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AJR 2003; 181:387-393
© American Roentgen Ray Society

Review

Correlation of Positron Emission Tomography and CT in Evaluating Pancreatic Tumors: Technical and Clinical Implications

Mannudeep K. Kalra1, Michael M. Maher, Giles W. Boland, Sanjay Saini and Alan J. Fischman

1 All authors: Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Founders House, 55 Fruit St., Boston, MA 02114.

Received December 11, 2002; accepted after revision February 4, 2003.

 
Address correspondence to A. J. Fischman.


Introduction
Top
 Introduction
Principles and Instrumentation...
 PET Protocol
 Role of PET in...
 Conclusion
 References
 
Pancreatic cancer is one of the most lethal cancers, with a poor 5-year survival rate [1]. The National Cancer Institute has projected 30,300 new cases and 29,700 deaths in 2002 in the United States, related to pancreatic cancer [1]. These deaths will contribute to 5% of all cancer deaths in the country. Aggressive tumor growth to surrounding peripancreatic tissues often precludes surgical resection, making early diagnosis imperative. Therefore, early preoperative diagnosis of pancreatic malignancies and accurate staging are critical for curative resection, which offers the best chance of survival [2].

Diagnostic evaluation of pancreatic cancer remains challenging, even with an expanding armamentarium of modalities available for pancreatic imaging including sonography, endoscopic sonography, catheter angiography, endoscopic retrograde cholangiopancreatography, CT, and MR imaging. Multidetector CT is regarded as the most efficient modality for imaging inflammatory and neoplastic diseases of pancreas [3–7].

The long-term survival rate of patients with pancreatic cancer is dependent on the presence of lymph node metastasis and invasion of peripancreatic tissues including blood vessels, anterior pancreatic capsule, and peripancreatic nerve roots [8]. Often, this information is obtained on a preoperative CT scan that allows detection and anatomic delineation of the mass [9]. However, CT findings in some patients with acute or chronic pancreatic inflammation can resemble those of pancreatic cancer [10]. Similarly, definitive diagnosis of early pancreatic cancer and differentiation of posttreatment recurrent and residual masses from fibrosis or postsurgical inflammation have often proved difficult with these cross-sectional anatomic imaging techniques [11]. In the absence of an identifiable pancreatic mass, equivocal or indeterminate CT findings for pancreatic malignancy may arise when one or more secondary signs are seen—for instance, contour deformity, focal enlargement, narrowing or obstruction of adjacent vessels or of the pancreatic duct and common bile duct, and stranding in peripancreatic fat.

FDG positron emission tomography (PET) is an imaging modality that takes advantage of selective uptake and retention of the radiotracer (FDG) by malignant cells for assessing pancreatic malignancies. Recent development of hybrid PET–CT scanners, a combined physiologic and anatomic modality, will likely enhance the diagnostic capabilities of PET in combining functional and morphologic data for characterizing pancreatic masses. With the availability of hybrid PET–CT and the emergence of more data on the use of PET in imaging of pancreatic malignancies, demand for hybrid scanning of pancreatic tumors is likely to increase. In the absence of specific data regarding the value of hybrid PET–CT scanners in the evaluation of patients with suspected pancreatic cancer, we provide a basis of PET–CT correlation in pancreatic malignancies and highlight the individual advantages and disadvantages of PET and CT. We describe the role of PET alone and as a complementary imaging technique to CT in the evaluation of pancreatic diseases and discuss the basic physics, techniques, and role of PET and hybrid PET–CT in pancreatic cancer.


Principles and Instrumentation of PET
Top
 Introduction
 Principles and Instrumentation...
PET Protocol
 Role of PET in...
 Conclusion
 References
 
PET permits radiolabeling with positron emitters (FDG) to create radiopharmaceutical agents that closely mimic endogenous molecules for evaluation of in vivo metabolic activity [12]. Differential glucose metabolism in malignant and nonmalignant cell types forms the basis of using FDG, a glucose analogue for PET imaging. Studies have confirmed that tumor cells rely on adenosine triphosphate generated from glycolysis for sustaining rapid replicating tissue, as opposed to the more efficient production of adenosine triphosphate by the Krebs cycle [11]. This results in a 19-fold increase in glucose consumption per mole of adenosine triphosphate produced, further enhanced by increased glucose transporter protein and activation of hexose monophosphate pathway, which provide the carbon backbone for DNA and RNA synthesis. The use of FDG PET is based on the observation that there is a greater incorporation of glucose and consequently its analogue, FDG, into malignant cells compared with most healthy cells [13, 14].

