Reducing Radiation Dose in Adult Head CT using Iterative Reconstruction – A Clinical Study in 177 Patients

Abstract

Purpose: To assess how ASIR (adaptive statistical iterative reconstruction) contributes to dose reduction and affects image quality of non-contrast cranial computed tomography (cCT).

Materials and Methods: Non-contrast emergency CT scans of the head acquired in 177 patients were evaluated. The scans were acquired and processed using four different protocols: Group A (control): 120 kV, FBP (filtered back projection) n = 71; group B1: 120 kV, scan and reconstruction performed with 20 % ASIR (blending of 20 % ASIR and 80 % FBP), n = 86; group B2: raw data from group B1 reconstructed using a blending of 40 % ASIR and 60 % FBP, n = 74; group C1: 120 kV, scan and reconstruction performed with 30 % ASIR, n = 20; group C2: raw data from group C1 reconstructed using a blending of 50 % ASIR and 50 % FBP, n = 20. The effective dose was calculated. Image quality was assessed quantitatively and qualitatively.

Results: Compared to group A, groups B1/2 and C1/2 showed a significantly reduced effective dose of 40.4 % and 73.3 % (p < 0.0001), respectively. Group B1 and group C1/2 also showed significantly reduced quantitative and qualitative image quality parameters. In group B2, quantitative measures were comparable to group A, and qualitative scores were lower compared to group A but higher compared to group B1. Diagnostic confidence grading showed groups B1/2 to be adequate for everyday clinical practice. Group C2 was considered acceptable for follow-up imaging of severe acute events such as bleeding or subacute stroke.

Conclusion: Use of ASIR makes it possible to reduce radiation significantly while maintaining adequate image quality in non-contrast head CT, which may be particularly useful for younger patients in an emergency setting and in follow-up.

Key Points:

• ASIR may reduce radiation significantly while maintaining adequate image quality

• cCT protocol with 20 % ASIR and 40 %ASIR/60 %FBP blending is adequate for everyday clinical use

• cCT protocol with 30 % ASIR and 50 %ASIR/50 %FBP blending is adequate for follow-up imaging

Citation Format:

• Kaul D, Kahn J, Huizing L et al. Reducing Radiation Dose in Adult Head CT using Iterative Reconstruction – A Clinical Study in 177 Patients. Fortschr Röntgenstr 2016; 188: 155 – 162

Zusammenfassung

Ziel: Es war das Ziel dieser Studie zu untersuchen, inwiefern die adaptive statistische iterative Rekonstruktion (ASIR) zur Dosisreduktion bei der nativen, craniellen Computertomografie (cCT) beitragen kann und welchen Einfluss sie auf die Bildqualität hat.

Material und Methoden: Es wurden 177 native cCT unter Notfallbedingungen durchgeführt. Insgesamt wurden 4 verschiedene Protokolle genutzt: Gruppe A (Kontrollgruppe): 120 kV, FBP (filtered back projection) n = 71; Gruppe B1: 120 kV, Scan und Rekonstruktion durchgeführt mit 20 % ASIR (Überblendung von 20 % ASIR und 80 % FBP), n = 86; Gruppe B2: Rohdaten aus Gruppe B1 wurden mit einer Überblendung von 40 % ASIR und 60 % FBP rekonstruiert, n = 74; Gruppe C1: 120 kV, Scan und Rekonstruktion durchgeführt mit 30 % ASIR, n = 20; Gruppe C2: Rohdaten aus Gruppe C1 wurden mit einer Überblendung von of 50 % ASIR and 50 % FBP rekonstruiert, n = 20. Die Effektivdosis aller CTs wurde berechnet; die Bildqualität wurde sowohl quantitativ als auch qualitativ evaluiert.

Ergebnisse: Im Vergleich zur Gruppe A zeigten die Gruppen B1/2 und C1/2 eine signifikant reduzierte Effektivdosis von 40,4 % und 73,3 % (p < 0,0001). Die Gruppen B1 und die Gruppen C1/2 zeigten dabei eine signifikant verminderte quantitative und qualitative Bildqualität. Die Gruppe B2 zeigte mit der Kontrollgruppe A vergleichbare Werte in der quantitativen Analyse, die qualitative Analyse zeigte schlechtere Werte als die Kontrollgruppe aber bessere Werte als Gruppe B1. Die diagnostische Konfidenz der Gruppen B1/2 war hoch genug für den routinemäßigen Gebrauch in der Klinik. Die diagnostische Konfidenz der Gruppe C2 war hoch genug für Folgebildgebungen bei vordiagnostizierten intracraniellen Blutungen und subakutem Schlaganfall.

Schlussfolgerung: ASIR bietet die Möglichkeit zur signifikanten Reduktion der Effektivdosis von craniellen CT bei ausreichend hoher Bildqualität für den täglichen klinischen Gebrauch. Dies ist insbesondere bei jungen Patienten und bei mehrfachen Folgeuntersuchungen von Vorteil.

Kernaussagen:

• Durch ASIR kann die Dosisexposition bei klinisch adäquater Bildqualität signifikant vermindert werden

• 20 % ASIR cCT mit 40 %ASIR/60 %FBP Überblendung sind ausreichend für täglichen klinischen Gebrauch

• 30 % ASIR cCTs mit 50 %ASIR/50 %FBP Überblendung sind ausreichend für Folgebildgebungen

Keywords

cranial computed tomography - cCT - iterative reconstruction - ASIR - dose reduction - filtered back projection

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