title: Spatial domain filtering for fast modification of the tradeoff between image sharpness and pixel noise in computed tomography.
abstract: In computed tomography (CT), selection of a convolution kernel determines the tradeoff between image sharpness and pixel noise. For certain clinical applications it is desirable to have two or more sets of images with different settings. So far, this typically requires reconstruction of several sets of images. We present an alternative approach using default reconstruction of sharp images and online filtering in the spatial domain allowing modification of the sharpness-noise tradeoff in real time. A suitable smoothing filter function in the frequency domain is the ratio of smooth and original (sharp) kernel. Efficient implementation can be achieved by a Fourier transform of this ratio to the spatial domain. Separating the two-dimensional spatial filtering into two subsequent one-dimensional filtering stages in the x and y directions using a Gaussian approximation for the convolution kernel further reduces computational complexity. Due to efficient implementation, interactive modification of the filter settings becomes possible, which can completely replace the variety of different reconstruction kernels.
authors.affiliation: Siemens AG, Medical Solutions, Computed Tomography Division, Siemensstr. 1, 91301 Forchheim, Germany. stefan.schaller@siemens.com
authors.forename: Stefan
authors.initials: S
authors.lastname: Schaller
authors.forename: J E
authors.initials: JE
authors.lastname: Wildberger
authors.forename: Rainer
authors.initials: R
authors.lastname: Raupach
authors.forename: Matthias
authors.initials: M
authors.lastname: Niethammer
authors.forename: Klaus
authors.initials: K
authors.lastname: Klingenbeck-Regn
authors.forename: Thomas
authors.initials: T
authors.lastname: Flohr
mesh_terms: D000465:Algorithms; D006801:Humans; D019047:Phantoms, Imaging; D011786:Quality Control; D011856:Radiographic Image Enhancement / Q000379:methods*; D013902:Radiography, Thoracic / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013269:Stochastic Processes; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*