Rapid quantitative CBF and CMRO2 measurements from a single PET scan with sequential administration of dual 15O-labeled tracers

Positron emission tomography (PET) with ¹⁵O tracers provides essential information in patients with cerebral vascular disorders, such as cerebral blood flow (CBF), oxygen extraction fraction (OEF), and metabolic rate of oxygen (CMRO₂). However, most of techniques require an additional C¹⁵O scan for compensating cerebral blood volume (CBV). We aimed to establish a technique to calculate all functional images only from a single dynamic PET scan, without losing accuracy or statistical certainties. The technique was an extension of previous dual-tracer autoradiography (DARG) approach, but based on the basis function method (DBFM), thus estimating all functional parametric images from a single session of dynamic scan acquired during the sequential administration of H₂¹⁵O and ¹⁵O₂. Validity was tested on six monkeys by comparing global OEF by PET with those by arteriovenous blood sampling, and tested feasibility on young healthy subjects. The mean DBFM-derived global OEF was 0.57±0.06 in monkeys, in an agreement with that by the arteriovenous method (0.54±0.06). Image quality was similar and no significant differences were seen from DARG; 3.57%±6.44% and 3.84%±3.42% for CBF, and −2.79%±11.2% and −6.68%±10.5% for CMRO₂. A simulation study demonstrated similar error propagation between DBFM and DARG. The DBFM method enables accurate assessment of CBF and CMRO₂ without additional CBV scan within significantly shortened examination period, in clinical settings.     

A dual label radiotracer technique for the simultaneous measurement of cerebral blood flow and the single-transit cerebral extraction of diffusion-limited compounds in rats

An inexpensive method is described which permits simultaneous quantification of the cerebrovascular extraction (E) of diffusion-limited compounds and cerebral blood flow (CBF) in rats. This method involves the use of two radioisotopic tracers: (a) a diffusion-limited, test tracer such as [³H]water; and (b) a reference tracer. The reference tracer is also used in the measurement of CBF. In the development and validation of this technique, results using two different types of reference tracers were compared. The reference tracers empoyed were: (a) [¹⁴C]butanol, a flow-limited (i.e. freely diffusible) compound; and (b) [¹⁴¹Ce]microspheres which embolize in the cerebromicrocirculation. Inclusion of [³H]water in the injection bolus permitted simultaneous measurement of E_w using both butanol and microspheres as the reference as well as concomitant measurement of CBF. Both tracers provided estimates of these values which behaved physiologically with respect to increasing arterial CO₂ content (p_aCO₂). In addition, the simultaneous measurement of E_w and CBF permitted calculation of the effective permeability of water across the blood-brain barrier (P_wS) which was discovered to increased with increasing p_aCO₂.     

A modified method for measurement of radiotracer permeation across the rat blood--brain barrier: the problem of correcting brain uptake for intravascular tracer

A modified technique to assess integrity of the rat blood--brain barrier is described in which a poorly permeating radiotracer is injected intravenously and its net permeation across the cerebral vasculature in 30 min is related to its time-averaged level in the circulation. At the termination of experiments, direct carotid arterial perfusion clears blood from brain in 30 s and permits measurement of the tracer level in brain parenchyma without correction for intravascular tracer. Constant-rate withdrawal of a single arterial blood sample throughout the period of tracer circulation replaces the need for repeated blood sampling and graph plotting to determine the time-integrated plasma tracer level. During the first 2-3 min following intravenous injection of [3H]mannitol or [14C]sucrose, permeation across the barrier occurred at a rate substantially greater than that measured for a 30 min circulation time. The relatively rapid uptake of these tracers into brain during the first few minutes after injection would explain in part why estimates of regional blood volume, calculated from ratios of brain vs blood tracer concentration after short circulation times, were much higher than values determined using [51Cr]erythrocytes.     

