# Diagnostic Value of the Split-Bolus CT Protocol in Blunt Abdominal Trauma: Comparison With Standard Portal Venous Phase Imaging

## TL;DR

This study compares two CT scan protocols for diagnosing abdominal injuries, finding that the split-bolus method offers better image quality without higher radiation risk.

## Contribution

The study demonstrates that the split-bolus CT protocol improves vascular and organ contrast in trauma imaging without increasing radiation exposure.

## Key findings

- The split-bolus protocol showed significantly higher contrast enhancement in the spleen, pancreas, and renal cortex compared to the standard portal venous protocol.
- Vascular enhancement was consistently better with the split-bolus protocol in key vessels like the portal vein and aorta.
- The split-bolus protocol reduced the need for delayed scans by enabling simultaneous arterial and venous injury evaluation.

## Abstract

Background

Blunt abdominal trauma is a significant cause of morbidity and mortality, particularly in young adults, and accurate imaging is essential for timely diagnosis and management. Computed tomography (CT) is the preferred modality in hemodynamically stable patients, with the routine portal venous (PV) phase protocol commonly employed. Recently, the split-bolus (SB) protocol has been proposed as an alternative, enabling simultaneous arterial and venous phase visualization in a single acquisition. This study compared the image quality, contrast enhancement, diagnostic accuracy, and radiation exposure of the SB protocol versus the standard PV protocol in evaluating blunt abdominal trauma.

Methods

A prospective observational study was conducted from September 2021 to August 2022 at Dr. Rajendra Prasad Government Medical College, Kangra. Seventy hemodynamically stable patients with suspected intra-abdominal injury were assigned to SB (n = 35) or PV (n = 35) CT protocols using a non-probability convenience sampling method. Organ and vascular attenuation values were measured in Hounsfield units (HU). Image quality was assessed on a five-point Likert scale, and organ injuries were graded using the Organ Injury Scale (OIS) by two experienced radiologists. Radiation dose metrics included the volume CT dose index (CTDIvol, mGy) and dose-length product (DLP, mGy·cm), which were recorded directly from the scanner console. Effective dose (mSv) was calculated by multiplying DLP by the standard abdominal conversion factor (k = 0.015). Statistical analysis included t-tests, chi-square tests, and weighted kappa statistics for inter-reader agreement, with p < 0.05 considered significant.

Results

The study population had a mean age of 35.6 ± 13.7 years, with a male predominance (75.7%). Solid organ injuries were identified in 88.6% of cases, most frequently involving the liver (52.9%) and spleen (34.3%). The SB protocol demonstrated significantly higher enhancement in the spleen (141.7 ± 27.8 HU vs. 119.6 ± 19.8 HU, p < 0.001), pancreas (121.7 ± 22.1 HU vs. 99.9 ± 13.6 HU, p < 0.001), and renal cortex (240.6 ± 45.1 HU vs. 179.9 ± 31.4 HU, p < 0.001), while hepatic enhancement was comparable (p = 0.834). Vascular enhancement was consistently superior with SB, particularly in the portal vein, aorta, inferior vena cava, and iliac vessels (all p < 0.05). Overall image quality was rated as good to excellent in both protocols, with no significant difference. Importantly, SB facilitated simultaneous evaluation of arterial and venous injuries and improved urinary tract opacification, reducing the need for delayed scans. Inter-reader agreement for OIS scoring was moderate to substantial (κ = 0.563 for SB; κ = 0.639 for PV). The mean CTDIvol and DLP were comparable between SB and PV groups (CTDIvol: X vs. Y mGy; DLP: X vs. Y mGy·cm, both p > 0.05). The derived effective dose was also similar (8.87 ± 2.85 mSv vs. 8.89 ± 3.05 mSv, p = 0.846).

Conclusions

The SB CT protocol provided superior vascular and parenchymal enhancement compared to the routine PV protocol without increasing radiation exposure. By consolidating arterial and venous phases into a single scan, SB streamlined trauma evaluation, enhanced diagnostic confidence in vascular and urinary tract injuries, and reduced the need for multiphase acquisitions.