Positron Emission Tomography PET Research Articles

Association between the use of antihypertensive medication and amyloid‐beta deposition in older adults with hypertension

AbstractBackgroundRecent evidences suggest that the use of antihypertensive medications (HTNmed) may decrease the incidence of Alzheimer’s disease (AD) dementia. We investigated whether the use of HTNmed is associated with in vivo AD pathologies, particularly cerebral beta‐amyloid (Aβ) deposition, and whether the relationship between HTNmed and cerebral Aβ deposition differs according to the characteristics of HTNmed in older adults.MethodParticipants were recruited from the Korean Brain Aging Study for the Early Diagnosis and Prediction of Alzheimer’s Disease (KBASE) cohort. Both cognitively normal and cognitively impaired older adults (age range: 55‐90 years) who met the following criteria of hypertension (HTN) were included for this study: i) clinical diagnosis of hypertension or ii) systolic blood pressure higher than 130mmHg or diastolic blood pressure higher than 80mmHg measured at baseline. All participants underwent comprehensive clinical assessment and [11C] Pittsburgh Compound B positron emission tomography PET for measuring Aβ deposition.ResultAmong total 413 older adults with hypertension, 227(54.8%) were taking HTNmed. Overall, individuals taking HTNmed showed significantly lower Aβ deposition compared to those without HTNmed (B = ‐0.104, p = 0.007), even after controlling age, sex, apolipoprotein E e4 positivity, and mean arterial blood pressure(MAP). Drug‐class specific analyses showed that the use of renin angiotensin system (RAS) inhibitor (i.e., angiotensin converting enzyme inhibitor and angiotensin receptor blocker) was associated with less cerebral Aβ deposition among older adults with HTNmed (B = ‐0.142, p = 0.006), but the use of other HTNmeds was not. In addition, the blood‐brain barrier permeability of HTNmed also did not have any relationship with Aβ deposition.ConclusionThe present finding suggests that the use of HTNmed, particularly RAS inhibitor, is associated with less Aβ deposition in older adults with hypertension. Further studies to explore the mechanism underlying the effect of RAS inhibitor on Aβ accumulation may provide clues for new therapeutic targets of AD.

The Role of Non-Invasive Multimodality Imaging in Chronic Coronary Syndrome: Anatomical and Functional Pathways.

Coronary artery disease (CAD) is one of the major causes of mortality and morbidity worldwide, with a high socioeconomic impact. Currently, various guidelines and recommendations have been published about chronic coronary syndromes (CCS). According to the recent European Society of Cardiology guidelines on chronic coronary syndrome, a multimodal imaging approach is strongly recommended in the evaluation of patients with suspected CAD. Today, in the current practice, non-invasive imaging methods can assess coronary anatomy through coronary computed tomography angiography (CCTA) and/or inducible myocardial ischemia through functional stress testing (stress echocardiography, cardiac magnetic resonance imaging, single photon emission computed tomography-SPECT, or positron emission tomography-PET). However, recent trials (ISCHEMIA and REVIVED) have cast doubt on the previous conception of the management of patients with CCS, and nowadays it is essential to understand the limitations and strengths of each imaging method and, specifically, when to choose a functional approach focused on the ischemia versus a coronary anatomy-based one. Finally, the concept of a pathophysiology-driven treatment of these patients emerged as an important goal of multimodal imaging, integrating 'anatomical' and 'functional' information. The present review aims to provide an overview of non-invasive imaging modalities for the comprehensive management of CCS patients.