Recognition site for the platelet receptor is present on the 15-residue carboxy-terminal fragment of the gamma chain of human fibrinogen and is not involved in the fibrin polymerization reaction

A pentadecapeptide, derived from a staphylococcal protease digest of the 27-residue carboxy-terminal cyanogen bromide fragment of human fibrinogen gamma chain, inhibits binding of 125I-fibrinogen to human platelet receptors and aggregation of platelets induced by ADP and fibrinogen. Amino acid composition and NH2 terminal analysis indicate that the isolated pentadecapeptide corresponds to residues 397 to 411 of the gamma chain. A synthetic peptide also inhibited binding of 125I-fibrinogen and aggregation of platelets. In contrast, the isolated pentadecapeptide and its parent 27-residue fragment lack inhibitory activity toward the polymerization reaction of fibrin monomer. Thus, the site recognizing the platelet receptor encompasses residues 397-411 of the gamma chain of fibrinogen and is distinct from the site(s) involved in polymerization of fibrin monomers.     

Kinetic modeling of 11C-LY2795050, a novel antagonist radiotracer for PET imaging of the kappa opioid receptor in humans

¹¹C-LY2795050 is a novel kappa opioid receptor (KOR) antagonist tracer for positron emission tomography (PET) imaging. The purpose of this first-in-human study was to determine the optimal kinetic model for analysis of ¹¹C-LY2795050 imaging data. Sixteen subjects underwent baseline scans and blocking scans after oral naltrexone. Compartmental modeling and multilinear analysis-1 (MA1) were applied using the arterial input functions. Two-tissue compartment model and MA1 were found to be the best models to provide reliable measures of binding parameters. The rank order of ¹¹C-LY2795050 distribution volume (V_T) matched the known regional KOR densities in the human brain. Blocking scans with naltrexone indicated no ideal reference region for ¹¹C-LY2795050. Three methods for calculation of the nondisplaceable distribution volume (V_ND) were assessed: (1) individual V_ND estimated from naltrexone occupancy plots, (2) mean V_ND across subjects, and (3) a fixed fraction of cerebellum V_T. Approach (3) produced the lowest intersubject variability in the calculation of binding potentials (BP_ND, BP_F, and BP_P). Therefore, binding potentials of ¹¹C-LY2795050 can be determined if the specific binding fraction in the cerebellum is presumed to be unchanged by diseases and experimental conditions. In conclusion, results from the present study show the suitability of ¹¹C-LY2795050 to image and quantify KOR in humans.     

Immunochemical method for quantitative evaluation of vasogenic brain edema following cold injury of rat brain

An immunochemical method is described for quantitative assessment of serum proteins and hemoglobin content in brain tissue homogenates. Using a combination of affinity chromatography and radioimmunoassay, the sensitivity of the method is 50 ng hemoglobin and 100 ng serum protein per assay, respectively. The method was used to measure cerebral hematocrit, blood volume and serum protein extravasation in rat brain at various times following cold injury. In control rats cerebral blood volume was 6.88 ± 0.15ml/100g and cerebral hematocrit 26.4 ± 0.86% (means±S.E.). Following cold injury blood volume did not significantly change, but there was a gradual increase of extravasated serum proteins, reaching a maximum of 21.54 ± 2.76mg/g d.w. after 8 hours. Thereafter protein content gradually declined, but even after 64 h it was distinctly increased. Protein extravasation was partly dissociated from the increase of brain water and sodium which reached a maximum already after 2 h and which normalized within 32 and 64 h, respectively. It is concluded that edema fluid associated with cold injury is not simply an ultrafiltrate of blood serum but consists of cytotoxic and vasogenic components which follow a different time course both during formation and resolution of edema.     

