肝細胞內顯影劑之動態磁振造影於慢性肝病纖維化的探討與功能性評估

Dynamic contrast-enhanced magnetic resonance imaging with hepatocyte -selective contrast agent in the evaluation of the extent and severity of liver fibrosis in patients with chronic liver disease

陳邦斌(Bang-Bin Chen)

指導教授 ： 施庭芳

國立臺灣大學/醫學院/臨床醫學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.02991

摘要

前言：
肝臟纖維化是慢性B肝或C 肝患者常見的變化，並會逐漸進展成肝硬化，造成門脈高壓、腹水、食道靜脈瘤等併發症，因此，如何早期診斷出肝纖維化是預防疾病惡化的重要課題。目前對於肝臟纖維化的診斷和分期的黃金標準是肝臟切片取樣。但是，肝臟切片取樣為一種侵入性檢查而且有潛在的危險性。目前有許多非侵入性檢查，希望可以取代肝臟切片的侵入性診斷方式，包括超音波、電腦斷層和磁振造影檢查。但是這些檢查對於早期肝硬化或輕微纖維化的偵測都不夠靈敏。
顯影劑注射增強動態影像為功能性影像，可計算出組織內血流的動力參數和灌流參數。Gd-EOB-DTPA為一肝臟特異性磁振造影顯影劑，其分子具肝特異性，所以可選擇性進入肝細胞內，再由膽汁排出。肝纖維化會影響血流和從小動脈到竇狀血管到靜脈之灌流，也會作用在竇狀血管到肝細胞之間。因此，我們假設該藥物在肝臟的顯影，會受肝纖維化影響其由竇狀血管進入肝細胞的速度及含量，若肝纖維化的程度越嚴重，肝臟顯影程度會越低，由於肝臟顯影速度及程度的不同，可以用顯影劑注射增強動態磁振造影來診斷和分期肝纖維化。
研究目的：
我們目的是對正常人和切片證實有肝病之患者做其磁振造影參數之比較。利用此顯影劑可分佈血管內和血管外細胞間隙的特性，配合顯影劑注射增強動態影像，來瞭解肝纖維化時肝臟血流動力的改變，計算不同血流參數的分佈和大小，並和組織切片的Metavir分期做比較，希望能得到肝臟纖維化整體的程度和範圍。利用此顯影劑可選擇性進入肝細胞的特性，計算不同時間後肝臟和總肝膽管顯影訊號的變化，並和組織切片的分期做比較，得到肝功能的改變和纖維化程度的關係。
研究方法與步驟：
我們收集了21 位健康受試者和58位慢性B肝或C肝患者，以肝臟特異性磁振造影顯影劑，配合顯影劑注射增強動態影像，進行肝臟磁振造影檢查。健康受試者為14位男性，7位女性，平均年齡39.1 ±2.7歲；病例組為慢性B肝或C肝患者且接受肝切片證實有慢性肝病者，41位男性，17位女性，平均年齡42.4 ±1.4歲，磁振造影在肝臟切片後2週內進行。由病理科醫師根據肝切片結果獨立判讀肝纖維化之 Metavir分數。其中10位健康受試者在一年後接受施打傳統顯影劑之動態影像肝臟掃瞄，來比較傳統顯影劑和肝內顯影劑的差別。
