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Australasian Physical & Engineering Sciences in Medicine: The Official Journal of the Australasian College of Physical Scientists and Engineers in Medicine (v.34, #4)
Use of a systematic review to inform the infection risk for biomedical engineers and technicians servicing biomedical devices by Anne-Louise Smith (pp. 431-440).
Many microorganisms responsible for hospital-acquired infections are able to stay viable on surfaces with no visible sign of contamination, in dry conditions and on non-porous surfaces. The infection risk to biomedical staff when servicing biomedical devices is not documented. An indirect approach has been used to examine the different aspects that will affect the risk of infection including a systematic review of microbial contamination and transmission relating to biomedical devices. A systematic review found 58% of biomedical devices have microbial contamination with 13% having at least one pathogenic organism. These microbes can persist for some months. Occupational-infections of biomedical service staff are low compared to other healthcare workers. A biomedical device with contaminated surface or dust was identified as the source of patient outbreaks in 13 papers. The cleaning agent most tested for removal of micro-organisms from devices was alcohol swabs, but sterile water swabs were also effective. However, manufacturers mainly recommend (74%) cleaning devices with water and detergent. Biomedical engineers and technicians have a small risk of being exposed to dangerous micro-organisms on most biomedical devices, but without skin breakage, this exposure is unlikely to cause ill-health. It is recommended that biomedical staff follow good infection control practices, wipe devices with detergent, sterile water or alcohol swabs as recommended by the manufacturer before working on them, and keep alcohol hand rubs accessible at all benches.
Keywords: Biomedical devices; Biomedical engineer; Medical technician; Occupationally acquired infection
Validation of image registration and fusion of MV CBCT and planning CT for radiotherapy treatment planning by T. Hannah Mary Thomas; D. Devakumar; S. Balukrishna; Henry Finlay Godson; B. Paul Ravindran (pp. 441-447).
In areas like adaptive therapy, multi-phase radiotherapy, and single fraction palliative treatment or in the treatment of patients with metal implants where megavoltage(MV) CT could be considered as a treatment planning modality, the reduced contrast in the MV CT images could lead to limited accuracy in localization of the structures. This would affect the precision of the treatment. In this study, as an extension our previous work on bespoke MV cone beam CT (MV CBCT), we propose to register the MV CBCT with kilovoltage (kV) CT for treatment planning. The MV CBCT images registered with kV CT would be effective for treatment planning as it would account for the inadequate soft tissue information in the MV CBCT and would allow comparison of changes in patient dimensions and assist in localization of the structures. The intensity based registration algorithm of the BrainSCAN therapy planning software was used for image registration of the MV CBCT and kV CT images. The accuracy of the registration was validated using qualitative and quantitative measures. The effect of image quality on the level of agreement between the contouring done on both the MV CBCT and kV CT was assessed by comparing the volumes of six structures delineated. To assess the level of agreement between the plans after the registration, two independent plans were generated on the MV CBCT and the planning CT using the posterior fossa of the skull as the target. The dose volume histograms and conformity indices of the plans were compared. The results of this study show that treatment planning with MV CBCT images would be effective, using additional anatomical structure information derived from registering the MV CBCT image with a standard kVCT.
Keywords: Megavoltage cone beam CT; Registration; Planning CT; Fusion; Validation
Combination of frequency and amplitude-modulated model for the synthesis of normal and wheezing sounds by Bing-Yuh Lu; Huey-Dong Wu; Shyang-Rong Shih; Fok-Ching Chong; Meng-Lun Hsueh; Yu-Luen Chen (pp. 449-457).
