Diagnostic Value of Photon-Counting CT in Subsegmental Pulmonary Embolism

Application of Photon-Counting Computed Tomography in the Diagnosis of Subsegmental Pulmonary Embolism

Pulmonary embolism (PE) is a serious and potentially life-threatening condition caused by blood clots in the lungs. A particular type, subsegmental pulmonary embolism (SSPE), involves very small branches of the pulmonary arteries. Although these clots occur in smaller vessels, their risk of recurrence and complications may be similar to larger clots.

Conventional CT pulmonary angiography (CTPA) is the standard imaging test for suspected PE, but image quality can sometimes be limited by motion artifacts, poor contrast filling, or body habitus, making the detection of SSPE challenging.

Photon-counting computed tomography (PCCT) is a new CT technology that provides higher image resolution, lower radiation dose, and improved visualization of small blood vessels. Early studies suggest PCCT may reduce motion artifacts and increase the accuracy of detecting SSPE compared with conventional CT.

This prospective cohort study will compare PCCT with dual-source CT in patients with suspected acute PE. The study aims to determine whether PCCT improves the detection rate and image quality for SSPE, and whether it can provide more reliable diagnostic information to guide clinical care.

Study Overview

• Status: Recruiting
• Conditions: Subsegmental Pulmonary Embolism; Photon-Counting Computed Tomography

Detailed Description

Pulmonary embolism (PE) is a leading cause of morbidity and mortality worldwide. Subsegmental pulmonary embolism (SSPE), defined as thrombi confined to subsegmental pulmonary arteries, may account for up to 20% of acute PE cases detected by multidetector CT. While distal in location, SSPE carries a risk of recurrent venous thromboembolism and mortality that is comparable to more proximal PE, suggesting that SSPE is not a benign entity. Accurate diagnosis is therefore clinically important, but remains challenging due to motion artifacts, poor contrast opacification, and the large number of small subsegmental vessels that must be evaluated.

Photon-counting computed tomography (PCCT) is a recently developed imaging technology that offers significant improvements over conventional energy-integrating detector CT (EID-CT). PCCT provides higher spatial resolution, direct spectral information, and the ability to generate virtual monoenergetic images and iodine maps in a single acquisition, while reducing radiation dose. Preliminary studies indicate that PCCT can minimize motion artifacts, improve image quality, and enhance visualization of small pulmonary arteries, potentially increasing the detection of SSPE.

This prospective observational cohort study will compare the diagnostic performance of PCCT with dual-source CT in patients with suspected acute PE. The primary outcome is the detection rate of SSPE. Secondary outcomes include image quality scores, radiation dose, and the added diagnostic value of PCCT in patients with negative findings on dual-source CT. By systematically evaluating image quality, detection yield, and radiation exposure, this study seeks to establish the potential role of PCCT as a superior diagnostic tool for SSPE in real-world clinical practice.

• Study Type: Observational
• Enrollment (Estimated): 696

Contacts and Locations

Study Locations

• China
  • Zhejiang
    • Hangzhou, Zhejiang, China, 310009
      • Recruiting
      • The Second Affiliated Hospital of Zhejiang University School of Medicine
      • Contact: min Yan, doctor; Phone Number: +86 13757118632; Email: zryanmin@zju.edu.cn

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Adults (≥18 years) presenting with clinical symptoms and signs suggestive of acute pulmonary embolism will be enrolled. Eligible patients are those with a simplified revised Geneva score ≥3 and abnormal findings on electrocardiogram, echocardiography, or pulse oximetry, which support the suspicion of pulmonary embolism. Patients will be prospectively recruited from the emergency department and inpatient wards of the Second Affiliated Hospital, Zhejiang University School of Medicine. The study population is representative of patients with suspected acute pulmonary embolism who require CT pulmonary angiography for diagnostic confirmation.

Description

Inclusion Criteria:

1. Age ≥ 18 years

2. Clinical manifestations supporting the diagnosis of acute pulmonary embolism, including:

   Acute onset or progressive dyspnea Unexplained hypoxemia Chest pain Hemoptysis Syncope or presyncope Combined with abnormal findings on electrocardiogram, echocardiography, or pulse oximetry

3. Revised simplified Geneva score ≥ 3
4. Written informed consent obtained from the patient or the patient's legally authorized representative

Exclusion Criteria:

1. Patients requiring prophylactic or therapeutic doses of anticoagulant medication for reasons other than venous thromboembolism (VTE).
2. Life expectancy less than three months.
3. Patients unable to undergo CT scanning due to severe condition or hemodynamic instability.
4. History of allergy to contrast media, renal insufficiency (creatinine clearance < 30 mL/min), or ongoing long-term dialysis.
5. Pregnancy.
6. Refusal to provide informed consent or inability to complete follow-up for any reason.

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort
Group 1Title: Conventional CT group; Description: Patients with suspected pulmonary embolism who undergo dual-source or energy-integrating detector CT pulmonary angiography (EID-CTPA).
Group 2 Title: Photon-counting CT group; Description: Patients with suspected pulmonary embolism who undergo photon-counting computed tomography (PCCT) for diagnosis.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Detection rate of subsegmental pulmonary embolism (SSPE) using photon-counting CT versus dual-energy CT	The proportion of patients with suspected acute pulmonary embolism in whom SSPE is detected on photon-counting CT compared with dual-energy CT. All scans will be independently assessed by two blinded radiologists to determine diagnostic yield.	perioperative period

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Objective image quality scores for SSPE diagnosis	ignal-to-Noise Ratio (SNR) and Contrast-to-Noise Ratio (CNR) will be calculated based on CT attenuation and image noise measured in standardized Regions of Interest (ROIs) within pulmonary vessels, the aorta, and paraspinal muscles. Higher SNR and CNR values indicate better objective image quality.	perioperative period
Subjective image quality scores for SSPE diagnosis	Radiologists will qualitatively assess image noise and motion artifacts using a 5-point Likert scale (1 = Unacceptable, 5 = Excellent). The average score of the readers will be used, with higher scores indicating better subjective image quality	perioperative period
Incidence of Venous Thromboembolism (VTE)	Occurrence of symptomatic VTE, defined as Deep Vein Thrombosis (DVT) or Pulmonary Embolism (PE), confirmed by objective imaging upon clinical suspicion	3 months

Collaborators and Investigators

• Sponsor: Second Affiliated Hospital, School of Medicine, Zhejiang University

Study record dates

Study Major Dates

• Study Start (Actual): January 1, 2026
• Primary Completion (Estimated): September 1, 2026
• Study Completion (Estimated): January 1, 2027

Study Registration Dates

• First Submitted: November 17, 2025
• First Submitted That Met QC Criteria: May 4, 2026
• First Posted (Actual): May 8, 2026

Study Record Updates

• Last Update Posted (Actual): May 8, 2026
• Last Update Submitted That Met QC Criteria: May 4, 2026
• Last Verified: September 1, 2025

More Information

Terms related to this study

• Other Study ID Numbers: 2025-1248

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No