Optimized semi-quantitative analysis of dopamine transporter SPECT to support visual image interpretation in the diagnosis of parkinsonian syndromes

Zur Differenzierung von neurodegenerativen und nicht-neurodegenerativen Ursachen eines klinisch unklaren Parkinsonsyndroms wird die Dopamintransporter-SPECT (DAT-SPECT) eingesetzt. Neben der visuellen Bildinterpretation unterstützt die semi-quantitative Analyse der striatalen Dopamintransporter-Verfügbarkeit die Befundung. Die vorliegende Dissertationsschrift fasst drei Studien zusammen, die klinisch relevante Parameter der Bildentstehung und Bildverarbeitung in der semi-quantitativen Analyse der DAT-SPECT identifizierten, optimierten und hinsichtlich ihrer diagnostischen Genauigkeit untersuchten. In der ersten Studie wurde eine vollautomatische Methode zur Abgrenzung der äußeren Kopfkontur als Teil der Schwächungskorrektur nach Chang implementiert und gegenüber einer klinisch etablierten halbautomatischen Methode validiert. Die Auswertung eines multizentrischen Datensatzes ergab, dass beide Methoden zur Kopfabgrenzung sowohl vergleichbare semi-quantitative Werte als auch eine vergleichbare diagnostische Genauigkeit lieferten. Damit kann die vollautomatische Methode für den Einsatz in der klinischen Versorgung empfohlen werden, da keine Interaktion durch den Nutzer erforderlich ist. Die zweite Studie untersuchte zwei Methoden zur semi-quantitativen Abschätzung der Tracer Bindung hinsichtlich ihrer diagnostischen Genauigkeit. Der auflösungsunabhängige specific uptake size index (SUSI) zeigte bei Datenerhebung an unterschiedlichen Kamerasystemen eine höhere diagnostische Genauigkeit als der Standardparameter, das sogenannte specific binding ratio (SBR). Dies ist besonders relevant für multizentrische Studien. Sobald jedoch nur ein Kamerasystem eingesetzt wurde, ist der Standardparameter SBR dem SUSI vorzuziehen, da dieser bei vergleichbarer diagnostischer Performance weniger anfällig gegenüber einer fehlerhaften Abschätzung der nicht-spezifischen Tracer-Bindung in der Referenzregion ist. Ziel der dritten Studie war die Untersuchung des Einflusses der Größe der Normaldatenbank (NDB) auf die diagnostische Genauigkeit einer semi-quantitativen Auswertung der DAT-SPECT. Dabei erfolgte eine Simulation von unterschiedlichen Größen der NDB (n=5, 10, 15, …, 50) durch zufälliges Ziehen aus dem Pool an Kontrollen und Validierung der jeweiligen NDB in der Gesamtkohorte anhand von Klassifizierungsgenauigkeit, Sensitivität und Spezifität. Die Analyse ergab, dass ein Mindestumfang von 25 bis 30 DAT-SPECT-Datensätzen zur Bildung einer NDB notwendig ist. Eine Vergrößerung der NDB über 40 Fälle hinaus führt hingegen zu keiner weiteren relevanten Steigerung der diagnostischen Genauigkeit.Dopamine transporter SPECT (DAT-SPECT) is an established method to differentiate neurodegenerative and non-neurodegenerative causes in clinically uncertain parkinsonian syndromes. Besides visual image interpretation, semi-quantitative analysis of the striatal dopamine transporter availability is used to support medical diagnosis. The present doctoral thesis summarizes three studies that identified, optimized and validated clinically relevant, semi-quantitative parameters of DAT-SPECT image acquisition and processing with reference to their diagnostic accuracy. The first study proposed a fully automatic segmentation method of the outer head contour as a part of attenuation correction according to Chang and validated this method to a well-established semi-automatic method. Both methods for head delineation showed comparable semi-quantitative properties as well as comparable diagnostic accuracy based on multi-center patient data. For this reason, we suggest to use the fully automatic method in clinical patient care since no user interaction is required. A direct comparison of two semi-quantitative methods for estimation of tracer binding in reference to diagnostic accuracy was the aim of the second study. The spatial resolution independent specific uptake size index (SUSI) provided a higher diagnostic accuracy compared to the commonly used parameter, the specific binding ratio (SBR), when image acquisition is performed at various camera systems. This is highly relevant for multi-center image acquisition. However, in single-camera/mono-center settings SBR should be favored over SUSI, since SBR seemed to be less sensitive towards errors of the estimate of non-specific tracer uptake in the reference region with comparable diagnostic performance to SUSI. Rationale of the third study was to evaluate the impact of the size of the normal database (NDB) on the diagnostic performance of semi-quantitative analysis in DAT-SPECT. For it, simulation of NDB with different sizes (n=5, 10, 15, …, 50) by randomly selecting subjects from the subcohort of normal controls was implemented and validation of each particular NDB based on the overall cohort was done concerning diagnostic accuracy, sensitivity and specificity as performance measures. The study results suggested that 25 to 30 DAT-SPECT data sets should be the minimum size of NDB. Increasing the size of NDB beyond 40 data sets provided only very small further improvement in diagnostic accuracy

