IRANIAN JOURNAL OF MEDICAL PHYSICS
Year:2005 | Volume:2 | Issue:6|Papers Count:10

Introduction: Pulsed photoacoustic imaging with wideband medical application is a technique in which the absorption of optieal pulse in chromophores produces ultrasonic thermoelastic waves. The waves are detected by an ultrasonic transducer at the surface of the tissue. The transducer with adequate resolution and acoustic sensitivity provides molecular imaging of superficial tissue structures such as the microvessels and skin. In this article, the sensitivity of the optical detection systems were measured in comparison with that of the calibrated hydrophone under the same experimental conditions. Material and Methods: A continuous Nd: YAG laser, a pulsed Nd: YAG laser, an optical stress detection system, a Fabry Perot detection system, a needle hydrophone, a fast-photodiode and a 500 MHz digital oscilloscope were used. Laser pulses (energy = 10 mJ, pulsewidth = 6 ns) were delivered via an optical fiber (600 mm) into an aqueous solution of Indocyanine Green (ICG). The pulses absorbed in the solution, and then acoustic waves produced and received by ultrasonic transducer at the surface of the tissue. The other side of the transducer was illuminated by the continuous laser at the wavelength of 532 nm .The modulated optical beam was detected by the photodiode and the digital oscilloscope. Therefore, a photoacoustic signal was observed as a bipolar signal on the oscilloscope monitor.The sensitivity of the of the optical stress transducer was measured in comparison with a Fabry Perot detection system and a needle hydrophone by measuring a signal to noise ratio (SNR) and a noise equivalent pressures (NEP).Results: The SNR of hydrophone, optical stress transducer and Fabry Perot were 56dB, 45 dB and 26 dB respectively. NEP of hydrophone, Fabry Perot detection system and optical stress detection system were 11 kPa, 13 kPa and 15 kPa, respectively. So NEP of Fabry Perot was 2 kPa higher than that of the Optical stress detection system.Discussion: NEP of Fabry Perot is higher that of the optical stress detection system. Because the bandwidth of the Fabry Perot was 8 MHz higher than that of the optical stresses detection system. Conclusion: The combination of high sensitivity and the small active area makes the optical stress system particularly suitable for photoacoustic imaging applications.

Introduction: One of the problems facing the patients who receive radiation for the treatment of tumor in the upper region of the esophagus is the significant dose to the spinal cord as a result of it being in the treatment field in most cases. This problem arises due to the close proximity of esophagus to cervical spinal cord, the obliquity of esophagus and difference in the thickness across the treatment field. Exceeding the tolerance dose of the cord will cause severe side effects such as spinal cord demyelinization and consequently resulting in the palsy of the organs. The objective of this study is to determine the dose received by the cervical spinal cord and the esophagus by TLD.Material and Methods: The study was carried out in a Plexiglas phantom that was specifically designed for this purpose. Three phantoms of neck area were built based on "Body Mass Index (B.M.I.)" and the "reference man" by use of Corel Draw 8 software. The phantoms were heavy, medium, and light built size. By use of "Alderson Rando Phantom" CT scan the location of the spinal cord and the esophagus in the upper, middle, and lower part of the field was marked.Results and Discussion: The dose was determined by placing TLD chips at each marked location inside each phantom and exposing them to radiation for ten different setups. Based on the result it was concluded that using a gantry angle of 57°, a 30° wedge and a 15° rotation of the head of the table toward the gantry head will result in esophagus and spinal cord receiving the maximum and minimum dose respectively.  

Introduction: Wound healing is a problem caused in neuropathy and circulatory disorders in diabetic patients. The influence of low level LASER in biologic phenomena especially its influence on wound healing is favored researchers recently. Recent studies indicate that wound healing is accelerated by low-level LASER therapy. The aim of this study is assessment of LASER influence on wound healing in diabetic mice. Materials and methods: 100 Albino Mice (20-25 gr) were selected randomly and divided into 2 groups:normal (IV injection of 0.2 cc normal saline) and diabetics (IV injection of streptozotocin 200 mg/kg). Each group was divided to test group (under LASER irradiation) and control group (without LASER irradiation). A circular wound was created on the right side of vertebral column. Then it was irradiated by low level LASER (3.13 j/cm2) twice a day and the macroscopic and microscopic process of wound healing were assessed. Over 14 days in macroscopic process, the decreasing of wound area based on the first day, third to thirteenth day, were measured daily and compared with each other. In microscopic assessment, wound healing based on the third, fifth, ninth and fourteenth day after wound creation were compared in different groups.Results and Discussion: According to our findings, a significant difference was found between test and control group based on wound healing (P<0.05), healing rate in test group was more, but healing time was shorter. So, low-level He-Ne LASER can accelerate wound healing in normal and diabetic mice and also shorten the healing process.

