مقايسه تاثير CBCT با CT بر ميزان آرتيفکت‌های اسکن ايمپلنت‌های دندانی

سابقه و هدف: امروزه توموگرافی کامپيوتری با پرتو مخروطی شکل (CBCT) به عنوان جايگزينی برای توموگرافی کامپيوتری (CT) در درمانهای دندانپزشکی می‌باشد. مواد فلزی به کار رفته در دندانپزشکی قادر به ايجاد آرتيفکتهايی حاصل از پديده سخت شدن پرتو می‌باشند. در اين مطالعه ميزان آرتيفکتهای ناشی از سخت شدن پرتو در تصاوير به دست آمده از دو دستگاه NewTom VG وPlanmeca Promax باSomatom Sensation 64-Slice CT مورد مقايسه قرار گرفت. مواد و روش‌ها: در اين مطالعه توصيفی از[IMP 1003-L-HD] Implant drilling Model استفاده شد. ايمپلنت ها (Dentis) با طول و قطر يکسان در نواحی کانين, پره مولر و مولر قرار داده شدند. تصاوير يکسان از هر دستگاه توسط دو نفر مشاهده‌گر ارزيابی شد. ميزان آرتيفکتها بر اساس مقياس تهيه شده طبق معيارهای کتب مرجع مورد بررسی قرار گرفت. نتايج به دست آمده توسط آزمون رتبه‌ای کروسکال واليس مورد بررسی و تجزيه و تحليل آماری قرار گرفت. يافته‌ها: رتبه وضوح تصوير در دستگاه NewTom برابر با48/0± 53/4 ، دستگاه Somatom برابر با 57/0±14/4 و دستگاه Planmeca برابر با 84/0±80/1 بود. تفاوت معنی‌داری در وضوح تصاوير در سه دستگاه مشاهده شد. (001/0 >P) نتيجه گيری: با توجه به ميزان اندک آرتيفکتهای فلزی در دستگاه NewTom VG ، همچنين دوز پايين تر وهزينه کمتر آن در مقايسه با CT ، استفاده از آن به منظور تصويربرداری از بيمارانی که دارای ترميم ها وسيع، پروتزهای متعدد و يا درمان های قبلی ايمپلنت می باشند توصيه می گردد

Metal artifact reduction in dental CT images using polar mathematical morphology

Most dental implant planning systems use a 3D representation of the CT scan of the patient under study as it provides a more intuitive view of the human jaw. The presence of metallic objects in human jaws, such as amalgam or gold fillings, provokes several artifacts like streaking and beam hardening which makes the reconstruction process difficult. In order to reduce these artifacts, several methods have been proposed using the raw data, directly obtained from the tomographs, in different ways. However, in DICOM-based applications this information is not available, and thus the need of a new method that handles this task in the DICOM domain. The presented method performs a morphological filtering in the polar domain yielding output images less affected by artifacts (even in cases of multiple metallic objects) without causing significant smoothing of the anatomic structures, which allows a great improvement in the 3D reconstruction. The algorithm has been automated and compared to other image denoising methods with successful results. (C) 2010 Elsevier Ireland Ltd. All rights reserved.This work has been supported by the project MIRACLE (DPI2007-66782-C03-01-AR07) of Spanish Ministerio de Educacion y Ciencia.Naranjo Ornedo, V.; Llorens Rodríguez, R.; Alcañiz Raya, ML.; López-Mir, F. (2011). Metal artifact reduction in dental CT images using polar mathematical morphology. Computer Methods and Programs in Biomedicine. 102(1):64-74. https://doi.org/10.1016/j.cmpb.2010.11.009S6474102

Reduction of artefacts caused by hip implants in CT-based attenuation-corrected PET images using 2-D interpolation of a virtual sinogram on an irregular grid

Purpose: Metallic prosthetic replacements, such as hip or knee implants, are known to cause strong streaking artefacts in CT images. These artefacts likely induce over- or underestimation of the activity concentration near the metallic implants when applying CT-based attenuation correction of positron emission tomography (PET) images. Since this degrades the diagnostic quality of the images, metal artefact reduction (MAR) prior to attenuation correction is required. Methods: The proposed MAR method, referred to as virtual sinogram-based technique, replaces the projection bins of the sinogram that are influenced by metallic implants by a 2-D Clough-Tocher cubic interpolation scheme performed in an irregular grid, called Delaunay triangulated grid. To assess the performance of the proposed method, a physical phantom and 30 clinical PET/CT studies including hip prostheses were used. The results were compared to the method implemented on the Siemens Biograph mCT PET/CT scanner. Results: Both phantom and clinical studies revealed that the proposed method performs equally well as the Siemens MAR method in the regions corresponding to bright streaking artefacts and the artefact-free regions. However, in regions corresponding to dark streaking artefacts, the Siemens method does not seem to appropriately correct the tracer uptake while the proposed method consistently increased the uptake in the underestimated regions, thus bringing it to the expected level. This observation is corroborated by the experimental phantom study which demonstrates that the proposed method approaches the true activity concentration more closely. Conclusion: The proposed MAR method allows more accurate CT-based attenuation correction of PET images and prevents misinterpretation of tracer uptake, which might be biased owing to the propagation of bright and dark streaking artefacts from CT images to the PET data following the attenuation correction procedur

Reduction of artefacts caused by hip implants in CT-based attenuation-corrected PET images using 2-D interpolation of a virtual sinogram on an irregular grid

Metallic prosthetic replacements, such as hip or knee implants, are known to cause strong streaking artefacts in CT images. These artefacts likely induce over- or underestimation of the activity concentration near the metallic implants when applying CT-based attenuation correction of positron emission tomography (PET) images. Since this degrades the diagnostic quality of the images, metal artefact reduction (MAR) prior to attenuation correction is required

Optimisation of whole-body PET/CT scanning protocols

Positron emission tomography (PET) has become one of the major tools for the in vivo localisation of positron-emitting tracers and now is performed routinely using 18F-fluorodeoxyglucose (FDG) to answer important clinical questions including those in cardiology, neurology, psychiatry, and oncology. The latter application contributed largely to the wide acceptance of this imaging modality and its use in clinical diagnosis, staging, restaging, and assessment of tumour response to treatment. Dual-modality PET/CT systems have been operational for almost a decade since their inception. The complementarity between anatomic (CT) and functional or metabolic (PET) information provided in a “one-stop shop” has been the driving force of this technology. Although combined anato-metabolic imaging is an obvious choice, the way to perform imaging is still an open issue. The tracers or combinations of tracers to be used, how the imaging should be done, when contrast-enhanced CT should be performed, what are the optimal acquisition and processing protocols, are all unanswered questions. Moreover, each data acquisition–processing combination may need to be independently optimised and validated. This paper briefly reviews the basic principles of dual-modality imaging and addresses some of the practical issues involved in optimising PET/CT scanning protocols in a clinical environment