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

Development and evaluation of metal artifact reduction and image segmentation techniques in PET/CT

Rekentechnieken om meer informatie uit PET-beeld te halen Artsen baseren hun behandelplan onder andere op beelden van een PET-scan. Maar deze zijn niet altijd vrij van onvolkomenheden, bijvoorbeeld door ruis of strepen veroorzaakt door metalen implantaten. Bovendien komen twee artsen op basis van dezelfde beelden vaak tot een andere conclusie. Mehrsima Abdoli ontwikkelde in haar promotieonderzoek verschillende rekentechnieken om de onvolkomenheden in PET-beelden te corrigeren. Met de resultaten die deze opleveren kunnen artsen en radiologen een preciezere diagnose stellen. Abdoli bestudeerde twee problemen: de strepen die metalen implantaten veroorzaken op PET-beelden, met als gevolg een onjuist of verkeerd beeld van het weefsel in de buurt van dat implantaat, en de moeilijkheid om tot een accurate inschatting te komen van de omvang van een tumor. Met betrekking tot dat eerste probleem stelt ze dat er verschillende technieken zijn om het beeld te corrigeren, en dat een combinatie van twee technieken (sinogram en interpolatie-gebaseerde technieken) de beste resultaten geeft. In het tweede deel van haar proefschrift stelt Abdoli dat het correct aflijnen van tumorvolume op PET-beelden lastig is, door de beperkte resolutie en ruis van die beelden. Handmatig aflijnen levert vaak verschillende berekeningen op. Na vergelijking van verschillende segmentatietechnieken, waarbij de tumor laagje voor laagje bestudeerd wordt, concludeert ze dat mogelijk is om het ruisniveau van PET-beelden te verminderen door in plaats van die segmentatietechnieken een vervormbaar contourmodel te gebruiken.

A virtual sinogram method to reduce dental metallic implant artefacts in computed tomography-based attenuation correction for PET

OBJECTIVE: Attenuation correction of PET data requires accurate determination of the attenuation map (mumap), which represents the spatial distribution of linear attenuation coefficients of different tissues at 511 keV. The presence of high-density metallic dental filling material in head and neck X-ray computed tomography (CT) scanning is known to generate streak artefacts in the resulting CT images and thus in the corresponding mumaps generated using CT-based attenuation correction. Consequently, an under/overestimation of activity concentration occurs in corresponding regions of the corrected PET images. The purpose of this study is to develop a simple yet practical approach for reduction of metallic dental implant artefacts in the generated mumaps. METHODS: Currently available sinogram-based metal artefact reduction (MAR) algorithms operate directly on the raw sinograms. These usually consist of huge files stored in proprietary format not easily disclosed by the manufacturers and thus are not straightforward to read and manipulate. The proposed method uses the concept of virtual sinograms produced by forward projection of CT images in Dicom format for MAR. The projection data affected by metallic objects are detected in the sinogram space through segmentation of metallic objects in the CT image followed by forward projection of the metal-only image. Thereafter, the affected sinogram bins are replaced by interpolated values from adjacent projections using the spline interpolation technique. The algorithm was assessed using a polyethylene phantom containing materials simulating different tissues and a dedicated jaw phantom scanned before and after the insertion of metallic objects, where the corrected and noncorrected mumaps were compared with the artefact-free mumap. In addition, the Jaszczak and standard germanium phantoms including four metallic inserts were scanned on a PET/CT scanner to evaluate the impact of the MAR procedure on PET data through the comparison of uncorrected and corrected PET images to the actual activity concentrations in the phantoms. The proposed algorithm was also applied to head and neck CT images of 10 patients with metallic dental implants. RESULTS: The MAR method proved to be practical in a clinical setting and reduced substantially the visible metal induced artefacts. The mean relative error in regions close to metallic objects is reduced by approximately 90%. The statistical analysis of the Jaszczak and solid Ge-68 phantoms PET images did not reveal statistically significant differences between the corrected and artefact-free images (P>0.05). Moreover, the evaluation of clinical studies did not reveal statistically significant differences between the attenuation coefficients of the corrected mumaps and the expected theoretical values. CONCLUSION: The proposed MAR method provides a simple and convenient approach allowing correction for the presence of metal artefacts caused by dental implants without the need to manipulate the complex raw CT data. Further evaluation using a larger clinical PET/CT database is under way to evaluate the potential of the technique in a clinical setting

Qualitative and quantitative assessment of metal artifacts arising from implantable cardiac pacing devices in oncological PET/CT studies: a phantom study

We evaluate the magnitude of metallic artifacts caused by various implantable cardiac pacing devices (without leads) on both attenuation maps (μ-maps) and positron emission tomography (PET) images using experimental phantom studies. We also assess the efficacy of a metal artifact reduction (MAR) algorithm along with the severity of artifacts in the presence of misalignment between μ-maps and PET images

A new imaging technology to reduce the radiation dose during uterine fibroid embolization

Background Uterine fibroid embolization (UFE) is a minimally invasive imaging-guided treatment using radiation exposure. Purpose To compare the patients' radiation exposure during UFE before and after introduction of a new X-ray imaging platform. Material and Methods Forty-one patients were enrolled in a prospective, comparative two-arm project before and after introduction of a new X-ray imaging platform with reduced dose settings, i.e. novel real-time image processing techniques (AlluraClarity). Demographic, pre-interventional imaging, and procedural data, including dose area product (DAP) and estimated organ dose on the ovaries and uterus, were recorded and angiographic quality of overall procedure was assessed. Results There were no significant differences in demographic characteristics and preoperative fibroid and uterine volumes in the two groups. The new imaging platform led to a significant reduction in mean total DAP (102 vs. 438 Gy.cm; P < 0.001), mean fluoroscopy DAP (32 vs. 138 Gy.cm; P < 0.001), mean acquisition DAP (70 vs. 300 Gy.cm; P < 0.001), and acquisition DAP estimated organ dose in ovaries (42 vs. 118 mGy; P < 0.001) and uterus (40 vs. 118 mGy, P < 0.001), without impairment of the procedure and angiographic image quality. Conclusion A substantial 77% reduction of DAP values and 64% and 66% reduction in organ dose on ovaries and uterus, respectively, was demonstrated with the new imaging platform, while maintaining optimal imaging quality and efficacy.status: publishe

Assessment of metal artifact reduction methods in pelvic CT.

Metal artifact reduction (MAR) produces images with improved quality potentially leading to confident and reliable clinical diagnosis and therapy planning. In this work, the authors evaluate the performance of five MAR techniques for the assessment of computed tomography images of patients with hip prostheses