The Effect of Limiting the Scan Range of Computed Tomography Pulmonary Angiography (to Reduce Radiation Exposure) on the Detection of Pulmonary Embolism: A Systematic Review.

Amayar Zaw,Rebecca Nguyen,Claudia C Dobler,Anthony Kaplan,Leon Lam

doi:10.3390/diagnostics11122179

Abstract

(1) Background: Computed tomography pulmonary angiography (CTPA) is the standard imaging test for the evaluation of acute pulmonary embolism (PE), but it is associated with patients’ exposure to radiation. Studies have suggested that radiation exposure can be reduced without compromising PE detection by limiting the scan range (the z-axis, going from up to down); (2) Methods: A literature search was conducted in MEDLINE and EMBASE on 17 July 2021. Studies were included if they enrolled patients who had undergone a CTPA and described the yield of PE diagnoses, number of missed filling defects and/or other diagnoses using a reduced z-axis in comparison to a full-length scan. To assess risk of bias, we modified an existing risk of bias tools for observational studies, the Newcastle-Ottawa Scale. Results were synthesized in a narrative review. Primary outcomes were the number of missed PE diagnoses (based on at least one filling defect) and filling defects; the secondary outcome was the number of other missed findings; (3) Results: Eleven cohort studies and one case-control study were included reporting on a total of 3955 scans including 1025 scans with a diagnosis of PE. Six different reduced scan ranges were assessed; the most studied was from the top of the aortic arch to below the heart, in which no PEs were missed (seven studies). One sub-segmental PE was missed when the scan coverage was 10 cm starting from the bottom of the aortic arch and 14.7 cm starting from the top of the arch. Five studies that reported on other findings all found that other diagnoses were missed with a reduced z-axis. Most of the included studies had a high risk of bias; (4) Conclusions: CTPA scan coverage reduction from the top of aortic arch to below the heart reduced radiation exposure without affecting PE diagnoses, but studies were generally at high risk of bias.

Highlights

Pulmonary embolism (PE) is a common and treatable disease that, if missed, can be associated with high morbidity and mortality, making efficient and accurate diagnosis important to ensure proper patient care [1]
Of the different types of z-axis length assessed, from the top of the aortic arch to below the heart was the most frequently investigated by seven studies, and no PE diagnoses were missed with this z-axis length
Diagnosis of a sub-segmental PE was missed once with two different reduced z-axis windows—a 10 cm window starting from the bottom of the arch and a 14.7 cm window starting from the top of the aortic arch

Summary

Introduction

Pulmonary embolism (PE) is a common and treatable disease that, if missed, can be associated with high morbidity and mortality, making efficient and accurate diagnosis important to ensure proper patient care [1]. Relative to other imaging modalities, CTPAs are fast and minimally invasive, highly specific for PE and widely accessible. They are a frequently ordered test to diagnose or exclude PE. The relatively low yield of the diagnostic test highlights the importance of clinical risk scores to help identify patients with high pre-test probability for PE, and the importance of weighing up risks and benefits of the imaging test. The most significant risk is the exposure to ionizing radiation. This is of particular concern in young and/or pregnant women, because of a potential long-term increased risk of breast cancer and possible harm to the fetus [5]. While identification of other pathologies can be beneficial, for example when identifying alternative etiologies of a patient’s symptoms, discovery of incidental findings can lead to potentially unnecessary further diagnostic investigations and treatments [7]

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