Fluorescence lifetime imaging microscopy (FLIM) is a powerful technique to non-invasively map the physical and chemical environment within microfluidic devices. In this work FLIM has been used in conjunction with a variety of other techniques to provide a greater insight into flow behaviour and fluid properties at the microscale. The pH-sensitive fluorescent dyes, fluorescein and C-SNARF 1, have been used to generate pH maps of microfluidic devices with a time-gated camera and a time-and-space-correlated single photon counting (TSCSPC) detector, respectively. Using time-gated detection and fluorescein, the fluorescence lifetime images allow for direct reading of the pH. The relative contribution to fluorescence of the acid and basic forms of C-SNARF 1 was spatially resolved on the basis of pre-exponential factors, giving quantitative mapping of the pH in the microfluidic device. Three dimensional maps of solvent composition have been generated using 2-photon excitation FLIM (2PE-FLIM) in order to observe the importance of gravitational effects in microfluidic devices. Two fluidic systems have been studied: glycerol concentration in the microfluidic device was measured using Kiton red; water concentration in a methanolic solution was measured using ANS. The density mismatch between two solutions of different composition induced a rotation of the interface between two streams travelling side by side in a microchannel. The experiment has provided evidence of non-negligible gravitational effects in microflows. 2PE-FLIM has superior capability than methods used previously to assess similar phenomena. FLIM and micro-particle imaging velocimetry (μ-PIV) have been implemented on a custom-built open frame microscope and used simultaneously for multimodal mapping of fluid properties and flow characteristics. It has been shown that viscosity mismatch between two streams induces a non-constant advective transport across the channel and results in a flow profile that deviates from the usual Poiseuille profile, characteristic of pressure driven flow in microfluidic devices.

Simultaneous optical imaging and MRI of a dorsal skin-fold window chamber mouse model is investigated as a novel methodology to study the tumor microenvironment. Simultaneous imaging with two modalities allows for cross-validation of results, integration of the capabilities of the two modalities in one study and mitigation of invasive factors, such as surgery and anesthesia, in an in-vivo experiment. To make this investigation possible, three optical imaging systems were developed that operated inside the MRI scanner. One of the developed systems was applied to estimate vascular kinetic parameters of tumors in a dorsal skin-fold window chamber mouse model with simultaneous optical and MRI imaging. The target of imaging was a molecular agent that was dual labeled with both optical and MRI contrast agents. The labeling of the molecular agent, characteristics of the developed optical systems, the methodologies of measuring vascular kinetic parameters using optical imaging and MRI data, and the obtained results are described and illustrated.

Multimodal image registration is essential when combining functional and structural imaging modalities. Among the most common combinations, numerous methods have been developed for co-registration of CT and PET, typically validated on human size scanners. However, only a few registration studies have been performed for the combination of small animal miniPET and microCT imaging. The Jonasson Center for Medical Imaging at KTH possesses an integrated miniPET/ microCT for pre-clinical research purposes. The motivation for this work is the need for the development of fusion method(s) for combining the data of these two modalities. In this work, a novel pipeline registration method, employing image processing and Mutual Information (MI) is proposed and implemented. The method starts with a pre-alignment step before acquisition of the miniPET/microCT volumes, followed by scaling, binarization and processing of the two volumes and finally, a registration procedure by Maximization of Mutual Information (MIM) as a voxel-based similarity metric. A established intrinsic landmarks based method is also implemented for comparison. For the validation of the methods, volumes acquired by in-house designed 3D printed Polyethylene (PE) phantoms, filled with multiple concentrations of FDG were used. The misalignment between corresponding points volumes after registration, is analyzed and compared in terms of absolute spatial distance. The proposed method based on 3D processed volumes outperformed the Landmarks based registration method, showing average misalignments of 0.5 mm. The registered volumes were also successfully visualized together using Alpha blending. By so, an automatic fusion method for miniPET/microCT has thus been implemented, presented and evaluated, raising prospects for multimodal imaging research at the Jonasson Center for Medical Imaging. / Kombinationen av funktionell och strukturell avbildning är vanlig inom medicinsk bildgivning, och koregistrering av bildvolymerna utgör en essentiell del i den multimodala framställningen. PET/CT-avbildning hör till de vanligast förekommande multimodala avbildningskombinationerna, och till följd av detta har ett antal koregistreringsmetoder utvecklats för just detta. Vad gäller pre-klinisk avbildning är dock validerade koregisteringsmetoder inte lika vanliga, och framförallt inom forskningsbaserad avbildning (där egendesignade scanners förekommer) är behovet av effektiva metoder tydligt. Inom Jonassons centrum för medicinsk avbildning på KTH har ett multimodalt miniPET/ microCT-system utvecklats, och det är just behovet av koregistering som utgjort basen för följande examensarbete. I följande arbete har en koregistreringsmetod baserad på fördefinierad bildbehandling och analys av gemensam information (mutual information, MI) implementerats och testats. Metoden bygger på ett initialt upplinjeringssteg innan microCT/ miniPET bildtagning. Efter detta genomförs en rad bildbehandlingssteg (skalning, binärisering) innan en slutgiltig koregistrering genomförs med hjälp av s.k. maximering av gemensam information (Maximization of Mutual Information, MIM). En etablerad landmärkesbaserad metod implementerades även som jämförelse. Metoderna testades sedan genom multimodal avbildning av egendesignade 3D-printade fantomer, fyllda med varierande aktivitet av FDG. Den föreslagna MI-metoden överträffade den etablerade landmärkesmetoden, med ett genomsnittligt koregistreringsfel på 0.5 mm. Visualisering av de koregistrerade volymerna genomfördes även genom så kallad alpha blending. Genom detta har en koregistreringsmetod för miniPET/microCT:n på Jonassons center för medicinsk avbildning implementerats och testats, vilket möjliggör för framtida studier av multimodal avbilning på KTH.

