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

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.

The Acceptability of Iterative Reconstruction Algorithms in Head CT: An Assessment of Sinogram Affirmed Iterative Reconstruction (SAFIRE) vs. Filtered Back Projection (FBP) Using Phantoms

“…The current research findings support a preference for low iteration strengths as reported in some abdominal and cranial studies [29][30][31]. Numerous other authors [1,6,27,[32][33][34][35] report the use of higher iteration strengths without loss of demarcation across multiple anatomic areas. There may be a number of reasons for opinion variation including the CT system used, the Table 2 for exposure protocol and image randomization numbers.…”

“…Significant differences in scores for diagnostic acceptability, lesion conspicuity, and total diagnostic ability were evident between optimized protocols but not for diagnostic confidence in pathology visualization. Unlike previous studies [6,9,15,21], significant differences were only seen when full-dose and reduced-dose FBP protocols were compared. This finding was not evident in the comparison of lower dose IR and FBP protocols, possibly due to the use of optimized low IR strengths in this study with resultant minimal alterations in noise patterns.…”

“…Traditional filtered back projection (FBP) methods yield noisy images, susceptible to artifacts dependent on the reconstruction filters and radiation doses applied [4], but theoretically iterative reconstruction (IR) allows optimization of dose and image quality [5] through noise and artifact minimization [6]. The most common hybrid IR algorithms perform an initial weighted FBP reconstruction prior to IR noise removal to maintain familiar image appearances [7].…”

“…The published literature is conflicting as to whether IR techniques can preserve low-contrast resolution as radiation dose is decreased [13]. This is of particular significance in head CT due to beam hardening through the skull base and the necessity for excellent grey and white matter differentiation [6]. In comparison to FBP, the noise-free appearance and over-smoothing of critical structures with IR can be detrimental when detecting subtle pathologic changes [14].…”

CT Pulmonary Angiography at Reduced Radiation Exposure and Contrast Material Volume Using Iterative Model Reconstruction and iDose4 Technique in Comparison to FBP

“…The ability to distinguish between noise and structures obviously diminishes with increasing IR strength when structures and differences in density become small. This has already been reported in a number of other studies, assessing iterative reconstruction algorithms of various vendors [39–41]. As a consequence the edges of the filling defects become diffuse with IMR, making it difficult to resolve small structures as small subsegmental emboli, even though the overall image noise is remarkably decreased by IMR.…”