Published online Mar 28, 2018. doi: 10.4329/wjr.v10.i3.24
Peer-review started: February 10, 2018
First decision: March 12, 2018
Revised: March 14, 2018
Accepted: March 19, 2018
Article in press: March 20, 2018
Published online: March 28, 2018
Processing time: 46 Days and 14.3 Hours
Pulmonary embolism is a common and serious medical problem often evaluated using computed tomography (CT) pulmonary angiography. In the clinical setting the disease course is not followed by embolic volume measurements; however in clinical pharmaceutical trials, measuring embolic load is useful to assess for drug efficacy, potency and optimal duration of treatment. Volume measurements can be made using semi-automated region-growing techniques and the goal of this study was to assess the accuracy of these measurements.
Our Core Research Imaging Lab group specializes in cardiovascular disease. Frequently we analyze data coming from multiple outside radiology centers where imaging protocols often vary from one site to another. To assess the validity of region growing volume measurements in CT pulmonary angiography, we devised this study to assess for significant differences in results with changes in acquisition and reconstruction of images that often occur in multicenter studies such as the ones in which we participate.
The overall goal was to validate the imaging assessment methods used in multicenter clinical trials evaluating treatment options for pulmonary embolism using CT angiography.
In this study ten blood clots were made and each clot was weighed on a laboratory precision scale and assessed for volume (the gold standard) using the water displacement method in graduated cylinders. Volume measurements were made on CT images of the blood clots in test tubes. The CT images were obtained with varying acquisition and reconstruction parameters and the clots were placed in diluted contrast material to simulate pulmonary emboli as they would appear in a CT angiogram. A single image analyst made the measurements using a semi-automated region growing algorithm using FDA-approved Siemens syngo.via image analysis platform. A mixed model statistical analysis was performed on the data.
Overall the study showed that varying the image acquisition parameters and using iterative reconstructions had no significant impact on clot volume measurements with, however, the exception of pitch.
The new findings of this study are that varying the image acquisition parameters and reconstructions did not have a significant impact on clot volume measurements, with the exception of pitch. In terms of pitch, pitch = 0.9 yielded higher volume measurements than with pitch = 0.6 or 1.2. This could be due to limitations in the accuracy of our gold standard, yet it is recommended to give pitch protocol guidance to sites for accuracy and repeatability in volume measurements. The present study confirms and validates research methods currently in use. The study found that using data acquired in the multicenter setting is viable for volume assessment of pulmonary emboli in pharmaceuticals research and thus, has an important impact on the development of therapies for this common and severe medical problem.
Our findings indicate that care must be taken when evaluating data from multiple centers while evaluating thrombus volume in pulmonary embolism and appropriate corrections made for differences in acquisition and reconstruction across the multiple sites. Future research can evaluate more imaging parameters such as tube current used for its role on pulmonary embolism thrombus volume quantification.