4.6 MR Findings
4.6.1 T，C+
Decreased T1-weighted signal intensity of the gland owe to decreased protein content due to glandular atrophy and fibrosis（also contributing to T1 hypo intensity）.Furthermore，the fibrotic changes of the parenchyma result in attenuation of the vascular supply reflected by decreased enhancement on immediate post gadolinium images（Roth 2012）（Figs.7.9a-d and 7.10a-c）.
4.6.2 Fat-Suppressed T2WI
Pseudocyst and necrotic areas show hyper intense.Gallstones and intraductal calculi show hypo intense or signal void.
Fig.7.9 Suspected chronic pancreatitis on MRI.A 46-year-old patient with isolated segmental finding.Axial T1-weighted fat-saturated spoiled gradient echo image（a）demonstrate the normal size and signal of pancreas.Arterial phase（b），pancreatic parenchymal phase（c）and portal venous phase（d）show the delayed enhancement of pancreatic parenchyma
4.6.3 MRCP
In early stage CP，the ducts and more specifically the side branches are first involved.These changes correspond to the distribution of fibrosis that primarily involves the base of the side branch that will appear narrowed with a clubbed appearance.These changes are better detected by MRCP after secretin administration.In advanced stages of the disease，the diagnosis is easily established at MRCP by identifying structural changes involving both the MPD and the side branches，such as dilatation，narrowing or stricture formation，irregular contour，and filling defects（Fig.7.10a，b）.These changes are better detected by MRCP.The major limitation of MRCP concerns the detection of calcifications.Calcifications are seen as hypo intense filling defects surrounded by a bright fluid.When calcifications are grouped or scattered throughout the pancreas，the bright signal of the ducts is dramatically decreased，which may preclude their detection and makes unenhanced CT mandatory.Uniform dilatation of the main pancreatic duct and relative sparing or only mild dilatation of side branches are typical features of the obstructive type（secondary to a tumor）of CP in the advanced stage.In chronic calcifying pancreatitis，the side branches are also involved and MPD dilatation may be diffuse or focal as a consequence of the extent of surrounding fibrosis.The associated complications such as pseudocysts and bile duct strictures are also detected by MRCP（Fig.7.11 c）.
4.6.4 Secretin-MRI and MRCP(https://www.daowen.com)
Secretin administration stimulates fluid and bicarbonate secretion by the pancreas，thereby improving pancreatic duct and side branch（Mensel et al.2014a）.For S-MRCP，2-dimensional MR is repeated every 30 s for 10 min after intravenous administration of 0.2 µg/kg body weight of Human secretin.Pre-and post-secretin images are then compared for changes in main pancreatic ductal caliber（compliance），better visualization of ducts and side branches，sphincter of Oddi function，and the duodenal filling（Boninsegna et al.2015；Sandrasegaran et al.2014；Mensel et al.2014b；Ketwaroo et al.2013）（Fig.7.12a-h）.Duodenal filling following S-MRCP is significantly reduced in CP patients with exocrine pancreatic insufficiency compared with healthy subjects（Bian et al.2014）.Pancreatic flow dynamics can be monitored after intravenous secretin administration，and measurement of the subsequent filling of the duodenum during MRCP can be used to evaluate the exocrine pancreatic function（Bian et al.2013）.Side-branch ectasia，mild ductal dilatation with loss of the normal gentle taper，and mural irregularities are the S-MRCP features of early-stage CP（Sherman et al.2014）.Secretin administration also increases the parenchymal signal intensity on T2WI.Decreased parenchymal signal is associated with loss of pancreatic acinar tissue（Lowenfels et al.1993）.
Fig.7.10 Chronic pancreatitis on MRI.Axial T1-weighted fat-saturated spoiled gradient echo image（a）and axial T2-weighted fat-saturated spoiled gradient echo image（b，c）demonstrate atrophy of the pancreas with a dilated bead-like appearance of the main pancreatic duct，and filling defects in the head of the pancreas（arrow）
Fig.7.11 Chronic pancreatitis on MRI.A 52-year-old male with history of recurrent severe epigastric pain.Axial Ti-weighted fat-saturated spoiled gradient echo image（a）and CoronalMRCP（b）demonstrate a dilatation of the main pancreatic duct，side-branch ectasia，and filling defects in the head of the pancreas（arrow）.A 45-yearold male with chronic pancreatitis Coronal MRCP（c）shows severe strictures of the main duct with pseudocyst formation in the head（arrow）
Fig.7.12 Secretin-MRCP demonstrates the duodenal filling in a chronic pancreatitis.Before（a）and 1（b），3（c），5（d），7（e），9 min（f）after secretin administration on 2-dimensional MRCP.Before（g）and 9 min（h）after secretin administration on 3-dimensional MRCP.Progressive filling of duodenum with pancreatic juice，from the bulb to the genu inferius，is shown.The main pancreatic duct is better depicted after secretin administration