IRANIAN JOURNAL OF MEDICAL PHYSICS
Year:2006 | Volume:3 | Issue:10|Papers Count:11

Introduction: In this study, ECG signals have been embedded into medical images to create a novel blind watermarking method. The embedding is done when the original image is compressed using the EZW algorithm. The extraction process is performed at the decompression time of the watermarked image.Materials and Methods: The multi-resolution watermarking with a secret key algorithm developed in this work is blind because during the EZW decoding only the secret key which includes the header information is used to extract the embedded information. There are two processes added to EZW coder including insertion process and extraction process. Results: Several grey scale MRI and CT images of size 256 x 256 and 512 x 512 pixels have been watermarked by embedding five different watermarks of size 512, 1024, 2048, 4096, 8192 bytes. The used images were divided into three categories such as MRI, CT and Mammography. Also they are in the size of 256×256 and 512×512. The ECG signal is one kind of normal ECG signal that has been utilized for experiments. In this experiment, the PSNR obtained between the original image and the compressed watermarked was found to be greater than 35 dB for all medical images from different modalities. This finding was also true for the PSNR between the original mark signal and its reconstruction. The β measured for the watermarked image was greater than 0.7 and for most of the images it was greater than 0.9. Discussion and Conclusion: The achieved PSR and β prove the imperceptibility of the method in addition to preserving the edges of the host image. The proposed method is able to utilize about 15% of the host image to embed mark signal that is suitable for most watermarking methods. The proposed method of selecting the insertion sites ensures three watermarking constraints: the Imperceptibility and Robustness, High percentage of watermark and Blindness.

Introduction: The process of discriminating among benign and malignant hyperplasia begun with subjective methods using light microscopy and is now being continued with computerized morphometrical analysis requiring some features. One of the main features called Volume Percentage of Stroma (VPS) is obtained by calculating the percentage of stroma texture. Currently, this feature is calculated by pathologists on a manual basis. The proposed algorithm can automatically calculate VPS with a good precision. This procedure could be the first and an essential step of diagnosing endometrial hyperplasia in the field of pathology. Materials and Methods: In this paper, a method based on logarithmic Gabor wavelets and mathematical morphology is proposed for the segmentation of texture. Attaining maximum joint space-frequency resolution is highly significant in the process of texture segmentation. The ability of logarithmic Gabor filters in the discrimination of texture bands at different scales and orientations has been used to segment stroma texture which is mainly located in the middle frequency bands from glandular elements. In the proposed algorithm, the logarithmic Gabor filter bank applied on the microscopic endometrial images and mathematical morphology is used for denoising. The segmentation method is averaging the weighted and denoised Gabor filter outputs.Results: The images used in this method segment with a good precision and can be used by pathologists to calculate volume percentage of stroma as an aided diagnosis feature. A sensitivity of 95.3, specificity of 95.6, accuracy of 95.4%, PPV of 98.4% and NPV of 88% was achieved in distinguishing between benign and malignant hyperplasia based on VPS.Discussion and Conclusion: The proposed procedure could be the first and an essential step of diagnosing endometrial hyperplasia in pathology. Based on these experiments, the logarithmic Gabor wavelet is one of the most effective methods in texture segmentation that can easily extract the texture information from the middle frequency bands and make it available to the segmentation algorithm.

