Repositioning the Bolus Tracking ROI to the Superior Vena Cava in CTPA Facilitates Contrast Volume Reduction

Optimising Bolus Tracking Technique by Repositioning the Region of Interest (ROI) at the Superior Vena Cava and Reducing Contrast Media Volume in Computed Tomography Pulmonary Angiography (CTPA)

This randomized controlled trial evaluates a protocol optimization for Computed Tomography Pulmonary Angiography (CTPA). The study investigates the impact of repositioning the bolus-tracking region-of-interest (ROI) from the standard pulmonary trunk (PT) to the superior vena cava (SVC). The goal is to compensate for the CT scanner's inherent transit delay time (TDT) to better align the scan with the peak arterial phase. By optimizing this timing, the study assesses whether contrast media volume can be safely reduced by 40% (from 50 ml to 30 ml) while maintaining diagnostic image quality and preventing venous contamination.

Study Overview

• Status: Completed
• Conditions: Pulmonary Embolism (PE); Pulmonary Artery Embolism
• Intervention / Treatment: Diagnostic test: Optimized CTPA Protocol

Detailed Description

Background and Rationale: Computed Tomography Pulmonary Angiography (CTPA) is the gold standard for diagnosing pulmonary embolism (PE). However, standard bolus tracking (BT) protocols that place the monitoring region-of-interest (ROI) on the main pulmonary trunk (PT) often face challenges due to the system's inherent Transit Delay Time (TDT). This delay, typically 5 seconds, can cause the diagnostic scan window to overlap with the venous phase, leading to suboptimal arterial opacification and venous contamination. This study proposes repositioning the monitoring ROI upstream to the superior vena cava (SVC) to utilize the TDT as transit time for the bolus, thereby aligning the scan window with the peak arterial phase.

Study Objectives: The primary objective is to evaluate the effect of SVC ROI repositioning on diagnostic image quality while investigating the feasibility of reducing contrast media (CM) volume by 40% (from 50 ml to 30 ml).

Methodology: This is a single-center, prospective, randomized controlled trial involving 72 adult patients. Participants are randomized into four protocol groups:

Group A (Control): ROI at PT, 50 ml contrast media. Group B: ROI at PT, 30 ml contrast media. Group C: ROI at SVC, 50 ml contrast media. Group D: ROI at SVC, 30 ml contrast media.

Protocol Details:

• Contrast Administration: Non-ionic contrast medium (370 mgI/ml) is injected at a rate of 4 ml/s, followed by a 20 ml saline flush.
• Bolus Tracking: An elliptical ROI is placed either on the PT (above the carina) or SVC depending on the group assignment.
• Triggering: The diagnostic scan is automatically initiated when enhancement reaches a threshold of 100 HU. The TDT is set to a fixed 5 seconds.
• Assessment: Diagnostic quality is assessed quantitatively by calculating arterial-venous enhancement differences (HU) and qualitatively via a 5-point Likert scale by three blinded radiologists.

• Study Type: Interventional
• Enrollment (Actual): 72
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Malaysia
  • Sabah
    • Kota Kinabalu, Sabah, Malaysia, 88200
      • Hospital Queen Elizabeth

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• All patients scheduled for a Computed Tomography Pulmonary Angiography (CTPA) examination.
• Provision of written informed consent by the subject, guardian, or medical specialist.
• Patients with an upper extremity intravenous (IV) line using a 16-20 gauge cannula.
• Patients with a stable heart rate between 60 and 120 beats per minute (bpm).

Exclusion Criteria:

