Iranian Journal of Medical Physics
Volume:2 Issue: 9, 2006

ntroduction: total body irradiation is a type of external radiotherapy which allows the delivery of a homogenous dose to the entire body while the critical organs such as lung, etc. can be shielded, if needed. The role of TBI is to suppress the patient's immune system prior to bone marrow transplantation in order to avoid the rejection of the donor bone marrow. in this study, some basic dosimetric parameters (percentage depth dose and dose rate) were measured under TBI condition for 60Co machine. A Perspex water phantom having dimensions of 30´30´30 cm and a farmer type ionization chamber (0.6 cc) were used to measure some parameters such as percentage depth dose.For the measurement of surface dose, a parallel plate ionization chamber was used. All the chambers in this study were used with a UNIDOS electrometer. A human phantom consisting of 3 sections (head and neck, trunk and hip) was used to check the accuracy of the dose delivered. The dose in the midpoint of the phantom was measured by a farmer type ionization chamber (0.3 cc) which was placed at the umbilicus level. The dose to be delivered was calculated by two 1. using the measured percentage depth dose and the dose rate under TBI condition 2. using the calculated percentage depth dose based on Mayneord factor and the dose rate for the TBI condition which was derived from the inverse square law.P-type Silicon diodes while being connected to a multi channel electrometer was used to investigate the dose uniformity throughout the whole body. For this purpose, the diodes were taped at several locations on the entrance and the exit side of the human phantom. there is an agreement between the measured and the calculated dose within 2.6 and 3% for the first and second method, respectively. The mean difference between the calculated and measured percentage depth dose was 0.71% with standard deviation of 0.96%. The dose uniformity through the whole body at the anterior and posterior side was within 6 and 5%, respectively. The measured dose in the midlobe of the lung shows that the delivered dose to the lungs was 14.14 Gy which is higher than the prescribed dose of 13.5 Gy. Discussion and the results of the dose delivered by both methods show that the difference between the calculated and measured values are within the acceptable level (±5%).The second method is recommended for the use in TBI calculation than the first one because it is simpler to use. Although the obtained result from the first method is in a better agreement with the measured data than the one from the second method.One of the main objectives in TBI is to achieve dose uniformity throughout the whole body. The results of this work on the human phantom show that dose uniformity was achieved. The measured dose in the midlobe of the lung shows that the delivered dose to the lung was higher than the prescribed dose, thus appropriate shielding should be used to reduce the lung dose. Based on the dose uniformity obtained in this work it is recommended that TBI treatment can be implemented in the radiotherapy centers throughout the country using Cobalt-60, provided proper lung shield is used.

Diagnostic radiography examinations of patients comprise the largest contribution to various medical uses of ionizing radiation. Investigation of dose reduction methods in diagnostic radiology has always been a primary aim of radiation protection research. Chest radiography examination is the most frequently performed radiological procedure. Although the patient dose from chest radiography is relatively low, but since a large population is involved it makes a significant contribution to the collective effective dose from all medical x-ray examinations. A total of 20 randomly selected x-ray units located in 16 public hospitals in 14 cities throughout Iran and 306 patients were included in this survey. The following five quality control tests have been performed using an UNFORS Mult-O-Meter, model 303: 1- kVp accuracy 2- Timer accuracy 3- mAs linearity 4- Exposure reproducibility 5- Filtration check. The Entrance Surface Dose (ESD) received by the patients was measured using thermoluminescence dosimeters (TLD-100) attached to the patient's skin. Complete details of quality control tests results, characteristics of patients, exposure parameters and patient dose values are presented in 9 figures and 3 tables. The results have shown wide variation of mean hospital doses. The difference between the maximum and minimum individual patient dose values varied up to a factor of 52.Discussion and Although the reasons for dose variations were complex, but in general, low tube potential, high mAs and low filtration were associated with high dose rooms. The 75 percentile value of the ESD distribution was 0.44 mGy and it is suggested to be used as "National Diagnostic Reference Level" of chest examination in PA projection in Iran. This study also demonstrated the need for performing routine quality control tests on x-ray units.