Introduction: Although Ultrasound imaging has many advantages such as being; noninvasive, nonionizing, less expense, real-time, portable, it has some disadvantages making the quality of its image poor. The most important artifact in an ultrasound image is speckle noise, thus many researches and approaches such as various kinds of filtering (mean, median, wiener) and other wavelet based methods have been developed for reducing such noise. In this work, we have studied and compared the result of implemention of these methods.Materials and Methods: In order to compare various methods for speckle noise reduction, some parameters such as MSE (Mean Square Error), S/MSE (Signal to Mean Square Error) and beta factor are defined. Using MATLAB Package, these methods are implemented some kidney ultrasound images with added artificial speckle noise.Results: According to our results it is found that ordinary and adaptive filtering methods not only can not reduce speckle noise adequately, but also they blured images. Therefore, they aren't good choice for speckle noise reduction. Among other methods which are able to reduce speckle using wavelet transform, it seems that universal thresholding method make image blured. In spite of the fact that Bayesian method could preserve details of image and reduce speckle noise adequately, due to its complex algorithm, large computation of the parameters of the pdf's (alpha, gamma, sigma) does not make it appropriate candidate. However bayes and normal thresholding approaches, due to their beta parameter close to one, and better SNR than universal thresholding, and the fact that they have less computation in compare with Bayesian approach, are the most appropriate methods for reducing speckle noise for sonography images.Conclusion: in order to our achievement it can be deduced that bayes and normal threresholding methods are the most efficient and useful methods.

Introduction: Breast cancer is the most frequently diagnosed cancer in women worldwide and there are approximately one million new cases annually. The treatment of breast cancer has shifted away from mastectomy and towards removing just the cancer leaving the normal breast tissue intact. Clinical impetus and justification for pursuing less invasive therapies to improve cosmetics have derived from success of breast conservation therapy in combination with adjuvant treatment modalities, such as radiotherapy, chemotherapy and hormonal therapy since the 1970. Applying ultrasonic waves is one of the non-invasive methods for treatment of cancer. In this method a transducer which is consisted of piezoelectric cells focuses the ultrasonic waves to a focal point. The absorbed energy changes to heat and destroys the cancerous tissue.Method and Materials: In the present paper, several parameters and methods of focusing ultrasonic waves in order to apply hyperthermia cancer therapy has been studied. Also a transducer capable of focusing waves on cancerous tissues with the aid of its piezoelectric-elements is introduced. The amount of absorbed energy was computed by solving numerically the acoustic pressure equation using Rayleigh-Summerfield Integral, with the intention to determine the optimum spatial array of piezoelectric elements for energy concentration. In order to control the treatment procedure, the numerical solution of Bio-heat Transfer Equation [BHTE], along with the finite-element simulation of thermal energy distribution in a breast cancerous tissue is considered. A three-dimensional finite element model for the study of temperature distribution in cancerous tissues of breast is presented. The temperature distribution in the breast cancerous tissues has been calculated and discussed.Results: Assuming the heat source at the center of the tumor location, the bioheat equation was solved for the model. Results showed that using the frequencies in the range of 470-520 kHz could produce enough power to raise the temperature of the focal point up to 45 degrees of centigrade. Also it is seen that the focal area where the peak: temperature is obtained is small so it this method has the ability to kill small tumors at early stages. Also, spatial distribution of the acoustic pressure indicates that the maximum amount of energy is concentrated in the focal zone. An increase in the number of piezoelectric elements will raise the amount of absorbed energy in the target zone and nearby tissues as well.Conclusions: Thermal treatment process modeling has been done using Pennes's bioheat transfer equation. Temperature distribution and the process of temperature rise in the focal region with time and distance is presented. The exact calculation of blood perfusion rate in the target tissue should be considered in the future studies.