Imaging Chronic Active Lesions in Multiple Sclerosis: a Consensus Statement from the North America Imaging in Multiple Sclerosis Cooperative (P11-3.009)

Imaging Chronic Active Lesions in Multiple Sclerosis: a Consensus Statement from the North America Imaging in Multiple Sclerosis Cooperative (P11-3.009)

Biodistribution of 89Zr-DFO-labeled avian pathogenic Escherichia coli outer membrane vesicles by PET imaging in chickens

Avian pathogenic Escherichia coli (APEC) is a serious systemic infectious disease in poultry infections, causing severe economic losses to the poultry industry. Previous studies have shown that secretion of virulence proteins was required for the pathogenicity of APEC through the secretion system. Outer membrane vesicles (OMVs) are a generalized secretion system of Gram-negative bacteria that play a key role in the long-distance delivery of virulence factors, but whether they are associated with the pathogenic mechanism of APEC has not been determined. In this study, OMVs were purified and characterized from AE17 (O2 serotype) by ultracentrifugation and density gradient centrifugation and their protein cargo was identified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). In addition, 89Zr was labeled after chelating AE17 OMVs by DFO and positron emission tomography PET imaging was used to track 89Zr-DFO-OMVs in chickens and to pathologically analyze the distribution sites. This study showed that AE17 OMVs were membrane vesicles ranging in size from 20 to 200 nm and proteomic analysis revealed the presence of virulence proteins, including adhesion proteins OmpA, OmpC, OmpF, OmpX, FimH, FimC and FigE, and serum resistance proteins OmpT and MliC and immune response regulator proteins (FliC). In addition, in vivo PET imaging to track the biodistribution of AE17 OMVs showed that AE17 OMVs were taken up by the lung region and the gastrointestinal and renal regions but were not detected in other areas. Pathological analysis of the tissue sites where AE17 OMVs were ingested showed inflammatory responses and damage. These findings suggested that AE17 OMVs not only contained a group of virulence proteins associated with AE17 infection but can also deliver these virulence proteins over long distances and caused tissue inflammatory damage. Our study revealed a previously unidentified causative microbial signal in the pathogenesis of APEC that could aid in the development of vaccines and antibiotics effective against APEC.

Does Motion Management Technique for Lung SBRT Influence Local Control? A Single Institutional Experience Comparing Abdominal Compression to Breath-Hold Technique

PurposeAbdominal compression (COMP) and breath-hold with an active breathing coordinator (ABC) device are 2 different respiratory motion management techniques used in lung stereotactic body radiation therapy (SBRT) practice. We compared local failure (LF) results for COMP versus ABC. Methods and MaterialsWe surveyed our institutional review board–approved prospective registry for patients who were treated with SBRT for either a primary lung cancer (PRIME) or an oligometastatic (OLIGO) diagnosis with a minimum of 6 months’ follow-up to determine their rates of local failure by motion management modality. ResultsFrom October 2003 to July 2014, 873 patients with 931 lesions were treated. Patient characteristics included: 455 (52.1%) female; median age of 73 years (range, 37-97); median Karnofsky performance status (KPS) of 80 (range, 40-100); and median BMI of 26.2 (range, 12.1-56.3). Tumor characteristics included: median tumor size of 2.2 cm (range, 0.7-10.0); median maximum standardized uptake value from positron emission tomography PET SUVmax of 7.5 (range, 0.8-59); 234 (25.4%) were central lesions; 830 (89.2%) lesions were PRIME; and 101 (10.8%) were OLIGO. Median follow-up and SBRT dose were 16.4 months and 50 G in 5 fractions, respectively. Overall crude rate of LF was 9.9%. Use of ABC was not associated with increased LF compared with COMP: hazard ratio (HR) = 1.043 (95% CI 0.48-2.29; P = .92). Three-year actuarial rates of LF for ABC versus COMP were 13.8% and 16.5%, respectively. After stratifying by OLIGO/PRIME, neither ABC nor COMP was significantly associated with LF. Central location may be associated with LF with ABC (HR = 2.087, P = .066). On univariate analysis, BMI, tumor size, PET SUV max and central location were associated with failure, with size the most significant. ConclusionsLF rates after lung SBRT were not influenced by form of motion control overall or when stratified by tumor type. Further study on LF rates for central tumors where ABC is used is warranted.

Multicenter Validation of Metabolic Abnormalities Related to PSP According to the MDS-PSP Criteria.