Introduction: Despite the fact that the clinical implementation of polymer gel dosimetry has been facilitated after the introduction of normoxic gels, there are still complications in its clinical routine use that are under investigation. In the current work, the feasibility of using a normoxic polymer gel dosimeter named MAGICA has been investigated for use in our clinical brachytherapy applications at Imam Hospital and the deviations between the results obtained from two different calibration methods were investigated. Materials and Methods: The gel fabrication was performed at Novin Medical Radiation Institute and 4 Perspex walled phantoms designed especially for brachytherapy irradiations were filled with the same gel, together with 15 plastic calibration test tubes. The test tubes were irradiated with a range of known doses using a cobalt-60 teletherapy unit and the phantoms were irradiated with two brachytherapy remote-after-loaders using Cs137 and Co60 brachytherapy sources according to the treatment planning data. Imaging was performed with a Multi-spin-echo protocol using a Siemens 1.5T MRI machine. Image processing was performed in MATLAB environment to extract R2 maps of the dose distributions. Gel fabrication, irradiation and imaging were performed at three different centers, so the dosimeters and test tubes were transferred from one center to another under non-uniform conditions. R2 values of the first dosimeter which was irradiated with a single cesium source were extracted from different distances from the source along a horizontal profile and correlated to the dose values at the same distances in treatment planning data. This was used as the second calibration method to extract the absolute measured values of the other three dosimeters. Diagrams of the absorbed dose versus distance were plotted for each dosimeter and the results obtained from the two calibration methods were compared. Results: Results of the measured values that were calibrated with the test tubes show a 3 to 6 Gy dose difference in plateaus and more than 2 mm distance to agreement gap in steep dose gradients. However, the results of using the second calibration method show at most a 0.36 Gy dose difference in plateaus and less than 2 mm distance to agreement gap in steep dose gradients. Discussion and Conclusion: As the gel fabrication, irradiation and imaging conditions were the same for all the gel dosimeters and the calibration tubes, the unexpected deviations between the results of the two calibration methods deserves more investigations. It seems plausible to attribute this deviation to the difference in the size of calibration test tubes and original dosimeters. From a practical point of view, as the origin of this effect has not yet been investigated, it would be best to use a calibration phantom with the same size and characteristics as the original dosimeters.

Introduction: It is believed that injury potential has a regulatory role in wound healing process and the application of exogenous electrical stimulation may serve to mimic the natural endogenous bioelectric current so that can improve the wound healing. Up to now, this hypothesis has not been researched in surgically acute wounds. Materials and Methods: Thirty nine male guinea pigs were randomly divided into one control group (sham treated) and two experimental groups (one DC anodal and one DC cathodal group). A full thickness skin incision having a length of 2.5 cm was made on the dorsum of each animal at a distance of 1 cm from spinous processes. The differential surface skin potential was measured before and immediately after the injury and also through the healing process until 21st days. Also the wound surface area was measured through the healing process.Results: Immediately after the injury, the wound site potential in all three groups increased significantly and reached its maximum at day 1 in the control and cathodal group and day 3 in anodal group (p<0.05). Only in anodal group, there was not significant difference between the basal initial potential and the wound potential at 1.

Introduction: One of the major problems in the development of nuclear medicine images is the presence of noise. The noise level in nuclear medicine images is usually reduced by the analysis of imaging data in a Fourier transform environment. The main drawback of this environment belongs to low signal to noise ratio in high frequencies because removing noise frequencies may remove data and times information as well. This problem becomes more serious when the most important signals are non-stationary. The aim of this research is to evaluate the effect of wavelet transform on nuclear medicine image. Materials and Methods: A brain phantom-like Hoffman phantom with 4 layers was used. Planar images were acquired from the phantom, with a total count of 107 (as reference image) and from each layer separately. The counts of planar images in each layer were increased from 100 to 700 kilo counts in seven steps. Different levels of white (Gaussian) noise was added to the reference images using MATLAB software. Simulation images using Simset software and NCAT phantom were also produced. Wavelet transform, Butterworth, Metz, Hanning(3×3) and Wiener filters were applied on all images. The Universal Image Quality Index (UIQI) was used to evaluate the image quality.Result: Wavelet transform can increase the value UIQI (UIQI = 0.7352). The effect of wavelet transform on the improvement of image quality is much better than Butterworth (UIQI = 0.3556) and Metz (UIQI = 0.3493) but almost the same as the effect of Wiener (UIQI = 0.7626) and Hanning (3*3) (UIQI = 0.8017). Discussion and Conclusion: Although wavelet transform is not the best method of reducing noise level, but its use can reduce the noise level like filters do. Assessment of commonly used thresholds as well as new design of a special threshold for wavelet transform in nuclear medicine images can improve the performance of this transform.

