There has been a proliferation and divergence of imaging-based tumor-specific response criteria over the past 3 decades whose purpose is to achieve objective assessment of treatment response in oncologic clinical trials. The World Health Organization (WHO) criteria, published in 1981, were the first response criteria and made use of bidimensional measurements of tumors. The Response Evaluation Criteria in Solid Tumors (RECIST) were created in 2000 and revised in 2009. The RECIST criteria made use of unidimensional measurements and addressed several pitfalls and limitations of the original WHO criteria. Both the WHO and RECIST criteria were developed during the era of cytotoxic chemotherapeutic agents and are still widely used. However, treatment strategies changed over the past decade, and the limitations of using tumor size alone in patients undergoing targeted therapy (including arbitrarily determined cutoff values to categorize tumor response and progression, lack of information about changes in tumor attenuation, inability to help distinguish viable tumor from nonviable components, and inconsistency of size measurements) necessitated revision of these criteria. More recent criteria that are used for targeted therapies include the Choi response criteria for gastrointestinal stromal tumor, modified RECIST criteria for hepatocellular carcinoma, and Immune-related Response Criteria for melanoma. The Cheson criteria and Positron Emission Tomography Response Criteria in Solid Tumors make use of positron emission tomography to provide functional information and thereby help determine tumor viability. As newer therapeutic agents and approaches become available, it may be necessary to further modify existing anatomy-based response-assessment methodologies, verify promising functional imaging methods in large prospective trials, and investigate new quantitative imaging technologies.

It is difficult to identify normal peritoneal folds and ligaments at imaging. However, infectious, inflammatory, neoplastic, and traumatic processes frequently involve the peritoneal cavity and its reflections; thus, it is important to identify the affected peritoneal ligaments and spaces. Knowledge of these structures is important for accurate reporting and helps elucidate the sites of involvement to the surgeon. The potential peritoneal spaces; the peritoneal reflections that form the peritoneal ligaments, mesenteries, and omenta; and the natural flow of peritoneal fluid determine the route of spread of intraperitoneal fluid and disease processes within the abdominal cavity. The peritoneal ligaments, mesenteries, and omenta also serve as boundaries for disease processes and as conduits for the spread of disease.

hronic pancreatitis (CP) is an inflammatory condition of the pancreas. Clinical manifestations of CP include one or more of the following: abdominal pain, which is often chronic and debilitating; episode(s) of acute pancreatitis; endocrine and/or exocrine insufficiency; and in some cases, development of pancreatic cancer. CP has a profound impact on the patient's quality of life (1). The natural course of CP is highly variable and no validated tools exist to predict disease progression in individual patients. There are no specific therapies available for treatment or prevention of this disease. Mechanistic definition and conceptual framework for disease evolution recently proposed based on international consensus (2) provides an opportunity to conduct translational and interventional studies to generate empirical data to advance the field.The histologic hallmarks of CP include fibrosis, chronic inflammation, and loss of acinar cells. Because histologic diagnosis is rarely pursued given the potential for complications, there is a need for a noninvasive biomarker of pancreatic fibrosis. This biomarker can be used in future trials to evaluate the efficacy of therapeutic agents, which may slow the progression or reverse the fibrosis observed in CP.Cross-sectional imaging is the most commonly used method to establish a diagnosis of acute pancreatitis and CP. Among cross-sectional imaging studies, CT is readily available and performed often in the setting of acute pancreatitis. It is widely acknowledged that MRI with MR cholangiopancreatography is more sensitive than is CT for detection of ductal and subtle parenchymal changes, especially during early stages of CP (3,4). However, the two

Purpose To determine if the T1 relaxation time of the pancreas can detect parenchymal changes in mild chronic pancreatitis (CP). Materials and Methods This Institutional Review Board (IRB)-approved, Health Insurance Portability and Accountability Act (HIPAA)-compliant retrospective study analyzed 98 patients with suspected mild CP. Patients were grouped as normal (n = 53) or mild CP (n = 45) based on history, presenting symptomatology, and concordant findings on both the secretin-enhanced magnetic resonance cholangiopancreatography (S-MRCP) and endoscopic retrograde cholangiopancreatography (ERCP). T1 maps were obtained in all patients using the same 3D gradient echo technique on the same 3T scanner. T1 relaxation times, fat signal fraction (FSF), and anterior–posterior (AP) diameter were correlated with the clinical diagnosis of CP. Results There was a significant difference (P < 0.0001) in the T1 relaxation times between the control (mean = 797 msec, 95% confidence interval [CI]: 730, 865) and mild CP group (mean = 1099 msec, 95% CI: 1032, 1166). A T1 relaxation time threshold value of 900 msec was 80% sensitive (95% CI: 65, 90) and 69% specific (95% CI: 56, 82) for the diagnosis of mild CP (area under the curve [AUC]: 0.81). Multiple regression analysis showed that T1 relaxation time was the only statistically significant variable correlating with the diagnosis of CP (P < 0.0001). T1 relaxation times showed a weak positive correlation with the pancreatic FSF (ρ = 0.33, P = 0.01) in the control group, but not in the mild CP group. Conclusion The T1 relaxation time of the pancreatic parenchyma was significantly increased in patients with mild CP. Therefore, T1 mapping might be used as a practical quantitative imaging technique for the evaluation of suspected mild CP.