It remains unclear whether the supportive imaging features described in the diagnostic criteria for progressive supranuclear palsy (PSP) are suitable for the full clinical spectrum. The aim of the current study was to define and cross-validate the pattern of glucose metabolism in the brain associated with a diagnosis of different PSP variants. A retrospective multicenter cohort study performed on 73 PSP patients who were referred for a fluorodeoxyglucose positron emission tomography PET scan: PSP-Richardson's syndrome, n = 47; PSP-parkinsonian variant, n = 18; and progressive gait freezing, n = 8. In addition, we included 55 healthy controls and 58 Parkinson's disease (PD) patients. Scans were normalized by global mean activity. We analyzed the regional differences in metabolism between the groups. Moreover, we applied a multivariate analysis to obtain a PSP-related pattern that was cross-validated in independent populations at the individual level. Group analysis showed relative hypometabolism in the midbrain, basal ganglia, thalamus, and frontoinsular cortices and hypermetabolism in the cerebellum and sensorimotor cortices in PSP patients compared with healthy controls and PD patients, the latter with more severe involvement in the basal ganglia and occipital cortices. The PSP-related pattern obtained confirmed the regions described above. At the individual level, the PSP-related pattern showed optimal diagnostic accuracy to distinguish between PSP and healthy controls (sensitivity, 80.4%; specificity, 96.9%) and between PSP and PD (sensitivity, 80.4%; specificity, 90.7%). Moreover, PSP-Richardson's syndrome and PSP-parkinsonian variant patients showed significantly more PSP-related pattern expression than PD patients and healthy controls. The glucose metabolism assessed by fluorodeoxyglucose PET is a useful and reproducible supportive diagnostic tool for PSP-Richardson's syndrome and PSP-parkinsonian variant. © 2020 International Parkinson and Movement Disorder Society.

Typical lung carcinoids: review of classification, radiological signs and nuclear imaging findings

In this comprehensive review we present an overview of the main aspects of classification, radiological signs and nuclear imaging findings of typical lung carcinoids (TCs). A literature search on the PubMed literature database was conducted using the terms “positron emission tomography—PET”, “PET/CT”, “FDG”, “18F-fluorodeoxyglucose”, “MDCT—Contrast-enhanced multi-detector computed tomography” “typical lung carcinoid” “SRS—Somatostatin receptor scintigraphy”, “68 Ga DOTA-peptides” alone and in combination, extending until December 2019. TCs are rare tumours, accounting for only 1–2% of all pulmonary neoplasms. They tend to occur usually in the fourth-to-sixth decade of life and are characterized by mitotic count of less 2/2 mm2 and absent necrosis. Contrast-enhanced multi-detector computed tomography (MDCT) is the most largely used imaging modality for the localization, characterization and staging of lung TCs. Nuclear medicine imaging assists MDCT in the diagnosis of these rare tumour entities, especially by somatostatin receptor scintigraphy, PET imaging with Gallium-68-tetrazacyclododecanetetraacetic acid (68 Ga DOTA-peptides) and with 18F-fluorodeoxyglucose (18F-FDG). TCs of lung are rare lung tumours placed within a defined classification system. MDCT morphological features combined with functional nuclear medicine imaging are an important tool for the detection of these rare neoplasms and contribute to their characterisation and staging. Therefore, MDCT and nuclear medicine parameters could give a preliminary orientation before the pathological examination, on the biological behaviour and the prognostic outcome of TCs.