肝臟掃瞄包括一般T1、 T2權重影像，之後進行顯影劑注射增強動態影像檢查，使用注射器從肘前靜脈依穩定速度將顯影劑注入人體，切面為斜冠狀切面，需同時包含主動脈和肝門脈；使用的是渦輪梯度序列，速度為每張0.2秒，共持續100秒，來分析血流動力和灌流之改變。在此之後50分鐘，將進行平衡時期之肝臟掃瞄，每分鐘會掃瞄肝臟一次，橫切面和冠狀切面輪流掃瞄。全部掃瞄時間會在一小時內完成。
分析方式包括肝臟纖維化肉眼判讀分析，顯影劑注射增強動態影像之血流參數分析，和肝臟平衡時期之顯影訊號曲線參數分析。我們先分析健康組和病例組之血流和顯影曲線參數是否有顯著差別，再根據纖維化程度分為三組，分析三組間參數是否有差別。
研究結果：
在肝臟纖維化肉眼判讀分析方面，用肉眼不易判讀纖維化嚴重程度。
在顯影劑注射增強動態影像之分析方面，比起健康人，病患的肝動脈灌流會上升，分佈體積在顯影劑進入肝細胞後會減少，顯影曲線的面積、曲線寬度、平均通過時間都較小。而纖維化越嚴重，曲線的上升斜率會越小，曲線下面積也會越小。
在肝臟和總肝膽管顯影訊號的變化方面，比起健康人，病患的肝臟顯影訊號曲線面積較小，但顯影比率上升。總膽管訊號曲線的參數則無顯著差別。若纖維化越嚴重，在肝臟平衡時期肝臟的顯影訊號會越低。
在傳統顯影劑和肝特異性顯影劑之比較方面，顯示在60秒前，肝內顯影劑大部分仍在肝細胞外，血流參數和傳統顯影劑無顯著差別；在100秒時，肝內顯影劑已大量進入肝細胞，血流參數和傳統顯影劑不盡相同，有其獨特之變化。
討論：
由於用肉眼難以判斷肝纖維化的嚴重程度，我們利用動態顯影技術的血流參數和肝特異性顯影劑的顯影訊號強度來做分級。我們發現在動態顯影和肝臟平衡時期，病例組的肝臟顯影速度和強度會比健康組小，因此在許多參數上，包括曲線面積、寬度和平均時間等都比健康組低，符合我們的假設，即肝纖維化會造成肝臟顯影訊號下降，而纖維化越嚴重，訊號下降越多。
在注射肝內顯影劑60秒內，此顯影劑大部分仍在細胞外空間，其分佈和傳統顯影劑相同。在60~ 100秒間時肝內顯影劑會大量從細胞間質進入肝細胞。分佈體積代表顯影劑停留在肝臟的體積。傳統顯影劑在100秒其分佈體積代表間質組織（即纖維化組織）；肝內顯影劑在100秒其分佈體積代表肝細胞。因此兩者在100秒時所計算出來的分佈體積會不同。
結論：
顯影劑注射增強動態肝臟磁造振影檢查是個非侵入性、具重現性且可定量的方法，配合肝特異性顯影劑，它可對肝纖維化之範圍及程度提供詳細之定量分析。此方式可進一步發展為替代標記、獨立的分類方式或是病理肝纖維化分期之間接參考依據。未來可利用此非侵入性檢查，結合分子影像扮演細胞內生物標記的角色，或配合抗纖維化藥物的使用，追蹤評估肝臟纖維化和肝功能的變化。