Often, clinical diagnosis is made by qualitative evaluation of the PET study, but semiquantitative evaluation of FDG activity offers an objective quantification of FDG uptake in the lesion. A semiquantifiable index called the "standard uptake value" is the most commonly measured index in PET [11]. It represents the metabolic activity in the lesion corrected for the weight of the patient and the dose administered. For measuring the standard uptake value, regions of interest are drawn over the whole lesion volumes as displayed on the different slices. The standard uptake value is derived from the aforementioned attenuation-corrected images by using the following formula [15]:


The fact that dedicated conventional PET scanners are expensive has prevented their widespread use [16]. Growth of PET scanning has been promoted by the availability of the dual-detector single-photon emission computed tomography (SPECT) camera, which has the advantage of providing single-photon and positron imaging capabilities in a single less expensive imaging device [17]. For detection of larger lesions (> 2 cm in diameter), both dual-detector SPECT and dedicated PET scanners are equally sensitive; however, the performance of the former is significantly inferior for lesions less than 2 cm in diameter [18]. Depending on the clinical question and type of equipment available, the FDG imaging procedure may include the following: limited field tomographic images for abnormalities localized in a known region of body, dynamic PET images in a limited field for quantifying regional metabolic rates, whole-body tomographic images to survey abnormal FDG accumulation, and transmission imaging for attenuation correction [11, 12].

Although CT and MR imaging provide high-resolution images with precise anatomic delineation of lesions, they are often less specific in differentiating benign from malignant lesions [19, 20]. PET, however, based on functional alterations of abnormal tissues, provides only limited anatomic localization of an abnormal region of uptake. Therefore, the combination of the two modalities helps in overcoming these disadvantages of both structural and functional imaging. Various computer algorithms are available for performing superimposition or fusion of CT and MR images with PET images [21, 22]. Results with the use of fused images of coregistered anatomic and functional data support the importance of correlative imaging [21–23]. More recently, precise coregistration of anatomic CT and functional PET images has been made possible by the introduction of hybrid PET–CT scanners that, in a single scanning session, offer the potential of increased diagnostic accuracy [24]. Images from hybrid scanners offer possibilities for improving the diagnosis and staging of tumors, identification and localization of disseminated disease, differentiating recurrent disease from postsurgical inflammatory change, improving radiation therapy planning, and monitoring the response of chemotherapy and radiation therapy [24].


PET Protocol
Top
 Introduction
 Principles and Instrumentation...
 PET Protocol
Role of PET in...
 Conclusion
 References
 
Before a PET study, patients are instructed to fast for at least 4 hr. This diminishes physiologic glucose use and reduces insulin levels, which decrease FDG uptake by normal background organs such as the heart and muscles. Fasting is also important because uptake of FDG in the tumor competes with endogenous glucose. To avoid FDG uptake in muscles during the distribution phase of injected FDG, the patient is instructed to avoid talking, chewing, and any muscular activity. Blood glucose levels are obtained in patients with a history of diabetes mellitus, and scanning is not performed when serum glucose levels exceed 200 mg/100 mL. Because of decreased FDG uptake by tumors in the presence of hyperglycemia, false-negative results may be shown on PET [25]. False-negative results may present a particular problem in the evaluation of suspected pancreatic tumors because patients with these tumors tend to have a higher prevalence of hyperglycemia [25]. Prior hydration and IV administration of 20 mg of furosemide (IV given 20 min after FDG administration) are prescribed in some institutions to reduce radioactivity in the kidneys and urinary tract and to reduce measurement artifacts caused by high radioactivity in the urinary system [11].

For imaging of pancreatic masses, approximately 10–15 mCi (370–555 MBq) of FDG is administered IV. Images are acquired after a delay of 45–60 min [26]. During this period, the patient is instructed to restrict all physical activity. We acquire images using a PC-4096 PET camera (Scanditronix, Uppsala, Sweden), which provides 15 contiguous slices at 6.5-mm intervals with an axial spatial resolution of 6.0-mm full-width at half-maximum intensity [26]. All images are reconstructed using a conventional filtered back-projection algorithm to an in-plane resolution of 7-mm full-width at half-maximum intensity. To ensure complete anatomic coverage of the areas of interest, images are acquired in four to eight contiguous bed positions. The axial images are reformatted in coronal and sagittal projections using a proprietary software program. Attenuation correction is performed from transmission images acquired with a rotating pin source containing a germanium-68 positron emitter. Focal accumulations of FDG are often quantified by drawing regions of interest and calculated using the standard uptake value, a simple method that uses the ratios of FDG uptake in tumors compared with those in normal tissues.