• Pregnancy, breastfeeding, or use of non-reliable methods of contraception.
• Patients with impaired renal function, including acute kidney injury or chronic kidney disease (CKD) with an eGFR less than 30 mL/min/1.73m².
• Patients with a lower extremity IV line, as this bypasses the Superior Vena Cava (SVC) and results in bolus tracking technique failure.
• Patients with a heart rate lower than 60 bpm or higher than 120 bpm.
• Patients with a cannula size of 22g or smaller, as it cannot accommodate the high flow rate (4 mL/s) required by the power injector.
• Patients with severe cardiac impairment or congenital heart disease.
• Patients with a Body Mass Index (BMI) exceeding 35 kg/m², as severe obesity causes beam hardening effects that degrade image quality.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Diagnostic
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Group A: PT-ROI, 50 ml (Control); Standard CTPA protocol using the bolus tracking technique with the monitoring region of interest (ROI) placed at the pulmonary trunk (PT) and 50 ml of contrast media.	Diagnostic test: Optimized CTPA Protocol; CTPA scans are performed on a 128-slice CT scanner using the bolus tracking technique. Non-ionic contrast medium (370 mgI/ml) is administered at a rate of 4 ml/s, followed by a 20 ml saline flush. The diagnostic scan is automatically triggered when enhancement in the monitoring region of interest (ROI) reaches a threshold of 100 HU, with a fixed transit delay time (TDT) of 5 seconds.
Experimental: Group B: PT-ROI, 30 ml; Modified CTPA protocol using the bolus tracking technique with the monitoring ROI at the pulmonary trunk (PT) and a reduced contrast volume of 30 ml.	Diagnostic test: Optimized CTPA Protocol; CTPA scans are performed on a 128-slice CT scanner using the bolus tracking technique. Non-ionic contrast medium (370 mgI/ml) is administered at a rate of 4 ml/s, followed by a 20 ml saline flush. The diagnostic scan is automatically triggered when enhancement in the monitoring region of interest (ROI) reaches a threshold of 100 HU, with a fixed transit delay time (TDT) of 5 seconds.
Experimental: Group C: SVC-ROI, 50 ml; Modified CTPA protocol using the bolus tracking technique with the monitoring ROI repositioned upstream to the superior vena cava (SVC) and 50 ml of contrast media.	Diagnostic test: Optimized CTPA Protocol; CTPA scans are performed on a 128-slice CT scanner using the bolus tracking technique. Non-ionic contrast medium (370 mgI/ml) is administered at a rate of 4 ml/s, followed by a 20 ml saline flush. The diagnostic scan is automatically triggered when enhancement in the monitoring region of interest (ROI) reaches a threshold of 100 HU, with a fixed transit delay time (TDT) of 5 seconds.
Experimental: Group D: SVC-ROI, 30 ml; Modified CTPA protocol using the bolus tracking technique with the monitoring ROI repositioned upstream to the superior vena cava (SVC) and a reduced contrast volume of 30 ml.	Diagnostic test: Optimized CTPA Protocol; CTPA scans are performed on a 128-slice CT scanner using the bolus tracking technique. Non-ionic contrast medium (370 mgI/ml) is administered at a rate of 4 ml/s, followed by a 20 ml saline flush. The diagnostic scan is automatically triggered when enhancement in the monitoring region of interest (ROI) reaches a threshold of 100 HU, with a fixed transit delay time (TDT) of 5 seconds.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Mean Difference in Hounsfield Unit (HU) Attenuation Between Pulmonary Artery and Pulmonary Vein	This quantitative measurement assesses the degree of arterial opacification relative to venous contamination by calculating the difference in Hounsfield Units (HU). It is calculated by subtracting the mean HU value of the pulmonary vein from the mean HU value of the pulmonary artery at the same anatomical level. A larger positive difference indicates superior arterial enhancement with minimal venous contamination.	At the time of post-procedural image analysis (approximately 48 hours after CTPA scan completion).

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Qualitative Image Quality Score using a 5-point Likert Scale	Qualitative assessment of CTPA images performed by three blinded senior radiologists using a 5-point Likert scale (1 = Unacceptable, 2 = Sub-optimal, 3 = Acceptable, 4 = Good, 5 = Excellent). The score evaluates overall arterial enhancement, presence of artifacts, and diagnostic adequacy.	Within 1 month following the CTPA scan.

Collaborators and Investigators

• Sponsor: Hospital Queen Elizabeth, Malaysia
• Collaborators: Universiti Sultan Zainal Abidin
• Investigators: Study Chair: Kamarul Amin. bin Abdullah @ Abu Bakar., Assoc. Prof. Ts. Dr., Universiti Sultan Zainal Abidin (UniSZA)

Study record dates

Study Major Dates

• Study Start (Actual): February 1, 2023
• Primary Completion (Actual): December 16, 2024
• Study Completion (Actual): December 16, 2024

Study Registration Dates

• First Submitted: January 8, 2026
• First Submitted That Met QC Criteria: January 8, 2026
• First Posted (Actual): January 15, 2026

Study Record Updates

• Last Update Posted (Actual): January 15, 2026
• Last Update Submitted That Met QC Criteria: January 8, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: Contrast Media; Pulmonary Embolism; Image Quality; Computed Tomography Pulmonary Angiography; Bolus Tracking; Superior Vena Cava; Low-volume Protocol
• Additional Relevant MeSH Terms: Vascular Diseases; Cardiovascular Diseases; Respiratory Tract Diseases; Lung Diseases; Embolism and Thrombosis; Embolism; Pulmonary Embolism
• Other Study ID Numbers: NMRR-20-699-54086 (IIR)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will be kept strictly confidential in accordance with the hospital's privacy policies and the informed consent agreement. To protect participant privacy, only aggregated results and statistical data will be reported in publications.

Drug and device information, study documents

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