فهرست مطالب

Frontiers in Biomedical Technologies - Volume:1 Issue: 4, 2015
  • Volume:1 Issue: 4, 2015
  • تاریخ انتشار: 1394/01/25
  • تعداد عناوین: 8
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  • Samaneh Kouchaki *, Konstantinos Eftaxias, Saeid Sanei Pages 233-239
    Purpose
    Sleep is a complex physiological state and an indicator of the changes in the brain function similar to those occurring in many psychiatric and neurological conditions. Since visual sleep scoring consuming process, automatic sleep staging methods, also called scoring, hold promise in diagnosing alterations in the sleep process and the sleep EEG more effectively.
    Method
    In this paper, a supervised approach for sleep scoring from single channel EEG signals is proposed. First, a supervised singular spectrum analysis (SSA) which is a subspace based method is used to extract the desired signal for each stage of sleep. Then, two recursive least square (RLS) adaptive filters are trained and used to identify first and deep sleep stages.
    Result
    The proposed system which can be considered as a filter bank for separating multiple signal subbands is tested using real EEG where the results verify the accuracy of the proposed method.
    Conclusion
    The overall result show the effectiveness of algorithm for detection of sleep stages from EEG signals often characterised by a sharp increase in delta and a rapid decrease in alpha as sleep deepens.
    Keywords: Adaptive filters, empirical mode decomposition, recursive least square, singular spectrum analysis, sleep EEG
  • Rezvan Ravanfar Haghighi, Sabyasachi Chatterjee, Pratik Kumar, Vani V. Chatterjee* Pages 240-251
    Purpose
    Attenuation of x-rays in any object is a combined effect of scattering and absorption of x-ray photons by the atoms in the material. While the scattering part dependents linearly upon the material’s electron density (ρe) and is weakly dependent on the energy (E) of the photon, the photoelectric part varies as [ρe Zxeff /Ey] where Zeff is the effective atomic number of the material. We aim to determine the exponents (x,y) which are crucial for many radiological studies.
    Methods
    In order to obtain exponent ‘y’, we find an equation in which the exponent x does not appear and the dependence on ‘y’ appears only linearly. Having thus reduced the problem to that of ‘one parameter fit’ in ‘y’, we generate the ‘data’ numerically from the numerical values of physical constants given in the NIST (The National Institute of Standards and Technology, or NIST) tables and determine ‘y’ from linear regression. The effect of the source spectrum on the effective value of ‘y’, denoted by ‘ym’ is studied for different low Zeff substances in different energy ranges.
    Results
    It is seen that with x-ray sources operating at 80, 100,120,140 kVp, the effective exponent ‘y’ progressively decreases, as the x-ray source spectrum is pushed to higher energy side. However, for most practical purposes y=2.99 may be used for a wide variety of low Zeffsubstances. For practical cases with different source spectra, the effective energy of the source and the effective photoelectric exponent are seen to increase as the thickness of the aluminum filter increases.
    Conclusion
    It thus follows that for applications such as DECT inversion, the appropriate values of ymought to be used that takes into account the appropriate source spectrum.
    Keywords: ray, DECT, Photoelectric effect, Compton effect, Exponents
  • Pardis Ghafarian*, Mohammad Reza Ay Pages 252-257
    Purpose
    Potential causes of misalignment between anatomical and functional images incardiac PET/CT imaging include respiratory and cardiac motion as well as bulk motion. In this study we evaluated the impact of respiratory and cardiac motion between CT and corresponding CT-based attenuation corrected (CTAC) PET images on apparent myocardial uptake.
    Methods
    PET projection data of the 4D XCAT phantom were analytically generated using an analytic simulator considering the effect of photon attenuation and Poisson noise. Theassessment of PET images was performed through qualitative interpretation by an experiencednuclear medicine physician and a volume of interest based quantitative analysis. Moreover,Box and Whisker plots were calculated and bull’s eye view analysis performed. PET imageswere also reoriented along the short, horizontal and vertical long axis views for a betterqualitative interpretation.
    Results
    The simulation study showed that using the attenuation map at end-exhalation of therespiratory phase consistently overestimated the activity concentration in all segments of themyocardial wall as opposed to using the end-inhalation attenuation map image which resulted inunderestimation
    Conclusion
    CT images acquired at end-exhalation could introduce larger errors compared toend-inhalation. These errors decrease significantly when the attenuation map was acquired atmid-inhalation or mid-exhalation phases of the respiratory cycle.
