CT pelvis (protocol)

The CT pelvis protocol serves as an outline for the acquisition of a pelvic CT. As a separate examination, it might be performed as a non-contrast or contrast study or might be combined with a CT hip or rarely with a CT cystogram. A pelvic CT might be also conducted as a part of other scans such as CT abdomen-pelvis, CT CAP, polytrauma CT or CT angiograms of the aorta or lower extremities, but those protocols are beyond the scope of this article and discussed separately.

Note: This article aims to frame a general concept of a CT protocol for the assessment of the 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.

Contrast doses apply for CT examinations in adults.

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

Indications

Typical indications include the following ^1-10:

• pelvic trauma

  • pelvic fractures

  • sacral fractures

  • pelvic haemorrhage

• inflammatory or infectious processes

• pelvic tumours

• postoperative setting

• implants and their complications (e.g. intrapelvic cup migration)

• foreign bodies

• pelvic interventions (e.g. CT-guided injections, biopsy, drainage)

• CT cystography

  • suspected bladder rupture or bladder leak

Purpose

The purpose of a pelvic CT in the setting of a traumatic injury or suspected fracture is their timely diagnosis as well as their classification and characterisation ^1,2.

In the case of haemorrhage or suspected vascular injuries, the primary goal of the CT is the detection of the bleeding vessel ³.

In the setting of inflammatory or neoplastic processes, the purpose of a CT pelvis is the localisation and characterisation of the respective process, its extent and its relation to the adjacent tissues as well as the detection of potential complications ^5-8.

The purpose of a CT during an intervention is image guidance and in this setting, the scan extent will be reduced to the respective segment ^9,10.

Technique

• patient position

  • supine position 

  • both arms elevated

• tube voltage

  • ≤120 kVp

• tube current

  • as suggested by the automated current adjustment mode 

• scout

  • mid-abdomen to below the lesser trochanter

• scan extent

  • including iliac crest and lesser trochanter

  • might vary depending on the indication

• scan direction

  • craniocaudal

• scan geometry

  • field of view (FOV): 300 mm (should be adjusted to increase in-plane resolution)

  • slice thickness: ≤0.625 mm, interval: ≤0.5 mm

  • reconstruction algorithm: bone, soft tissue

• contrast injection considerations

  • non-contrast (e.g. fractures, foreign body)

  • contrast volume:  70-100 mL

  • biphasic acquisition with monophasic injection (arterial ± venous)

    • contrast volume: 80-100ml with 30-40 mL saline chaser at 4-5 mL/s

    • bolus tracking: aorta abdominal

    • arterial acquisition: minimal scan delay

    • venous acquisition: ~40 seconds after an arterial phase or 65-80 seconds after contrast injection

  • single acquisition with monophasic injection (venous)

    • contrast volume: 70-100ml (0.1 mL/kg) with 30-40 mL saline chaser at 2-3 mL/s

    • scan delay: 65-80 seconds or 40-50 seconds after bolus tracking

  • single acquisition with a biphasic injection or split bolus

    • 50-75 ml contrast media at 2-3 mL/s

    • 50 ml contrast media and 30-50 ml saline chaser at 4 mL/s starting at ~ 45 seconds

    • scan delay: 70 seconds

• respiration phase

  • single breath-hold: inspiration

• multiplanar reconstructions

  • axial images: strictly axial to the pelvic axis

  • coronal images: strictly coronal to the pelvic axis

  • sagittal images: sagittal aligned through the centre of the sacral bone and the pubic symphysis

  • slice thickness: bone ≤2 mm, soft tissue ≤3 mm, overlap 50%

Practical points

• patient positioning prior to scanning might reduce and facilitate multiplanar reconstructions

• reconstructions in both standard kernel and high-resolution kernels

• depending on the exact indication the scan might require an extension of the scan field

• dose optimisation

  • use iterative reconstruction algorithms if available

  • adjust expected CTDIvol and noise to patient size

• imaging of implants ¹

  • use metal artifact reduction algorithms

  • use monochromatic reconstructions in dual-energy CT scans

  • use additional wide window setting

  • might require a higher tube voltage