Low Level Laser Therapy (L.L.L.T.) can expedite the process of woundhealing for the patients suffering from painfull and slow healing wounds. The best energy density which was measured in the previous study was 3.13 J/cm2. In this research, it is tried to find the best fractionation of this energy density. 120 male mice each weighing 20-25 grams were selected. A wound with a 10 mm in diameter was created on the right side of the lumbar area of all 120 mice. The Mice were randomly divided into six groups, one control group without radiation exposure and five test groups radiated by low power He–Ne laser. All the test groups received a constant energy density of 3.13 J/cm2 but in various fractionations. The test groups received laser as following:A: one exposure in a day (3.13 J/cm2 per day for five days from day one through day five)B: two exposures in a day (2 × 1.56 J/cm2 per day for five days from day one through day five at 12 hr intervals)C: two exposures in a day (2 × 1.56 J/cm2 per day for five days from day six through day ten at 12 hr intervals) D: three exposures in a day (3 × 1.06 J/cm2 per day for five days from day one through day five at 8 hr intervals)E: four exposures in a day (4 × 0.78 J/cm2 per day for five days from day one through day five at 6 hr intervals) The speed of wound healing which was the surface area of the wound, was measured in all groups. It clearly showed that in some of the test groups the healing process was faster and there was a significant difference in the speed of the healing process when compared with the control group. Discussion and Application of L.L.L.T. with low power He–Ne laser expedites the healing process at the early stages of healing, but more research is to be carried out to clarify the effect of L.L.L.T. at later stages.

Colorectal cancer is one of the most widely occurring cancers among the aging population and the second leading cause of cancer related deaths. The use of 3D imaging to acquire virtual anatomic models of colon provides a minimally invasive diagnostic tool for the detection of colorectal polyps and cancer. This procedure termed virtual colonoscopy (V.C.) has in recent years been developed as an alternative method of massive population screening to examine the entire colon for early cancer detection. There are some problems which make colon segmentation a difficult task like the colon has complex shape and it is not the only gas-fill structure in abdomen, and a lot of areas with high CT number like bones, Contrast Enhanced Fluid (CEF) in colon and small bowel. A two-stage method for an automated segmentation of the colonic walls in volumetric CT data is proposed.

In this study, a two-stage algorithm was used. The aims of the first stage were to eliminate the extra objects and also to restrict the region of interest (ROI) in half-resolution as an input for fine process in second stage. In this phase, the multistage method performs segmentation using adaptive threshold, morphology operation and region growing using automated seed generation technique leading to a tissue characterization. This stage generates colon borders in half-resolution dataset. In the second phase, an edge sharpening, a modified region growing and an outer boundary tracking are applied to make fine borders in colon segmentation. The region growing in the second phase makes use of local adaptive thresholding instead of global view on database voxels.

To evaluate the results, certain tests for both stages of the algorithm were applied. In the total 82 datasets, the result showed 72 cases as excellent, 7 cases as good, 2 cases as fair and 1 case as poor in the segmentation process. Discussion and

An efficient segmentation method in half-sized volume data using an anatomical-oriented approach was developed to overcome the long processing time. The anatomical orientation guarantees the preservation of the segmentation accuracy while moving from half-resolution to full resolution. The output from the first stage can be used as a segmentation map for any complicated colon lumen extraction. The results demonstrate that the error of leakage to extra colonic can be minimized.

Photo-acoustic that idiomatically is called optoacoustic or laser-ultrasound is a technique that uses optical energy for the generation of ultrasound waves in various media. The waveform of the generated ultrasound contains useful information about the optical properties of the absorbing media and is influenced by laser pulse specifications. The obtained pressure signal undergoes changes prior to reaching the transducer due to the propagation in the media. In this research, the effect of laser parameters, the properties of the absorbent media and acoustic diffraction in generated ultrasound wave, have been investigated.

In this research, a frequency domain has been introduced for the generation of acoustic pressure as a result of laser energy reception transfer functions in two modes of forward and backward. By the use of this model, the effect of the pulse duration, the profile and wavelength of laser and also the absorption coefficient of the sample in the generated ultrasound properties have been investigated. A transfer function for the acoustic diffraction has been introduced and the effect of diffraction in ultrasound waveform has been simulated. Also the effect of the longitudinal and the radial distance of ultrasound transducer from the irradiated surface and also the ultrasonic source dimension that is influenced by laser beam diameter in ultrasound waveform, have been surveyed. All the simulations have been accomplished in MATLAB7 software platform.

Increasing laser pulse duration causes an increase in the amplitude of ultrasound and a decrease in its frequency content. The increase in the amplitude causes an increase in the absorption coefficient of the sample. The generated optoacoustic waves in response to lasers with Gaussian and asymmetric Gaussian profile are not significantly different, consequently Gaussian pulse can be used in modeling with good approximation. As a result of acoustic diffraction while propagating in media, a backward single pole wave changes to a bipolar one. An increase in ultrasonic source dimension (laser beam diameter) causes an increase in the amplitude and the width of the optoacoustic waves.Discussion and

To design a laser-ultrasound system with maximum efficiency, one has to choose a laser wavelength in which tissue has a high absorption coefficient. The pulse duration and the beam diameter of the laser should be chosen correctly with respect to the ultrasonic transducer properties.