Based on communication theory, this study proposes a model to synthesize normal and wheezing sounds. The model included five parts: the flow source as a transmitter, the frequency and amplitude-modulated (FM–AM) sounds, the accompanying noise as a modulator, the airway wall as a medium, and the microphone as a receiver. The hypothesis of modulation builds on that the deviation of frequency and amplitude of the sounds which cause from the deviation of collision speed of the air flow on the wall. The model was successful to simulate the normal breath and wheezing sounds. Furthermore, it provided a correct proof for the CORSA description, which indicates that the wheeze was contained in the domain frequency at 400 Hz, but a number of investigators have suggested that the range is actually between 80–1,600 Hz and 350–950 Hz by filter theory. This study modifies the signal source in Wodicka et al. model, and describes it in functional blocks. In fact, the design of the signal source base on the knowledge of the lung sound studies, especially the analysis of components in the frequency and time domains. We synthesized the required components to reproduce the lung sounds, and proposed a mechanism of wheeze which was examined by the computer simulation in the points of the system engineering view.
Keywords: Amplitude modulation (AM); Frequency modulation (FM); Model; Lung sound; Respiration acoustic signal; Wheeze
Long-term two-dimensional pixel stability of EPIDs used for regular linear accelerator quality assurance by B. W. King; L. Clews; P. B. Greer (pp. 459-466).
The long-term stability of three clinical electronic portal imaging devices (EPIDs) was studied to determine if longer times between calibrations can be justified. This would make alternatives to flood-field calibration of EPIDs clinically feasible, allowing for more effective use of EPIDs for dosimetry. Images were acquired monthly for each EPID as part of regular clinical quality assurance over a time period of approximately 3 years. The images were analysed to determine (1) the long-term stability of the EPID positioning system, (2) the dose response of the central pixels and (3) the long term stability of each pixel in the imager. The position of the EPID was found to be very repeatable with variations less than 0.3 pixels (0.27 mm) for all imagers (1 standard deviation). The central axis dose response was found to reliably track ion chamber measurements to better than 0.5%. The mean variation in pixel response (1 standard deviation), averaged over all pixels in the EPID, was found to be at most 0.6% for the three EPIDs studied over the entire period. More than 99% of pixels in each EPID showed less than 1% variation. Since the EPID response was found to be very stable over long periods of time, an annual calibration should be sufficient in most cases. More complex dosimetric calibrations should be clinically feasible.
Keywords: Epid; Stability; Long-term; Quality assurance; Calibration
A new approach to dose estimation and in-phantom figure of merit measurement in BNCT by using artificial neural networks by R. Ahangari; H. Afarideh (pp. 467-479).
In-phantom figures of merit of the radiobiological dose distribution are the main criteria for evaluation of the boron neutron capture therapy (BNCT) plan and neutron beam evaluation. Since in BNCT there are several reactions, which contribute to the total dose of the tissue, the calculation of the dose distribution is complicated and requires lengthy and time-consuming simulations. Any changes in the beam shaping assembly (BSA) design would lead to the change of the neutron/gamma spectrum at exit of therapeutic window. As a result of any changes in the beam spectrum, the dose distribution in the tissue will be altered; therefore, another set of lengthy and time-consuming simulations to recalculate the dose distribution would have to be performed. This study proposes a method that applies artificial neural network (ANN) for quick dose prediction in order to avoid lengthy calculations. This method allows us to estimate the depth–dose distribution and in-phantom figures of merit for any energy spectrum without performing a complete Monte Carlo code (MCNP) simulation. To train the ANNs for modeling the depth–dose distribution, this study used a database containing 500 simulations of the neutron depth–dose distribution and 280 simulations of the gamma depth–dose distribution. The calculations were carried out by the MCNP for various mono-energetic neutrons, ranging from thermal up to 10 MeV energy and 280 gamma energy group, ranging from 0.01 MeV up to 20 MeV, through the SNYDER head phantom which is located at the exit of the BSA. The trained ANN was capable of establishing a map between the neutron/gamma beam energy and the dose distribution in the phantom as an input and a response, respectively. The current method is founded upon the observation that the dose which is released by the beam of composite energy spectrum can be decomposing into the various energy components which make the neutron/gamma spectrum. Therefore, in this procedure the neutron/gamma energy spectrum was converted into several energy groups and dose response of each group was predicted by the trained ANN. Total dose distribution of the entire spectrum is equal to summation of dose response of each group. If the neutron/gamma spectrum as an input changes, the dose response of that as an output can be predicted by the trained ANN in no time rather than hours or days by MCNP simulations. To check the validity of this method, this study compared full calculation of the depth–dose distribution with prediction of ANN for that. The result of this comparison shows that artificial neural networks model the dose distribution in phantom successfully and result in a great accurate prediction.
