Imaging of the Pancreas 421 Imaging Modalities

Imaging of the pancreas is done for diagnosis, staging, and surveillance of benign or malignant conditions of the gland; surveillance includes monitoring of the disease, the effects of treatments, and the biological processes [10]. Imaging is faced with formidable obstacles in the case of pancreatic cancer because of the complexity of the disease and its high incidence of metastasis. Early neoplas-tic changes are difficult to detect and diagnose. Most of the available imaging techniques fail to detect early signs of pancreatic cancer. It is almost always detected after it has been spread beyond the gland. Imaging of the pancreas may be done in a variety of ways:

1. Computed tomography (CT); standard [11, 12], helical [7,13, 14], andmul-tidetector [8,15] with the latter becoming the dominant modality of choice.

3. Magnetic resonance cholangiopancreatography (MRCP) [18, 19].

4. Endoscopic retrograde cholangiopancreatography (ERCP) [20]

5. Endoscopic ultrasonography (EUS) [21, 22]

6. Positron emission tomography (PET) [23, 24]

The usage of one technique over another depends on availability, purpose of imaging, and expertise. Additional considerations in the selection of an imaging modality include the desired accuracy of the procedure for providing staging information, or its ability to perform simultaneous biopsy of the tumor, or its capacity to facilitate therapeutic procedures. Detection usually starts with transabdominal sonography to identify causes of pain. After sonography, CT is used as the primary modality for diagnosis and staging. MRI is also used for staging. MRCP and ERCP imaging provide additional information on the level of obstruction of the biliary or pancreatic ductal systems. Fine-needle aspiration of suspected pancreatic lesions can be done with EUS for increased biopsy specificity. Specificity is a problem with all imaging modalities as they do not make it possible to distinguish between pancreatic cancer and other pancreatic pathology, e.g., chronic pancreatitis, mucinous cystadenoma, and intraductal papillary mucinous neoplasms [10].

Today the most common modality for pancreatic imaging is helical CT, which has significantly improved outcomes relative to the standard CT or the other imaging modalities. Standard abdominal CT scans can help detect 70-80% of pancreatic carcinomas [3, 13]. But 40-50% of tumors smaller than 3 cm are missed, and these are the tumors most likely to be resectable. Helical CT improved significantly the resolution of conventional CT for pancreatic tumor imaging [25]. Helical CT has also impacted staging and treatment monitoring procedures and is now probably the most useful imaging technique for such investigations. Helical CT is the technique that will be focused on in this chapter.

Priorities set by the NCI Review Group for pancreatic cancer imaging include [2] (a) increase specificity of current imaging modalities, (b) increase sensitivity of current imaging modalities for small invasive and preinvasive lesions in both normal and abnormal pancreas, (c) develop and test molecular imaging techniques, (e) develop and test screening and surveillance imaging protocols for high-risk patients, and (f) develop and test noninvasive techniques to accurately define the effect of treatment. Computer aided diagnosis (CAD) schemes are computer algorithms that could assist the physician (radiologist or oncologist) in the interpretation of the radiographic images and the evaluation of the disease. CAD could play several roles in the above imaging priorities and contribute in several recommendations and research directions. CAD using CT scans seems to be the logical first step in the development of computer tools for pancreatic cancer because of the major role of CT in this area, the large amount of information available in CT scans, and the considerable potential for improvements that could have significant clinical impact independent of magnitude.

Continuous Source &

Detector Rotation /

Continuous Source &

Detector Rotation /

Figure 4.3: Schematic diagram of the helical CT set-up and operation principle including cross-section (slice) plane (x,y), and 2 axis orientation.

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