There is a substantial controversy about the role of skin receptors in the excitation of spinal motor neurons. The purpose of this study was to determine the effect of topical anesthesia and cold temperature on the excitation of spinal motor neurons in healthy non-athletic men.

10 volunteers were tested in four separated sessions. Control group #1 (placebo ointment with ambient temperature), test group #1 (anesthetic ointment with ambient temperature), control group #2 (cold placebo ointment), test group # 2 (cold anesthetic ointment). Soleus H-reflex and Mh- wave recruitment curve parameters were used to evaluate the changes in the excitability of motor neuron. The anesthetic ointment used was benzocaine 5% which was rubbed around T11. Vaseline was used as the placebo ointment. H-reflex was recorded five times for nine different intensities, prior to, immediately after and 30 minutes after using the ointment.

Fit L3 slope, fit L5 slope and peak to peak amplitude of H-reflex decreased 30 minutes after the application of anesthetic ointment at ambient temperature (p<0.05).Fit L3 slope, fit L5 slope and peak to peak amplitude of H-reflex decreased immediately and 30 minutes after the application of cold placebo ointment (p<0.05).Peak to peak amplitude of H-reflex decreased 30 minutes after the application of cold anesthetic ointment (p<0.05).

Based on the above results, it was concluded that topical anesthesia causes a decrease in the stimulation of motor neurons by desensitizing the low threshold skin receptors and reducing their basic activity. Additionally, cold temperature could cause a decrease in the stimulation of motor neurons by the stimulation of thermo-receptors and reducing the firing rate of surface mechanoreceptors. Different skin receptors depend on the intensity, duration and place of the stimulus, have different effects on the excitability of the spinal motor neurons. Cutaneous afferents in addition with muscle afferents, have convergence on common spinal interneurons and determines motor neurons excitability.

The measurement of skin thickness is an important method in diagnosis, control of treatment and studying the effects of drugs and their dosage on skin diseases. The development of high frequency ultrasound imaging systems in recent years has made the measurement of skin layers thickness possible. In this paper, a new method of identifying skin layers and measuring their thickness using B-scan ultrasound images is presented. The B-scan images of skin have been obtained using a Dermascan unit model C (Cortex Technology, Denmark) with a 20 MHz probe. In this research, feature matching and neuro-fuzzy classifier have been used to determine the boundaries between the skin layers. Feature matching is necessary for constructing the probability matrix followed by the neuro-fuzzy classifier which is used to extract the boundaries of skin layers. After finding these boundaries, a thickness of different skin layers is calculated. The proposed method has been tested on 50 ultrasound images. The results obtained for the distinction of different skin layers and the calculated skin thickness were compared against the result obtained from two dermatologists who examined the cases and the thickness calculated by histological technique, respectively. By applying this algorithm, different skin layers are extracted with 86% accuracy. The results of this method were also confirmed by histological experiments with a precision of one hundredth of a millimeter. Discrete cosine transform (DCT) coefficients feature has showed that it has the best performance for the identification of skin layers.Discussion and The neuro-fuzzy classifier can be used as a reliable tool for processing ultrasound images of skin. In contrast to existing methods, the proposed method doesnt require initialization and it has good noise immunity. Therefore, this method can be applied to clinical routine to find the effects of drugs precisely.

Although low energy laser therapy has been shown to enhance collagen production and wound healing but its effect on cartilage stiffness has not been reported. The aim of this study was to evaluate the biomechanical behaviour of the repaired surfaces of defective articular cartilage in the patellar groove of rabbit femur after a pulsed low level Gallium-Arsenide (GA-AS) laser irradiation. osteochondral defects of 5 mm in diameter and 4 mm deep were drilled in the femoral patellar groups of forty-one adolescent male rabbits and were examined at 4, 8 and 16 weeks. They were divided into six groups (3 experimental and 3 control groups). The experimental groups received pulsed GA-AS laser irradiation (890 nm) having energy density of 4.8 j/cm². For the control groups, the surgical procedure was the same as the experimental ones, but only placebo laser treatment was applied. The untreated defects were allowed to heal spontaneously. The knee joint were removed, and the defects were examined bio-mechanically by in situ indentation method at three time intervals (4, 8 and 16 weeks post treatment). The thickness, instantaneous and equilibrium indentation stiffness were measured during the test. Although no difference was observed in cartilage the mechanical properties after 4, 8 and 16 weeks period in the two groups (laser and control), differences between the laser and the control group were found at the 8th week period in the equilibrium elastic modulus which was significantly higher in the laser group than the control one. The average thickness of normal patellar groove cartilage in the normal limb of both groups was detected (0.4± 0.03).Discussion and GA-AS laser irradiation improves the stiffness of repairing cartilage at 8 week after injury.