上矢状窦和乙状窦血栓形成的临床和磁共振诊断七例报告

目的分析上矢状窦、乙状窦血栓形成的临床特点、形成原因、磁共振成像及磁共振血管造影对其诊断的价值。方法回顾性分析７例经磁共振检查确诊的硬脑膜静脉窦血栓形成病人的临床资料及影像学特点,其中男２例,女５例,年龄１５～３４岁。病后３～１１天行磁共振检查,主要观察水肿、静脉性梗死或出血、硬脑膜异常强化及静脉窦内异常信号,部分病人复查时可观察到再通。结果硬脑膜静脉窦血栓形成７例皆有明确原因,临床表现多样,主要为亚急性颅内压增高、抽搐、肢体瘫痪或昏迷。ＭＲＩ常规ＳＥ序列Ｔ１、Ｔ２加权示窦内高信号,脑实质水肿或合并出血、梗死,强化后显示闭塞静脉窦附近硬脑膜异常强化;磁共振脑血管造影（ＭＲＡ）的ＰＣ法示静脉窦高血流信号丢失,２例分别于病后２９及３７天复查ＭＲＩ,结果显示再通,硬脑膜异常强化消失。经降颅内压、抗凝,合并炎症者给予抗生素、激素治疗,１例外伤引起者经手术治疗,７例均治愈。结论硬脑膜静脉窦血栓形成是较为少见的脑血管病,且病情重,ＭＲＩ／ＭＲＡ可帮助确诊。早期治疗可明显改善预后。     

Validation of the automated method VIENA: An accurate,precise, and robust measure of ventricular enlargement

Background: In many retrospective studies and large clinical trials, high‐resolution, good‐contrast 3DT1 images are unavailable, hampering detailed analysis of brain atrophy. Ventricular enlargement then provides a sensitive indirect measure of ongoing central brain atrophy. Validated automated methods are required that can reliably measure ventricular enlargement and are robust across magnetic resonance (MR) image types. Aim: To validate the automated method VIENA for measuring the percentage ventricular volume change (PVVC) between two scans. Materials and Methods: Accuracy was assessed using four image types, acquired in 15 elderly patients (five with Alzheimer's disease, five with mild cognitive impairment, and five cognitively normal elderly) and 58 patients with multiple sclerosis (MS), by comparing PVVC values from VIENA to manual outlining. Precision was assessed from data with three imaging time points per MS patient, by measuring the difference between the direct (one‐step) and indirect (two‐step) measurement of ventricular volume change between the first and last time points. The stringent concordance correlation coefficient (CCC) was used to quantify absolute agreement. Results: CCC of VIENA with manual measurement was 0.84, indicating good absolute agreement. The median absolute difference between two‐step and one‐step measurement with VIENA was 1.01%, while CCC was 0.98. Neither initial ventricular volume nor ventricular volume change affected performance of the method. Discussion: VIENA has good accuracy and good precision across four image types. VIENA therefore provides a useful fully automated method for measuring ventricular volume change in large datasets. Conclusion: VIENA is a robust, accurate, and precise method for measuring ventricular volume change. Hum Brain Mapp 35:1101–1110, 2014. © 2013 Wiley Periodicals, Inc.     

Performance of two relatively new quantitative D-dimer assays (Innovance D-dimer and AxSYM D-dimer) for the exclusion of deep vein thrombosis

Introduction

D-dimer assays are now widely used as the first-line test in the diagnostic algorithm of suspected deep vein thrombosis (DVT). The aim of this study was to evaluate the performance of two relatively new quantitative D-Dimer assays (Innovance™ and AxSYM®) by comparison with a clinical gold standard.

Patients and methods

311 samples from outpatients with clinical suspicion of DVT, included in a prospective management study, was analysed (prevalence of DVT 23%). The diagnostic workup included estimation of pre-test probability, D-dimer determination, objective imaging as well as 3 month clinical follow up of negative patients.

