CT chest abdomen-pelvis (protocol)

The CT chest-abdomen-pelvis protocol serves as an outline for an examination of the trunk covering the chest,  abdomen and pelvis. It is one of the most common CT examinations conducted in routine and emergencies. It can be combined with a CT angiogram.

Note: This article aims to frame a general concept of a CT protocol for the assessment of the chest, abdomen and pelvis. 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.

For specific protocols for the investigation of chest, liver, pancreas, adrenals and kidneys or the aorta please refer to the specific protocols.

A typical CT of the chest, abdomen and pelvis might look like as follows:

Indications

Typical indications include an evaluation or monitoring of the following ^1-3:

• suspected tumours or fluid collections of the chest, abdomen and pelvis
• diagnosis and staging of malignancies
• traumatic injuries
• infections and inflammatory conditions
• patients with sepsis or fever of unknown origin
• evaluation of vascular abnormalities
• postoperative follow-up
• pre and posttransplant evaluation
• congenital abnormalities

Purpose

The purpose of a CT chest-abdomen-pelvis includes but is not limited to the detection, characterisation and localisation of the following conditions ^1-3:

• tumours, metastasis and lymph nodes
• air collections outside the lungs and the gastrointestinal tract
• abnormal or organ calcifications
• abnormal fluid collections including haemorrhage or soft tissue oedema
• blunt and penetrating abdominal and pelvic injuries
• organ manifestations of systemic disease above and below the diaphragm
• multiphasic protocols:
  • arterial phase: hypervascular tumours and vascular lesions
  • venous phase: depiction of hepatic metastases, venous thrombosis etc.

Technique

• patient position
  • supine position, body centred within the gantry
  • both arms elevated
• tube voltage
  • ≤120 kVp
• tube current
  • as suggested by the automatic exposure control  
• scout
  • above the lung apices to the symphysis
• scan extent
  • includes lung apices and pubic symphysis
  • in the case of a multiphasic scan or split acquisition, there will be different scan ranges
• scan direction
  • craniocaudal
• scan geometry
  • field of view (FOV): 350 mm (should be adjusted to increase in-plane resolution)
  • slice thickness: ≤0.75 mm, interval: ≤0.5 mm
  • reconstruction algorithm: soft tissue, bone
• oral contrast
  • positive contrast agent (abscesses, infectious conditions): as per preparation guide
  • neutral contrast agent (oncologic or vascular conditions): 1000 ml water 20-30 min before the scan
• contrast injection considerations
• non-contrast (if contrast medium is contraindicated or not needed)
• biphasic arterial ± venous acquisition
  • contrast volume: 70-100ml  (0.1 mL/kg) with 30-40 mL saline chaser at 3-5 mL/s
  • bolus tracking: abdominal aorta
  • arterial phase: minimal scan delay
  • portal venous phase: 30-50 seconds after the arterial phase or 60-80 seconds after contrast injection
• single acquisition with a monophasic injection (venous phase):
  • contrast volume: 70-100ml  (0.1 mL/kg) with 30-40 mL saline chaser at 3 mL/s
  • portal venous acquisition: 60-80 sec after contrast injection
• single acquisition with a biphasic injection or split bolus ⁴
  • 65-80 ml contrast media at 2,5 mL/s
  • 15-40 ml contrast media and 30-50 ml saline chaser at 2,5-3 mL/s starting 40 sec after contrast injection
  • venous acquisition: 60-80 sec after contrast injection
• respiration phase
  • single breath-hold: inspiration
  • if a single breath is not possible consider dual-phase over chest and abdomen-pelvis
• 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
  • slice thickness: soft tissue ≤3 mm, bone ≤2 mm overlap 20-40%

Practical points

• patient positioning before scanning might reduce patient dose and facilitate multiplanar reconstructions
• depending on the exact indication the scan might require an extension of the scan field
• consider 30 ml intravenous contrast media followed by saline chaser 5 min before the scan
• dose optimisation ^5-7
  • use iterative reconstruction algorithms if available
  • adjust expected CTDIvol and noise to patient size
  • make use of automatic exposure control
  • consider employing manufacturer-specific protocols for best results
  • consider dual-energy and split-bolus protocols instead of multiple acquisitions