When do patients undergo a mono-phase, bi-phase, or tri-phase computed tomography (CT) abdominal scan?

From the Guidelines

Patients should undergo a mono-phase, bi-phase, or tri-phase CT abdominal scan based on the specific clinical question being investigated, with the choice of protocol depending on the suspected pathology and considerations such as radiation exposure and renal function. When evaluating for non-vascular pathologies such as kidney stones, bowel obstruction, or appendicitis, a mono-phase CT scan is typically performed, usually in the portal venous phase 1. For suspected liver lesions or pancreatic pathology, bi-phase CT scans are commonly used, including arterial and portal venous phases to capture different enhancement patterns 1. Tri-phase CT scans are indicated for hypervascular lesions, renal masses, or active bleeding, and include non-contrast, arterial, and portal venous phases 1. Some key points to consider when choosing a CT scan protocol include:

• The timing of the phases, with arterial phase occurring 25-30 seconds after contrast injection, portal venous phase at 60-70 seconds, and delayed phase at 3-5 minutes 1
• Radiation exposure, which increases with multiple phases 1
• The patient's renal function, as contrast administration may be limited in those with impaired kidney function 1
• The use of dedicated imaging protocols and comprehensive analysis of imaging findings 1 It is also important to consider the clinical context and the specific diagnostic question being asked, as well as the potential benefits and limitations of each protocol 1. In general, the choice of CT scan protocol should be tailored to the individual patient's needs and the suspected pathology, with the goal of providing the most accurate and useful diagnostic information while minimizing risks and limitations 1.

From the Research

CT Abdominal Scan Phases

The decision to perform a mono-phase, bi-phase, or tri-phase computed tomography (CT) abdominal scan depends on the specific clinical indication and the suspected pathology.

• Mono-phase CT scan: This type of scan may be used for certain conditions where a single phase of contrast enhancement is sufficient for diagnosis, such as in the evaluation of abdominal trauma or in follow-up exams for known conditions.
• Bi-phase CT scan: Bi-phase CT scans are commonly used in the evaluation of liver and pancreatic pathologies. For example, a study published in Radiology in 1997 2 found that dual-phase helical CT scans (arterial and venous phases) were useful in detecting pancreatic malignancies, although the addition of an arterial phase scan did not significantly improve tumor detection. Another study published in Radiology in 1996 3 found that two-phase helical CT with pancreatic and hepatic phases provided better tumor-pancreas contrast and vascular enhancement.
• Tri-phase CT scan: Tri-phase CT scans are often used in the evaluation of liver lesions, particularly hypervascular liver tumors. A study published in Aktuelle Radiologie in 1995 4 described the use of a 3-phase spiral CT scan (native, arterial, and portal perfusion phases) in a patient with multifocal nodular hyperplasia. This technique allowed for the assessment of the entire liver in distinct phases of perfusion.

Clinical Indications

The choice of CT scan phase depends on the clinical indication and the suspected pathology. For example:

• Liver lesions: A study published in Seminars in liver disease in 2001 5 emphasized the importance of multiphasic CT protocols in detecting hypervascular liver tumors.
• Pancreatic tumors: A study published in Radiology in 1996 3 found that two-phase helical CT with pancreatic and hepatic phases provided better tumor-pancreas contrast and vascular enhancement.
• Abdominal trauma: A mono-phase CT scan may be sufficient in the evaluation of abdominal trauma.

Contrast Enhancement

The timing of contrast administration and scan acquisition is critical in CT abdominal scans. A study published in AJR. American journal of roentgenology in 1994 6 reviewed the principles of lesion detection and the effects of various contrast techniques on lesion visualization, highlighting the importance of understanding the rationale behind each technique and the impact on the quality of the examination.