Computed tomography pulmonary angiography (CTPA) remains the gold standard for diagnosing pulmonary embolism (PE). Despite continuous technical advances, reducing the volume of contrast agent (CA) remains a priority—particularly in vulnerable patients with renal impairment or multiple comorbidities. Traditional bolus tracking methods, while widely used, do not account for individual variations in cardiovascular function, often resulting in overuse of contrast. A recent study evaluates a personalised high-pitch CTPA protocol using a test bolus technique to tailor scan timing and achieve diagnostic-quality imaging with significantly less contrast agent.
Tailoring Contrast Administration: A Test Bolus Approach
A core limitation of conventional bolus tracking is its inability to account for patient-specific haemodynamic variability. Standard protocols rely on fixed delay times and large volumes of CA to compensate for unknowns in blood circulation. This generalised approach can lead to unnecessary contrast use, especially in modern scanners capable of fast acquisition times.
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The test bolus technique offers a refined alternative by directly measuring the contrast enhancement curve within the pulmonary trunk. In this study, the test bolus method determined the individual time of peak contrast enhancement, which was then multiplied by 1.15 to define a personalised scan delay. By doing so, the protocol aligned scan initiation with optimal vascular opacification, minimising waste and improving efficiency.
This method was implemented across a multi-phase study involving 97 patients referred for suspected PE. The study group (n=77) received only 20 mL of Iomeron 400, significantly less than the 50 mL administered in the control group (n=31). Despite the lower dose, diagnostic performance was preserved, showing that precision timing could offset reduced contrast volume without sacrificing image quality.
Image Quality and Diagnostic Value
The investigation included both objective and subjective assessments of image quality. Objectively, attenuation values in the pulmonary trunk were understandably lower in the reduced contrast group, yet remained well above the diagnostic threshold of 200 Hounsfield units (HU) in 93.5% of cases. Signal-to-noise and contrast-to-noise ratios were also reduced but did not compromise diagnostic clarity. Subjectively, radiologists rated central and peripheral pulmonary artery enhancement as good to very good across all cohorts, irrespective of contrast volume.
Furthermore, the study noted a significant reduction in streak artefacts from residual venous contrast. These artefacts, often visible in the superior vena cava when excess contrast remains in circulation during imaging, were notably fewer in the reduced contrast group. This not only improved diagnostic conditions but highlighted the inefficiency of excess CA in standard protocols.
Among a subset of six patients who underwent both standard and reduced-dose protocols, the results were mixed. Two showed improved imaging with the personalised approach, while four had slightly lower image quality but still exceeded the diagnostic HU threshold. These findings reinforce the view that standard protocols may routinely deliver more contrast than necessary, particularly when individualised timing is not considered.
Implications for Broader Clinical Practice
This study demonstrates that a personalised scan delay can enable meaningful reductions in contrast agent volume during CTPA without compromising diagnostic capability. Notably, the protocol was effective across a diverse patient population, including individuals with obesity, previous lung surgery and cardiovascular or oncological conditions—groups often excluded from similar trials.
Reducing CA dose has direct benefits for patient safety, particularly in those at risk of contrast-induced nephropathy. Additionally, the reduced dose resulted in a lower radiation burden, with a 29% decrease in effective dose observed in the study group compared to controls. These benefits align with the ALARA (As Low As Reasonably Achievable) principle and support broader efforts to minimise procedural risk.
Although the test bolus technique introduces a minor additional step, future integration with algorithm-driven timing software could streamline this process further. If validated in CTPA as it has been in coronary CT angiography, such software could eliminate the need for a preliminary bolus entirely, paving the way for routine use of ultra-low contrast protocols.
Personalised high-pitch CTPA using a test bolus-guided delay represents a clinically viable strategy for reducing contrast agent exposure while preserving image quality. This approach respects inter-patient variability and challenges the assumption that higher contrast volumes are necessary for diagnostic accuracy. By demonstrating its effectiveness across a broad patient population, the study supported the integration of personalised contrast timing into routine CTPA practice, offering safer, more efficient imaging for all patients.
Source: European Journal of Radiology
Image Credit: iStock
