Impact of optical coherence tomography scanning density on quantitative analyses in neovascular age-related macular degeneration

PURPOSE: To assess the influence of varying B-scan frame-sampling densities on retinal thickness and volume measurements from spectral domain optical coherence tomography (OCT) in eyes with neovascular age-related macular degeneration (AMD). METHODS: Volume OCT data (512 × 128 macular cube over 6 × 6 mm) were collected from 39 eyes with neovascular AMD. All 128 B-scans in each image set were manually segmented, allowing quantification of the neurosensory retina, subretinal fluid (SRF), subretinal hyperreflective material (SRHM), and pigment epithelium detachment (PED). Thickness maps were generated for less dense subsets of scans, ranging from every other (64 B-scans) to every 64th (2 B-scans). For each less dense subset, foveal central subfield thickness and total macular volume (TMV) were compared with values obtained using all 128 scans (considered the reference). RESULTS: For each parameter, the mean absolute difference compared with the reference increased with reducing B-scan density. However, these differences did not reach statistical significance until frame-sampling density was reduced to every eighth scan (ie, 16 B-scans spaced 375 μm apart) for neurosensory retina, and every fourth scan (ie, 32 B-scans spaced 188 μm apart) for SRF, SRHM, and PED. For neurosensory retina, the mean (% error) and maximum (% error) absolute differences in TMV were 0.02 mm(3) (0.24%) and 0.06 mm(3) (0.79%), respectively. Similarly, at a density of 32 B-scans, mean and maximum differences for SRF were 0.004 mm(3) (3.47%) and 0.02 mm(3) (22.22%), respectively. The mean differences for SRHM and PED were 0.01 mm(3) (8.03%) and 0.01 mm(3) (4.04%), respectively. CONCLUSIONS: A minimum of 16 equally spaced B-scans, covering a 6 × 6 mm area, appears necessary to generate retinal thickness measurements similar to those obtained using all 128 B-scans in eyes with choroidal neovascularization (CNV). When considering other CNV lesion features, a minimum of 16 B-scans for SRF and PED, and 32 B-scans for SRHM are required to generate volume maps similar to ground-truth values. These findings may have implications for the design of acquisition and grading protocols for clinical trials using OCT in neovascular AMD

Configuration mixing investigation in germanium isotopes through measurement of E0 transition strengths

Experimental and theoretical studies of the germanium isotopes on the neutron-rich side of the stability valley point increasingly toward the emergence of triaxiality, configuration mixing, and shape coexistence phenomena. Studies of the E0 strengths, which can provide a direct measure of the amount of configuration mixing, are lacking. Thus, determining E0 transition strengths is essential for an understanding of the evolution of structures in the Ge isotopes. Beta-decay experiments populating excited states in the 72,74,76,78Ge isotopes were performed at the TRIUMF-ISAC radioactive beam facility. Gamma-ray and electron spectroscopic investigations have been performed, to measure E0 strengths between states of J > 0, exploiting the GRIFFIN spectrometer combined with the PACES silicon detector array. Preliminary results from this study are presented