CT pancreas (protocol)

The CT pancreas protocol serves as an outline for a dedicated examination of the pancreas. As a separate examination, it is usually conducted as a biphasic contrast study and might be conducted as a part of other scans such as  CT abdomen-pelvis, CT chest-abdomen-pelvis.

Note: This article aims to frame a general concept of a CT protocol for the assessment of the pancreas. Protocol specifics will vary depending on CT scanner type, specific hardware and software, radiologist and perhaps referrer preference, patient factors e.g. implants, specific indications.

A typical CT of the pancreas might look like as follows:

Indications

Typical indications include an evaluation of the following ^1-4:

• jaundice
• evaluation of pancreatic tumours and/or cystic lesions
• acute or chronic pancreatitis
• complications of pancreatic diseases
• unclear findings on ultrasound or CT abdomen
• pancreatic interventions (e.g. CT-guided biopsy, drainage)

Purpose

The purposes of a pancreatic CT includes the following ^1-4:

• detection and characterisation of pancreatic tumours
  • arterial phase: hypervascular lesions e.g. neuroendocrine tumours, vascular lesions
  • pancreatic phase: depiction of hypoattenuating tumours such as pancreatic ductal adenocarcinoma
  • portal venous phase: depiction of hepatic metastases, venous thrombosis etc.
• detection and characterisation of cystic pancreatic lesions
• acute pancreatitis
  • staging and severity assessment (best-done ≥2-3days after symptom onset)
  • search for aetiology (choledocholithiasis, autoimmune pancreatitis, groove pancreatitis etc.)
  • detection of complications in early and late phases including extrapancreatic complications
  • confirmation of the diagnosis of pancreatitis (only if clinically unclear - rare)
• chronic pancreatitis
• identification and characterisation of pancreatic calcifications

Technique

• patient position
  • supine position, abdomen centred within the gantry
  • both arms elevated
• tube voltage
  • ≤120 kVp
• tube current
  • as suggested by the automatic exposure control 
• scout
  • diaphragm to the iliac crest (or symphysis)
• scan extent
  • arterial/pancreatic phase: mid diaphragm to the iliac crest
  • venous phase: above the diaphragm to the iliac crest, might be extended to include the whole pelvis
• scan direction
  • craniocaudal
• scan geometry
  • field of view (FOV): 350 mm (should be adjusted to increase in-plane resolution)
  • slice thickness: ≤0.625 mm, interval: ≤0.5 mm
  • reconstruction kernelalgorithm: soft tissue kernel (e.g. I30), bone kernel (e.g. I70)​
• oral contrast
  • neutral contrast agent: 800 ml water 20-30min before the scan
• contrast injection considerations
  • non-contrast (rarely indicated)
  • biphasic pancreatic ± venous acquisition (pancreatic mass)
    • contrast volume: 70-120ml  (0.1 mL/kg) with 30-40 mL saline chaser at 3-5 mL/s
    • optional bolus tracking: abdominal aorta
    • pancreatic phase: scan delay 15-20 sec after trigger or 35-40 sec after contrast injection
    • portal venous phase: 30 sec after the pancreatic phase or 65-70 sec after contrast injection
  • biphasic arterial ± venous acquisition (neuroendocrine tumours)
    • contrast volume: 70-120ml  (0.1 mL/kg) with 30-40 mL saline chaser at 4-5 mL/s
    • bolus tracking: abdominal aorta
    • arterial phase: minimal scan delay
    • portal venous phase: 40 seconds after the arterial phase or 60-70 seconds after contrast injection
  • single acquisition with a monophasic injection (venous phase)
    • contrast volume: 70-120ml  (0.1 mL/kg) with 30-40 mL saline chaser at 3-5 mL/s
    • portal venous phase: 65-70 sec after contrast injection
• respiration phase
  • single breath-hold: inspiration
• multiplanar reconstructions
  • axial images:strictly axial to the body axis
  • coronal images: strictly coronal to the body axis
  • sagittal images: strictly sagittal to the body axis, aligned through the centre of the vertebral bodies and the sternum
  • slice thickness: soft tissue ≤2,5 mm, bone ≤2 mm overlap 20-40%

Practical points

• patient positioning prior to scanning might reduce and facilitate multiplanar reconstructions
• depending on the exact indication the scan might require an extension of the scan field
• consider coronal curved planar or paracoronal reformations
• dual-energy CT with monochromatic reconstructions is thought to improve tissue contrast ^5-7
• dose optimisation
  • use iterative reconstruction algorithms if available
  • adjust expected CTDIvol and noise to patient size
  • make use of automatic exposure control