Author: Zahra Alyani Nezhad, Carrie Bartels, Rachel Bladorn, Sean D. Rose, Kelsey Schluter, Timothy P. Szczykutowicz 👨🔬
Affiliation: Departments of Radiology and Medical Physics, University Wisconsin-Madison, University of Wisconsin Madison, University of Wisconsin-Madison, University of Texas at Houston Medical School, University of Wisonsin-Madison 🌍
Purpose: Pulmonary embolism is a life-threatening condition, and computed tomography pulmonary angiography (CTPA) is the gold standard for diagnosis. Inadequate contrast enhancement often leads to a high repeat rate. One of the most common causes of suboptimal contrast enhancement is improper scan timing. The purpose of this study is to determine the optimal scan delay for CTPA exams though retrospective study and prospective trials.
Methods: A retrospective analysis was performed on patients who underwent CTPA (contrast volume=86ml, scanned at tube potential of 80, 100 and 120 kV). We recorded the mean time relative to injection duration that produced the highest PA CT enhancement. Time points were derived from DICOM header tags and injection duration was calculated from contrast volume divided by injection rate. Based on these results, a prospective trial was conducted to evaluate patients undergoing CTPA with scan delays set to the injection duration, adjusted by the identified optimal time point (i.e., using a fixed scan delay based on the bolus volume). To assess the significance of PA enhancement increases, the 120 kV tube potential cohort in the bolus-tracking group was compared to the PA enhancement in the same tube potential cohorts from the trials.
Results: Maximum PA enhancement occurred approximately 2.5-3 s after injection completion in bolus-tracking cohort with 44 patients. Hence, prospective trials were done with scan delay equal 2s+injection duration (37 patients) and 4s+inejtcion duration (30 patients), respectively. 25th, 50th, and 75th percentiles of PA enhancement was [261, 299, 330]/[322, 370, 424]/[126, 171, 367] for bolus-tracking cohort, 2s-trial, and 4s-trial respectively. Mann-Whitney U test showed statistical increase in PA enhancement in 2s-trial compared to bolus tracking cohort (p<0.05).
Conclusion: A scan delay of 2 seconds plus the injection duration results in higher pulmonary artery (PA) enhancement relative to using bolus tracking and 4 second fixed delay.