Efficient Evaluation of Low-contrast Detectability of Deep-CNN-based CT Reconstruction Using Channelized Hotelling Observer on the ACR Accreditation Phantom

Abstract

As deep-learning-based denoising and reconstruction methods are gaining more popularity in clinical CT, it is of vital importance that these new algorithms undergo rigorous and objective image quality assessment beyond traditional metrics to ensure diagnostic information is not sacrificed. Channelized Hotelling observer (CHO), which has been shown to be well correlated with human observer performance in many clinical CT tasks, has a great potential to become the method of choice for objective image quality assessment for these non-linear methods. However, practical use of CHO beyond research labs have been quite limited, mostly due to the strict requirement on a large number of repeated scans to ensure sufficient accuracy and precision in CHO computation and the lack of efficient and widely acceptable phantom-based method. In our previous work, we developed an efficient CHO model observer for accurate and precise measurement of low-contrast detectability with only 1-3 repeated scans on the most widely used ACR accreditation phantom. In this work, we applied this optimized CHO model observer to evaluating the low-contrast detectability of a deep learning-based reconstruction (DLIR) equipped on a GE Revolution scanner. The commercially available DLIR reconstruction method showed consistent increase in low-contrast detectability over the FBP and the IR method at routine dose levels, which suggests potential dose reduction to the FBP reconstruction by up to 27.5%.

Keywords: Image quality assessment; channelized Hotelling observer (CHO); protocol optimization; radiation dose reduction.

Figure 1.

ACR phantom image and Gabor filters used in the CHO calculation: a) ensemble image with signal (red) and background (blue and yellow) ROI, b) initial reference 12-channel filter and optimal 4-channel filter.

Figure 2.

Sample images of the low-contrast model using four reconstruction methods (FBP, IR, and deep learning method at medium (DLIR-M) and high (DLIR-H) strength levels.

Figure 3.

Index of detectability of the 6-, 5-, and 4-mm objects by five reconstruction methods: FBP, IR, deep learning method at low (DLIR-L), medium (DLIR-M) and high (DLIR-H) strength levels.