Results

No significant differences were seen in sensitivity and negative predictive values between Innovance, AxSYM and the reference assays. The area under the ROC curve was slightly lower for the AxSYM assay and the correlation to the reference assays was only moderate (r < 0.8) whereas the agreement with the Vidas assay was near excellent (κ = 0.8). The Innovance assay reached the highest AUC, showed a strong correlation with the reference assays (r ≥ 0.9) and a good agreement with the Vidas assay (κ = 0.76). In combination with a low pre-test probability score the Innovance assay reached a NPV of 100% (95% CI, 92-100) and the AxSYM assay 98% (95% CI, 87-100).

Conclusion

The Innovance and AxSYM assays show an overall good and comparable performance for the exclusion of DVT when compared to the established assays. Our results for the AxSYM assay indicate that the optimal cut-off value needs to be further evaluated.     

Exclusion of venous thromboembolism: evaluation of D-Dimer PLUS for the quantitative determination of D-dimer

The objective of this study was to evaluate if D-Dimer PLUS (Dade Behring, USA), a rapid fully automated assay, could be used as an initial screening test in the diagnosis of venous thromboembolism (VTE). Samples from 274 consecutive symptomatic patients with suspected pulmonary embolism (n=229; 79% outpatients, 21% inpatients), deep venous thrombosis (n=37; 84% outpatients, 16% inpatients) or suspected for both complications (n=8) were tested with this D-dimer assay with a Sysmex CA-1500 Coagulation Analyzer. Clinical probability for pulmonary embolism (PE) or deep venous thrombosis (DVT) was staged according to a pretest risk score proposed by Wells. Final diagnosis of PE and/or DVT was established by spiral-computed tomography of the pulmonary arteries or compression ultrasonography, respectively. PE was diagnosed in 13.5% of the patients, whereas DVT was confirmed in 17.7% of the patients. The optimal cut-off value for exclusion of venous thromboembolism was 130 mug/l, and sensitivity, specificity and negative predictive value (NPV) were 95.0% (95% CI: 92.4-97.6), 30.4% (95% CI: 25.0-35.8) and 97.2% (95% CI: 95.2-99.2), respectively. In fact, two patient with PE were missed using D-Dimer PLUS; both cases were outpatients. In conclusion, this assay appears to be safe when implemented in an algorithm based on clinical assessment, D-dimer concentration, and radiological diagnostic techniques to stratify the risk for PE or DVT. However, higher sensitivities and negative predictive values were claimed in the scarce published reports for the D-Dimer PLUS assay than found in this study.     

Optical coherence tomography for the quantitative study of cerebrovascular physiology

Doppler optical coherence tomography (DOCT) and OCT angiography are novel methods to investigate cerebrovascular physiology. In the rodent cortex, DOCT flow displays features characteristic of cerebral blood flow, including conservation along nonbranching vascular segments and at branch points. Moreover, DOCT flow values correlate with hydrogen clearance flow values when both are measured simultaneously. These data validate DOCT as a noninvasive quantitative method to measure tissue perfusion over a physiologic range.     

A method for the isolation of α-granules from human platelets

A method for the isolation of α-granules is described. A two-step French pressure cell homogenization procedure which directly produced an organelle concentrate suited for loading on density gradients was developed. The procedure was optimalized with respect to recovery of intact α-granules. The organelle homogenate was loaded to 17.5 – 27.5% metrizamide gradients and centrifuged. Organelle aggregate formation was minimized by controlling the ionic conditions and the shape of the gradient. The α-granules were separated from lysosomes and dense bodies, but overlapped with the mitochondria. The α-granules were recovered from the gradient in order to omit the major amount of mitochondria from the final preparation. A washing procedure which introduced a minimum of α-granule adhesivity and fragility is presented.     