Keywords: Boron neutron capture therapy; Radiobiological dose distribution; Artificial neural network; MCNP simulation; Beam shaping assembly
Quantification of image quality using information theory by Takanaga Niimi; Hisatoshi Maeda; Mitsuru Ikeda; Kuniharu Imai (pp. 481-488).
Aims of present study were to examine usefulness of information theory in visual assessment of image quality. We applied first order approximation of the Shannon’s information theory to compute information losses (IL). Images of a contrast-detail mammography (CDMAM) phantom were acquired with computed radiographies for various radiation doses. Information content was defined as the entropy Σp i log(1/p i ), in which detection probabilities p i were calculated from distribution of detection rate of the CDMAM. IL was defined as the difference between information content and information obtained. IL decreased with increases in the disk diameters (P < 0.0001, ANOVA) and in the radiation doses (P < 0.002, F-test). Sums of IL, which we call total information losses (TIL), were closely correlated with the image quality figures (r = 0.985). TIL was dependent on the distribution of image reading ability of each examinee, even when average reading ratio was the same in the group. TIL was shown to be sensitive to the observers’ distribution of image readings and was expected to improve the evaluation of image quality.
Keywords: Information theory; Contrast-detail phantom; Digital mammography; Image quality; Visual assessment
Motion effects on SUV and lesion volume in 3D and 4D PET scanning by J. Callahan; D. Binns; L. Dunn; T. Kron (pp. 489-495).
To assess the effect of lesion motion and respiration rate on Standardised Uptake Value (SUV) and the ability of 4D PET to restore any loss in SUV and distortion of lesion volume on two PET/CT systems. A Perspex phantom with four cylindrical reservoirs filled with 18F-FDG was used in this study. The cylinders measured 5, 10, 15, and 20 mm in diameter. A GE Discovery STE8 (GE Medical Systems Milwaukee, WI) and a Siemens Biograph 64/40 (Siemens Medical Solutions, Erlangen, Germany) scanner was used to acquire a stationary un-gated PET scan of the phantom. Multiple 10 min list mode 4D PET scans were acquired using the Varian RPM on the GE camera and the Anzai Gating system on the Siemens camera. The phantom was scanned at five different respiratory rates and motion amplitudes in a sinusoidal fashion, 15 RPM/1 cm, 15 RPM/2 cm, 15 RPM/4 cm, 30 RPM/2 cm and 7.5 RPM/2 cm (RPM-respirations per minute). Each scan was reconstructed into ten bins and as an un-gated static image. The SUVmax, SUVmean and volume were measured for all four reservoirs using Siemens TrueD analysis software. With increasing lesion movement the SUVmax and SUVmean decreased and the volume increased with the SUVmax in the smallest lesion underestimated by up to a factor of four. The SUVmax, SUVmean and volume were mostly recovered using 4D imaging regardless of amount of lesion displacement. The larger lesions showed better count recovery and volume correction than the smaller lesions. The respiratory rate had no effect of SUV or volume. Un-gated imaging of moving lesions decreases apparent SUV in small lesions significantly and overestimates volumes. 4D PET scanning recovers most of the apparent loss in SUV and distortion of volumes.
Keywords: Respiratory; Gated; 4D; PET
A novel human–machine interface based on recognition of multi-channel facial bioelectric signals by Iman Mohammad Rezazadeh; S. Mohammad Firoozabadi; Huosheng Hu; S. Mohammad Reza Hashemi Golpayegani (pp. 497-513).
