ultra-short echo time sequence. In this thesis, we present recent advances in magnetic resonance pulmonary perfusion imaging, including magnetic resonance perfusion imaging using gadolinium contrasts agents (CE-MRI) or spin labeling of blood using naturally flowing spins as the source of intravascular signal (ASL). First, we apply flow-sensitive alternating inversion recovery (FAIR) and CE-MRI techniques in normal subjects, and demonstrate that FAIR imaging for pulmonary perfusion in the coronal plane provides equivalent rPBF information with CE-MRI only in the absence of tracer saturation effects, hence, FAIR should be carefully exercised to avoid misleading interpretations. Second, we show that discrepancy exists between lung perfusion scintigraphy (PS) and CE-MRI, resulted from the abnormal flow dynamic in patients with complex cardiovascular circulation such us patients with congenital heart diseases. A remedy using limited integration has been proposed, which provides consistent perfusion result as PS. We conclude that CE-MRI is facilitate in pulmonary perfusion and has significant potential for clinical use.