A new rapid bedside assay for quantitative testing of D-Dimer (Cardiac D-Dimer) in the diagnostic work-up for deep vein thrombosis

The accuracy of a new bedside, rapid and quantitative D-Dimer assay (Cardiac D-Dimer) was evaluated in outpatients with clinically suspected deep vein thrombosis (DVT); VIDAS test was used as reference method. Eighty consecutive outpatients with suspected DVT of a lower limb were included in the study. Patients were classified as DVT positive or negative according to results of objective test (serial CUS), pretest clinical probability and 3-month follow-up. DVT was diagnosed in 32/80 patients (40%). The performance of the two D-Dimer assays was comparable, as indicated by the areas under the ROC curves (0.89 and 0.88, for Cardiac D-Dimer and VIDAS, respectively) and the coefficient of correlation (r=0.91). The reproducibility of the test was acceptable (from 6.2% to 12.0%). The sensitivity and negative predictive values were 100% for both tests. The specificity (SP) and positive predictive values (PPV) were similar (SP: 50.0% and 52.0%, PPV: 57.1% and 58.2%, for Cardiac D-Dimer and VIDAS, respectively). The Cardiac D-Dimer test proved to be very accurate and produced results fully comparable to those obtained with the VIDAS test. Since the test can be directly performed in the emergency room within a few minutes, it seems to have great clinical potential. The place of this assay in the diagnostic strategy of DVT remains to be determined in prospective management studies.     

Characterization of GTP-γ-S binding to isolated human platelet plasma membranes and its relationship with the stimulation of a phospholipase C activity

Binding parameters for the interaction of GTP-γ-[³⁵_S] with isolated platelet plasma membranes have been studied. Analysis of the data by a non-linear curve fitting program indicates that the interaction can be satisfactory described by a model with a single, high affinity binding site (Kd = 0.3 ±0.07 μM and Bm = 0.4 ±0.2 nmoles of GTP-γ-S/mg of membrane protein). Binding is selectively inhibited by GDP-β-S and GMP-PNP (1 μM), but not affected by ATP, CTP, ITP, or UTP, even at mM concentration. Optimal conditions for the interaction were 30°C and pH 8.0. Incubation of the isolated membranes with GTP-γ-S results in a measurable phospholipase C activity (as detected both by a breakdown of phosphoinositides and an increase of inositide phosphates) which under our experimental conditions is only slightly enhanced by addition of cytosolic proteins. Our results indicate that platelet plasma membranes contain all the necessary elements for signal transduction through the diacylglycerol/inositolphosphates pathway.     

A radioisotopic method for the simultaneous quantitation of regional cerebral blood flow and glucose utilization in small dissected samples: Validation studies and values in the nitrous oxide-anesthetized rat

A method is described for the simultaneous determination of the rates of regional cerebral blood flow (rCBF) and regional cerebral glucose utilization (rCMRgl) in 6–7 mg brain samples dissected from multiple areas of interest. The method utilizes [¹³¹I]-iodoantipyrine ([¹³¹l]IAP) to measure rCBF by indicator fractionation, and [¹⁴C]2-deoxyglucose to measure rCMRgl. [¹³¹I]IAP was synthesized with specific activity exceeding 350 Ci/mmol and radiochemical purity greater than 99.5% by the radioiodination of antipyrine with Na¹³¹I. A triple-counting strategy was developed to quantitate¹⁴C activity of the dissected brain samples in the presence of¹³¹I. The factors contributing to the propagated error of the double-label separation strategy were defined and optimal assay parameters were determined. The separation strategy was validated by measuring rCBF simultaneously with both [¹³¹I]IAP (x) and [¹⁴C]IAP (y) in a series of rats. The equation of the regression line was y = 1.025 x −0.065 (correlation coefficient 0.985), denoting excellent agreement. In another series of 5 normocapnic rats anesthetized with nitrous oxide, rCBF and rCMRgl were measured simultaneously. In individual animals, the rates of rCBF within 14–16 brain areas were closely coupled to their respective rates of glucose metabolism. For the group data, the linear regression equation relating rCBF (y) to rCMRgl (x) was y = 1.76 x + 0.13 (correlation coefficient 0.93,P < 0.001). These studies provide direct evidence, based upon data obtained in the same brain, of a close coupling of regional metabolic rate and blood flow.     

