Optimizing Suboptimal/Nondiagnostic Computed Tomographic Pulmonary Angiography

Hung Lin (SUNY Downstate Medical Center), Paul Fang (SUNY Downstate Medical Center), Justin Holder (SUNY Downstate Medical Center), Stephen Waite (SUNY Downstate Medical Center), Jennifer Martino (SUNY Downstate Medical Center)

Background

Computed tomographic pulmonary angiography (CTPA) is the most commonly performed diagnostic imaging modality to investigate patients with suspected PE. Inevitably, a fraction of CTPA are diagnostically suboptimal, posing a management dilemma for the referring clinicians. Limited literature estimates the incidence of limited CTPAs ranging from 5.9% to 27%.

Objectives

This objective of this quality improvement project was to determine the percentage of limited CTPA at our institution, identify the causes of limited and nondiagnostic CTPAs in our institution and improve the quality of CTPAs.

Methods

A baseline percentage of limited CTPAs was first calculated by retrospectively examining all CTPAs conducted during a 3-month period between March 1st 2017 and May 31st 2017, a total of 218 studies. All studies were reviewed for imaging quality by two residents and two cardiothoracic fellowship trained attendings. Imaging quality was assessed for motion, contrast enhancement, noise, and artifact. Hounsfield Units (HU) of less than 200 measured in the main pulmonary artery (MPA) was considered suboptimal opacification. Potential contributing factors were grouped into four major categories, namely patient, radiologist, technologist, and equipment (Graph 1). Our technique was optimized based on current literature recommendations. After allowing for an adjustment period, we evaluated all CTPAs performed during a 2-month period between January 1st and February 28th 2018, a total of 173 studies. All studies were reviewed in the same manner, by the same radiologists

Results

Of the initial 218 consecutive CTPAs, 92 (42%) studies were limited for evaluation of PE. The most common reason for a limited study was poor opacification of pulmonary arteries and respiratory motion. Modifications were as follows. Contrast density was increased, by changing from Omipaque 300 to Omipaque 350. Contrast volume was reduced from 120 ml to 90 ml. The triggering threshold for scanning was lowered from 150 HU to 130 HU. In normal weight patients, the kilovoltage peak was decreased to 100 kilovoltage. Imaging algorithm was changed from filtered back projection to iterative reconstruction. The importance of proper breathing instruction and correct placement of region of interest on the MPA was reinforced with the technicians via a multiple in-service trainings. Of the 173 consecutive CTPAs after the implementing the modifications, 46 studies (26.5%) were limited.

Conclusion

The percentage of CTPA with limited results in our institution was unacceptably high at 42%, higher than the percentage reported in literature. Through modifying multiple causes, the percentage of limited CTPAs was improved to 26.5%, which signified a nearly 50% reduction and fell within the cited range. There remain non-modifiable factors, such as excessive respiratory motion, pre-existing cardiopulmonary disease, and body habitus. Further improvement may be achieved through caudal-cranial imaging acquisition and practicing breathing instruction prior to scanning.

Implications for the Patient

Adequate CTPA allows well-established treatment algorithm. However, there is no clear guidance on managing patients with indeterminate CTPA. Therefore it is of paramount importance to achieve CTPA with optimal quality as much as possible. We hope our methods may be useful to other institutions to improve their CTPA quality.

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