- Détails du magazine
- Première publication
- 30 Dec 2008
- Période de publication
- 4 fois par an
- Accès libre
Pages: 85 - 91
In the standardization of panoramic radiography quality, the education and training of beginners on panoramic radiographic imaging are important. We evaluated the relationship between positioning error factors and multiple image analysis results for reproducible panoramic radiography.
Using a panoramic radiography system and a dental phantom, reference images were acquired on the Frankfurt plane along the horizontal direction, midsagittal plane along the left–right direction, and for the canine on the forward–backward plane. Images with positioning errors were acquired with 1–5 mm shifts along the forward– backward direction and 2–10° rotations along the horizontal (chin tipped high/low) and vertical (left–right side tilt) directions on the Frankfurt plane. The cross-correlation coefficient and angle difference of the occlusion congruent plane profile between the reference and positioning error images, peak signal-to-noise ratio (PSNR), and deformation vector value by deformable image registration were compared and evaluated.
The cross-correlation coefficients of the occlusal plane profiles showed the greatest change in the chin tipped high images and became negatively correlated from 6° image rotation (r = −0.29). The angle difference tended to shift substantially with increasing positioning error, with an angle difference of 8.9° for the 10° chin tipped low image. The PSNR was above 30 dB only for images with a 1-mm backward shift. The positioning error owing to the vertical rotation was the largest for the deformation vector value.
Multiple image analyses allow to determine factors contributing to positioning errors in panoramic radiography and may enable error correction. This study based on phantom imaging can support the education of beginners regarding panoramic radiography.
- panoramic radiography
- quantitative evaluation
- deformable image registration
- peak signal-to-noise ratio
- Accès libre
Pages: 92 - 103
Plastic scintillation detectors (PSD) have been developed for over four decades and are widely used in a variety of fields, but one can find relatively few reports of their clinical use compared to other dosimetric solutions.
The inexpensive detector setup made of a Saint-Gobain BC-400 plastic scintillator and commercially available on the market CMOS-based DSLR Pentax camera was investigated. Build PSD detectors were irradiated with 6, 10 and 15 MV flattening filtered (FF) and 6 and 10 MV flattening filter free (FFF) photon beams using a clinical linear accelerator. Data were processed using Matlab software to remove background and artefacts. A comparison of the spatial resolution parameters to the Gafchromic EBT3 films was performed.
Average dose difference between TPS and PSD was 1.1%. The measured spatial resolution was 0.29 mm, and it differed from the film by 1.1%. MTF50 for PSD was 0.57 mm higher than the Gafchromic film. Signal to dose fit function with an R-square equal to 0.999 was established. The standard deviation of mean pixels value for a series of measurements was below 0.1%, for variable dose rate dependence was below 0.6% and for different energies 1.1%.
It was demonstrated that such a setup allows a satisfactory signal-to-dose dependence and provides high spatial resolution at an affordable price compared to a 2D ion chamber or a diode detector array. Moreover, PSDs are reusable and provide a simple readout compared to Gafchromic films commonly used in radiotherapy departments.
Variable parameters of the camera allow to select signal values at the optimal level. The system presented excellent signal stability, high image resolution and a simple signal-to-dose relationship which encourages further work to investigate PSDs for use in radiation therapy departments.
- plastic scintillation detectors
- Gafchromic films
- Accès libre
Comparison of noise-power spectrum and modulation-transfer function for CT images reconstructed with iterative and deep learning image reconstructions: An initial experience study
Pages: 104 - 112
Deep learning image reconstruction (DLIR) is a very recent image reconstruction method that is already available for commercial use. We evaluated the quality of DLIR images and compared it to the quality of images from the latest adaptive statistical iterative reconstruction (ASIR-V) algorithm in terms of noise-power spectrum (NPS) and modulation-transfer function (MTF).
We scanned a Revolution QA phantom (GE Healthcare, USA) and a 20 cm water phantom (GE Healthcare, USA) with our 512 multi-slice computed tomography (CT) scanner. Images of the tungsten wire within the Revolution QA phantom were reconstructed with a 50 mm field of view (FOV). The images were reconstructed with various ASIR-V strengths (i.e. 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100%) and DLIRs (i.e. low, medium, and high) to assess the MTF. The images from the 20 cm water phantom were reconstructed with the same configuration to assess the NPS.
