{"id":11594,"date":"2026-04-13T12:14:18","date_gmt":"2026-04-13T12:14:18","guid":{"rendered":"https:\/\/www.proefschriftmaken.nl\/portfolio\/youssef-chahid\/"},"modified":"2026-04-22T14:38:25","modified_gmt":"2026-04-22T14:38:25","slug":"youssef-chahid","status":"publish","type":"us_portfolio","link":"https:\/\/www.proefschriftmaken.nl\/en\/portfolio\/youssef-chahid\/","title":{"rendered":"Youssef Chahid"},"content":{"rendered":"","protected":false},"excerpt":{"rendered":"","protected":false},"author":8,"featured_media":11991,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"us_portfolio_category":[45],"class_list":["post-11594","us_portfolio","type-us_portfolio","status-publish","has-post-thumbnail","hentry","us_portfolio_category-new-template"],"acf":{"naam_van_het_proefschift":"Evaluation of factors affecting nuclear medicine examinations","samenvatting":"Het tweede deel van het proefschrift gaat in op de mogelijke invloed van medicatie op onderzoeken binnen de nucleaire geneeskunde. Hoofdstuk 4 bouwt voort op eerder werk uit 2008 en beschrijft in een systematische literatuur review de mogelijke invloed van medicijnen en verslavende middelen, zoals tabak en alcohol, op de binding van [123I]-FP-CIT. Deze radiotracer bindt aan de dopamine transporter (DAT) die vooral tot expressie komt in het striatum, en wordt klinisch toegepast bij pati\u00ebnten met de ziekte van Parkinson, waarbij er op klinische gronden twijfel is over de diagnose. Deze review identificeerde medicijnen die van invloed kunnen zijn op de resultaten van DAT-beeldvorming, en biedt praktische aanbevelingen voor het staken van medicatie voorafgaand aan de scans.\n\nHoofdstuk 5 onderzoekt de invloed van langwerkende somatostatineanalogen (SSA\u2019s) op de opname van [68Ga]Ga-DOTA-TATE bij pati\u00ebnten met neuro-endocriene tumoren. Verscheidene richtlijnen geven aan dat het gebruik van SSA\u2019s gestaakt moet worden omdat het mogelijk interfereert met de [68Ga]Ga-DOTA-TATE binding aan somatostatine receptoren. Onze studie toonde echter aan dat pati\u00ebnten die SSA\u2019s gebruiken een hogere standardized uptake value maximum tumour-to-liver ratio (SUVmax TLR) hadden dan degenen die geen SSA\u2019s gebruikten. Dit geeft aan dat SSA\u2019s de opname van [68Ga]Ga-DOTA-TATE niet negatief be\u00efnvloedden, waardoor het niet nodig is om [68Ga]Ga-DOTA-TATE PET\/CT beeldvorming uit te stellen tot 4 weken na de laatste toediening van SSA\u2019s.\n\nHoofdstuk 6 onderzoekt het mechanisme achter de gerapporteerde verminderde leveropname van [68Ga]Ga-DOTA-TATE bij pati\u00ebnten die SSA\u2019s gebruiken. Hoewel het mechanisme nog onduidelijk is, wordt gesuggereerd dat SSA\u2019s mogelijk een remmend effect hebben op cytochroom P450 3A4 (CYP3A4), wat het metabolisme van radioactieve tracers zou kunnen be\u00efnvloeden en daarmee zou bijdragen aan de verminderde leveropname. In een studie met 70 pati\u00ebnten vonden we echter geen significante verschillen in SUVmax TLR tussen pati\u00ebnten die CYP3A4-remmers gebruikten en pati\u00ebnten die dat niet deden. Dit suggereert dat CYP3A4-remmers, zoals amiodaron en diltiazem, geen invloed hebben op de opname van [68Ga]Ga-DOTA-TATE.\n\nHet derde deel van het proefschrift benadrukt het belang van analytische methoden binnen de nucleaire geneeskunde, met specifieke aandacht voor de meting van de transcapillary escape rate van albumine (TERalb) als een vroegtijdige indicator van vasculaire schade. In hoofdstuk 7 evalueerden we de invloed van bloedafname-schema\u2019s en mono- versus bi-exponenti\u00eble analyses op de berekening van TERalb. Hieruit bleek dat het starten van bloedafnames 20 minuten na toediening van [125I]-rHSA resulteerde in een aanzienlijk lagere TERalb in vergelijking met afnameschema\u2019s die startten na 3 of 5 minuten. Bovendien bleek bi-exponenti\u00eble kinetische modellering niet significant te verschillen in uitkomst van mono-exponenti\u00eble analyse. Dit benadrukt de noodzaak om de metingen van TERalb te standaardiseren en geeft de voorkeur aan het gebruik van een mono-exponentieel model met bloedafnames die 20 minuten na toediening van [125I]-rHSA beginnen.\n\nSamenvattend biedt dit proefschrift inzicht in factoren die van invloed zijn op verscheidene onderzoekstechnieken binnen de nucleaire geneeskundige, waarbij pati\u00ebnt-, medicatie- en analysemethode-gerelateerde aspecten worden behandeld. Het belicht overwegingen met betrekking tot het optimaliseren van de nauwkeurigheid en betrouwbaarheid van nucleaire geneeskundige procedures, wat bijdraagt aan de optimalisatie van dit vakgebied binnen de moderne geneeskunde.","summary":"Nuclear medicine examinations have become indispensable tools in modern medicine. These imaging techniques, such as positon emission tomography (PET) and single photon emission computed tomography (SPECT), provide invaluable insights into physiological processes within the human body, enabling early disease detection, staging, treatment planning, and treatment monitoring. However, the accuracy of nuclear medicine tools is not solely dependent on technology but is deeply influenced by patient-related characteristics, medication use, and analytical methods. A comprehensive understanding of these factors is essential for the accurate interpretation of nuclear medicine examinations.\n\nThis thesis is structured into three main parts, each addressing distinct aspects of factors that may affect nuclear medicine examinations, namely patient-related, medication-related, and analytical method-related factors.