Pulmonary embolism diagnosis : a clinical comparison between conventional planar and SPECT V/Q imaging using Krypton 81m – with CTPA as the gold standard

Ngoya, Patrick Sitati
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Stellenbosch : University of Stellenbosch
ENGLISH ABSTRACT: Single photon emission computed tomography (SPECT) with a superior contrast resolution has been shown to be more sensitive and specific with a lower nondiagnostic rate than planar imaging in many nuclear medicine studies but it is still not being routinely implemented in V/Q studies at many centres including Tygerberg Hospital. There are many studies on V/Q SPECT using Technegas as a ventilation agent but very limited studies available on 81m Kr gas. Aim: To clinically compare conventional planar and SPECT V/Q imaging using 81mKr gas in the diagnosis of pulmonary embolism, with CTPA as the gold standard. Patients and Methods: All patients referred with clinical suspicion of pulmonary embolism were assessed. The inclusion criteria were normal chest radiograph, normal renal function and no contrast allergy. Exclusion criteria were age below 18 years old, pregnancy, abnormal chest radiograph, abnormal serum creatinine/urea levels and unstable patients. A Well’s score was assigned to each enrolled patient. Perfusion scintigraphy was performed after intravenous injection 125 MBq of 99mTc MAA. Ventilation scintigraphy was performed with 81mKr gas. On a dual head camera, SPECT was done before planar acquisition, while perfusion was done before ventilation imaging in the same position. Planar V/Q images consisted of 6 standard views. All V/Q SPECT images were reconstructed using ordered-subset expectation-maximization (OSEM) algorithm and a post-reconstruction 3D Butterworth filters were applied. V/Q Planar and V/Q SPECT images were later evaluated and reviewed separately and reported based on recent EANM guidelines blinded to the CTPA results. All patients underwent multi-slice CTPA examinations on a 40-detector row scanner. The images were later assessed and reported blinded to the V/Q results. Statistical analysis was done using the Fisher exact test for comparison of categorical variables and the one-way ANOVA for continuous variables (p<0.05 was significant). Results: A total of 104 consecutive patients were referred with clinical suspicion of pulmonary embolism. Seventy-nine patients were excluded from this study mostly due to abnormal serum creatinine/urea levels. Only 25 patients were included in this study, with a mean age of 48 ± 19 years, and 64% being females. When compared to CTPA as gold standard, the prevalence of PE was 16% [5% – 37% at 95% CI], sensitivity 75% [21% – 99% at 95% CI], specificity 90% [68% – 98% at 95% CI], positive predictive value 60% [17% – 93% at 95% CI], negative predictive value 95% [73% – 100% at 95% CI] and diagnostic accuracy 88% [69% – 97%at 95% CI] for both V/Q Planar and SPECT. V/Q Planar showed a lower reader confidence i.e. could only clearly resolve 72% of cases compared to V/Q SPECT, which could precisely interpret all cases, showed more and better delineated mismatch vs match and segmental vs non-segmental defects. All patients who were scored as PE unlikely on Wells’ score (4) had PE ruled out on CTPA (p=0.04581) as well as 89% of patients on V/Q SPECT and V/Q Planar. Conclusion: Based on this study, V/Q Planar and V/Q SPECT have a similar diagnostic performance in patients with a normal or near normal chest X-rays.