Les phéochromocytomes et les paragangliomes (PCC/PGL) sont des tumeurs neuroendocrines rares qui se développent aux dépens de la médullosurrénale et des paraganglions sympathiques et parasympathiques. Près de 40% des patients ont une prédisposition génétique, et, à ce jour 13 gènes de prédisposition ont été identifiés. Les mutations du gène SDHB sont un facteur de risque de malignité et de mauvais pronostic qui conduisent à une perte de fonction de la succinate déshydrogénase (SDH), enzyme du complexe mitochondrial II. Il en résulte une accumulation intracellulaire de succinate responsable du phénomène dit de « pseudohypoxie » qui stimule la production de VEGF et donc l’angiogenèse, ainsi que l’expression du transporteur membranaire du glucose GLUT-1. Le surrisque de malignité liée à SDHB et l’absence de traitement curatif des formes métastatiques de PCC/PGL justifient l’élaboration d’un modèle murin permettant de mettre en place des essais précliniques. L’obtention d’un modèle murin prédisposé au PCC/PGL par mutation du gène Sdhb s’étant révélée infructueuse, notre équipe a finalement généré des cellules chromaffines Sdhb-/- immortalisées (imCC Sdhb-/-) dont l’implantation dans le coussinet adipeux sous-cutané (Fat-pad) de souris nudes NMRI a permis l’établissement du premier modèle de tumeurs porteuses d’une inactivation complète du gène Sdhb. La caractérisation phénotypique du modèle a été réalisée par imagerie multimodalité in vivo, comparativement à un groupe contrôle de souris ayant reçu des imCC non mutées (WT). L’angiogenèse tumorale évaluée par imagerie optique retrouve une expression des intégrines αvβ3 plus marquée dans le groupe Sdhb-/- avec une rétention du traceur prolongée 12 h après injection. L’IRM dynamique de contraste (IRM-DCE), montre un rehaussement tumoral global nettement plus important dans le modèle Sdhb-/-, que le post-traitement par le logiciel PhysioD3D permet d’attribuer à une augmentation du volume capillaire intratumoral. Sur le plan métabolique, la consommation globale de glucose mesurée par TEP au 18FDG est également plus marquée dans les tumeurs Sdhb-/-. Enfin, la spectroscopie par résonance magnétique (1H-MRS) a mis en évidence une accumulation de succinate dans les tumeurs Sdhb-/-, non retrouvée dans les tumeurs WT. Ce résultat a été confirmé par spectrométrie de masse et cette technique innovante de détection du succinate in vivo a été transférée avec succès en clinique pour l’exploration des patients porteurs de PCC/PGL. En conclusion, l’imagerie in vivo a permis de distinguer le phénotype des tumeurs Sdhb-/- de celui des WT, avec une néoangiogenèse, une microcirculation et un métabolisme glucidique augmentés. Ces résultats permettent de proposer des études précliniques de réponse précoce aux traitements. La détection de l’accumulation de succinate par 1H-MRS ouvre la possibilité d’un diagnostic « métabolique » préopératoire pour détecter les patients de mauvais pronostic. / Pheochromocytomas and paragangliomas (PCC/PGL) are rare neuroendocrine tumours that arise from chromaffin cells of the adrenal medulla, sympathetic and parasympathetic paraganglia respectively. Around 15% of PCC are malignant. SDHB mutations are associated with malignancy and poor prognosis. SDH deficiency leads to succinate accumulation that induces a cellular pseudohypoxic phenotype, promoting in particular VEGF and GLUT-1 expression and increasing angiogenesis and glucose metabolism. The high malignancy hazard associated with SDHB and the absence of curative treatment of metastatic forms of the disease make it essential to develop a mouse model for preclinical trials launching. The quest for a predisposed mouse model of Sdhb-deficient tumors being unsuccessful, Sdhb-/- and wild-type (WT) immortalized mouse chromaffin cells previously generated in the laboratory were propagated in the fat pad of NMRI nude mice, thereby providing the first pattern of Sdhb- deficient tumors. These mice were compared to a control group receiving non-mutated imCC (WT) and characterization was performed in vivo by multimodality imaging. Optical imaging assessing the tumor angiogenesis with Angiostamp®, an RGD fluorescent peptide, found an increased expression of integrins αvβ3 in the Sdhb-/- group 12 h after tracer injection. Dynamic contrast enhanced MRI (DCE-MRI) showed an overall tumor enhancement significantly higher in the Sdhb-/- model secondary to an increase of the tumor blood flow (F) and of the intratumoral capillary volume fraction (Vb) (compartmental analysis using PhysioD3D software). Metabolic imaging assessed by 18FDG-PET confirmed the expected high glucose consumption by Sdhb-/- tumors. Finally, magnetic resonance spectroscopy (1H-MRS) detected succinate accumulation in Sdhb-/- tumors and not in WT tumors. This result was confirmed by mass spectrometry and this innovative procedure for in vivo detection of succinate was translated into patients suffering from PCC/PGL. A succinate peak was specifically observed in SDHx-related PCC/PGL patients. In conclusion, these results show strong differences between Sdhb-/- and WT allografts and suggest that preclinical therapeutic studies could be implemented in this unique model of Sdhb-deficient tumour. Our noninvasive, highly sensitive and specific method allowing in vivo detection of succinate, the major biomarker of SDHx-mutated tumors was translated into clinical imaging.