Purpose To determine if T1-weighted MR signal of the pancreas can be used to detect early CP. Methods A retrospective analysis was performed on 51 suspected CP patients, who had both secretin-enhanced magnetic resonance cholangiopancreatography (S-MRCP) and an intraductal secretin stimulation test (IDST). There were 29 patients in normal and 22 patients in the low bicarbonate group. Bicarbonate level, total pancreatic juice volume, and excretory flow rate were recorded during IDST. Signal intensity ratio of pancreas (SIR), fat signal fraction, pancreatograms findings, and grade of duodenal filling were recorded on S-MRCP by two blinded radiologists. Results There was a significant difference in the signal intensity ratio of the pancreas to spleen (SIRp/s) between the normal and low bicarbonate groups (p < 0.0001). A significant positive correlation was found between pancreatic fluid bicarbonate level and SIRp/s (p < 0.0001). SIRp/s of 1.2 yielded sensitivity of 77% and specificity of 83% for detection of pancreatic exocrine dysfunction (AUC: 0.89). Conclusion T1-weighted MR signal of the pancreas has a high sensitivity and specificity for the detection of parenchymal abnormalities related to exocrine dysfunction and can therefore be helpful in evaluation of suspected early CP.

Extracellular volume fraction and T1 mapping may provide quantitative metrics for determining the presence and severity of acinar cell loss and aid in the diagnosis of CP.

Magnetic resonance cholangiopancreatography (MRCP) is the most effective, safe, noninvasive magnetic resonance (MR) imaging technique for the evaluation of the pancreaticobiliary ductal system. The MRCP imaging technique has substantially improved during the past 2 decades and is based mainly on the acquisition of heavily T2-weighted MR images, with variants of fast spin-echo sequences. MRCP can also be performed by utilizing the hormone secretin, which stimulates a normal pancreas to secrete a significant amount of fluid while transiently increasing the tone of the sphincter of Oddi. The transient increase in the diameter of the pancreatic duct improves the depiction of the ductal anatomy, which can be useful in patients in whom detailed evaluation of the pancreatic duct is most desired because of a suspicion of pancreatic disease. Improved depiction of the ductal anatomy can be important in (a) the differentiation of side-branch intraductal papillary mucinous neoplasms from other cystic neoplasms and (b) the diagnosis and classification of chronic pancreatitis, the disconnected pancreatic duct syndrome, and ductal anomalies such as anomalous pancreaticobiliary junction and pancreas divisum. In patients examined after pancreatectomy, stimulation with secretin can give information about the patency of the pancreaticoenteric anastomosis. Duodenal filling during the secretin-enhanced phase of the MRCP examination can be used to estimate the excretory reserve of the pancreas. Secretin is well tolerated, and complications are rarely seen. Secretin-enhanced MRCP is most useful in (a) the evaluation of acute and chronic pancreatitis, congenital variants of the pancreaticoduodenal junction, and intraductal papillary mucinous neoplasms and (b) follow-up of patients after pancreatectomy.

Objective: The aim of this study was to determine the association of the pancreatic steatosis with obesity, chronic pancreatitis (CP), and type 2 diabetes mellitus. Methods: Patients (n = 118) were retrospectively identified and categorized into no CP (n = 60), mild (n = 21), moderate (n = 27), and severe CP (n = 10) groups based on clinical history and magnetic resonance cholangiopancreatography using the Cambridge classification as the diagnostic standard. Visceral and subcutaneous compartments were manually segmented, and fat tissue was quantitatively measured on axial magnetic resonance imaging. Results: Pancreatic fat fraction showed a direct correlation with fat within the visceral compartment (r = 0.54). Patients with CP showed higher visceral fat (P = 0.01) and pancreatic fat fraction (P < 0.001): mild, 24%; moderate, 23%; severe CP, 21%; no CP group, 15%. Patients with type 2 diabetes mellitus showed higher pancreatic steatosis (P = 0.03) and higher visceral (P = 0.007) and subcutaneous fat (P = 0.004). Interobserver variability of measuring fat by magnetic resonance imaging was excellent (r ≥ 0.90–0.99). Conclusions: Increased visceral adipose tissue has a moderate direct correlation with pancreatic fat fraction. Chronic pancreatitis is associated with higher pancreatic fat fraction and visceral fat. Type 2 diabetes mellitus is associated with higher pancreatic fat fraction and visceral and subcutaneous adiposity.