The MTF was similar for both reconstruction algorithms of DLIR and ASiR-V. The peak frequency (fp) of the DLIR low was comparable to that from ASIR-V at 50, 60, 70%; the DLIR medium was comparable to ASIR-V at 80%; and the DLIR high was comparable to ASIR-V at 100%. The average frequency (fA) of the DLIR low was comparable to that from ASIR-V at 40%; the DLIR medium was comparable to ASIR-V at 50%; and the DLIR high was comparable to ASIR-V at 70%. Both the DLIR and ASIR-V were able to reduce noise, but they had a different texture.
The noise in the DLIR images was more homogenous at high and low frequencies, while in the ASIR-V images, the noise was more concentrated at high frequencies. The MTF was similar for both reconstruction algorithms. The DLIR method showed a better noise reduction than the ASIR-V reconstruction.
- noise power spectrum
- modulation transfer function
- Accès libre
Pages: 113 - 129
The relevance of this study lies in the fact, that today the search for biocompatible materials for the management of bone defects is of importance. Such materials could become an alternative to transplants. For the replacement of bone defects, two-phasic bioactive ceramics of hydroxyapatite and β-tricalcium phosphate is a very attractive biomaterial due to its excellent biocompatibility and osteoconductivity, but the results of its use are quite controversial due to insufficient bioactivity. The purpose of this work is to investigate the osseointegration properties of two-phase bioactive ceramics doped with silicon (HTdSi), both as a single component and a component in combination with platelet-rich fibrin, as well as in comparison with the well-known imported analogue – BIO, which consists of β-tricalcium phosphate, also as an independent component and a component in combination with platelet-rich fibrin. In the experiment, the rabbits of the New Zealand white breed at the age of 3 months and with an average weight of 2.5 kg were used. The terms of implantation are 30, 60, 90 and 180 days. The advantages of the domestic bio-composite are substantiated on the basis of clinical, radiological and histological studies.
In the experiment, the rabbits of the New Zealand white breed at the age of 3 months and with an average weight of 2.5 kg were used. The terms of implantation are 30, 60, 90 and 180 days.
The osteointegration properties of two-phase bioactive ceramics doped with silicon (HTdSi), both as a single component and in combination with platelet fibrin, were investigated, as well as in comparison with the known imported analog - BIO, which contains β-tricalcium phosphate, both as a single component and in combination with platelet fibrin.
The advantages of domestic biocomposite are substantiated on the basis of clinical, radiological and histological studies.
- bioactive calcium-phosphate ceramics
- clinical and radiological studies
- histological studies
- Accès libre
Effect of the Small Field of View and Imaging Parameters to Image Quality and Dose Calculation in Adaptive Radiotherapy
Pages: 130 - 142
The use of cone beam computed tomography (CBCT) for dose calculation in adaptive radiotherapy has been investigated in many studies. Proper acquisition and reconstruction of preset parameters could improve the accuracy of dose calculation based on CBCT images. This study evaluated the impact of the modified image acquisition and preset reconstruction parameter available in X-Ray Volumetric Imaging (XVI) to improve CBCT image quality and dose calculation accuracy.
Calibration curves were generated by scanning the CIRS phantom using CBCT XVI Elekta 5.0.4 and Computed Tomography (CT) Simulator Somatom, which served as CT image reference. Rando and Catphan 503 phantoms were scanned with various acquisition and reconstruction parameters for dose accuracy and image quality tests. The image quality test is uniformity, low contrast visibility, spatial resolution, and geometrical scale test for each image by following the XVI image quality test module.
Acquisition and reconstruction parameters have an impact on the Hounsfield Unit (HU) value that is used as the HU-Relative Electron Density (RED) calibration curve. The dose difference for all the calibration curves was within 1% and passed the gamma passing rate. Images acquired using 120 kVp, F1 (with Bowtie Filter), and 50 mA (F1-120-50-10) scored the highest Gamma Index (GI) of 98.5%. For the image quality test, it scored 1.20% on the uniformity test, 2.14% on the low contrast visibility test, and 11 lp/cm on the spatial resolution test. However, F1-120-50-10 reconstructed with different reconstructions scored 3.83% and 4 lp/cm in contrast and spatial resolution test, respectively.
CBCT reconstruction parameters work as a scatter correction. It could improve the dose accuracy and image quality. Nevertheless, without adequate CBCT acquisition protocols, it would produce an image with high uncertainty and cannot be fixed with reconstruction protocols. The F1-120-50-10 protocols generate the highest dose accuracy and image quality.
- adaptive radiotherapy
- calibration curve
- cone beam computed tomography