Image quality of multiplanar reconstruction of pulmonary CT scans using adaptive statistical iterative reconstruction

Abstract

Objective: We investigated the image quality of multiplanar reconstruction (MPR) using adaptive statistical iterative reconstruction (ASIR).

Methods: Inflated and fixed lungs were scanned with a garnet detector CT in high-resolution mode (HR mode) or non-high-resolution (HR) mode, and MPR images were then reconstructed. Observers compared 15 MPR images of ASIR (40%) and ASIR (80%) with those of ASIR (0%), and assessed image quality using a visual five-point scale (1, definitely inferior; 5, definitely superior), with particular emphasis on normal pulmonary structures, artefacts, noise and overall image quality.

Results: The mean overall image quality scores in HR mode were 3.67 with ASIR (40%) and 4.97 with ASIR (80%). Those in non-HR mode were 3.27 with ASIR (40%) and 3.90 with ASIR (80%). The mean artefact scores in HR mode were 3.13 with ASIR (40%) and 3.63 with ASIR (80%), but those in non-HR mode were 2.87 with ASIR (40%) and 2.53 with ASIR (80%). The mean scores of the other parameters were greater than 3, whereas those in HR mode were higher than those in non-HR mode. There were significant differences between ASIR (40%) and ASIR (80%) in overall image quality (p<0.01). Contrast medium in the injection syringe was scanned to analyse image quality; ASIR did not suppress the severe artefacts of contrast medium.

Conclusion: In general, MPR image quality with ASIR (80%) was superior to that with ASIR (40%). However, there was an increased incidence of artefacts by ASIR when CT images were obtained in non-HR mode.

Figure 1

Multiplanar reconstruction (MPR) images of inflated and fixed lung in high-resolution (HR) mode (a–c) and non-HR mode (d–f). CT images were reconstructed with adaptive statistical iterative reconstruction (ASIR) (0%) (a,d), ASIR (40%) (b,e) and ASIR (80%) (c,f). Normal structures were more clearly seen using ASIR in HR mode (arrow head). Streak artefacts were more severe using ASIR in non-HR mode (arrow).

Figure 2

Axial CT images of contrast medium in high-resolution (HR) mode (a–c) and non-HR mode (d–f). The area surrounded by a dashed line is shown, magnified, in the upper right-hand corner of the image. CT images were reconstructed with adaptive statistical iterative reconstruction (ASIR) (0%) (a,d), ASIR (40%) (b,e) and ASIR (80%) (c,f). Mild streak artefacts (arrowhead) were reduced using ASIR, but severe streak artefacts (arrow) were more prominent using ASIR, especially in non-HR mode.

Figure 3

Multiplanar reconstruction images of contrast medium in high-resolution (HR) mode (a–c) and non-HR mode (d–f), which were obtained with adaptive statistical iterative reconstruction (ASIR) (0%) (a,d), ASIR (40%) (b,e) and ASIR (80%) (c,f). The area surrounded by a dashed line is shown, magnified, in the upper right-hand corner of the image. Mild streak artefacts (arrow) become unclear, and the margins of contrast medium become clear using ASIR in HR mode. Severe streak artefacts (arrow head) become dense and clear using ASIR in non-HR mode.

Figure 4

Axial CT images (a,b) and multiplanar reconstruction (MPR) images of left upper lung (c,d) in high-resolution mode on enhanced CT. CT images were reconstructed with adaptive statistical iterative reconstruction (ASIR) (0%) (a,c) and ASIR (80%) (b,d). Although streak artefacts owing to contrast medium of left subclavian vein were seen in ASIR (0%) (a), mild streak artefacts were reduced in ASIR (80%) (b). Noise was reduced and the normal structures such as vessels or bronchus were more clearly seen in MPR image with ASIR (80%) (d) compared with ASIR (0%) (c).