Feasibility of omitting the unenhanced phase in CT angiography for acute aortic pathologies

Q: What is the clinical evidence from this study?

Study design: Cohort. Population: Confirmed acute aortic pathology (aneurysm, classic aortic dissection, intramural hematoma, or penetrating atherosclerotic ulcer) (n=160). Intervention: Contrast-only CT angiography (CTA) protocol (arterial and delayed phases, omitting unenhanced phase) vs. Conventional full multiphase CTA protocol (unenhanced, arterial, and delayed phases). Primary outcome: Diagnostic non-inferiority in detection rates across 640 aortic segments (specifically aortic dissection detection rate and radiation dose reduction) (Difference in detection proportion -0.003 for dissection; DLP reduction 32.1 ± 5.7%, 95% CI -0.003 to 0.002, p=0.500 (dissection); <0.001 (radiation dose reduction)).

Q: What does this research mean for the field?

A contrast-only CT angiography protocol provides non-inferior diagnostic detection of acute aortic pathologies compared to a multiphase protocol while reducing radiation dose by approximately 32%. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

Q: What question did this study set out to answer?

To evaluate whether a contrast-only CT angiography protocol is non-inferior to a conventional multiphase protocol for detecting acute aortic pathologies while reducing radiation dose.

Soo Buem Cho; Jieun Byun

doi:10.1371/journal.pone.0362760

November 13, 2026PLoS ONEOpen Access

Feasibility of omitting the unenhanced phase in CT angiography for acute aortic pathologies

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Key result

Contrast-only CTA matches multiphase CTA accuracy for acute aortic syndromes while cutting radiation dose ~32%.

Difference in detection proportion -0.003 for dissection; DLP reduction 32.1 ± 5.7%
95% CI -0.003 to 0.002
P=0.500 (dissection); <0.001 (radiation dose reduction)
n=160

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Why the study?

The feasibility of omitting the unenhanced phase in a contrast-only CTA protocol compared with a conventional multiphase protocol for detecting and characterizing acute aortic pathologies and reducing radiation dose needed evaluation.

Does a contrast-only CTA protocol (omitting the unenhanced phase) provide non-inferior diagnostic detection of acute aortic pathologies while reducing radiation dose compared to a standard multiphase CTA protocol in patients with confirmed aortic pathology?

Key Points

To evaluate whether a contrast-only CT angiography protocol is non-inferior to a conventional multiphase protocol for detecting acute aortic pathologies while reducing radiation dose.
Retrospective review of 160 patients (mean age 69.7 ± 14.6 years; 117 men) who underwent multiphase CT angiography across 3 scanners for suspected acute aortic syndrome.
Two independent radiologists evaluated 640 predefined aortic segments across separate sessions for aneurysms, dissections, intramural hematomas, and penetrating atherosclerotic ulcers.
Diagnostic non-inferiority was assessed using generalized estimating equations with a prespecified 5% margin, alongside radiation dose metrics (CTDI vol and DLP).
The contrast-only protocol met non-inferiority criteria within the 5% margin for all major pathologies, showing identical aneurysm detection (33.6% vs. 33.6%; p = 1.000) and comparable dissection detection (15.6% vs. 15.9%; p = 0.500).
Detection rates were slightly higher in the contrast-only protocol for intramural hematomas (5.8% vs. 5.0%; p = 0.180) and penetrating atherosclerotic ulcers (5.8% vs. 4.7%; p = 0.065) due to minor false-positive calcification interpretations.
Omitting the unenhanced phase significantly decreased radiation exposure, lowering mean DLP from 1392.4 ± 706.7 mGy·cm to 954.0 ± 500.9 mGy·cm and mean CTDI vol from 18.6 ± 9.2 mGy to 12.7 ± 6.6 mGy (both p < 0.001), representing a 32% reduction.

Study Design

Type

Cohort (n=160)

Blinding

Independent evaluation by two experienced radiologists with a 4-week washout interval between protocols

Multicenter

No

Structured PICO

Does a contrast-only CTA protocol (omitting the unenhanced phase) provide non-inferior diagnostic detection of acute aortic pathologies while reducing radiation dose compared to a standard multiphase CTA protocol in patients with confirmed aortic pathology?

P

Population

160 patients (mean age 69.7 years, 26.9% female) with confirmed acute aortic pathology (aneurysm, dissection, IMH, or PAU) providing 640 aortic segments in a single-center retrospective cohort in South Korea.

I

Intervention

Contrast-only CT angiography (CTA) protocol consisting of arterial and delayed phases (omitting the unenhanced phase), using 120 mL intravenous iohexol (350 mg I/mL; 600 mg I/kg based on a 70 kg standard) injected at 4 mL/s, interpreted independently by two experienced radiologists.

C

Comparator

Standard full multiphase CTA protocol consisting of unenhanced, arterial, and delayed phases in the same patients (paired intra-patient comparison evaluated after a 4-week washout interval).