Progress of diagnosis and treatment of cholangiocarcinoma

Due to the high degree of malignancy and low surgical resection rate of cholangiocarcinoma, as well as the immaturity of postoperative adjuvant chemotherapy and targeted therapy drugs, the mortality rate of patients with cholangiocarcinoma is high and the long-term prognosis is poor. With the improvement of clinical diagnosis and treatment, preoperative evaluation and surgical technique, the diagnosis and treatment of cholangiocarcinoma have made some progress. The early stage of cholangiocarcinoma is lack of specific manifestations, so the patient has lost the opportunity of R0 resection when diagnosed. Early diagnosis can improve the patient′s R0 resection and long-term survival after surgery. The diagnostic accuracy can be improved by contrast enhanced ultrasound, enhanced magnetic resonance, positron emission tomography PET, etc. Dominated by comprehensive therapy in the treatment of bile duct carcinoma, strive for R0 resection for resectable cholangiocarcinoma, distant metastasis occurred after bile duct carcinoma can be combined with new adjuvant chemotherapy according to the review situation decides whether it is feasible to surgery, postoperative chemotherapy, molecular targeted therapy, body directional radiation therapy, and other comprehensive solutions in order to improve the long-term survival rate. This article reviews the recent progress in the pathogenesis, diagnosis and treatment of cholangiocarcinoma. Key words: Bile duct neoplasms; Diagnosis; Therapeutic uses

Comparison of Cardio Vascular Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (Pet) for Detection of Myocardial Viability

Coronary artery disease (CAD) remains the most common cause of death. However, the number of deaths from myocardial infarction has decreased. Mortality from congestive heart failure has more than doubled. It is important to note that CAD accounts for the majority (almost 70%) of congestive heart failure cases. In the clinical management of patients with symptom of heart condition by CAD, the correct assessment of cardiac muscle viability is crucial to guide treatment and this will be as a result of revascularization of dysfunctional however viable heart muscle can improve cavity perform and future survival. Generally nuclear imaging, stress echocardiography and stress electrocardiography have been the clinical main step for assessing myocardial viability as well as to detect myocardial Ischemia. Recently cardiovascular MR (CMR) is a rapidly emerging non-invasive imaging technique, providing high resolution images of the heart in any desired plane and without radiation. CMR has the unique ability to evaluate several markers of myocardial viability that are of proven value. The focus of the present study is on the rapidly emerging clinical role of cardiovascular MRI in the detection of viable myocardium. Objective: To assess the role of cardiovascular MRI for detection of myocardial viability

Predictive value of pre-treatment FDG PET in patients with non-Hodgkin lymphoma treated with radioimmunotherapy: a systematic review

We aimed to systematically review studies addressing the value of baseline FDG PET as predictive biomarker for response to RIT in patients with NHL. We searched (last update: March 2019) the databases PubMed, PMC, Google Scholar and Medline using both as text and as MeSH (Medical Subject Headings) terms the following: “positron emission tomography—PET”, “PET/CT”, “FDG”, “18F-fluorodeoxyglucose”, and “radioimmunotherapy”, ‘90Y-ibritumomab tiuxetan” and “non-Hodgkin lymphoma” and “follicular lymphoma”. Among all the retrieved articles, we selected only those specifically analyzing role, predictive and overall value of pretreatment FDG PET in patients with NHL submitted to RIT. The initial search retrieved seventy articles, however, only eight specifically analyzed the predictive value of pretreatment FDG PET in patients with NHL submitted to RIT and were thus discussed. Eight studies in 254 patients evaluated the role of FDG PET as a predictor of response prior to RIT. Despite several methodological issues, patients- and lesion-based analyses carried out to-date seem to suggest a relevant prognostic role of both morphological computed tomography and metabolic imaging. Although it is still not possible to specifically define the best PET-based predictor (i.e. SUVmax, TLG, MTV), FDG-PET is a promising tool for a more accurate and individualized selection of NHL patients candidates to RIT. The availability of FDG PET examinations in homogenous group of patients included in already completed clinical trials might be used in the next future also to specifically assess the prognostic value of baseline FDG PET in patients treated with RIT based on the study design.

Ketamine and Ceftriaxone-Induced Alterations in Glutamate Levels Do Not Impact the Specific Binding of Metabotropic Glutamate Receptor Subtype 5 Radioligand [18F]PSS232 in the Rat Brain.