Diagnostic performance of the specific uptake size index for semi-quantitative analysis of I-123-FP-CIT SPECT: harmonized multi-center research setting versus typical clinical single-camera setting

Introduction: The specific uptake size index (SUSI) of striatal FP-CIT uptake is independent of spatial resolution in the SPECT image, in contrast to the specific binding ratio (SBR). This suggests that the SUSI is particularly appropriate for multi-site/multi-camera settings in which camera-specific effects increase inter-subject variability of spatial resolution. However, the SUSI is sensitive to inter-subject variability of striatum size. Furthermore, it might be more sensitive to errors of the estimate of non-displaceable FP-CIT binding. This study compared SUSI and SBR in the multi-site/multi-camera (MULTI) setting of a prospective multi-center study and in a mono-site/mono-camera (MONO) setting representative of clinical routine. Methods: The MULTI setting included patients with Parkinson’s disease (PD, n = 438) and healthy controls (n = 207) from the Parkinson Progression Marker Initiative. The MONO setting included 122 patients from routine clinical patient care in whom FP-CIT SPECT had been performed with the same double-head SPECT system according to the same acquisition and reconstruction protocol. Patients were categorized as “neurodegenerative” (n = 84) or “non-neurodegenerative” (n = 38) based on follow-up data. FP-CIT SPECTs were stereotactically normalized to MNI space. SUSI and SBR were computed for caudate, putamen, and whole striatum using unilateral ROIs predefined in MNI space. SUSI analysis was repeated in native patient space in the MONO setting. The area (AUC) under the ROC curve for identification of PD/“neurodegenerative” cases was used as performance measure. Results: In both settings, the highest AUC was achieved by the putamen (minimum over both hemispheres), independent of the semi-quantitative method (SUSI or SBR). The putaminal SUSI provided slightly better performance with ROI analysis in MNI space compared to patient space (AUC = 0.969 vs. 0.961, p = 0.129). The SUSI (computed in MNI space) performed slightly better than the SBR in the MULTI setting (AUC = 0.993 vs. 0.991, p = 0. 207) and slightly worse in the MONO setting (AUC = 0.969 vs. AUC = 0.976, p = 0.259). There was a trend toward larger AUC difference between SUSI and SBR in the MULTI setting compared to the MONO setting (p = 0.073). Variability of voxel intensity in the reference region was larger in misclassified cases compared to correctly classified cases for both SUSI and SBR (MULTI setting: p = 0.007 and p = 0.012, respectively). Conclusions: The SUSI is particularly useful in MULTI settings. SPECT images should be stereotactically normalized prior to SUSI analysis. The putaminal SUSI provides better diagnostic performance than the SUSI of the whole striatum. Errors of the estimate of non-displaceable count density in the reference region can cause misclassification by both SUSI and SBR, particularly in borderline cases. These cases might be identified by visual checking FP-CIT uptake in the reference region for particularly high variability

Ultrasound and microbubbles to beat barriers in tumors: Improving delivery of nanomedicine