Role of PET in Pancreatic Tumors
Top
 Introduction
 Principles and Instrumentation...
 PET Protocol
 Role of PET in...
Conclusion
 References
 
In contrast to the excellent delineation of normal pancreatic anatomy on cross-sectional structural imaging modalities, the normal pancreas is not visualized on PET because glucose use is low in the fasting state and is comparable to the soft-tissue background. Consequently, a focus of abnormal uptake of FDG in the pancreas is seen as an abnormal "hot spot." However, some FDG uptake is noted in normal liver, renal parenchyma, gastrointestinal tract, and urinary collecting system [27].

Pancreatic Adenocarcinoma
Like most other malignancies, pancreatic cancer is also associated with increased glucose consumption and can be assumed to be present if an intense focal FDG accumulation is seen in the pancreatic area [14, 22] (Fig. 1A, 1B). Although the pancreas is anatomically close to the liver, which usually shows a normal weak-to-moderate uptake, FDG accumulation in pancreatic tumors exceeds the FDG concentration in the normal liver. PET has been shown to be more accurate than other imaging methods in detecting pancreatic cancer [28–31]. For lesions less than 2-cm in diameter, the sensitivity of PET is superior to that achieved on CT, particularly if the tumor is hypermetabolic [32, 33]. CT is superior to PET for diagnosis of pancreatic cancers greater than 4 cm in diameter. The loss of accuracy of PET in assessing tumors larger than 4 cm is partly related to the low metabolic rates in portions of larger tumors. Friess et al. [32] have reported an overall sensitivity and specificity of 94% and 88%, respectively, for PET of pancreatic malignancy. In a recent prospective study comprising 74 patients with a pancreatic mass (1–10 cm) suspicious for pancreatic cancer, the overall sensitivity (96%) and specificity (78%) of PET were found to be superior to those of CT (91% and 56%) [29]. The results of some recent studies assessing the accuracy of PET in pancreatic cancer are summarized in Table 1.



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  		Fig. 1A. —50-year-old woman with biopsy-proven pancreatic adenocarcinoma. Positron emission tomography image shows intense FDG uptake in pancreatic bed (arrow).

 


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  		Fig. 1B. —50-year-old woman with biopsy-proven pancreatic adenocarcinoma. CT correlation scan shows soft-tissue mass (arrow) in pancreas that is suspicious for pancreatic malignancy and is encasing superior mesenteric artery.

 

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  		TABLE 1 Accuracy, Sensitivity, and Specificity of FDG Positron Emission Tomography for Detection of Pancreatic Cancer

 

Determining the stage of pancreatic cancer as a predictor of prognosis either by preoperative or intraoperative assessment is controversial because most patients with this cancer have a short survival expectancy, regardless of tumor stage [1, 11]. However, it has been shown by analyzing each staging factor that patients with small tumors (< 2 cm) or tumors without lymph node metastases seem to have a better prognosis [32]. Although PET has some advantages for detecting pancreatic cancer with a higher sensitivity and is better for differentiating pancreatic cancer from benign disorders, other modalities such as CT and MR imaging provide more anatomically precise images. The sensitivity of 71% for detecting lymph node metastasis on PET reported initially by Bares et al. [31] was downgraded to 61% after a subsequent study with a larger cohort of patients that was evaluated by the same investigators [34].

Similarly, studies have been reported in which FDG PET failed to detect pancreatic cancer in early stages (disease limited to the pancreas or adjacent structures such as the bile duct and duodenum without lymph node involvement) [9]. However, PET imaging may change therapeutic management by revealing unsuspected metastases to liver, bones, and lungs, thus avoiding the morbidity and mortality rates associated with unnecessary surgical interventions. In addition, Bares et al. [35] have documented that PET allowed avoidance of laparotomies by "upstaging" the disease in 17% of patients who were originally regarded as candidates for curative resection on the basis of preoperative CT and angiography. Recently, Jadvar and Fischman [26] have reported treatment alterations in 15% of patients due to PET localization of pancreatic cancer. In comparison with CT, FDG PET provides more reliable detection of hepatic metastases greater than 1 cm in patients with pancreatic cancer [36] (Fig. 2A, 2B, 2C). In patients with intrahepatic biliary dilatation, PET images should be reviewed with caution for determining the presence of liver metastases because they can show false-positive results in the liver in the presence of marked intrahepatic cholestasis [36]. For suspicious lesions less than or equal to 1 cm detected on CT, FDG PET can define malignancy in 43% of patients in the absence of dilated bile ducts.



