Metal implants on abdominal CT: does split-filter dual-energy CT provide additional value over iterative metal artifact reduction?

Abstract

Purpose To assess image quality and metal artifact reduction in split-filter dual-energy CT (sfDECT) of the abdomen with hip or spinal implants using virtual monoenergetic images (VMI) and iterative metal artifact reduction algorithm (iMAR). Methods 102 portal-venous abdominal sfDECTs of patients with hip (n = 71) or spinal implants (n = 31) were included in this study. Images were reconstructed as 120kVp-equivalent images (Mixed) and VMI (40–190 keV), with and without iMAR. Quantitative artifact and image noise was measured using 12 different ROIs. Subjective image quality was rated by two readers using a five-point Likert-scale in six categories, including overall image quality and vascular contrast. Results Lowest quantitative artifact in both hip and spinal implants was measured in VMI190keV-iMAR. However, it was not significantly lower than in MixediMAR (for all ROIs, p = 1.00), which were rated best for overall image quality (hip: 1.00 [IQR: 1.00–2.00], spine: 3.00 [IQR:2.00–3.00]). VMI50keV-iMAR was rated best for vascular contrast (hip: 1.00 [IQR: 1.00–2.00], spine: 2.00 [IQR: 1.00–2.00]), which was significantly better than Mixed (both, p < 0.001). VMI50keV-iMAR provided superior overall image quality compared to Mixed for hip (1.00 vs 2.00, p < 0.001) and similar diagnostic image quality for spinal implants (2.00 vs 2.00, p = 0.51). Conclusion For abdominal sfDECT with hip or spinal implants MixediMAR images should be used. High keV VMI do not further improve image quality. IMAR allows the use of low keV images (VMI50keV) to improve vascular contrast, compared to Mixed images. Graphical abstract

Combining iterative metal artifact reduction and virtual monoenergetic images severely reduces hip prosthesis-associated artifacts in photon-counting detector CT

“…As reported previously 15 , 23 , 28 , combining IMAR and high keV VMI led to the appearance of new hypodense artifacts adjacent to implants, suggesting a local overcorrection of artifacts. These new artifacts intensify with higher keV VMI and thereby limit diagnostic assessment of surrounding tissue.…”

“…Several studies have investigated the effects of VMI and IMAR for reduction of artifacts in dual energy EID-CT 9 , 20 – 26 . A recent study investigating split-filter EID-CT with images reconstructed at 120 kVp-equivalent, reported that PI images in combination with IMAR leads to best artifact reduction 15 . In contrast, most previous EID-CT studies reported best artifact reduction for high-energy VMI in combination with IMAR 23 – 26 .…”

“…As recently reported for EID-CT, in PCD-CT IMAR is superior to VMI for the reduction of extensive artifacts but may lead to distortion and blurring. VMI effectively reduces minor artifacts without distorting images 15 , 23 .…”

“…Furthermore, values and standard deviation of X-ray attenuation was evaluated in muscle tissue, bone and bladder tissue with and without presence of artifacts. Hereby, differences in attenuation and gradient of attenuation of tissue were measured and an adjusted attenuation and image noise assessed as proposed previously 15 . Adjusted attenuation was assessed to differentiate artifact reduction from regular changes in Hounsfield units (HU) for differing VMI energy levels.…”

Updates on the Applications of Spectral Computed Tomography for Musculoskeletal Imaging

“…To mitigate such limitations, iterative metal-artifact reduction (iMAR) algorithms can be utilized at lower energy levels. This allows for vascular visualization and minimizes the large number of metal artifacts typically associated with lower energy levels [84]. iMAR algorithms use an iterative loop to identify areas in the image affected by metal hardware, estimate what the image should look like without the metal hardware, and then correct and refine the image to reduce metal artifacts [91].…”