Pavone P, Laghi A, Catalano C, Panebianco V, Pediconi F, Fabiano S, Passariello R
Istituto di Radiologia, Università degli Studi La Sapienza, Policlinico Umberto I. Roma, Italia.
Tumori. 1999 Jan-Feb;85(1 Suppl 1):S6-10.
The role of MR imaging in the assessment of pancreatic adenocarcinoma is in identification, characterization and staging of the neoplastic lesion. Technique optimization is required in order to obtain high qualities images competitive with spiral CT. The choice of imaging protocol is strictly related to the available equipment as well as fast imaging capabilities. Contrast-enhanced study using breath-hold sequences is required if working at high field strength with high gradient performance; on mid-low field strength nonbreath-hold acquisition techniques, using respiratory compensation techniques, can be implemented. The use of fat saturation pulses may increase the sensitivity of MR in detecting pancreatic lesions. Other advantages of MR imaging are represented by the availability of additional noninvasive techniques for the evaluation of the biliary tree (MR-cholangiopancreatography) and splanchnic vessels (MR-angiography). Lesion identification is based on TIw sequences where the lesion appears hypointense compared with the surrounding pancreas; increased lesion-pancreas contrast is obtained when fat suppression is used. On dynamic studies following gadolinium injection, pancreatic tumors are hypovascular compared with surrounding normal pancreatic gland. Problems in correctly defining the size of the lesions may be encountered in patients presenting with inflammatory changes of the pancreatic parenchyma surrounding the carcinoma (epineoplastic pancreatitis). For lesion characterization MRI is not able to characterize focal pancreatic lesions, allowing a differential diagnosis between pancreatic cancer and focal hypertrophic chronic pancreatitis. Even the use of MR-cholangiopancreatography is not helpful for characterizing focal pancreatic masses. MR imaging is accurate in local staging (assessment of peripancreatic fat infiltration) thanks to the higher contrast resolution, but in vascular staging and in the evaluation of lymphnodal involvement it suffers the same limitations as computed tomography. Future perspective are represented by the use of magnetic resonance angiography for the evaluation of vascular encasement and the use of specific contrast agents for lymphadenopathy. Identification of hepatic metastases with MRI has been proven to be high, with sensitivity and specificity comparable to CT. The use of liver-specific contrast agents (either positive or negative) is becoming almost routine and it is proving to further improve the diagnostic value of MRI.
磁共振成像在胰腺腺癌评估中的作用在于识别、表征肿瘤性病变并进行分期。为了获得与螺旋CT相媲美的高质量图像，需要进行技术优化。成像方案的选择与可用设备以及快速成像能力密切相关。如果在具有高梯度性能的高场强下工作，需要使用屏气序列进行对比增强研究；在中低场强下，可以采用使用呼吸补偿技术的非屏气采集技术。脂肪饱和脉冲的使用可能会提高磁共振成像检测胰腺病变的敏感性。磁共振成像的其他优势体现在可用于评估胆管树（磁共振胰胆管造影）和内脏血管（磁共振血管造影）的额外非侵入性技术。病变识别基于T1加权序列，在该序列中病变相对于周围胰腺呈低信号；使用脂肪抑制时，病变与胰腺之间的对比度会增加。在注射钆剂后的动态研究中，胰腺肿瘤相对于周围正常胰腺组织血供较少。在患有癌周胰腺实质炎症改变（肿瘤周围胰腺炎）的患者中，可能会遇到正确界定病变大小的问题。对于病变表征，磁共振成像无法区分局灶性胰腺病变，无法鉴别胰腺癌和局灶性肥厚性慢性胰腺炎。即使使用磁共振胰胆管造影也无助于表征局灶性胰腺肿块。由于更高的对比度分辨率，磁共振成像在局部分期（评估胰腺周围脂肪浸润）方面很准确，但在血管分期和评估淋巴结受累方面，它与计算机断层扫描存在相同的局限性。未来的发展方向包括使用磁共振血管造影评估血管包绕情况以及使用特定的造影剂评估淋巴结病变。磁共振成像对肝转移的识别率很高，其敏感性和特异性与CT相当。肝脏特异性造影剂（阳性或阴性）的使用几乎已成为常规操作，并且已证明能进一步提高磁共振成像的诊断价值。
