Dual-energy CT (DECT) was introduced to address the inability of conventional single-energy computed tomography (SECT) to distinguish materials with similar absorbances but different elemental compositions. However, material decomposition algorithms based purely on the physics of the underlying attenuation process have several limitations, leading to low signal-to-noise ratio (SNR) in the derived material-specific images. To overcome these, we trained a convolutional neural network (CNN) to develop a framework to reconstruct non-contrast SECT images from DECT scans. We show that the traditional physics-based decomposition algorithms do not bring to bear the full information content of the image data. A CNN that leverages the underlying physics of the DECT image generation process as well as the anatomic information gleaned via training with actual images can generate higher fidelity processed DECT images.
Progressive calcification of Bruch's membrane (BM) causes considerable visual morbidity in patients with pseudoxanthoma elasticum (PXE). Since calcification is hyperreflective on optical coherence tomography (OCT), our aim was to measure BM calcification with OCT imaging. Methods: Case-control study with 45 patients with PXE under 40 years (range, 11-39) and 25 controls (range, 14-39). Spectralis HRA-OCT imaging consisted of seven macular B-scans with 250-μm spacing. Retinal segmentation was performed with the IOWA Reference Algorithms. MATLAB was used to extract and average z-axis reflectivity profiles. Layer reflectivities were normalized to the ganglion cell and inner plexiform layers. Both median and peak layer reflectivities were compared between patients with PXE and controls. The discriminative value of the retinal pigment epithelium (RPE)-BM peak reflectivity was analyzed using receiver operating characteristic analysis. Results: The reflectivity profile of patients with PXE differed from controls in the outer retinal layers. The normalized median RPE-BM reflectivity was 41.1 (interquartile range [IQR], 26.3-51.9) in patients with PXE, compared with 22.5 (IQR, 19.3-29.5) in controls (P = 2.09 × 10 −3). The normalized RPE-BM peak reflectivity was higher in patients with PXE (67.5; IQR, 42.1-84.2) than in controls (32.7; IQR, 25.7-38.9; P = 2.43 × 10 −5) and had a high discriminative value with an area under the curve of 0.85 (95% confidence interval, 0.76-0.95). In patients with PXE under 40 years, increasing age did not have a statistically significant effect on the RPE-BM peak reflectivity (patients under 20 years: 44.
Purpose
Progressive calcification of Bruch’s membrane (BM) causes considerable visual morbidity in patients with pseudoxanthoma elasticum (PXE). Since calcification is hyperreflective in SD‐OCT imaging, our aim was to quantify BM calcification using SD‐OCT.
Methods
We performed a ‘proof of concept’ study with 45 PXE patients under 40 years and 25 age‐matched controls. Spectralis HRA‐OCT imaging was performed, consisting of 7 macular B‐scans with 250 µm distance in between. Retinal segmentation was performed using OCT Explorer (and visually verified per B‐scan on correct segmentation and an intact outer retinal layer). Matlab was used to extract and average z‐axis intensity profiles for each set of B‐scans. Mean layer intensities normalized to the GCL‐IPL layer were used for descriptive analysis. Intensity ratios, defined as the retinal pigment epithelium (RPE)‐BM peak intensity relative to another layer, were calculated to quantify RPE‐BM intensity. These ratios were compared with the control group to find a discriminative value using ROC analysis.
Results
The age of the groups were comparable, with a mean age of 27.0 years in PXE patients and 26.9 years in the control group. The median normalized intensity of the RPE‐BM was 34.0 (IQR 24.7–42.3) in patients with PXE, compared to 20.4 (IQR 17.2–24.4) in normal controls (p < 0.001). The RPE‐BM/ ellipsoid zone (EZ) ratio was the most discriminative with an AUC of 0.97 (95% CI 0.92–1). In PXE patients, the median ratio was 1.79 (IQR 1.33; 2.63) compared to 0.75 in controls (IQR 0.61; 0.97). The RPE‐BM/EZ ratio increased with age in PXE patients: 1.14 (IQR 1.01–1.32) in patients under 20 (n = 7), 1.81 (IQR 1.35–2.19) in patients aged 20–30 years (n = 22) and 2.35 (IQR 1.68–3.08) in patients aged 30–40 (n = 16) (p = 0.010).
Conclusions
We demonstrated that BM calcification is quantifiable as hyperreflectivity in young PXE patients, that the RPE‐BM/EZ intensity ratio can discriminate between PXE and normal controls, and that this intensity ratio increases with age.
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