Introduction: A major problem with ultrasound imaging is the difficulty in distinguishing clearly between different types of skin lesions. As a solution to the above problem, the use is made by skin characterization in which skin parameters are extracted directly from the backscattered ultrasound signals. Most of the skin characterization methods, which have been employed so far, are based on the measurement of the changes in the magnitude of the envelope of backscattered signal. In this paper a new method for skin characterization utilizing both the envelope and also the shape of the backscattered signal, is presented.Materials and Methods: In the proposed method, the treatment of each layer of skin is modeled as a filter whose transfer function is estimated and extracted using system identification methods such as wiener filtering, minimum variance deconvolution and higher order statistics. The proposed method has been applied to the simulated data as well as the real data, which has been obtained using an ultrasonic scanner, and appropriate experimental setup. The experiments have been carried out using phantoms, which have been prepared in such a way to provide similar geometric and acoustical properties of the skin and the lesions during the ultrasonic imaging.To evaluate the independency of the method to the depth of lesion, 60 positions at three different depths were scanned in two separate phantoms, which were proposed for each skin lesion.Results: The results of the experiments have shown lesions of the same type exhibit similar transfer functions. Classification methods can be used to distinguish between the lesions. Using morphologic features and minimum distance classifier we have been able to separate the skin lesions in each phantom with an error of approximately 5%.Discussion: Obtained results show that system identification and approaches, which used in this paper, can identify and separate lesions in different depths of skin. So the suggested method helps dermatologists to identify some skin lesions without using higher frequencies (which led to reductions in depth of imaging respectively).

Introduction: Dosimetry of radiotherapy treatment beams is a very important procedure because successful radiation therapy requires an accurate delivery of dose to a cancerous volume of tissue. Clarkson method is an important and efficient procedure in radiotherapy. It is used to calculate the PDD (percent depth dose) at open portion of irregular fields which are partially blocked. This method is not applicable in cases such as the calculation of PDD under points that are partially or fully blocked or are under beam attenuators like wedge filters. The aim of this study is to calculate the PDD for points under a step-filter by the use of Clarkson method. In order for the PDD under the step-filter to be considered as PDD in a wedged field the number of steps in the filter should be sufficient.Materials and Methods: The PDDs were calculated with different step-filters with sizes: 8. 8, 8. 10, 8. 12, 8. 14, 8. 16cm2 in Cobalt-60 fields, the depths of calculations were: 5, 10, 15, 20 cm. In this research, the calculated and measured values of (PDD)d=5 / (PDD)d=15  and (PDD)d=10 / (PDD)d=20 were compared. A software Microsoft Excel 2000 was used for calculation. Dose measurements were carried out in a water phantom by a Farmer type ionization chamber.Results: The differences between the calculated and measured (PDD)d=5 / (PDD)d=15 and (PDD)d=10 / (PDD)d=20 were determined and the average of the absolute values were calculated as: 0.3861, 0.3347, 0.2381, 0.2416 _ and 0.3293 which were related to fields: 8. 8to 8. 16 cm2 respectively. This value for all fields is equal to 0.3059.Discussion: With respect to lack of a strict formula for the calculation of the percent depth dose under wedge filter, the presented formula could be used to save time in the treatment planning.

Introduction: functional magnetic resonance imaging is a good non-invasive method for the evaluation and mapping of human brain especially visual cortex.One of the most important subjects in this background is optimizing visual stimuli in various forms of visual tasks for acquiring significant and robust signals.Materials and methods: The effects of physical parameters of visual stimuli on fourteen health volunteers for detecting visual cortical activity are evaluated by functional magnetic resonance imaging. These parameters were temporal & frequency (TF), the different patterns of activation including: square wave and sine wave grating, and two different states of rest including black and white screen.Results: The results show that BOLD signal will be maximally in the TF of 8 Hz, and using the black screen in the rest state. However there isn't significant difference between square-wave and sine-wave grating in producing visual activation in cortex.Discussion and Conclusion: Physical parameters of visual tasks are effective in detecting visual cortical activity, and it is necessary to pay attention to them for taking significant and robust signal. The visual tasks with TF of 8 Hz and one pattern of square-wave or sine-wave in activation state, and black screen in rest state are optimally suitable for fMRI studies. These results are consistent with recent studies, optical mechanisms of the eye and neuronal function in visual cortex.