Biomedical subjects

Bilgin Keserci

Publications and source records attributed to Bilgin Keserci.

4 recordsLinked to original sources

PubMed2006

Optimization of self-reference thermometry using complex field estimation.

Referenceless, or self-reference, thermometry is a technique for mapping temperature differences in the region of interest (ROI) using the baseline phase estimated by extrapolating the field in the surrounding region for estimation (RFE) and subtracting the estimated baseline from the measured field. In the present work a self-reference technique based on complex field estimation using 2D polynomials comprising complex-valued coefficients was proposed and optimized. Numerical simulations with a Gaussian-profiled phase distribution demonstrated that the ROI radius had to be 2.3-2.5 times the standard deviation (SD) of the Gaussian function in order to keep the error below 8% of the peak phase change. The area ratio between the ROI and the RFE had to be larger than 2.0 to maintain the error level. Based on the simulations, and phantom and volunteer experiments, the complex-based method with independently optimized polynomial orders for the two spatial dimensions was compared with the phase-based method using the similar-order optimization strategy. The complex-based method appeared to be useful when phase unwrapping was not removed. Otherwise, the phase-based method yielded equivalent results with less polynomial orders.

Body Temperature↗

PubMed2004

Macular translocation surgery and retinal circulation times.

PURPOSE: To quantify and compare the retinal circulation times before and after macular translocation surgery. METHODS: In nine patients undergoing macular translocation with 360-degree retinotomy, arm-retina and arteriovenous passage times were quantified from preoperative and postoperative scanning laser fluorescein angiograms. A control group of eight patients who had not undergone any intraocular surgery was also evaluated. The time that between injection into the antecubital vein and the appearance of fluorescein at two selected points on superotemporal and inferotemporal arteries near the disk provided the arm-retina time. For the arteriovenous passage time, 50% of the maximal fluorescence time difference was assessed from the intensity curves of arteries and corresponding veins at the same points for the arm-retina time. Postoperative measurements were obtained an average of 10.6 months after surgery. RESULTS: No significant difference was noted between preoperative and postoperative values of the arm-retina time (mean +/- SD: 14.41 +/- 2.73 seconds versus 14.67 +/- 3.85 seconds, respectively; P = 0.84) or that of the arteriovenous passage time (2.66 +/- 0.74 seconds versus 2.47 +/- 0.68 seconds, respectively; P = 0.37) in the study group. The arm-retina time (14.96 +/- 2.01 seconds) and arteriovenous passage time (2.44 +/- 0.68 seconds) in the control group did not differ from preoperative and postoperative arm-retina times (P = 0.65 and P = 0.85) and arteriovenous passage times (P = 0.54 and P = 0.93) in the study group. The arteriovenous passage time correlated with the degree of retinal rotation around the optic disk in the study group (r = -0.70; P = 0.04). CONCLUSION: Macular translocation surgery does not alter retinal macrocirculation in the long term.

Aged↗

PubMed2003

Wavelet-packet-based texture analysis for differentiation between benign and malignant liver tumours in ultrasound images.

The purpose of this study was to apply a novel method of multiscale echo texture analysis for distinguishing benign (hemangiomas) from malignant (hepatocellular carcinomas (HCCs) and metastases) focal liver lesions in B-mode ultrasound images. In this method, regions of interest (ROIs) extracted from within the lesions were decomposed into subimages by wavelet packets. Multiscale texture features that quantify homogeneity of the echogenicity were calculated from these subimages and were combined by an artificial neural network (ANN). A subset of the multiscale features was selected that yielded the highest performance in the classification of lesions measured by the area under the receiver operating characteristic curve (Az). In an analysis of 193 ROIs consisting of 50 hemangiomas, 87 hepatocellular carcinomas and 56 metastases, the multiscale features yielded a high A: value of 0.92 in distinguishing benign from malignant lesions, 0.93 in distinguishing hemangiomas from HCCs and 0.94 in distinguishing hemangiomas from metastases. Our new multiscale texture analysis method can effectively differentiate malignant from benign lesions, and thus has the potential to increase the accuracy of diagnosis of focal liver lesions in ultrasound images.

Carcinoma, Hepatocellular↗

PubMed2002

Computerized detection of pulmonary nodules in chest radiographs based on morphological features and wavelet snake model.

We have developed a new computer-aided diagnosis scheme for automated detection of lung nodules in digital chest radiographs based on a combination of morphological features and the wavelet snake. In our scheme, two processes were applied in parallel to reduce the false-positive detections after initial nodule candidates were selected. One process consisted of adaptive filtering for enhancement of nodules and suppression of normal lung structures, followed by extraction of conventional morphological features. The other process consisted of a novel approach for elimination of false positives called the edge-guided wavelet snake model. In the latter process, multiscale edges of the candidate nodules were extracted to yield parts of the nodule boundaries. A wavelet snake was then used for fitting of these multiscale edges for approximation of the true boundaries of nodules. A boundary feature called the weighted overlap between the snake and the multiscale edges was calculated and used for elimination of false positives. Finally, the weighted overlap and the morphological features were combined by use of an artificial neural network for efficient reduction of false positives. Our scheme was applied to a publicly available database of digital chest images for pulmonary nodules. Receiver operating characteristic analysis was employed for evaluation of the performance of each process in the scheme. The combined features yielded a large reduction of false positives, and thus achieved a high performance in discriminating between true and false positives. These results show that our new method, in particular the false-positive reduction method based on the wavelet snake, is effective in improving the performance of a computerized scheme for detection of pulmonary nodules in chest radiographs.

Adult↗