    Keywords: Cardiac PET, CT, misalignment artifacts, attenuation correction, respiratory motion, cardiac motion
  • Tahereh S. Jafarzadeh Kashi, Maryam Hajihasani, Soolmaz Heidari, Kimia Khoshroo*, Reza Masaeli, Mohammadreza Tahriri Pages 258-264
    Purpose
    The properties of resin-based composites as polymeric materials are related to the quality of polymerization. Microhardness measurement is an indirect method to predict this quality. Irradiation time and distance as factors related to light-curing process play important roles in this issue. The purpose of this study was to evaluate the effect of irradiation time and distance on the microhardness values of three different commercial nanohybrid resin-based composites.
    Methods
    A total of 180 disk-shaped specimens (60 specimens for each commercial resin-based composite) from three nanohybrid resin-based composites [Grandio (Voco), Simile (Pentron) and Tetric N- Ceram (Ivoclar Vivadent)] in A2 shade were prepared. The specimens were randomly subdivided in 6 subgroups (3 subgroups for evaluating irradiation time: 10 s, 20 s and 40 s, 3 subgroups for irradiation distance: 0 mm, 3 mm and 9 mm) which 10 specimens from each commercial resin-base composite were used for each subgroup. Vickers microhardness test was performed for the top and bottom surfaces of each sample using a microhardness tester under a 200 gr load and a dwell time of 15 s. Three random indentations were taken for each surface and a mean value was calculated. Data were analyzed by two and three way ANOVA and Tukey’s post-hoc test at the 95% significance level.
    Results
    The microhardness distances showed statistically significant differences between the groups on both top and bottom surfaces values for different irradiation times and distances (p value ≤ 0.001).The only exception was Simile group which there was no significant difference for microhardness values between 0 and 3 mm distances. Grandio showed the highest microhardness values among others.
    Conclusions
    Increasing the irradiation time and decreasing the irradiation distance caused to increase the microhardness values. Also, the microhardness of the resin-based composites was affected by the chemical structure of the material.
    Keywords: Distance, Irradiation, Light cure, Microhardness, Resin, based composite, Time
  • Hojjat Mahani, Alireza Kamali, Asl*, Mohammad Reza Ay Pages 265-270
    Purpose
    Mechanical calibration of camera plays an important role in nuclear imaging to acquire a more qualified and quantized scintigram. The objective of this work was to quantitatively evaluate planar resolution and sensitivity of a tilted Anger camera using a Monte Carlo simulation.
    Methods
    For this purpose, spatial resolution and system sensitivity of a tilted-head, LEHR collimated gamma-camera were evaluated using Monte Carlo simulation. To do so, tilt-angle of camera’s head was considered to vary from -10 to 10 degrees from the baseline. The Monte Carlo simulated data were validated by means of a comparison with experimental data. In addition, the performance of the system was analyzed both in spatial and frequency domains.
    Results
    Spatial resolution, in terms of FWHM, for simulated and measured point-spread functions (PSFs), at the rest-position has a value of 7.22 mm and 7.43 mm, respectively. The results also show that the spatial resolution monotonically increases as the absolute value of tilt angles increases, up to a degradation factor of 2.02 for a typical scintillation-camera. System sensitivity exhibits a constant behavior for all tilt-angles with a maximum statistical fluctuation of 2%.
    Conclusion
    While a head tilt has no effect on the sensitivity of the camera, it can result in a poor and spatially variable planar spatial resolution and contrast of the images provided by the tilted-scanner.
    Keywords: spatial resolution, image quality, tilted, head, gamma, camera, Monte Carlo simulation
  • Azadeh Emami, Hossein Ghadiri *, Pardis Ghafarian Pages 271-278
    Purpose
    Accurate performance assessment of bone mineral density (BMD) methods is crucial due to the fact that a high level of exact estimation of bone situation is needed for correct diagnosis. Variation of parameters like sensitivity and error ratio highly affects the densitometry results that may induce some level of uncertainty in diagnosis. So, designing an algorithm for correction is necessary to assure examiners about measurement results.
    Methods
    In this study several phantoms consisting of soft tissue- and bone-equivalent materials were devised to accurately test bone densitometry systems. To the best of our knowledge there is no unique phantom to be able to use for evaluation of both Dual Energy X-ray Absorptiometry (DEXA) and Quantitative Computed Tomography (QCT) in a wide range of density. The main motivation of this study was to design a reliable and easy to use phantom. A QCT quality control, quality assurance, and Plexiglas cylindrical phantoms as a spine phantom were designed and constructed to assess different bone densities. Four inserts in spine phantom with precisely wide range of K2HPO4 solutions were used for simulation of bone tissues and to determine the BMD systems characteristics. The designed phantoms were also used for performance assessment of BMD systems. We used a sinogram-based analytical CT simulator to model the complete chain of CT data acquisition for QCT method as well.