AFRIKAANSE OPSOMMING: Enkelfoton emissie rekenaartomografie (EFERT) met beter kontrasresolusie is bewys om meer sensitief en spesifiek met ‘n laer nie-diagnostiese opbrengs as planare beelding in verskeie kerngeneeskunde ondersoeke te wees. In Tygerberg Hospitaal, soos in verskeie ander sentra, word dit egter steeds nie roetineweg vir ventilasie-perfusiestudies (V/Q) geïmplementeer nie. Daar is verskeie EFERT V/Q studies met Technegas as ventilasie agens, maar beperkte studies met 81m Kr gas beskikbaar. Doel: Om konvensionele planare en EFERT V/Q beelding vir die diagnose van pulmonale embolisme met mekaar te vergelyk, met rekenaartomografie pulmonale angiografie (RTPA) as goue standaard. Pasiënte en Metodes: Alle pasiënte wat met ‘n kliniese vermoede van pulmonale embolisme verwys is, is geevalueer. Die insluitingskriteria was ’n normale borskas Xstraal, normale nierfunksie en geen kontrasallergie nie. Uitsluitingskriteria was pasiënte jonger as 18 jaar, swanger pasiënte, abnormale borskas X-straal, abnormale serum kreatinien / ureumvlakke en onstabiele pasiënte. ’n Wells telling is vir elke pasiënt wat in die studie ingesluit is, bepaal. Perfusiebeelding is uitgevoer na die intraveneuse toediening van 125 MBq 99mTc MAA. Ventilasiestudies is gedoen met 81mKr gas. Die V/Q EFERT studies is voor die planare beelding met ’n dubbelkop gammakamera uitgevoer. Perfusiebeelding is voor die ventilasie in dieselfde posisie verkry. V/Q planare beelding het bestaan uit 6 standaard beelde. Alle V/Q EFERT is met “ordered-subset expectationmaximization” (OSEM) algoritmes verwerk, en post-rekonstruksie 3D Butterworth filters is toegepas. V/Q planare en V/Q EFERT beelding is later afsonderlik en sonder RTPA inligting volgens onlangse EANM riglyne evalueer en gerapporteer. ‘n Veelsnit RTPA met ‘n 40 snit skandeerder is op alle pasiënte uitgevoer. Die beelde is later beoordeel en gerapporteer sonder inagneming van die V/Q beeldingsresultate Statistiese verwerking is gedoen met die Fisher presisietoets vir vergelyking van kategoriese veranderlikes en die eenrigting ANOVA vir kontinue veranderlikes (p<0.05 is statisties betekenisvol). Resultate: ‘n Totaal van 104 opeenvolgende pasiënte met ‘n kliniese vermoede van pulmonale embolisme is verwys. Nege-en-sewentig pasiënte is uitgesluit, in die meeste gevalle as gevolg van abnormale serum kreatinienvlakke. Slegs 25 pasiënte is ingesluit, met ’n gemiddelde ouderdom van 48 ± 19 jaar, en 64% vroue. In vergelyking met RTPA as goudstandaard, was die prevalensie van PE 16% [5% – 37% met 95% VI], sensitiwiteit 75% [21% – 99% met 95% VI], spesifisiteit 90% [68% – 98% met 95% VI], positiewe voorspellingswaarde 60% [17% – 93% met 95% VI], negatiewe voorspellingswaarde 95% [73% – 100% met 95% VI] en diagnostiese akkuraatheid van 88% [69% – 97% met 95% VI] vir beide planare en EFERT V/Q beelde. V/Q planare beelde het ‘n laer lesersvertroue getoon, nl. dat slegs 72% van gevalle opgelos kon word relatief tot V/Q EFERT beelde, wat in alle gevalle presies geïnterpreteer kon word, met meer en beter omskrewe nie-ooreenstemmende teenoor ooreenstemmende en segmentele teenoor nie-segmentele defekte. In alle pasiënte met ‘n Wells puntetelling van 4 is PE met die RTPA uitgeskakel (p=0.04581), terwyl dit in 89% van pasiënte met V/Q EFERT en planare beelde uitgeskakel is. Gevolgtrekking: Gebaseer op hierdie studie het V/Q planare en EFERT beelding ‘n ooreenstemmende diagnostiese prestasie in pasiënte met ’n normale of naby normale borskas X-straal.
Thesis (MScMedSC (Medical Imaging and Clinical Oncology. Nuclear Medicine))--University of Stellenbosch, 2010.
Pulmonary embolism, Single photon emission computed tomography, Dissertations -- Nuclear medicine, Theses -- Nuclear medicine