This paper presents a novel human–machine interface for disabled people to interact with assistive systems for a better quality of life. It is based on multi-channel forehead bioelectric signals acquired by placing three pairs of electrodes (physical channels) on the Frontalis and Temporalis facial muscles. The acquired signals are passed through a parallel filter bank to explore three different sub-bands related to facial electromyogram, electrooculogram and electroencephalogram. The root mean square features of the bioelectric signals analyzed within non-overlapping 256 ms windows were extracted. The subtractive fuzzy c-means clustering method (SFCM) was applied to segment the feature space and generate initial fuzzy based Takagi–Sugeno rules. Then, an adaptive neuro-fuzzy inference system is exploited to tune up the premises and consequence parameters of the extracted SFCMs rules. The average classifier discriminating ratio for eight different facial gestures (smiling, frowning, pulling up left/right lips corner, eye movement to left/right/up/down) is between 93.04% and 96.99% according to different combinations and fusions of logical features. Experimental results show that the proposed interface has a high degree of accuracy and robustness for discrimination of 8 fundamental facial gestures. Some potential and further capabilities of our approach in human–machine interfaces are also discussed.
Keywords: Human–machine interfaces; Multi-channel facial bioelectric signals; Subtractive fuzzy c-means clustering; Adaptive neuro-fuzzy inference system (ANFIS)
Myocardial ischemia analysis based on electrocardiogram QRS complex by Jinzhong Song; Hong Yan; Zhi Xu; Xinming Yu; Ruiyun Zhu (pp. 515-521).
Electrocardiogram (ECG) is an economic, convenient, and non-invasive detecting tool in myocardial ischemia (MI), and its clinical appearance is mainly exhibited by the changes in ST–T complex. Recently, QRS complex characters were proposed to analyze MI by more and more researchers. In this paper, various QRS complex characters were extracted in ECG signals, and their relationship was analyzed systematically. As a result, these characters were divided into two groups, and there existed good relationship among them for each group, while the poor relationship between the groups. Then these QRS complex characters were applied for statistical analysis on MI, and five characters had significant differences after ECG recording verification, which were: QRS upward and downward slopes, transient heart rate, angle R and angle Q. On the other hand, these QRS complex characters were analyzed in frequency domain. Experimental results showed that the frequency features of RR interval series (Heart Rate Variability, HRV), and QRS barycenter sequence had significant differences between MI states and normal states. Moreover, QRS barycenter sequence performed better.
Keywords: Electrocardiogram (ECG); Myocardial ischemia (MI); QRS complex characters; Heart rate variability (HRV); QRS barycenter
Characterization of a Fricke dosimeter at high energy photon and electron beams used in radiotherapy by O. Moussous; S. Khoudri; M. Benguerba (pp. 523-528).
The dosimetric features of the Fricke dosimeter in clinical linear accelerator beams are considered. Experimental data were obtained using various nominal energies 6 and 18 MV, 12 and 15 MeV, including the 60Co γ-ray beam. The calibration of the dosimeters was performed using the ionization chamber as a reference dosimeter. Some general characteristics of Fricke dosimeter such as energy dependence, optical density (OD)-dose relationship, reproducibility, accuracy, dose rate dependence were analyzed. The Fricke solution shows linearity in OD-dose relationship, energy independence and a good reproducibility over the energy range investigated. The Fricke dosimeter was found to be suitable for carrying out absorbed dose to water measurements in the calibration of high energy electron and photon beams.
Keywords: Fricke dosimeter; Energy dependence; Reproducibility; Radiotherapy
Lessons learned from a HDR brachytherapy well ionisation chamber calibration error by Claire Dempsey (pp. 529-533).
The outcomes of a recent brachytherapy well-type ionization chamber calibration error are given in the hope that other brachytherapy treatment centres may better understand the importance of each entry stated in a well chamber calibration certificate. A Nucletron Source Dosimetry System (SDS) PTW well-type ionization chamber was sent for a biennial calibration in September 2010. Upon calibration of the chamber, it was discovered that the previous calibration (in July 2008) contained a +2.6% error in the chamber calibration coefficient. Investigation of the information on the 2008 well chamber calibration certificate indicated the source of the error, which could or should have been detected by both the calibration laboratory and/or the radiation therapy department upon return of the chamber. Consideration must be given to all values and conditions given on the calibration certificate when accepting a ionization chamber back from a calibration laboratory. The issue of whether the source strength from the source calibration certificate or the measured source strength from the calibrated ionization chamber should be entered into the treatment unit is also raised.
