Value of virtual monochromatic spectral images with metal artifact reduction algorithm in dual-energy computed tomography-guided microcoil localization of pulmonary nodules

Abstract

To evaluate the clinical value of virtual monochromatic spectral (VMS) images with metal artifact reduction (MAR) algorithm in dual-energy computed tomography (DECT)-guided microcoil localization of pulmonary nodules.Fifty-one patients underwent DECT after placement of microcoils on small pulmonary nodules before video-assisted thoracoscopic surgery (VATS). Optimal energy level (in keV) was defined as the level at which CT values of nodules were equivalent to those of 120 kVp images and with no serious metal artifacts. VMS images at optimal keV and at 50, 90,110, and 140 keV with and without MAR were reconstructed. Image quality was scored using a 3-point scale: 1 = excellent, minimal artifacts; 2 = good, mild artifacts; and 3 = poor, extensive artifacts. Image quality scores between the VMS-only and VMS + MAR groups were compared;74 keV was found to be the optimal level for VMS images. The image quality of the VMS + MAR images at 74 keV were significantly better than VMS-only images (1.35 ± 0.59 vs 2.11 ± 0.87, P = .005). There was no difference in image quality score among VMS + MAR images at 74 keV and higher energy levels.VMS images from DECT at 74 keV with MAR can reduce artifacts from microcoils and improve image quality for microcoil localization of pulmonary nodules.

Figure 1

Images of 74 keV virtual monochromatic spectral (VMS): the CT value of lung nodules was closest to that of the 120 kVp image. Image (A) (120 kVp): the CT value of a lung nodule was –544.6 HU. Image (B) (spectral curve of lung nodules): the CT value of the same lung nodule as function of photon energy, decreasing with the increase of keV value. Image (C) (74 keV): the CT value of the lung nodule was –544.5 HU.

Figure 2

Localization with microcoil tailing: the microcoil head was released at the lung tissues near the nodules, but the microcoil tail was coiled on visceral pleural surface. Image (A) (VMS-only image): serious metal artifacts, unclear display of microcoil head/tail, poor image quality (score of 3). Image (B) (VMS + MAR image): metal artifacts greatly reduced, clear display of microcoil head/tail, excellent image quality (score of 1).

Figure 3

Hemorrhage caused by the puncturing. Image (A) (VMS-only image): some metal artifacts not seriously influencing the visualization for hemorrhage, good image quality (score of 2). Image (B) (VMS + MAR image): metal artifacts greatly reduced, clear display of microcoil head and hemorrhage, excellent image quality (score of 1).

Figure 4

Hemorrhage caused by the puncturing. Image (A) (VMS-only image): severe metal 4artifacts seriously influencing the visualization for hemorrhage, poor image quality (score of 3). Image (B) (VMS + MAR image): metal artifacts greatly reduced, clear display of hemorrhage, excellent image quality (score of 1).

Figure 5

Nodule adjacent to the pleura, microcoil localization on visceral pleural surface near the nodule. Image (A) (VMS-only image): concealment of nodules (as directed by arrow) and pleura by metal artifact, non-judgment on whether the microcoil head was placed on visceral pleural surface near the nodules, poor image quality (score of 3). Image (B) (VMS + MAR images): metal artifacts greatly reduced, more clear display of nodules (as directed by arrow), pleura and rib, excellent image quality (score of 1).

Figure 6

Nodules adjacent to microcoil head. Image (A) (VMS-only image): concealment of nodules by metal artifact, poor image quality (score of 3). Image (B) (VMS + MAR image): metal artifacts greatly reduced, excellent image quality (1 score).

Figure 7

VMS + MAR images at 50 keV, 74 keV, 90 keV, 110 keV, and 140 keV: as compared with other images, the VMS + MAR images at 50 keV had a more serious metal artifact and a higher image noise; between the VMS + MAR images at 74 keV and higher energy levels, the severities of metal artifact were not significantly different.