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dc.contributor.advisorSitter, Beathe
dc.contributor.authorLow, Peter
dc.date.accessioned2020-06-04T16:00:56Z
dc.date.available2020-06-04T16:00:56Z
dc.date.issued2019
dc.identifier.urihttps://hdl.handle.net/11250/2656646
dc.description.abstractAdskillige typer for magnetisk resonans billedvægtninger er anbefalet til den bedst mulige fremstilling af multipel sklerose læsioner i rygmarven. Den diagnostiske virkningsfuldhed varierer mellem dem, grundet forskelle i kontrast forhold. Short-tau inversion-recovery (STIR) har god kontrast, men har historisk set syntes at mangle specificitet grundet billedartefakter og støj. Phase-Sensitive Inversion-recovery (PSIR) har vist god potential for bedre kontrast på 3 tesla scannere, men er ikke undersøgt på 1.5 tesla. Højere opløsning på scanninger, særligt tre-dimensionelle scanninger kan muligvis føre til opdagelsen af flere læsioner. Et studie blev gennemført for at undersøg de relative diagnostisk virkningsfuldhed på 1.5 teslaer, ved scanning af hele rygmarven for fire vægtninger. Følgende sekvensvægtninger blev inkluderet i studiet: T2, PSIR, to-dimensionel STIR (2D-STIR) og tre-dimensionel STIR (3D-STIR). Hver vægtning blev scannet over to anatomiske områder – den cervikale og thorakale rygmarv. Scantider på cirka fire minutter, samt anatomisk dækning af billeder var ens for alle vægtninger. Opløsning variererede mellem vægtningerne. To radiologer, en på overlæge niveau og en på afdelingsniveau, adskilleligt evalueret på hver vægtninger, hver for sig. Opdagelse af læsioner blev noteret efter højde-position i columna vertebralis og subjektive vurderinger af artefakter og støj blev også indsamlet. Kappa værdier for enighed blev beregnet mellem radiologerne for hver vægtning. Efterfølgende samledes radiologerne til et konsensus review af alle patienter med alle vægtninger, samt axiale rekonstruktioner af 3D-STIR sekvenserne. Denne referens standard anvendtes til beregning af sensitivitet, og positiv prædiktiv værdi (PPV). Kontrast-til-støj forhold (CNR) målinger udførtes på læsioner angivet på referens standarden, ved brug af regions-of-interest, som var ens i størrelse og placering mellem vægtningerne. 2D-STIR ydede den højeste sensitivitet og opdagede flere læsioner end alle andre vægtninger, dog kan der være tale om billed-baseret selektions-bias, samt den ikke-perfekte referens standard. Forskelle i antal opdagede læsioner var statistisk signifikant for begge radiologer på cervikale scanninger og for en radiolog på thorakale. 2D-STIR ydede også en signifikant bedre CNR end alle andre vægtninger. PPV og enighed for denne sekvenstype var høje og sammenlignelig med T2-vægtningen. Diagnosticerbarheden blev ikke forstyrret af artefakter eller støj i større grad på 2D-STIR end på T2. PSIR var den mindst sensitive vægtning, trods at CNR var bedre end på T2. 3D-STIR tilføjet flere læsioner end T2 eller PSIR, når samlet med 2D-STIR fund. Disse ekstra læsioner var mindre i størrelse end den overordnet gennemsnit. Dog var 3D-STIR svært påvirket af støj og muligvis også samtidig-felts artefakter. PPV og enighed var lavest for 3D-STIR, . 2D-STIR er ikke længere mere påvirkelig overfor artefakter end T2 og har god PPV samt enighed mellem radiologer. Denne sekvens er måske nu pålidelig nok til at blive anvendt alene. PSIR havde betydeligt lav sensitivitet, særligt på thorakale scanninger og CNR var signifikant værre end på 2D-STIR. 3D-STIR var slemt påvirket af støj og billedartefakter, men kan muligvis tjene godt som anden sekvens ved cervikale scanninger, hvis undersøgelsestider tillader. T2 er også et pålideligt valg som anden sekvens og denne er lige anvendelig til thorakale såvel cervikale scanning.
dc.description.abstractVarious types of magnetic resonance image weightings are recommended for the detection of multiple sclerosis lesions in the spinal cord. There are varying levels of diagnostic efficacy between them, due to differences in contrast ratios. Short-tau inversion-recovery (STIR) has good contrast, but has historically been viewed as lacking specificity due to imaging artefacts and noise. Phase-sensitive inversion-recovery (PSIR) has shown potential for greater contrast at 3 teslas, but has not been investigated at 1.5 tesla. Higher resolution scans, particularly three-dimensional scans can possibly detect more lesions. A study was conducted in order to investigate relative diagnostic efficacies at 1.5 tesla for the whole spinal cord for four image-weightings. The following sequence weightings were included in this study: T2, PSIR, two-dimensional short-tau inversion-recovery (2D-STIR) and three-dimensional short-tau inversion-recovery (3D-STIR). Each weighting was scanned over two areas of anatomy – the cervical and thoracic spinal cord. Scan times of roughly four minutes and area coverage were the same for all weightings. Resolutions were varied. Two radiologists, one of consultant level, one of departmental level, separately evaluated each sequence weighting alone. Detection of lesions was recorded by level in the spinal column, and subjective evaluations of artefacts and noise were also measured. Kappa values for agreement between radiologists were calculated for each weighting. Subsequently, both radiologists consensus-reviewed all patients with the use of all images available including axial reconstructions of the 3D-STIR acquisition. This reference standard was used to calculate sensitivities and positive-predictive-values (PPV). Contrast-to-noise measurements (CNR) were done for consensus confirmed lesions by the use of regions-of-interest, which were of identical size and position between weightings. 2D-STIR had the highest sensitivity and detected more lesions than all other sequences, though there may be issues with image-based selection bias and the imperfect reference standard. This difference was statistically significant for both radiologists on cervical coverage scans and for one radiologist on thoracic scans. 2D-STIR also had significantly greater CNR than all other sequences for both areas of coverage. PPV and agreement for this sequence were high and comparable with that of T2. Diagnosis was no more affected by artefacts and noise on 2D-STIR than T2. PSIR was the least sensitive sequence, despite having a slightly better CNR than T2. 3D-STIR added a greatest number of lesions when added to 2D-STIR findings, than PSIR or T2. These additional lesions were smaller in size than the overall average. But 3D-STIR was badly affected by noise and possibly concomitant field artefacts. PPV was lowest for 3D-STIR. 2D-STIR is no more affected by artefacts than T2 and has good PPV and agreement. This sequence is now perhaps good enough to be used alone. PSIR had poor sensitivity especially on thoracic scans and CNR was significantly worse than 2D-STIR. 3D-STIR was very badly affected by noise and imaging artefacts, but can perhaps serve as a good secondary sequence for cervical scanning if examination times allow. T2 is also a reliable choice as a secondary sequence and is just as useful for thoracic scanning as for cervical.
dc.languageeng
dc.publisherNTNU
dc.titleDetektion af Rygmarvslæsioner ved Multipel Sklerose. Sammenligning af Magnetisk Resonans Vægtninger
dc.typeMaster thesis


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