\n\nIn the first part of this thesis, the focus is on the exploration of which various patient-related factors can influence the outcomes of nuclear medicine examinations, with a specific focus on breast cancer patients. It is well known that accurate sentinel lymph node (SLN) staging is essential for both prognosis and treatment in patients with breast cancer [1]. However, preoperative lymphoscintigraphy may fail to visualize the SLN in some patients. Reported rates of SLN nonvisualization vary between 2% and 28% [2-6]. Different patient characteristics (body mass index (BMI), age) and tumour characteristics (size, location, palpability) have been found to be associated with SLN nonvisualization [2-6]. Although the injected dose of radiotracers and injection technique seem to be correlated with SLN non-visualization [2], information on the potential impact of the level of experience, for example, in radiotracer preparation or the level of experience of the administrator, is absent. In chapter 1, we describe a large retrospective study that we have performed which included 1886 SLN procedures to identify potential unknown independent factors associated with SLN nonvisualization on lymphoscintigraphy [7]. The SLN nonvisualization rate was 25.1% on lymphoscintigraphy at 4 hours post-injection. The SLN nonvisualization rate decreased to 9.4% after reinjection of the radiopharmaceutical. Multivariable analysis showed that age \u2265 70 years, BMI \u2265 30 kg\/m2, and nonpalpable tumours were independent predictors of SLN nonvisualization. Tumour location, brand of radiopharmaceutical, injected dose and volume, experience of preparer, and administrator were not associated with SLN nonvisualization.\n\nIn conclusion, our results support the robustness of SLN detection on lymphoscintigraphy, independent of the experience of the radiotracer preparer or administrator. Our study demonstrated that reinjection of the radiotracer, in a peri- or intra-tumoural injection setting, is a viable option to enhance SLN visualization rates. Another potential strategy to reduce SLN nonvisualization rate to 2.0% may involve a multisite injection technique: i.e., simultaneous injection of peritumoral, subcutaneous, and subareolar regions [8]. Based on our results, it may be valuable to initiate future research studies examining the potential reduction of preoperative SLN nonvisualization in patients with non-palpable tumours, aged \u2265 70 years, or with a BMI \u2265 30 kg\/m2 through the implementation of simultaneous intratumoral and periareolar injections. Additionally, it would be intriguing to explore whether these risk factors remain valid when SLN procedures are performed using hybrid tracers, such as indocyanine green (ICG) in combination with [99mTc]Tc-nanocolloid [9].\n\nIn chapter 2, we comment on the interesting findings of Quak et al. that age and BMI are significantly associated with breast density [10]. They showed that patients with a high-fat content in breast tissue were, based on univariate analysis, significantly more at risk of SLN nonvisualization compared to patients with less fatty breast densities [11]. Due to the lack of performing a multivariable analysis, it was not possible to properly assess the possible influence of breast density for SLN nonvisualization in relation to other risk factors such as natural ageing and BMI. For that reason, we conducted a large retrospective study, as described in chapter 3, to reproduce their claim that breast density is an independent predictor of SLN nonvisualization on lymphoscintigraphy [12]. However, after performing a multivariable analysis in 758 breast cancer patients, we concluded that only age \u2265 70 years, BMI \u2265 30 kg\/m2, and nonpalpable tumours were independent predictors of SLN nonvisualization. Differences in tumour size, BI-RADS classification, or breast density were not significantly associated with SLN nonvisualization. Thus, parameters derived from mammography or breast MRI are not useful for predicting SLN nonvisualization on lymphoscintigraphy.\n\nIn conclusion, we have shown that interpretations based on univariate analysis can be misleading. Therefore, it is preferable to perform larger studies with multivariable analysis to adjust for confounders. Based on our findings, we conclude that parameters obtained from mammography or breast MRI do not enhance the previously described multivariable model, which incorporates age, BMI, and tumour palpability, for predicting SLN nonvisualization.\n\nThe second part of this thesis explores the influence of medications on nuclear medicine examinations. In chapter 4, we conducted a systematic review of the","auteur":"Youssef Chahid","auteur_slug":"youssef-chahid","publicatiedatum":"26 juni 2024","taal":"EN","url_flipbook":"https:\/\/ebook.proefschriftmaken.nl\/ebook\/youssefchahid?iframe=true","url_download_pdf":"","url_epub":"","ordernummer":"FTP-202604131211","isbn":"978-94-6469-936-4","doi_nummer":"","naam_universiteit":"Universiteit van Amsterdam","afbeeldingen":11991,"naam_student:":"","binnenwerk":"","universiteit":"Universiteit van Amsterdam","cover":"","afwerking":"","cover_afwerking":"","design":""},"_links":{"self":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/11594","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio"}],"about":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/types\/us_portfolio"}],"author":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/comments?post=11594"}],"version-history":[{"count":1,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/11594\/revisions"}],"predecessor-version":[{"id":11597,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/11594\/revisions\/11597"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media\/11991"}],"wp:attachment":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media?parent=11594"}],"wp:term":[{"taxonomy":"us_portfolio_category","embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio_category?post=11594"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}