18F-FDG PET,the early phases and the delivery rate of 18F-AV45 PET as proxies of cerebral blood flow in Alzheimer's disease: Validation against 15O-H2O PET

IntroductionDual-biomarker positron emission tomography (PET), providing complementary information on cerebral blood flow and amyloid-β deposition, is of clinical interest for Alzheimer's disease (AD). The purpose of this study was to validate the perfusion components of early-phase ¹⁸F-florbetapir (eAV45), the ¹⁸F-AV45 delivery rate (R1), and ¹⁸F-FDG against ¹⁵O-H₂O PET and assess how they change with disease severity.MethodsThis study included ten controls, 19 amnestic mild cognitive impairment, and 10 AD dementia subjects. Within-subject regional correlations between modalities, between-group regional and voxel-wise analyses of covariance per modality, and receiver operating characteristic analyses for discrimination between groups were performed.ResultsFDG standardized uptake value ratio, eAV45 (0–2 min) standardized uptake value ratio, and AV45-R1 were significantly associated with H₂O PET (regional Pearson r = 0.54–0.82, 0.70–0.94, and 0.65–0.92, respectively; P < .001). All modalities confirmed reduced cerebral blood flow in the posterior cingulate of patients with amnestic mild cognitive impairment and AD dementia, which was associated with lower cognition (r = 0.36–0.65, P < .025) and could discriminate between patient and control groups (area under the curve > 0.80). However, eAV45 was less sensitive to reflect the disease severity than AV45-R1 or FDG.DiscussionR1 is preferable over eAV45 for accurate representation of brain perfusion in dual-biomarker PET for AD.     

A computer-aided method for the quantitative analysis of dendritic arborizations reconstructed from serial sections

We present a methodology for measuring precisely defined morphological parameters on complete dendritic arborizations. Brains are sectioned through anatomical planes which are defined with reference to ventricular landmarks. For each neuron, drawn through the camera lucida, dendritic points are defined and identified by means of a numerical topological codification. The 3-dimensional coordinates of each point are measured on a video computer microscope with reference to a cartesian system of axes which are oriented with reference to the anatomical planes of the brain. The data points from several serial sections are stored section by section and re-ordered by a computer program. Quantitative data concerning the diameters of the dendrites and the number and the dimensions of their spines are also stored. From these data, various quantitative morphological parameters may be computed. The accuracy of the video computer microscope is measured. The different existing computerized systems and the contribution of computerized techniques are discussed.     

Further evidence for a unique developmental compartment in the cerebellum of the meander tail mutant mouse as revealed by the quantitative analysis of Purkinje cells

The cerebellum of the meander tail mutant mouse (mea/mea) is characterized by a relatively normal cytoarchitecture posteriorly with an abrupt transition to an anterior region in which there is abnormal foliation, agranularity, and Purkinje cell (PC) ectopia. This study presents the results of a qualitative and quantitative analysis of the PC in the mea/mea cerebellum. Developmental and morphological analyses reveal that the PC in the anterior region of the mea/mea cerebellum do not form a monolayer during the first week of postnatal development as they do in the wild type mouse. In the adult mea/mea, the dendrites of these ectopic cells are atrophic and disoriented. Quantitative studies in adult animals reveal that while the total number of PC is normal, the number of PC in the affected anterior region of the mea/mea cerebellum is greater than the number of PC in the anterior lobe, as classically defined by the primary fissure, of the normal animal. These data suggest that 1) the developmental morphology of the PC in the anterior region is abnormal, probably due to the lack of granule cells at early postnatal times; 2) the total number of PC in the cerebellum is normal, and 3) the defect is not restricted to the anterior lobe but involves a portion of the posterior lobe. The latter supports the notion that the mutant gene affects a unique developmental compartment in the cerebellum which does not coincide with the classic adult boundary, the primary fissure, between the anterior and posterior lobes. © 1996 Wiley-Liss, Inc.