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: This study presents a scientifically quantified case study that underscores the importance of the medical physicist’s contribution to contrast enhancement optimization.
Methods: CT pulmonary angiography (CTPA) with bolus-tracking was assessed for repeat rates and optimal scan timing for maximum pulmonary artery (PA) enhancement. Based on these findings, we conducted prospective trials using the determined optimal scan delay. The trial with the lowest repeat rate and significant enhancement increase was adopted as the new institutional protocol. Medical physicists quantified iodine enhancement and calculated exam timeliness in cases of poor enhancement on the new protocol that were repeated with bolus-tracking.
Results: CTPA of 55 patients using bolus-tracking showed a 7% repeat rate. The highest peak enhancement occurred 2.5-3s after injection completion. Prospective trials of 37 patients with 2s+injection delays and 30 patients with 4s+injection delays had a 5% and 36% repeat rates, respectively. Mann-Whitney U test showed statistical increase in PA enhancement in 2s-trial compared to bolus-tracking cohort (p<0.05). Hence, the 2s+injection duration was selected as the optimal scan delay, leading to a 44% repeat rate (12 cases) in 27 patients. Five cases had breath motion, one was due to technician error, and six were repeated with bolus tracking, showing a delay of about injection duration+2s resulted in proper enhancement. Repeat rates with the new protocol were higher than expected based on the 2s-trial. Medical physicist’s analysis revealed that CT technologists misadjusted scan delay due to a mismatch between the scanner protocol (programmed based on patients’ effective diameter) and the contrast protocol (based on patients’ weight).
Conclusion: We reported an analysis of CTPA optimization. Medical physicists identified causes of failure and designed new timing delays. Without a medical physicist's involvement, the high repeat rate of the original protocol might have been assumed to be unavoidable.