CT Detectability of Small Low-Contrast Hypoattenuating Focal Lesions: Iterative Reconstructions versus Filtered Back Projection

Abstract

Purpose To investigate performance in detectability of small (≤1 cm) low-contrast hypoattenuating focal lesions by using filtered back projection (FBP) and iterative reconstruction (IR) algorithms from two major CT vendors across a range of 11 radiation exposures. Materials and Methods A low-contrast detectability phantom consisting of 21 low-contrast hypoattenuating focal objects (seven sizes between 2.4 and 10.0 mm, three contrast levels) embedded into a liver-equivalent background was scanned at 11 radiation exposures (volume CT dose index range, 0.5-18.0 mGy; size-specific dose estimate [SSDE] range, 0.8-30.6 mGy) with four high-end CT platforms. Data sets were reconstructed by using FBP and varied strengths of image-based, model-based, and hybrid IRs. Sixteen observers evaluated all data sets for lesion detectability by using a two-alternative-forced-choice (2AFC) paradigm. Diagnostic performances were evaluated by calculating area under the receiver operating characteristic curve (AUC) and by performing noninferiority analyses. Results At benchmark exposure, FBP yielded a mean AUC of 0.79 ± 0.09 (standard deviation) across all platforms which, on average, was approximately 2% lower than that observed with the different IR algorithms, which showed an average AUC of 0.81 ± 0.09 (P = .12). Radiation decreases of 30%, 50%, and 80% resulted in similar declines of observer detectability with FBP (mean AUC decrease, -0.02 ± 0.05, -0.03 ± 0.05, and -0.05 ± 0.05, respectively) and all IR methods investigated (mean AUC decrease, -0.00 ± 0.05, -0.04 ± 0.05, and -0.04 ± 0.05, respectively). For each radiation level and CT platform, variance in performance across observers was greater than that across reconstruction algorithms (P = .03). Conclusion Iterative reconstruction algorithms have limited radiation optimization potential in detectability of small low-contrast hypoattenuating focal lesions. This task may be further complicated by a high degree of variation in radiologists' performances, seemingly exceeding real performance differences among reconstruction algorithms. © RSNA, 2018 Online supplemental material is available for this article.

Quality evaluation of image‐based iterative reconstruction for CT: Comparison with hybrid iterative reconstruction

“…No NPS peak shift occurred using IIR, except for 2.5 mGy, whereas the NPS peak of ADMIRE shifted by 20%-30% compared to FBP, confirming the values reported by Christianson et al9 The peak shift causes an unnatural image texture9,14,15 and may alter the search pattern and image perception of radiologists. 6.…”

“…This trend was more remarkable when using the stronger ADMIRE 5. The peak shift causes an unnatural image texture 9,14,15 and may alter the search pattern and image perception of radiologists. 14 Therefore, IIR images might have greater clinical acceptability.…”

“…When using ADMIRE, the NPS decreased with its increasing strength level, and the distribution was changed to low-frequency dominant, especially for ADMIRE 5. The NPS peak frequencies, which can be used to evaluate noise texture change, 9,14,15 were 0.24, 0.18, 0.16, and 0.24 cycles/mm for FBP, ADMIRE 3, ADMIRE 5, and IIR, respectively, at CTDI vol of 10 mGy.…”

Accelerating iterative coordinate descent using a stored system matrix

“…Statistical iterative reconstruction has several potential advantages and has been implemented specifically for the purpose of dose reduction. The dose reduction possible from SIR varies with the study . Unfortunately, automated methods for assessing dose reduction are difficult and traditional MTF and NPS metrics are not useful .…”

“…The dose reduction possible from SIR varies with the study. [4][5][6] Unfortunately, automated methods for assessing dose reduction are difficult and traditional MTF and NPS metrics are not useful. 7 Clinical studies comparing SIR to filtered backprojection (FBP) have shown an advantage for SIR at very low doses.…”