الفهرس 
Embryologic DevelopmentOnly 14 pages are availabe for public view
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Abstract
Pancreatic cancer is the fourth leading cause of cancer deaths across the globe it is one of the most deadly solid tumors, with an overall 5-year survival rate of less than 5%.
Due to a non-specific clinical presentation, it is often diagnosed at an advanced stage and is rarely amenable for curative treatment. Several studies have shown that patients with early stage pancreatic lesions (<3 cm) without lymphatic invasion have a significantly better prognosis with a 5-year survival rate of up to 25–30% following surgical resection. Therefore early diagnosis and appropriate staging are still essential to define the best care and to improve patient survival.
Imaging by Contrast enhanced CT has long been the standard of care for the diagnosis and staging of cancers in the abdomen, due to the differences in contrast enhancement of tumor tissue versus normal background tissue.
The advantages of MDCT, which include high spatial resolution, rapid data acquisition and various postprocessing techniques, are suited perfectly for imaging of the pancreas and the complex peri-pancreatic anatomy. Excellent visualization of the pancreatic parenchyma in various phases of contrast enhancement facilitates early detection of small pancreatic lesions. Postprocessing techniques not only facilitate accurate staging of pancreatic cancer but also provide a vascular road map for the operating surgeon.
The sensitivity of CT in detection of pancreatic tumors is more than 90 % when direct and indirect signs are used for diagnosis. However, the potential to differentiate exocrine (non-endocrine) tumors of pancreas is limited.
Perfusion CT (CTp) offers the potential of more detailed evaluation of tumor vasculature. Visualization of tumors can be attributed to abnormalities in the vasculature. Angiogenesis is an important step in the process of cancer development and is essential for tumor growth. Angiogenic vasculature in tumors generally has a high vasculature density with vessels that are dilated, tortuous, have abnormal branching patterns, and lack the well-organized structure of arterioles, capillaries, and veins found in normal tissues. As a result, blood volume and blood flow are abnormally high in tumor tissue. In addition, tumor blood vessels are immature and leaky. Therefore, contrast agents pass through the tumor vascular epithelium into the extravascular space more rapidly than in the normal tissue. As a result, the attenuation due to contrast agents is greater in the tumor than the surrounding tissue. Microvessel density has been established as a prognostic indicator for many cancers and the initiation of angiogenesis is thought to be a requirement for metastasis.
CTp is performed with the acquisition of a series of images before, during, and after the passage of a bolus of contrast through the vasculature. During image acquisition, the CT table does not move and the scan is limited by the width of the detectors, which is 2 cm in 4-16 slice scanners and 4 cm in 64-slice scanners. The selection of the region of interest is therefore critical. The chronological changes in x-ray attenuation during CTp are directly proportional to the concentration of iodinated contrast material in the tissues. During the first pass of the contrast agent (dynamic phase), the agent is largely confined to within the vasculature and the change in attenuation largely depends on blood flow and blood volume. In the later phase, differences in concentration of the agent in the extravascular space are detected, which are dependent on permeability of the vasculature. The mean transit time (MTT) and estimated values for blood flow and blood volume are calculated from the dynamic phase, and the permeability surface-area product (PS) is calculated from the delayed washout of the contrast material.
CTp has value in pancreatic cancer imaging for:differentiating between endocrine and exocrine tumors.
Magnetic resonance may be used as alternative imaging modality to CT, when renal insufficiency or contrast sensitivity prevent the use of iodinated intravenous contrast material or when the biliary tree study is primarily requested.
Magnetic resonance imaging is a powerful imaging technique for evaluating pancreatic neoplasms. Improvements in MR pulse sequences, MRCP have resulted in a highly reliable means of detecting and staging pancreatic neoplasms and distinguishing malignant from benign pancreatic disease processes.