Rofo 2013; 185(08): 741-748
DOI: 10.1055/s-0033-1335937
Neuroradiologie
© Georg Thieme Verlag KG Stuttgart · New York

Intraindividual Evaluation of the Influence of Iterative Reconstruction and Filter Kernel on Subjective and Objective Image Quality in Computed Tomography of the Brain

Intraindividueller Vergleich des Einflusses von iterativer Rekonstruktion und Filterkernel auf die subjektive und objektive Bildqualität der Computertomografie des Neurokraniums
J. H. Buhk
1   Department of Neuroradiology, University Medical Center Hamburg Eppendorf, Germany
,
A. Laqmani
2   Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg Eppendorf, Germany
,
H. C. von Schultzendorff
2   Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg Eppendorf, Germany
,
D. Hammerle
2   Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg Eppendorf, Germany
,
S. Sehner
3   Institute of Medical Biometry and Epidemiology, University Medical Center Hamburg Eppendorf, Germany
,
G. Adam
2   Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg Eppendorf, Germany
,
J. Fiehler
4   Neuroradiology, University Medical Center Hamburg-Eppendorf, Hamburg
,
H. D. Nagel
5   Dr. HD Nagel, Science & Technology for Radiology, Buchholz, Germany
,
M. Regier
2   Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg Eppendorf, Germany
› Author Affiliations
Further Information

Publication History

09 January 2013

23 May 2013

Publication Date:
30 July 2013 (online)

Abstract

Objectives: To intraindividually evaluate the potential of 4th generation iterative reconstruction (IR) on brain CT with regard to subjective and objective image quality.

Methods: 31 consecutive raw data sets of clinical routine native sequential brain CT scans were reconstructed with IR level 0 (= filtered back projection), 1, 3 and 4; 3 different brain filter kernels (smooth/standard/sharp) were applied respectively. Five independent radiologists with different levels of experience performed subjective image rating. Detailed ROI analysis of image contrast and noise was performed. Statistical analysis was carried out by applying a random intercept model.

Results: Subjective scores for the smooth and the standard kernels were best at low IR levels, but both, in particular the smooth kernel, scored inferior with an increasing IR level. The sharp kernel scored lowest at IR 0, while the scores substantially increased at high IR levels, reaching significantly best scores at IR 4. Objective measurements revealed an overall increase in contrast-to-noise ratio at higher IR levels, which was highest when applying the soft filter kernel. The absolute grey-white contrast decreased with an increasing IR level and was highest when applying the sharp filter kernel. All subjective effects were independent of the raters’ experience and the patients’ age and sex.

Conclusion: Different combinations of IR level and filter kernel substantially influence subjective and objective image quality of brain CT.

Zusammenfassung

Zielsetzung: Diese Studie untersucht das Potenzial eines Iterativen Rekonstruktionsverfahrens (IR) der 4. Generation hinsichtlich einer möglichen Verbesserung der subjektiven und objektiven Bildqualität der Computertomografie des Neurokraniums (CCT).

Material und Methoden: 31 konsekutive native sequentielle CCT-Rohdatensätze aus der klinischen Routine wurden mit einem prototypischen Rekonstruktionsrechner nachrekonstruiert. Pro Datensatz wurden insgesamt 12 Rekonstruktionen mit folgenden IR Stufen angefertigt: 0 (= gefilterte Rückprojektion = Kontrolle), 1, 3 und 4; jeweils kombiniert mit 3 unterschiedlichen Filterkerneln (weich/standard/hart). Fünf Radiologen mit unterschiedlicher Erfahrung führten die unabhängige Bewertung der Bildqualität nach einer 4-stufigen Ordinalskala durch. Ergänzend wurde eine ROI-Analyse von Bildkontrast und Bildrauschen durchgeführt. Die statistische Auswertung erfolgte in einem Random Intercept Model.

Ergebnisse: Die Kernel „weich“ und „standard“ erhielten höchste subjektive Bewertungen bei niedrigen IR-Stufen mit fallender Tendenz bei ansteigenden IR Stufen, insbesondere den weichen Kernel betreffend. Der Kernel „hart“ erhielt kontinuierlich höhere Bewertungen mit steigender IR-Stufe. Die objektiven Messungen ergaben eine insgesamt ansteigendes Kontrast-zu-Rausch-Verhältnis mit steigender IR-Stufe, der Grau-Weiß-Kontrast nahm mit ansteigender IR-Stufe etwas ab. Alle beobachteten Effekte wiesen keine signifikante Abhängigkeit von der Erfahrung des Betrachters oder von Alter und Geschlecht der Patienten auf.

Schlussfolgerungen: Durch unterschiedliche Kombinationen von IR-Stufe und Filterkernel lässt sich die subjektive und objektive Bildqualität der CCT substantiell beeinflussen.

 
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