Keywords: Brachytherapy; Chamber; Calibration
The HVL in soft tissue and the AAPM and IEC exposure indices by John Poletti (pp. 535-543).
Manual exposure settings for radiographic projections were once based on a points system which assumed that the HVL in soft tissue is 3.0 cm and that each change of 1.0 cm of soft tissue corresponded to a change of 25% in image receptor dose. A set of mAs steps and equivalent kVp steps was estimated that would give appropriate technique factors for changes in patient thickness. With the advent of rare-earth screen-film systems and AEC systems the points system fell into disuse. Screen-film imaging systems have almost entirely been replaced by CR or DR systems and recently, standardised exposure indices have been recommended by the AAPM and IEC to provide exposure guidance for these systems. If the fundamental assumptions on which the points system was based are still valid for modern high-frequency generators and digital imaging systems, then there would be an elegant correspondence between the predictions of the points system and the requirements for correction of exposure errors indicated by the AAPM and IEC indices. This study estimated the HVL and attenuation per cm in soft tissue using computer simulation, finding that practically, the HVL is between 2.0 and 5.0 cm and attenuation per cm ranges from 15 to 25%. The study concluded that agreement between the points system predictions and the true effects of technique factors changes on dose to the image receptor was moderately good, that use of the points system and technique charts based on this system should be encouraged and that use of the IEC or AAPM digital exposure indices should be standardised.
Keywords: X-ray; Patient dose; Digital imaging systems; Exposure settings
Lack of backscatter factor measurements in HDR applications with MOSkins by Anna Hayton; Annette Haworth; David Waterhouse; Stephen Todd; Joseph Pillainayagam (pp. 545-552).
Measurements of backscatter correction factors for intra operative (IOBT) HDR brachytherapy applicators were made using Centre for Medical Radiation Physics (CMRP), MOSFET devices. In clinical use there is an absence of backscatter material above the IOBT applicator, leading to a lower dose than predicted by conventional TG-43 dose calculations. To estimate the uncertainty in the MOSFET measurements, the dosimetric characteristics, including reproducibility, stability, linearity, and angular and energy response were measured using a HDR Ir-192 source, kilovoltage treatment unit and a high energy linac. Measurements were compared with previously published Monte Carlo data. Variability of the response of the MOSFETs due to angular variation contributed the largest uncertainty in dose measurements. Using the IOBT applicator without adequate scatter material resulted in a reduction of delivered dose of on average 10%, but was dependent on the location on the applicator and the treatment field size. Theoretical calculations based on previously published study indicated an expected reduced dose of on average 4%. MOSFET devices provide an ideal measurement tool in the presence of high dose gradients, however, the dosimetric characteristics of the detector must be accounted for when estimating the uncertainty.
Keywords: MOSFET; IOBT; Backscatter; HDR; Brachytherapy
Determination of RW3-to-water mass-energy absorption coefficient ratio for absolute dosimetry by Katrina Y. T. Seet; Peta M. Hanlon; Paul H. Charles (pp. 553-558).
The measurement of absorbed dose to water in a solid-phantom may require a conversion factor because it may not be radiologically equivalent to water. One phantom developed for the use of dosimetry is a solid water, RW3 white-polystyrene material by IBA. This has a lower mass-energy absorption coefficient than water due to high bremsstrahlung yield, which affects the accuracy of absolute dosimetry measurements. In this paper, we demonstrate the calculation of mass-energy absorption coefficient ratios, relative to water, from measurements in plastic water and RW3 with an Elekta Synergy linear accelerator (6 and 10 MV photon beams) as well as Monte Carlo modeling in BEAMnrc and DOSXYZnrc. From this, the solid-phantom-to-water correction factor was determined for plastic water and RW3.
Keywords: Dosimetry; Solid phantom; Plastic water; RW3
Erratum to: ROPES eye plaque brachytherapy dosimetry for two models of 103Pd seeds
by Pooneh Saidi; Mahdi Sadeghi; Alireza Shirazi; Claudio Tenreiro (pp. 641-641).