Successful delivery of drugs and nanomedicine to tumors requires a functional vascular network, extravasation across the capillary wall, penetration through the extracellular matrix, and cellular uptake. Nanomedicine has many merits, but penetration deep into the tumor interstitium remains a challenge. Failure of cancer treatment can be caused by insufficient delivery of the therapeutic agents. After intra-venous administration, nanomedicines are often found in off-target organs and the tumor extracellular matrix close to the capillary wall. With circulating microbubbles, ultrasound exposure focused toward the tumor shows great promise in improving the delivery of therapeutic agents. In this review, we address the impact of focused ultrasound and microbubbles to overcome barriers for drug delivery such as perfusion, extravasation, and transport through the extracellular matrix. Furthermore, we discuss the induction of an immune response with ultrasound and delivery of immuno-therapeutics. The review dis-cusses mainly preclinical results and ends with a summary of ongoing clinical trials.publishedVersio

Real-time intravital multiphoton microscopy to visualize focused ultrasound and microbubble treatments to increase blood-brain barrier permeability

The blood-brain barrier (BBB) is a key challenge for the successful delivery of drugs to the brain. Ultrasound exposure in the presence of microbubbles has emerged as an effective method to transiently and locally increase the permeability of the BBB, facilitating para- and transcellular transport of drugs across the BBB. Imaging the vasculature during ultrasound-microbubble treatment will provide valuable and novel insights on the mechanisms and dynamics of ultrasound-microbubble treatments in the brain. Here, we present an experimental procedure for intravital multiphoton microscopy using a cranial window aligned with a ring transducer and a 20x objective lens. This set-up enables high spatial and temporal resolution imaging of the brain during ultrasound-microbubble treatments. Optical access to the brain is obtained via an open-skull cranial window. Briefly, a 3-4 mm diameter piece of the skull is removed, and the exposed area of the brain is sealed with a glass coverslip. A 0.82 MHz ring transducer, which is attached to a second glass coverslip, is mounted on top. Agarose (1% w/v) is used between the coverslip of the transducer and the coverslip covering the cranial window to prevent air bubbles, which impede ultrasound propagation. When sterile surgery procedures and anti-inflammatory measures are taken, ultrasound-microbubble treatments and imaging sessions can be performed repeatedly over several weeks. Fluorescent dextran conjugates are injected intravenously to visualize the vasculature and quantify ultrasound-microbubble induced effects (e.g., leakage kinetics, vascular changes). This paper describes the cranial window placement, ring transducer placement, imaging procedure, common troubleshooting steps, as well as advantages and limitations of the method.publishedVersio

Impact of the size of the normal database on the performance of the specific binding ratio in dopamine transporter SPECT

Background: This study investigated the impact of the size of the normal database on the classification performance of the specific binding ratio (SBR) in dopamine transporter (DAT) SPECT with [123I]FP-CIT in different settings. Methods: The first subject sample comprised 645 subjects from the Parkinson's Progression Marker Initiative (PPMI), 207 healthy controls (HC), and 438 Parkinson's disease (PD) patients. The second sample comprised 372 patients from clinical routine patient care, 186 with non-neurodegenerative parkinsonian syndrome (PS) and 186 with neurodegenerative PS. Single-photon emission computed tomography (SPECT) images of the clinical sample were reconstructed with two different reconstruction algorithms (filtered backprojection, iterative ordered subsets expectation maximization (OSEM) reconstruction with resolution recovery). The putaminal specific binding ratio (SBR) was computed using an anatomical region of interest (ROI) predefined in standard (MNI) space in the Automated Anatomic Labeling (AAL) atlas or using hottest voxels (HV) analysis in large predefined ROIs. SBR values were transformed to z-scores using mean and standard deviation of the SBR in a normal database of varying sizes (n = 5, 10, 15,…, 50) randomly selected from the HC subjects (PPMI sample) or the patients with non-neurodegenerative PS (clinical sample). Accuracy, sensitivity, and specificity for identifying patients with PD or neurodegenerative PS were determined as performance measures using a predefined fixed cutoff on the z-score. This was repeated for 10,000 randomly selected normal databases, separately for each size of the normal database. Mean and 5th percentile of the performance measures over the 10,000 realizations were computed. Accuracy, sensitivity, and specificity when using the whole set of HC or non-neurodegenerative PS subjects as normal database were used as benchmark. Results: Mean loss of accuracy of the putamen SBR z-score was below 1% when the normal database included at least 15 subjects, independent of subject sample (PPMI or clinical), reconstruction method (filtered backprojection or OSEM), and ROI method (AAL or HV). However, the variability of the accuracy of the putamen SBR z-score decreased monotonically with increasing size of normal database and was still considerable at size 15. In order to achieve less than 5% "maximum" loss of accuracy (defined by the 5th percentile) in all settings required at least 25 to 30 subjects in the normal database. Reduction of mean and "maximum" loss of accuracy of the putamen SBR z-score by further increasing the size of the normal database was very small beyond size 40. Conclusions: The results of this study suggest that 25 to 30 is the minimum size of the normal database to reliably achieve good performance of semi-quantitative analysis in dopamine transporter (DAT) SPECT, independent of the algorithm used for image reconstruction and the ROI method used to estimate the putaminal SBR

