Dependency of image quality on acquisition protocol and image processing in chest tomosynthesis-a visual grading study based on clinical data

Abstract

Objective: To compare the quality of images obtained with two different protocols with different acquisition time and the influence from image post processing in a chest digital tomosynthesis (DTS) system.

Methods: 20 patients with suspected lung cancer were imaged with a chest X-ray equipment with tomosynthesis option. Two examination protocols with different acquisition times (6.3 and 12 s) were performed on each patient. Both protocols were presented with two different image post-processing (standard DTS processing and more advanced processing optimised for chest radiography). Thus, 4 series from each patient, altogether 80 series, were presented anonymously and in a random order. Five observers rated the quality of the reconstructed section images according to predefined quality criteria in three different classes. Visual grading characteristics (VGC) was used to analyse the data and the area under the VGC curve (AUC_VGC) was used as figure-of-merit. The 12 s protocol and the standard DTS processing were used as references in the analyses.

Results: The protocol with 6.3 s acquisition time had a statistically significant advantage over the vendor-recommended protocol with 12 s acquisition time for the classes of criteria, Demarcation (AUC_VGC = 0.56, p = 0.009) and Disturbance (AUC_VGC = 0.58, p < 0.001). A similar value of AUC_VGC was found also for the class Structure (definition of bone structures in the spine) (0.56) but it could not be statistically separated from 0.5 (p = 0.21). For the image processing, the VGC analysis showed a small but statistically significant advantage for the standard DTS processing over the more advanced processing for the classes of criteria Demarcation (AUC_VGC = 0.45, p = 0.017) and Disturbance (AUC_VGC = 0.43, p = 0.005). A similar value of AUC_VGC was found also for the class Structure (0.46), but it could not be statistically separated from 0.5 (p = 0.31).

Conclusion: The study indicates that the protocol with 6.3 s acquisition time yields slightly better image quality than the vender-recommended protocol with acquisition time 12 s for several anatomical structures. Furthermore, the standard gradation processing (the vendor-recommended post-processing for DTS), yields to some extent advantage over the gradation processing/multiobjective frequency processing/flexible noise control processing in terms of image quality for all classes of criteria. Advances in knowledge: The study proves that the image quality may be strongly affected by the selection of DTS protocol and that the vendor-recommended protocol may not always be the optimal choice.

Figure 1.

A chest tomosynthesis examination is performed with the patient standing in the PA. Information was derived from Fujifilm, Tokyo, Japan. PA, posteroanterior.

Figure 2.

The DTS series with 12 and 6.3 s acquisition times, were first reconstructed according to the recommendation by the vendor (standard processing) and transferred to the PACS. Then the same reconstructed DTS images were reprocessed with the same image processing parameters as the current conventional chest images and transferred to PACS. DTS, digital tomosynthesis; PACS. picture archiving and communication system.

Figure 3.

The interface of ViewDEX 2.0 adapted to VGC study in chest tomosynthesis. VGC, visual grading characteristics.

Figure 4.

An example of a VGC curve, reflecting how the proportion of images that are judged as being of higher quality than a certain threshold for protocol identity ID 65 (with acquisition times 6.3 s) varies with this proportion for protocol ID 76 (with acquisition times 12 s), when the threshold is altered, for the disturbance class of criteria.VGC, visual grading characteristics.