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  		Fig. 2A. —58-year-old man after Whipple surgery. Contrast-enhanced CT image shows enhancing lesion (arrow) in segment VI of liver that is too small to characterize.

 


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  		Fig. 2B. —58-year-old man after Whipple surgery. Coronal image of positron emission tomography data shows intense FDG uptake in corresponding region (arrow).

 


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  		Fig. 2C. —58-year-old man after Whipple surgery. Contrast-enhanced CT scan acquired 6 months after B shows larger enhancing lesion (arrow) in same region, suggestive of metastasis.

 

Glucose metabolic rate as determined by quantifiable FDG uptake has been reported to be useful in determining patient prognosis [37]. A recent study has reported that patients with pancreatic cancer with a high standard uptake value (> 3) have a significantly lower mean survival period of 5 months in comparison with those having a standard uptake value of less than 3 (mean survival period of 14 months) [38]. In a similar study, Zimny et al. [38] have also documented that glucose metabolism, as determined on FDG PET, provides additional prognostic information in patients with pancreatic cancer. In their study, the median survival rate in patients with a standard uptake value of less than 6.1 was 9 months (95% confidence interval [CI], 6–12 months) versus 5-month survival rates in patients with a standard uptake value equal to or greater than 6.1. (95% CI, 4–6 months).

Conflicting reports are found in the literature concerning the utility of the standard uptake value in distinguishing cancer from focal pancreatitis [9, 31, 39]. Some researchers have reported that the standard uptake threshold value for differentiation of inflammatory disease from pancreatic cancer cannot be defined [9, 39]. However, with a cutoff of 2.1 for the standard uptake value, Koyama et al. [40] have reported significant (p < 0.0001) differences between benign and malignant pancreatic diseases. In comparison with structural imaging modalities, FDG PET has been generally reported to be more effective for differentiating pancreatic cancer from chronic inflammation. A distinct difference in FDG accumulation patterns of pancreatic cancer and chronic pancreatitis has been reported, with relatively low levels of FDG uptake in chronic pancreatitis with a diffuse distribution pattern [31]. In a recent study, Nakamoto et al. [41] have reported that the retention index with a standard uptake value obtained at 2 hr after injection provided higher diagnostic accuracy (91.5%) than the standard uptake value alone (83%) in differentiating malignant and benign lesions of the pancreas. They documented that standard uptake values of malignant lesions increase over time in comparison with those of benign pancreatic lesions after injection of FDG.

According to some investigators, kinetic analysis of FDG uptake in pancreatic lesions may be more accurate than the standard uptake value for determining whether a lesion is benign or malignant [39]. Finally, pancreatic tumor imaging with PET has been reported to be helpful in the monitoring and follow-up of patients who have undergone chemotherapy, radiation therapy, or surgical resection [42, 43]. In the immediate postoperative period and after chemotherapy or radiation therapy, typically inflammatory change surrounds the pancreas. Under these circumstances, structural imaging modalities are of limited use in differentiating inflammation or scar tissue from tumor mass because they rely on size, morphology, and enhancement of the abnormal lesions. Using these imaging features with structural imaging techniques in the early posttreatment period, the differentiation of tumor from inflammation is frequently difficult and can only be determined by monitoring the presence or absence of progression on serial studies. On the contrary, PET uses the criterion of decrease in metabolic activity, which is appreciable on PET at an earlier stage in the posttreatment period than reduction in size of the lesion seen on structural imaging studies [11, 33]. This decrease makes PET a suitable modality for assessing the response of pancreatic neoplasms to treatment (Fig. 3A, 3B, 3C, 3D). The role of FDG PET in monitoring patients after intraoperative radiotherapy for unresectable pancreatic cancer has been recently evaluated [44]. FDG PET was found to be more useful in monitoring patients for early response after intraoperative radiotherapy in comparison with CT because decrease in metabolic tumor activity occurred before a decrease in tumor size.



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  		Fig. 3A. —Positron emission tomography (PET) and CT correlation in 72-year-old man with recurrence after Whipple surgery for pancreatic cancer. Contrast-enhanced CT image shows ill-defined soft-tissue mass (arrow) in pancreatic bed, involving celiac artery.