關鍵字

顯影劑注射增強動態肝臟磁造振影影像 ； Gd-EOB-DTPA肝特異性顯影劑 ； 肝纖維化

並列摘要

Chronic liver disease is an important disease in Taiwan. A large percentage of these patients will develop chronic hepatitis, liver fibrosis and cirrhosis and then hepatic tumors. The evaluation of liver fibrosis currently needs pathological grading from the invasive biopsy procedure. Noninvasive imaging of liver fibrosis would reduce biopsy-related risks and costs and thus potentially eliminate sampling errors and enable global liver assessment. Although the presence of cirrhosis can be confirmed by using ultrasonography, computed tomography, and magnetic resonance imaging, these findings are insensitive in the detection of early cirrhosis and milder fibrosis.
The possibility of noninvasively diagnosing cirrhosis on the basis of the hepatic texture alterations seen on contrast material–enhanced MR images has been suggested. After injection of superparamagnetic iron oxides or gadolinium chelates, hyperintense reticulations can be observed against the hypointense liver background. Besides, the delayed distribution of extracellular gadolinium chelates in fibrotic tissue is well documented. For these reasons, it may be possible to diagnose cirrhosis and grade liver fibrosis on gadolinium-chelated agent on the basis of hepatic texture alterations.
The current image modalities such MRI with extra-cellular contrast agents could only detect the liver with abnormal vascularity or tumor formation. Gd-EOB-DTPA is hepatocyte-specific contrast agent, which distributed through the blood vessel to the intravascular, extra-vascular interstitial space and intracellular space of hepatocyte. Thus, the effectiveness and enhancement pattern will be influenced by the degree of liver fibrosis. Because Gd-EOB-DTPA is taken up selectively into normal hepatocytes and subsequently excreted into the bile, this agent is particularly advantageous for differentiating between normal tissue and abnormal liver tissue such as chronic liver disease.
The purpose of our study is to develop a non-invasive method for evaluation of liver fibrosis by using comprehensive dynamic contrast-enhanced MR imaging (DCE-MRI) using Gd-EOB-DTPA, with histologic analysis as reference standard.
DCE-MRI with Gd-EOB-DTPA was performed in 79 subjects (healthy group, 21 subjects, 14 male, 7 female, mean age, 39.1 years；hepatitis group, 41male, 17 female, mean age, 42.4 years). The following estimated perfusion parameters were measured with a dual-input single-compartment (Van Beers) model: absolute arterial blood flow (Fa), absolute portal venous blood flow (Fp), absolute total liver blood flow (Ft) (Ft = Fa + Fp), arterial fraction (ART), distribution volume (DV), and mean transit time (MTT) of Gd-EOB-DTPA. The curve analysis model uses parameters including Peak, slope, area under curve(AUC), full width at half maximum (FWHM), and mean time (MT) to evaluate the signal-intensity curve of liver after injection of Gd-EOB-DTPA.
These 79 subjects were assigned into three groups according to fibrotic stage. The AVONA and the nonparametric Kruskal-Wallis test were used to compare perfusion and curve parameters between groups. There was an increase in Fa, ART, and a decrease in DV, AUC, FWHM and MT in hepatitis group compared with healthy group. The slope and AUC were lower in advanced fibrosis group compared with those without fibrosis.
In hepatic equilibrium phase (2~50 minutes after injection of Gd-EOB-DTPA), the signal of liver and common hepatic ducts were measured. We use parameters including average signal (Ave), maximal enhanced signal (Max), maximal enhanced ratio (Max %) and summed signal (Sum) to evaluate the signal-intensity curve of liver and common hepatic duct. There was an increase in Max %, and a decrease in Sum in hepatitis group compared with healthy group. The Ave was lower in advanced fibrosis group compared with those without fibrosis.
The perfusion parameters of DCE-MRI with Gd-EOB-DTPA and Gd-DTPA were compared in 10 healthy subjects. At 60 seconds after injection, there was no significant difference of perfusion parameters between these two contrast agents. At 100 seconds after injection, there was a decrease in Ft, and an increase in DV and MT in Gd-EOB-DTPA compared with those using Gd-DTPA. These findings implied that Gd-EOB-DTPA entered hepatocytes in a large mount at 100 seconds after injection.
Collagen deposition in the space of Disse is associated with restricted diffusion of Gd-EOB-DTPA in the extravascular space and its transportation into the liver in fibrotic and cirrhotic livers; thus, there is an expected decrease in signal enhancement throughout the liver. The distribution volume, reflects hepatocyte volume, is also decreased in liver with hepatitis and fibrosis.
In conclusion, we found that DCE-MRI with Gd-EOB-DTPA is a feasible and noninvasive imaging modality in which multiple perfusion and curve parameters can be measured and potentially used as biomarkers of liver fibrosis. The development of noninvasive imaging methods to detect and grade fibrosis throughout the entire liver would represent a major advance in the understanding of liver disease. These capabilities would enable serial follow-up of patients and assessment of therapy response; and serve as a powerful research tool for therapy development.

並列關鍵字

DCE-MRI ； Gd-EOB-DTPA ； Liver fibrosis

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