    Results
    In this research it is demonstrated that by decreasing of bone mineral densities an increasing trend in error ratio of measured densities and declining trend in methods sensitivities were observed in the both DEXA and QCT methods, that may cause some level of uncertainty in low densities. It has been shown that between the ranges of 20 and 100 mg/cc K2HPO4 concentrations, the error ratio in both DEXA and QCT techniques is more than 20%. Sensitivity values in incremental mineral contents ranges between 20-60 mg/cm3and 260-300 mg/cm3 reveal an upward trend between 0.93 and 1.45 for QCT and from 0.59 to 1.44 for DEXA, respectively.
    Conclusion
    A novel phantom was designed with capability of easily supporting wide range of densities and using in both DEXA and QCT techniques to measure and compare the sensitivity and error of systems. Our phantom showed excellent capability for accurate determination of BMD, particularly in low density bones. In this study it is demonstrated that the sensitivity and error ratio is affected by bone density that may cause uncertain results especially in low densities.
    Keywords: QCT Phantom, Quantitative Computed Tomography, DEXA, Bone mineral density
  • Mohammad Keshtkar*, Abbas Takavar, Mohammad Hassan Zahmatkesh, Ali Vaezzadeh, Mehrdad Gholami, Zeinab Ghasemian Pages 279-283
    Purpose
    Dosimetry is an integral part of radiotherapy and dose verification is one of the important stages in modern radiotherapy. Nowadays gel dosimeters are the only dosimeters that can record dose distribution in three dimensions only with a single measurement. The purpose of this study was to evaluate the capability of polymer gel dosimetry in dose verification of compensator-based IMRT.
    Methods
    A cerrobend slab with 4 cm thickness was manufactured and percentage depth dose curves for 18 MV photon beam and 10×10 cm2 field size were obtained by ionization chamber and polymer gel dosimeter. Then, an anthropomorphic pelvic phantom with gel inserts was constructed and irradiated with compensator-based IMRT technique.
    Results
    A comparison of the result of dose measurements with ion chamber and gel dosimeter showed that in spite of changing mean beam quality, compensators have no effect on response of gel dosimeter. Besides, according to distance to agreement (DTA) analysis there was good agreement between calculated and gel measured dose distributions.
    Conclusions
    The methodology presented in this work proved the feasibility of polymer gel dosimeter as an ideal tool for pretreatment IMRT QA and also the constructed phantom can be used efficiently in other radiotherapy techniques. Future works will be focused on the development of lung equivalent polymer gel dosimeter.
    Keywords: compensator, gel dosimetry, MRI, IMRT
  • Javad Hasani Bidgoli, Seyed Mousa Sadrhosseini, Ali Safavi Naeini, Hooshang Saberi, Mohammad Jalal Sadeghi, Saeed Karmifard, Habib Salimi, Alireza Ahmadian*, Farzam Farahmand, Saeed Sarkar Pages 284-291
    Purpose
    In this report, a thorough validation of PARSISS Image Guided Surgery has been presented.
    Methods
    Different experiments have been designed to evaluate Parsiss navigation system under three main scopes: first, a phantom study using a sophisticated precise phantom with 732 landmarks was constructed by 3d printing with layers of 16 micron thickness and 0.1 mm precision; second, performing preclinical cadaver experiment with titanium placed markers; and third, clinical evaluation which was carried out on 957 cases from 2010 to 2014.
    Results
    Results obtained from three evaluation methods showed that the system was found reliable and usable. Briefly, the average registration error in PARSISS precise phantom test was reported lower than 2 mm which is clinically acceptable and reasonable in neurosurgery and ENT surgeries. In clinical evaluation, surgeons approved the accuracy and reliability of the system in thorough clinical evaluation in 94% of cases of 957 patients.
    Conclusion
    In this study, the results of all three approaches were positive and reliable. Especially, evaluations using a large number of patients showed that the PARSISS surgical navigation system has shown a high level of reliability in clinical procedures.
    Keywords: Image Guided Surgery, Navigation, Minimal Invasive Surgery, Skull Base Surgery, Endoscopic Surgery, Neurosurgery