Background Caseous mitral annular calcification (CMAC) is a rare liquefactive variant of mitral annular calcification (MAC) and superficially mimics a cardiac vegetation or abscess. CMAC is viewed as a benign condition of MAC, while MAC has clinical implications for patients’ lives. Correctly diagnosing CMAC is essential in order to avoid unnecessary interventions, cardiac surgery or even psychological suffering for the patient. Case presentation We report on 6 patients with suspected intra-cardiac masses of the mitral annulus that were referred to our institution for further clarification. A definitive diagnosis of CMAC was achieved by combining echocardiography (Echo), cardiac magnetic resonance imaging (MRI) and cardiac computed tomography (CT) for these patients. Echo assessed the mass itself and possible interactions with the mitral valve. MRI was useful in differentiating the tissue from other benign or malign neoplasms. CT revealed the typical structure of CMAC with a “soft” liquefied centre and an outer capsule with calcification. Conclusion CMAC is a rare condition, and most clinicians and even radiologists are not familiar with it. CMAC can be mistaken for an intra-cardiac tumour, thombus, vegetation, or abscess. Non-invasive multimodality imaging (i.e. Echo, MRI, and CT) helps to establish a definitive diagnosis of CMAC and avoid unnecessary interventions especially in uncertain cases.

<p dir="ltr">Human brain tumors present significant challenges due to their heterogeneous nature, known as intra-tumoral heterogeneity (ITH), which evolves over space and time, leading to treatment resistance and poor patient outcomes. Current diagnostic methods rely on pre-surgical imaging and single biopsy samples, providing only a partial understanding of the tumor microenvironment (TME) and often resulting in incomplete targeting of tumor mutations, leaving residual disease vulnerable to recurrence. Our hypothesis proposes a novel approach: utilizing multimodal and multiparametric <i>in vivo</i> imaging to map the cellular and molecular characteristics of the TME. By correlating imaging signatures with underlying somatic and genomic aberrations, we aim to develop a predictive model guiding personalized targeted therapies to effectively address the heterogeneity of brain tumors.</p><p dir="ltr">To achieve this goal, we designed, tested, and validated a predictive model through a pilot study using clinical MRI scans and one stereotactic biopsy sample. Subsequently, we optimized a multimodal and multiparametric imaging protocol including MRI and PET scans, to acquire comprehensive morphological, functional, and molecular data from the TME. Additionally, we established a detailed pipeline for subject recruitment, data collection, and post-processing to ensure the robustness and reliability of our model.</p><p dir="ltr">This innovative approach has the potential to overcome the limitations of current diagnostic methods by providing a comprehensive understanding of the TME using minimally-invasive imaging techniques. By correlating imaging data with ground truth pathology and genomics, this model will enhance brain tumor diagnosis and facilitate the implementation of targeted therapies, ultimately improving treatment response and patient outcomes.</p>