Introduction: The low regeneration of bone in defective bones causes therapeutic problems. Various strategies to assess the healing of bone defects have been used which they include histological and histo-chemical analysis in an invasive study. The purpose of this study was to determine the ultrasonic parameters of bone as a promising noninvasive technology for assessing bone repair process. Materials and Methods: A total of twenty seven Newsland male rabbits being 4 month old were selected and a hole of 3 mm in diameter was bored in the mid region of their right tibia bone. After causing the injury to the right tibia the ultrasonic parameters including amplitude dependent speed of sound (AD-SOS) and bone radial thickness were measured on the injured tibia and the normal one (left tibia) at different time intervals (1, 8 and 15 day group). The bone transmission time (BTT) and ultrasonic bone profile index (UBPI) were estimated by AD-SOS which is calculated based on fast wave amplitude, signal dynamic and thickness. The rabbits in each group were sacrificed and histology study was performed on the injured tibia. Results: The results obtained from the histological sections in 1, 8 and 15 day post-injury, show ongoing normal healing process in the 8 and 15 day group. The bone repair was characterized by bone trabecular formation and osteoblast cell activity. The mean AD-SOS parameter for the 1, 8, 15 day and normal bone was 2265, 2203, 2176 and 1990 m/s, respectively, suggesting a non-invasive measurement to assess bone repair process. The measured result was in agreement which the histological analysis (p-value<0.05 with ANOVA analysis). Discussion and Conclusion: The findings suggest that AD-SOS parameter might be suitable to assess the architectural quality of bone trabecular and repair process.

Introduction: one of the minimally invasive methods of treatmenting liver malignancies is Radiofrequency Ablation (RFA) which can be applied to primary or secondary tumors. Nevertheless, the disease recurrence is probable after RFA application partially due to the inadequate capability of temperature monitoring of the target tissue and visualizing the thermal damage. The goal of this work was to study the possibility of real-time temperature monitoring of liver tissue undergoing RFA. For this purpose, variations of brightness in DICOM ultrasonic images were investigated. Materials and Methods: 10pieces of fresh bovine liver underwent RFA in ex vivo experiments. Active and passive needle electrodes were inserted into the tissue and a micro-thermometer was placed between them using ultrasonography guidance to invasively monitor temperature changes. Corresponding to each degree of temperature up to 70˚C, ultrasonic images were acquired followed by turning the RF generator off and taking the images down to 30˚C. Ultrasonic images were delivered to a PC via PACS and processed in order to investigate the subsequent changes of brightness corresponding to temperature changes. Correlation analysis was performed between the changes of brightness and temperature variations with a 95% confidence level. Results: this study showed that during tissue warm-up between 20 ˚C and 50 ˚C, tissue brightness of the ultrasound images increases linearly (r = 0.99). As temperature rises between 50 ˚ and 70 ˚C, the variation of brightness shows a non-linear behavior due to microbubble formation. During the cool-down process, the brightness once again behaves linearly (r = 0.98) and the variation rate of brightness is faster in the cool-down than that of the warm-up. So that at the end of RFA, when the temperature reaches the initial level the tissue is approximately 60% more hypoechoic. The results are the same for both frequencies employed.Discussion and Conclusion: it seems that the changes of brightness in the ultrasound images can be used for real-time thermal monitoring during radiofrequency ablation.

Introduction: To write a computational program to calculate the average glandular dose in Mammography with Rh-Rh target-filter and also use it as an accurate and fast method of dose calculation founder different situations.Materials and Methods: In this research, the Sobol-Wu parameters are used to write a FORTRAN code for glandular dose calculation in Rh-Rh target-filter mammograms. The code calculates the glandular dose for Rh-Rh target-filter mammograms for the input parameters such as tube voltage in kV scale, half-value layer (HVL) of the incident x-ray spectrum in mm Al, breast thickness in cm and glandular tissue fraction (g).Results: The average glandular dose variation has been calculated against the voltage of mammogram X-ray tube for d = 5 cm, HVL = 0.35 mm Al and different value of g. Also the results related to the average glandular absorbed dose variation per unit roentgen against the glandular fraction of breast tissue for kV=28, HVL = 0.387 mm Al and different value of d are presented. Discussion and Conclusion: The results of this research are in good agreement with the computational results of J. M. Boone and the experimental results of E. L. Gingold et al. Also the code is fast, accurate and user friendly, that can be used for dose optimization in mammography imaging.