Perceived Dark Rim Artifact in First-Pass Myocardial Perfusion Magnetic Resonance Imaging Due to Visual Illusion

OBJECTIVE: To demonstrate that human visual illusion can contribute to sub-endocardial dark rim artifact in contrast-enhanced myocardial perfusion magnetic resonance images.MATERIALS AND METHODS: Numerical phantoms were generated to simulate the first-passage of contrast agent in the heart, and rendered in conventional gray scale as well as in color scale with reduced luminance variation. Cardiac perfusion images were acquired from two healthy volunteers, and were displayed by the same gray and color scales used in the numerical study. Before and after k-space windowing, the left ventricle (LV)-myocardium boarders were analyzed visually and quantitatively through intensity profiles perpendicular the boarders.RESULTS: k-space windowing yielded monotonically decreasing signal intensity near the LV-myocardium boarder in the phantom images, as confirmed by negative finite difference values near the board ranging −1.07 to −0.14. However, the dark band still appears, which is perceived by visual illusion. Dark rim is perceived in the in-vivo images after k-space windowing that removed the quantitative signal dip, suggesting that the perceived dark rim is a visual illusion. The perceived dark rim is stronger at peak LV enhancement than the peak myocardial enhancement, due to the larger intensity difference between LV and myocardium. In both numerical phantom and in-vivo images, the illusory dark band is not visible in the color map due to reduced luminance variation.CONCLUSION: Visual illusion is another potential cause of dark rim artifact in contrast-enhanced myocardial perfusion MRI as demonstrated by illusory rim perceived in the absence of quantitative intensity undershoot.

Indocyanine Green Angiographic Features of Myopic Subfoveal Choroidal Neovascularization as a Prognostic Factor after Photodynamic Therapy

PURPOSE: To determine the influence of clinical features and Indocyanine green (ICG) angiographic features on the visual outcome of patients with myopic sub-foveal choroidal neovascularization (CNV) who received photodynamic therapy (PDT). METHODS: Thirty-six consecutive patients (39 eyes) with myopic CNV who were followed up for more than one year after PDT were enrolled in this study. Clinical features included age, gender, refractive error, great linear dimension, and subretinal hemorrhage. ICG features included the lesion size, lacquer cracks, hypofluorescence surrounding the CNV (dark rim), peripapillary atrophy size, and visible prominent choroidal veins under the macula. Linear regression analysis was performed using the change in visual acuity (delta logMAR) as the dependent variable and the above factors as independent variables. RESULTS: At one-year follow-up after PDT, a younger age (p=0.002) and the presence of a dark rim (p=0.002) were significantly correlated with an improvement of visual acuity (decrement in logMAR) after PDT. Other factors had no significant influence on changes in visual acuity. CONCLUSIONS: Younger patients and patients with a dark rim on ICG angiography had a higher chance of visual improvement after PDT in myopic CNV.

ICGA Findings and Clinical Features of Idiopathic Choroidal Neovascularization

PURPOSE: The purspose of this study was to investigate the ICGA findings and clinical features of idiopathic choroidal neovascularization (CNV) which is one of the important causes of CNV developed under 50 years of age. METHOD: We performed FAG and ICG angiography in 26 eyes (25 patients) which were diagnosed as idiopathic CNV and investigated the visual acuity, associated retinal findings, and treatment modality. RESULTS: The locations of CNV were subfoveal in 11 eyes, juxtafoveal in 11 eyes, extrafoveal in 4 eyes. All CNV were less than 1 disc diameter in size. On ICG angiography, hyperfluorescent neovascular network CNV was visible in early phase in 22 out of 26 eyes. Twelve eyes had dark rim surrouding the CNV, and 10 eyes had focal choroidal vascular dilation near the CNV. Twelve eyes showed obvious choroidal hyperpermeability in late phase, and 3 eyes showed the hypofluorescent dark spot near the CNV. Final visual acuity was improved in 9 eyes, decreased in 4 eyes, and unchanged in 13 eyes. CONCLUSION: Idiopathic CNV was small in size and located mostly in foveal area. ICG angiography showed CNV with various angiographic patterns, and the visual prognosis was relatively good.