An automated method for comparing motion artifacts in cine four-dimensional computed tomography images.

The aim of this study is to develop an automated method to objectively compare motion artifacts in two four-dimensional computed tomography (4D CT) image sets, and identify the one that would appear to human observers with fewer or smaller artifacts. Our proposed method is based on the difference of the normalized correlation coefficients between edge slices at couch transitions, which we hypothesize may be a suitable metric to identify motion artifacts. We evaluated our method using ten pairs of 4D CT image sets that showed subtle differences in artifacts between images in a pair, which were identifiable by human observers. One set of 4D CT images was sorted using breathing traces in which our clinically implemented 4D CT sorting software miscalculated the respiratory phase, which expectedly led to artifacts in the images. The other set of images consisted of the same images; however, these were sorted using the same breathing traces but with corrected phases. Next we calculated the normalized correlation coefficients between edge slices at all couch transitions for all respiratory phases in both image sets to evaluate for motion artifacts. For nine image set pairs, our method identified the 4D CT sets sorted using the breathing traces with the corrected respiratory phase to result in images with fewer or smaller artifacts, whereas for one image pair, no difference was noted. Two observers independently assessed the accuracy of our method. Both observers identified 9 image sets that were sorted using the breathing traces with corrected respiratory phase as having fewer or smaller artifacts. In summary, using the 4D CT data of ten pairs of 4D CT image sets, we have demonstrated proof of principle that our method is able to replicate the results of two human observers in identifying the image set with fewer or smaller artifacts.

Effect of phacoemulsification on corneal thickness.

PURPOSE: To determine the immediate effect on corneal thickness of cataract extraction using phacoemulsification. DESIGN: Prospective consecutive nonrandomized humans undergoing standard small-incision phacoemulsification and intraocular lens insertion. METHODS: Corneal thickness was measured immediately preoperative and postoperatively in 58 consecutive patients undergoing phacoemulsification in the absence of other ocular abnormalities. Corneal thickness was determined centrally and in the midperiphery of four quadrants. The last 17 eyes were also evaluated for the effect of pressure from a Honan balloon on corneal thickness. SETTING: Faculty practice in medical school and university hospital. The cornea thinned in all five of the measured locations, with statistical significance being reached only in the four midperipheral quadrants. Pressure from the Honan balloon resulted in a negligible increase in corneal thickness preoperatively. CONCLUSIONS: Corneas were found to have thinned statistically significantly immediately after phacoemulsification; however, the degree of thinning has doubtful clinical significance and does not represent a significant dehydration of the cornea during the surgical procedure.

Photorefractive keratectomy versus laser in situ keratomileusis for the treatment of spherical hyperopia.

OBJECTIVE: To compare photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in treating spherical hyperopia using the VISX STAR S2 excimer laser. INTERVENTION: Fifteen consecutive eyes of 15 patients underwent PRK, and 16 consecutive eyes of 16 patients underwent LASIK (follow-up: 12 months). MAIN OUTCOME MEASURES: Postoperative pain, uncorrected visual acuity (UCVA), deviation from intended correction, and loss of best spectacle-corrected visual acuity (BSCVA). RESULTS: Mean preoperative spherical equivalent was + 2.18 diopter [D] for PRK and + 2.03D for LASIK. All PRK patients experienced significant postoperative pain that required systemic medication, whereas LASIK patients had minor and transient discomfort. Mean deviation from intended correction was -0.83D, + 0.01D, and + 0.18D at 1, 6, and 12 months after PRK, and + 0.22D, +0.30D, and + 0.40D at 1, 6, and 12 months after LASIK (P = 0.002 at 1 month). A higher proportion of LASIK eyes had a UCVA of 20/20 or better at all time points (P = 0.013 and 0.025 at 1 and 3 months, respectively). There was no statistically significant difference between both groups in BSCVA loss. CONCLUSIONS: LASIK and PRK are comparable in efficacy and safety. However, PRK was more painful, with an initial and temporary myopic over-correction that did not occur after LASIK. Stability was achieved between 3 and 6 months following PRK, and one month following LASIK.