Journal of Cardiovascular Computed Tomography
Original Research ArticlePrevalence and nature of excluded findings at reduced scan length CT angiography for pulmonary embolism
Introduction
CT pulmonary angiography (CTPA) has become the preferred method for diagnosing pulmonary embolism (PE).1, 2 The need for rapid and accurate PE diagnosis combined with the widespread availability of multidetector CT have led to a significant increase in the number of patients being imaged for PE by CT both in emergency department and hospitalized patients.3, 4 Unfortunately, the radiation dose associated with CTPA can be substantial, ranging from 2 to 20 mSv1, 5, 6; thus, efforts to reduce dose are warranted. Because scan length is linearly related to radiation dose,7 reduction of scan length has the potential to significantly decrease patient dose without altering the diagnostic accuracy for PE detection provided that the z-axis coverage is adequate. Scan length reduction also leads to shorter breath-hold durations and may in turn decrease or eliminate breathing-related artifacts. It has been suggested that a scan length from just above the aortic arch to just below the heart maintains diagnostic accuracy for PE while yielding an average scan length of 16.3 cm and decreasing z-axis coverage by 37%.8 More recently, it has been shown that even further reduction of scan length to a fixed value of 14.2 cm is possible.9
With scan length reduction, however, important additional or alternative diagnoses may be excluded from the imaging volume and therefore go undetected. These undetected findings may or may not be relevant to the clinical presentation. The purpose of this study was to determine the prevalence and nature of excluded findings at reduced scan length CTPA.
Section snippets
Methods
Our hospital’s institutional review board approved the design of this retrospective study, and all data were handled in compliance with the Health Insurance Portability and Accountability Act. Informed consent was waived because this study was conducted on existing CTPA data sets.
Results
A total of 341 CTPA studies were conducted during the review period of which 6 were repeat studies that were not included in the analysis. Therefore, 335 studies were reviewed (200 women (60%); age, 56 ± 18 years). Of these 28 (8%) were positive for PE. The average scan length of the original studies was 28.0 ± 3.4 cm, and the reduced scan range would have decreased z-axis coverage by 49% ± 6%. The average DLP was 476 ± 210 mGy · cm, and the average effective dose was 8.1 ± 3.6 mSv.
There were a
Discussion
Scan length is an important determinant of radiation dose at CTPA and 3 recent studies have reported that scan length can be reduced substantially while maintaining diagnostic accuracy for PE.8, 9, 10 A scan length extending from just above the aortic arch to just below the heart (∼16.3 cm) reduces mean scan length by ≤38% compared with standard z-axis coverage. This scan range is appealing because it permits comprehensive simultaneous evaluation of the thoracic aorta, the pulmonary arteries,
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Conflict of interest: The authors report no conflicts of interest.