Aortic stenosis is the most common acquired heart valve condition. Open-heart surgical aortic valve replacement is an effective treatment for patients who receive it. However, approximately one-third of patients who require this treatment do not receive it due to the risks associated with the surgery. Percutaneous aortic valve replacement (PAVR) is a minimally invasive technique that can replace the aortic valve of patients contraindicated for open-heart surgery. Although PAVR is now entering clinical practice, a closed bore hybrid x-ray/MRI (CBXMR) imaging system is under development to improve the safety and efficacy of PAVR. This system will harness the complementary strengths of x-ray imaging (surgical tool/vascular imaging) and MRI (cardiac soft tissue contrast) to deploy a bioprosthesis in the aortic annulus. An x-ray C-arm will be placed about 1 m from the entrance of the MRI scanner to facilitate smooth intermodality patient transfer during the procedure. The performance of a rotating-anode x-ray tube in the magnetic fringe field of a 1.5 T MRI scanner was investigated. A rotating-anode x-ray tube provides the fluoroscopy and angiography needed for PAVR. The magnetic fringe field can affect the ability of the x-ray tube to dissipate heat. It was shown that the fringe field perpendicular to the anode rotation axis can reduce anode rotation frequency. These effects can limit the maximum permissible power that can be safely dissipated on the anode track during a single exposure. In the fringe field strengths at the C-arm position (4-5 mT), anode rotation frequency only decreased by about 1%, which will have negligible impact on tube heat loadability. The fringe field can cause a field of view shift. The field of view shifted by approximately 3 mm, which can be corrected by active magnetic shielding and further collimation. An active magnetic shielding system was constructed that can correct focal spot deflection. These results are facilitating the construction of a prototype CBXMR system, the goal of which is to improve success rates for PAVR procedures.

Aortic stenosis is the most common acquired heart valve condition. Open-heart surgical aortic valve replacement is an effective treatment for patients who receive it. However, approximately one-third of patients who require this treatment do not receive it due to the risks associated with the surgery. Percutaneous aortic valve replacement (PAVR) is a minimally invasive technique that can replace the aortic valve of patients contraindicated for open-heart surgery. Although PAVR is now entering clinical practice, a closed bore hybrid x-ray/MRI (CBXMR) imaging system is under development to improve the safety and efficacy of PAVR. This system will harness the complementary strengths of x-ray imaging (surgical tool/vascular imaging) and MRI (cardiac soft tissue contrast) to deploy a bioprosthesis in the aortic annulus. An x-ray C-arm will be placed about 1 m from the entrance of the MRI scanner to facilitate smooth intermodality patient transfer during the procedure. The performance of a rotating-anode x-ray tube in the magnetic fringe field of a 1.5 T MRI scanner was investigated. A rotating-anode x-ray tube provides the fluoroscopy and angiography needed for PAVR. The magnetic fringe field can affect the ability of the x-ray tube to dissipate heat. It was shown that the fringe field perpendicular to the anode rotation axis can reduce anode rotation frequency. These effects can limit the maximum permissible power that can be safely dissipated on the anode track during a single exposure. In the fringe field strengths at the C-arm position (4-5 mT), anode rotation frequency only decreased by about 1%, which will have negligible impact on tube heat loadability. The fringe field can cause a field of view shift. The field of view shifted by approximately 3 mm, which can be corrected by active magnetic shielding and further collimation. An active magnetic shielding system was constructed that can correct focal spot deflection. These results are facilitating the construction of a prototype CBXMR system, the goal of which is to improve success rates for PAVR procedures.