Metal artifact reduction in patients with total hip replacements: evaluation of clinical photon counting CT using virtual monoenergetic images

Abstract

Objectives To investigate photon-counting CT (PCCT)–derived virtual monoenergetic images (VMI) for artifact reduction in patients with unilateral total hip replacements (THR). Methods Forty-two patients with THR and portal-venous phase PCCT of the abdomen and pelvis were retrospectively included. For the quantitative analysis, region of interest (ROI)–based measurements of hypodense and hyperdense artifacts, as well as of artifact-impaired bone and the urinary bladder, were conducted, and corrected attenuation and image noise were calculated as the difference of attenuation and noise between artifact-impaired and normal tissue. Two radiologists qualitatively evaluated artifact extent, bone assessment, organ assessment, and iliac vessel assessment using 5-point Likert scales. Results VMI110keV yielded a significant reduction of hypo- and hyperdense artifacts compared to conventional polyenergetic images (CI) and the corrected attenuation closest to 0, indicating best possible artifact reduction (hypodense artifacts: CI: 237.8 ± 71.4 HU, VMI110keV: 8.5 ± 122.5 HU; p < 0.05; hyperdense artifacts: CI: 240.6 ± 40.8 HU vs. VMI110keV: 13.0 ± 110.4 HU; p < 0.05). VMI110keV concordantly provided best artifact reduction in the bone and bladder as well as the lowest corrected image noise. In the qualitative assessment, VMI110keV received the best ratings for artifact extent (CI: 2 (1–3), VMI110keV: 3 (2–4); p < 0.05) and bone assessment (CI: 3 (1–4), VMI110keV: 4 (2–5); p < 0.05), whereas organ and iliac vessel assessments were rated highest in CI and VMI70keV. Conclusions PCCT-derived VMI effectively reduce artifacts from THR and thereby improve assessability of circumjacent bone tissue. VMI110keV yielded optimal artifact reduction without overcorrection, yet organ and vessel assessments at that energy level and higher were impaired by loss of contrast. Clinical relevance statement PCCT-enabled artifact reduction is a feasible method for improving assessability of the pelvis in patients with total hip replacements at clinical routine imaging. Key Points • Photon-counting CT-derived virtual monoenergetic images at 110 keV yielded best reduction of hyper- and hypodense artifacts, whereas higher energy levels resulted in artifact overcorrection. • The qualitative artifact extent was reduced best in virtual monoenergetic images at 110 keV, facilitating an improved assessment of the circumjacent bone. • Despite significant artifact reduction, assessment of pelvic organs as well as vessels did not profit from energy levels higher than 70 keV, due to the decline in image contrast.

Photon-counting detector CT – first experiences in the field of musculoskeletal radiology

“…6). Similar results were also shown for artifact reduction after total hip replacement [87]. For the reduction of dental metal artifacts, IMAR showed promising results.…”

Metal Artifact Reduction in Photon-Counting Detector CT

“…20,21 These clinical studies also found best results for VMIs at an energy level of 110 keV. [18][19][20] However, some studies did not see a significant reduction in artifacts with VMIs alone, which might be connected to the deviations in CT numbers also observed in this study. 17,18 Nonetheless, these studies still found additional benefits when combining iMAR and VMIs.…”

“…14,28 Although some current clinical studies yield similar results for the optimum VMI energy level, other levels might still be better suited for specific implants or clinical tasks. [18][19][20] In conclusion, both iMAR and VMI at energy levels from 110 keV to 150 keV were independently effective for metal artifact reduction on the clinical photon-counting CT scanner, but yielded the strongest artifact reduction when both methods were combined. We…”

“…The main limitation of the current study is that the results from the photon-counting CT scanner were not compared with a conventional CT scanner with energy-integrating detector. Although clinical data were not evaluated as part of this study, and clinical implants can be more complex in shape, size, and composition than the evaluated metal rods, the results show good agreement with previous clinical studies on metal artifact reduction in PCD-CT. [17][18][19][20][21] In addition, the evaluation was focused on ROI measurements in preselected positions. Further studies should also investigate the impact of metal artifacts on clinical tasks, for example, diagnostic performance.…”

Comparison of Bone Evaluation and Metal Artifact between Photon-Counting CT and Five Energy-Integrating-Detector CT under Standardized Conditions Using Cadaveric Forearms

“…Increasing the keV setting in a VMI can effectively eliminate beam hardening due to metal implants [17,25]. Recently, the same phenomenon was observed using PCCT [24,26,27], with one study reporting that a 130 keV VMI of patients with spinal implants had significantly fewer metal artifacts than a 65 keV VMI [24]. They also suggested that VMIs produced using PCCT had fewer metal artifacts than standard EIDCT images.…”