Influence of CT metal artifact reduction on SPECT/CT quantification of bone scintigraphy – Retrospective study for selected types of metal implants

Abstract

Aim Implanted metal prostheses can cause severe artifacts in reconstructed computed tomography (CT) images. To reduce the diagnostic impact of these artifacts and improve attenuation correction in single photon emission computed tomography (SPECT), an algorithm of iterative metal artifact reduction (iMAR) for SPECT/CT systems was developed. The aims of this study were (a) to assess the difference in visual image quality by comparing CT and SPECT images reconstructed with and without iMAR and (b) to determine the influence of iMAR on quantitative ^99mTc-uptake in SPECT/CT.

Methods This retrospective study includes 21 patients with implanted metal prostheses who underwent SPECT/CT bone scintigraphy. CT data were reconstructed with iMAR and without (noMAR) and were used for attenuation correction of SPECT data for xSPECT Quant and xSPECT Bone reconstruction. The effect of iMAR on image quality was evaluated by visual analysis and the effect on quantitative SPECT/CT was assessed by measuring HU values and absolute uptake values (kBq/mL) in volumes of interest (VOIs).

Results There was a significant reduction of visible metal artifacts with iMAR (p<0.01) in the CT images, but visual differences in the SPECT images were minor. The values of quantitative tracer uptake in VOIs near metal implants were lower for iMAR vs. noMAR xSPECT Quant (p<0.01). Only VOIs near metal showed significant differences in HU values, which were 14.6% lower for iMAR CT (p<0.01).

Conclusion The use of iMAR reduces metal artifacts in CT and improves the perceived image quality. Although in some cases a significant difference in the quantitative evaluation of SPECT/CT was observed, the influence of iMAR can be considered small in relation to other factors in the clinical setting.

Zusammenfassung

Ziel Implantierte Metallprothesen verursachen schwere Artefakte in rekonstruierten Computertomografiebildern (CT). Zur Verbesserung der diagnostischen Aussagekraft und der Schwächungskorrektur in der Einzelphotonen-Emissionscomputertomografie (SPECT) wurde ein Algorithmus zur iterativen Reduktion von Metallartefakten (iMAR) für SPECT/CT-Systeme entwickelt. Ziel der Studie war es, (a) den visuellen Unterschied durch den Vergleich von CT- und SPECT-Bildern, rekonstruiert mit und ohne iMAR, zu bewerten und (b) den Einfluss von iMAR auf die quantitative ^99mTc-Aufnahme bei der SPECT/CT zu bestimmen.

Methoden Die retrospektive Studie umfasst 21 Patient*innen mit implantierten Metallprothesen, bei denen eine SPECT/CT-Knochenszintigrafie durchgeführt wurde. Die CT-Daten wurden mit iMAR und ohne (noMAR) rekonstruiert und zur Schwächungskorrektur der SPECT-Daten für die xSPECT-Quant- und xSPECT-Bone-Rekonstruktion verwendet. Der Effekt von iMAR auf die Bildqualität wurde durch eine visuelle Analyse bewertet, und der Einfluss auf die quantitative SPECT/CT wurde durch Messung der HU-Werte und der absoluten Aufnahmewerte (kBq/mL) beurteilt.

Ergebnisse Im Gegensatz zu den SPECT-Bildern wurden durch iMAR die Artefakte in den CT-Bildern signifikant reduziert (p<0,01). Die Werte der Tracer-Aufnahme nahe der Metallimplantate waren bei iMAR im Vergleich zu noMAR xSPECT Quant geringer (p<0,01). Bei den CT-HU-Werten betrug dieser Unterschied 14,6% (p<0,01).

Schlussfolgerung Die Anwendung von iMAR reduziert Metallartefakte in der CT und verbessert die Bildqualität. Obwohl teilweise signifikante Unterschiede in der quantitativen SPECT/CT-Auswertung beobachtet wurden, kann der Einfluss von iMAR im Verhältnis zu anderen Faktoren in der Klinik als gering angesehen werden.

Keywords

iMAR - Bone-Scintigraphy - quantitative SPECT reconstruction - metal artifacts - Tc-99m-DPD

Publication History

Received: 29 March 2022

Accepted after revision: 17 June 2022

Article published online:
09 August 2022

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