 


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  		Fig. 3B. —Positron emission tomography (PET) and CT correlation in 72-year-old man with recurrence after Whipple surgery for pancreatic cancer. Contrast-enhanced CT image shows mass (arrow) with portal vein thrombosis.

 


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  		Fig. 3C. —Positron emission tomography (PET) and CT correlation in 72-year-old man with recurrence after Whipple surgery for pancreatic cancer. Coronal PET image shows intense uptake of radiotracer FDG in pancreatic head region (arrow) suggestive of recurrent or residual tumor.

 


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  		Fig. 3D. —Positron emission tomography (PET) and CT correlation in 72-year-old man with recurrence after Whipple surgery for pancreatic cancer. PET image obtained in transverse plane shows increased metabolic activity (arrow) in pancreatic region suggestive of recurrent or residual tumor.

 

A number of factors may affect the diagnostic accuracy of PET for pancreatic cancer. Both false-negative and false-positive results can occur with PET for preoperative diagnosis of pancreatic cancer. Superior sensitivity in tumor detection has been reported in euglycemic patients compared with those with elevated glucose levels [25]. False-negative results of PET are common in the presence of hyperglycemia. Zimny and Buell [25] have reported a 92% sensitivity of PET for detecting pancreatic cancer in euglycemic patients compared with 85% in patients with hyperglycemia. More important, some studies have shown that early-stage pancreatic cancers can give rise to false-negative results on PET, suggesting a major limitation of PET imaging in detection of pancreatic cancer with the existing PET scanner resolution [9, 30]. False-negative results have been reported in two of six patients with periampullary cancer in a study comprising 80 patients with pancreatic diseases [30]. However, diagnosis of early-stage disease free of peripancreatic extension and with a small pancreatic mass is also difficult on conventional structural imaging, including CT [19, 23, 24]. False-positive results can occur in chronic active pancreatitis and autoimmune pancreatitis [45]. In such cases, diffusely increased uptake of FDG should raise suspicion of a diffuse inflammatory process rather than pancreatic cancer, which most often reveals localized accumulation. Conversely, focal uptake of the radiotracer compound by the inflamed pancreatic parenchyma or papilla, inflammatory scars, and irradiated tissues may be indistinguishable from pancreatic malignancy [9, 32]. FDG uptake in these benign conditions may be due to increased metabolic activity in the inflamed pancreatic parenchyma or scar tissue. Focal uptake of FDG has also been reported after insertion of a nasobiliary tube; in patients with thrombosis of the portal vein; and after hemorrhage into pancreatic pseudocysts, overlying peripancreatic lymph nodes, and retroperitoneal fibrosis [31, 32].

Because of limited spatial resolution, PET cannot match CT in its ability to assess surgical resectability of pancreatic neoplasms—that is, it cannot assess vascular encasement. In addition, PET does not accurately detect local invasion of adjacent visceral structures such as the stomach or duodenum, which is important in planning curative or palliative surgery and interventional radiology procedures. Given the limitations of FDG PET related to resolution and the absence of anatomic landmarks in addition to its inaccuracy (false-negative and false-positive results), we believe that FDG PET performed in isolation has a limited role in the imaging of pancreatic cancer. However, it promises to be a useful adjunctive imaging modality to structural techniques for identifying and characterizing malignant lesions not seen or equivocal on anatomic imaging [46–48]. Despite its limited resolution, FDG PET does affect clinical management by detecting unknown metastatic disease, which can make a previously perceived resectable tumor unresectable.

Pancreatic Endocrine Tumors
Pancreatic endocrine tumors can be divided into 10 subcategories, which include insulinomas, gastrinomas (Zollinger-Ellison syndrome), vasoactive intestinal polypeptide tumors (VIPomas, Verner-Morrison syndrome), glucagonomas, somatostatinomas, adrenocorticotropic hormone–releasing tumors (ACTHomas), growth hormone–releasing factor secreting tumors (GRFomas), nonfunctioning endocrine tumors, pancreatic endocrine tumors causing carcinoid syndrome, and those causing hypercalcemia [49]. There have been remarkable improvements in imaging of small pancreatic lesions with technical innovations in CT, sonography, MR imaging, and, recently, scintigraphy with radiolabeled somatostatin analogues indium-111 pentetreotide (Octreoscan, Mallinckrodt, St. Louis, MO) [50]. Despite the recent advances and development of new imaging modalities, intraoperative localization and endoscopic sonography procedures seem to remain the most reliable and successful methods for diagnosis and localization of pancreatic endocrine tumors [50]. FDG PET has limited accuracy for evaluation of pancreatic neuroendocrine tumors, particularly in those that are small at presentation. In a recent study, FDG PET was found to have no significant advantage over CT, MR imaging, and sonography in the evaluation of small pancreatic endocrine tumors (sensitivity of 53%) [51].