Effects of spermidine supplementation on cognition and biomarkers in older adults with subjective cognitive decline (SmartAge)—study protocol for a randomized controlled trial

Background: Given the global increase in the aging population and age-related diseases, the promotion of healthy aging is one of the most crucial public health issues. This trial aims to contribute to the establishment of effective approaches to promote cognitive and brain health in older individuals with subjective cognitive decline (SCD). Presence of SCD is known to increase the risk of objective cognitive decline and progression to dementia due to Alzheimer’s disease. Therefore, it is our primary goal to determine whether spermidine supplementation has a positive impact on memory performance in this at-risk group, as compared with placebo. The secondary goal is to examine the effects of spermidine intake on other neuropsychological, behavioral, and physiological parameters. Methods: The SmartAge trial is a monocentric, randomized, double-blind, placebo-controlled phase IIb trial. The study will investigate 12 months of intervention with spermidine-based nutritional supplementation (target intervention) compared with 12months of placebo intake (control intervention). We plan to recruit 100 cognitively normal older individuals with SCD from memory clinics, neurologists and general practitioners in private practice, and the general population. Participants will be allocated to one of the two study arms using blockwise randomization stratified by age and sex with a 1:1 allocation ratio. The primary outcome is the change in memory performance between baseline and post-intervention visits (12 months after baseline). Secondary outcomes include the change in memory performance from baseline to follow-up assessment (18months after baseline), as well as changes in neurocognitive, behavioral, and physiological parameters (including blood and neuroimaging biomarkers), assessed at baseline and post-intervention. Discussion: The SmartAge trial aims to provide evidence of the impact of spermidine supplementation on memory performance in older individuals with SCD. In addition, we will identify possible neurophysiological mechanisms of action underlying the anticipated cognitive benefits. Overall, this trial will contribute to the establishment of nutrition intervention in the prevention of Alzheimer’s disease

Ultrafast Microscopy Imaging of Acoustic Cluster Therapy Bubbles: Activation and Oscillation

Acoustic Cluster Therapy (ACT®) is a platform for improving drug delivery and has had promising pre-clinical results. A clinical trial is ongoing. ACT® is based on microclusters of microbubbles–microdroplets that, when sonicated, form a large ACT® bubble. The aim of this study was to obtain new knowledge on the dynamic formation and oscillations of ACT® bubbles by ultrafast optical imaging in a microchannel. The high-speed recordings revealed the microbubble–microdroplet fusion, and the gas in the microbubble acted as a vaporization seed for the microdroplet. Subsequently, the bubble grew by gas diffusion from the surrounding medium and became a large ACT® bubble with a diameter of 5–50 μm. A second ultrasound exposure at lower frequency caused the ACT® bubble to oscillate. The recorded oscillations were compared with simulations using the modified Rayleigh–Plesset equation. A term accounting for the physical boundary imposed by the microchannel wall was included. The recorded oscillation amplitudes were approximately 1–2 µm, hence similar to oscillations of smaller contrast agent microbubbles. These findings, together with our previously reported promising pre-clinical therapeutic results, suggest that these oscillations covering a large part of the vessel wall because of the large bubble volume can substantially improve therapeutic outcome.publishedVersio