O

Outcome

Diagnostic non-inferiority (prespecified 5% margin, Δ = -0.05) for segment-level detection of major acute aortic pathologies (aneurysm, dissection, IMH, and PAU) across 640 aortic segments.surrogate

Main Result

Effect estimate: Difference in detection proportion -0.003 for dissection; DLP reduction 32.1 ± 5.7% (95% CI -0.003 to 0.002)

Absolute Event Rate: 15.6% vs 15.9%

p-value: p=0.500 (dissection); <0.001 (radiation dose reduction)

Omitting the unenhanced phase in aortic CTA reduces radiation dose by ~32% while maintaining non-inferior diagnostic detection of major aortic pathologies, supporting its selective use in serial surveillance imaging of established aortic disease.

Limitations

Retrospective single-center study with limited numbers of relatively uncommon pathologies such as IMH and PAU
Intentionally enriched cohort including only pathology-confirmed cases with no true-negative cases, preventing extrapolation to initial emergency rule-out of acute aortic syndrome
Circular reference standard using the full multiphase protocol without independent external confirmation (e.g., surgical findings)
All scans performed on recent-generation CT scanners, limiting generalizability to older equipment
All interpretations performed by two highly experienced radiologists (>15 years of CTA experience), limiting generalizability to less-experienced readers
Retrospective single-center design with limited sample size for rarer entities like IMH and PAU
Enriched cohort restricted to confirmed aortic pathology without true-negative cases, precluding application to initial emergency rule-out of acute aortic syndrome
Circular reference standard relying on the full multiphase CT protocol rather than independent surgical or longitudinal confirmation
Use of recent-generation multidetector CT scanners only, which may limit generalizability to older scanners
Evaluations performed exclusively by two radiologists with >15 years of experience

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Implication

Contrast-only CTA may enable lower-radiation aortic imaging in established disease; leaves open prospective validation before changing acute protocols.

Abstract

Objectives To evaluate the feasibility of a contrast-only computed tomography angiography (CTA) protocol versus a conventional multiphase protocol for detecting and characterizing acute aortic pathologies, and reducing radiation dose. Materials & methods This retrospective study included 160 patients who underwent multiphase CTA for evaluating acute aortic syndrome. Two readers independently evaluated 640 predefined aortic segments for the presence of aneurysms, dissections, intramural hematomas (IMH), and penetrating atherosclerotic ulcers (PAU). Non-inferiority was assessed using generalized estimating equations with a prespecified 5% margin. Inter-protocol and inter-reader agreements were calculated using Cohen’s kappa. Radiation dose also was compared . Results The contrast-only protocol demonstrated non-inferiority to the full protocol for detecting all major aortic pathologies, with all confidence intervals falling within the 5% margin. Detection rates were identical for aneurysms (33.6% vs. 33.6%; p = 1.000) and similar for dissections (15.6% vs. 15.9%; p = 0.500). Detection rates were slightly higher with the contrast-only protocol for IMH (5.8% vs. 5.0%) and PAU (5.8% vs. 4.7%), primarily reflecting false-positive interpretation. Interprotocol agreement was perfect for aneurysm shape and rupture status (kappa = 1.000) but lower for mural thrombus characterization (kappa = 0.703). The contrast-only protocol achieved a 32.1 ± 5.7% reduction in mean DLP and 32.4 ± 4.5% for CTDI vol (both, p < 0.001). Conclusion In patients with acute aortic pathology, a contrast-only protocol demonstrated non-inferior diagnostic performance to the full multiphase protocol, with comparable reader agreement and a 32% reduction in radiation dose. These findings suggest that omitting the unenhanced phase may be feasible in selected clinical scenarios, particularly in patients undergoing serial surveillance imaging, where cumulative dose reduction is a priority.

Discussion

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Cite This Study

Cho et al. (2026) conducted a cohort in Confirmed acute aortic pathology (aneurysm, classic aortic dissection, intramural hematoma, or penetrating atherosclerotic ulcer) (n=160). Contrast-only CT angiography (CTA) protocol (arterial and delayed phases, omitting unenhanced phase) vs. Conventional full multiphase CTA protocol (unenhanced, arterial, and delayed phases) was evaluated on Diagnostic non-inferiority in detection rates across 640 aortic segments (specifically aortic dissection detection rate and radiation dose reduction) (Difference in detection proportion -0.003 for dissection; DLP reduction 32.1 ± 5.7%, 95% CI -0.003 to 0.002, p=0.500 (dissection); <0.001 (radiation dose reduction)).

synapsesocial.com/papers/6af88c410e4d8f4b089c1b43 https://doi.org/10.1371/journal.pone.0362760

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Feasibility of omitting the unenhanced phase in CT angiography for acute aortic pathologies

Figures

Key Points

Study Design

Structured PICO

Main Result

Limitations

Ask about this paper

Implication

Abstract

Discussion

Cite This Study

Feasibility of omitting the unenhanced phase in CT angiography for acute aortic pathologies

Figures

Key Points

Study Design

Structured PICO

Main Result

Limitations

Ask about this paper

Implication

Abstract

Discussion

Cite This Study

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