Increased uptake of another positron-emitting agent, serotonin precursor 5-hydroxytryptophan labeled with carbon-11, in carcinoids has been reported [52]. In addition, Ahlstrom et al. [52] have documented use of 11C-L-dihydroxyphenylalanine and 5-hydroxytryptophan as labeled radiopharmaceutical agents to detect endocrine pancreatic tumors on PET. Functioning pancreatic endocrine tumors, particularly glucagonomas or metastases from such tumors, were easier to visualize on PET than on CT. PET was found to be less sensitive than CT for detecting nonfunctional endocrine tumors. Increased uptake of a radioactive-labeled radiotracer during a PET study is usually highly suspicious for malignancy, and therefore any uptake in a nonmalignant or low-grade malignant endocrine neoplasm may be confusing. To date, no studies assess the value of the PET–CT correlation in the diagnosis and management of pancreatic endocrine tumors [51]. Image fusion of anatomic CT with a metabolic PET study may help in localization of the tumor and thus aid in operative management.

Cystic Pancreatic Neoplasms
CT is valuable in the detection of cystic tumors of the pancreas and their precise anatomic localization. It also provides useful information about the local extent of the tumor. Whereas the anatomic and morphologic information help in establishing the diagnosis of most neoplasms, differentiation of benign from malignant neoplasms is difficult if not sometimes impossible on CT. In such circumstances, morphologic imaging on CT can be correlated with PET images to obtain complementary information about the presence of malignancy. In addition, tumor markers with CT and PET correlation can further strengthen confidence in preoperative diagnostic evaluation of patients with pancreatic cystic lesions.

Selective uptake of FDG provides strong evidence for the existence of malignancy in the region of uptake. A positive result characterized by FDG accumulation strongly suggests malignancy and, therefore, a need for resection. On the other hand, a negative PET result can show a benign tumor that may be managed conservatively with limited resection or, in selected high-risk patients, with either follow-up, biopsy, or both. PET has been shown to be more accurate than CT in distinguishing benign from malignant pancreatic cystic lesions. Sperti et al. [53] have evaluated the reliability of FDG PET in distinguishing benign from malignant cystic lesions of the pancreas in 56 patients with suspected cystic tumors. They reported that sensitivity, specificity, and positive and negative predictive values were 94%, 97%, 94%, and 97%, respectively, for FDG PET in determining if cystic pancreatic lesions were malignant. For the same cohort of patients, the corresponding values for CT were 65%, 87%, 69%, and 85%, respectively.


Conclusion
Top
 Introduction
 Principles and Instrumentation...
 PET Protocol
 Role of PET in...
 Conclusion
References
 
FDG PET offers a noninvasive alternative for the evaluation of pancreatic malignancies based on metabolic activity of the lesions. The sensitivity and specificity of FDG PET in detecting pancreatic cancer and differentiating benign and malignant pancreatic lesions have been validated by numerous studies [54–56]. Because of superior spatial and contrast resolution, CT and MR imaging provide information regarding local tumor invasion and surgical resectability, information that cannot be gained from PET images. However, PET offers a reliable method of differentiating recurrent or residual tumor from inflammatory or scar tissue, detecting unsuspected metastases, and evaluating pancreatic masses with equivocal CT diagnosis (Fig. 4). In these circumstances, using metabolic information from PET in correlation with the structural resolution of CT may provide a unique manner of imaging pancreatic tumors that combines the complementary information obtained from both imaging modalities.



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  		Fig. 4. —Diagram shows proposed imaging algorithm for pancreatic cancer. PET = positron emission tomography.

 


References
Top
 Introduction
 Principles and Instrumentation...
 PET Protocol
 Role of PET in...
 Conclusion
 References
 

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T. Beyer, G. Antoch, S. Muller, T. Egelhof, L. S. Freudenberg, J. Debatin, and A. Bockisch
Acquisition Protocol Considerations for Combined PET/CT Imaging
J. Nucl. Med., January 1, 2004; 45(90010): 25S - 35.
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