Several studies showed that [11C]ABP688 binding is altered following drug-induced perturbation of glutamate levels in brains of humans, non-human primates and rats. We evaluated whether the fluorinated derivative [18F]PSS232 can be used to assess metabotropic glutamate receptor 5 (mGluR5) availability in rats after pharmacological challenge with ketamine, known to increase glutamate, or ceftriaxone, known to decrease glutamate. In vitro autoradiography was performed on rat brain slices with [18F]PSS232 to prove direct competition of the drugs for mGluR5. One group of rats were challenged with a bolus injection of either vehicle, racemic ketamine, S-ketamine or ceftriaxone followed by positron emission tomography PET imaging with [18F]PSS232. The other group received an infusion of the drugs during the PET scan. Distribution volume ratios (DVRs) were calculated using a reference tissue model. In vitro autoradiography showed no direct competition of the drugs with [18F]PSS232 for the allosteric binding site of mGluR5. DVRs of [18F]PSS232 binding in vivo did not change in any brain region neither after bolus injection nor after infusion. We conclude that [18F]PSS232 has utility for measuring mGluR5 density or occupancy of the allosteric site in vivo, but it cannot be used to measure in vivo fluctuations of glutamate levels in the rat brain.

Primary CNS Lymphomas: Challenges in Diagnosis and Monitoring.

Primary Central Nervous System Lymphoma (PCNSL) is a rare neoplasm that can involve brain, eye, leptomeninges, and rarely spinal cord. PCNSL lesions most typically enhance homogeneously on T1-weighted magnetic resonance imaging (MRI) and appear T2-hypointense, but high variability in MRI features is commonly encountered. Neurological symptoms and MRI findings may mimic high grade gliomas (HGGs), tumefactive demyelinating lesions (TDLs), or infectious and granulomatous diseases. Advanced MRI techniques (MR diffusion, spectroscopy, and perfusion) and metabolic imaging, such as Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) or amino acid PET (usually employing methionine), may be useful in distinguishing these different entities and monitoring the disease course. Moreover, emerging data suggest a role for cerebrospinal fluid (CSF) markers in predicting prognosis and response to treatments. In this review, we will address the challenges in PCNSL diagnosis, assessment of response to treatments, and evaluation of potential neurotoxicity related to chemotherapy and radiotherapy.

Aberrant Connectivity in Mild Cognitive Impairment and Alzheimer Disease Revealed by Multimodal Neuroimaging Data

Background: Making use of multimodal data simultaneously to understand the neural mechanism of mild cognitive impairment (MCI) has been in the focus nowadays. The simultaneous use of multimodal data can take advantage of each modality which may only provide the view of one specific aspect of the brain. Objective: To this end, the present study used structural magnetic resonance imaging (sMRI), fluorodeoxyglucose positron emission tomography (FDG-PET) and florbetapir PET to reveal the integrated brain network between MCI and normal controls (NCs). Methods: In this study, 116 MCI, 116 NC and 116 Alzheimer disease (AD) subjects from the Alzheimer's Disease Neuroimaging Initiative were included for the evaluation of the brain covariance graphic model. Sparse inverse covariance estimation was utilized to get the graphic model. Results: The connections among different brain regions were quite different between NC and MCI or between MCI and AD subjects (p < 0.01). The number of connections, which were represented by the covariance among different brain regions in the graphic model, decreased from NC to MCI and then AD, especially in the temporal lobe, occipital-parietal lobe and parietal-temporal lobe. Conclusion: These findings are good evidence to reveal the difference between MCI or AD and NC, and enhance the understanding of MCI.

Prognostic value of amyloid PET scan in normal pressure hydrocephalus.

Amyloid positron emission tomography ([18F] florbetaben (FBB) PET) can be used to determine concomitant Alzheimer's disease (AD) in idiopathic normal pressure hydrocephalus (iNPH) patients. FBB PET scans and the tap test were performed in 31 patients with clinically suspected iNPH, and amyloid positive (iNPH/FBB+) and negative (iNPH/FBB-) groups were compared with respect to clinical characteristics. We evaluated prognostic value of FBB PET scans by analyzing the response to the tap test using a linear mixed model. We also performed a multivariable regression analysis to investigate whether amyloid PET positivity can predict the positive tap test response independent of other AD biomarkers. The results showed that the iNPH/FBB+ group (7/31, 22.6%) had a higher percentage of APOE4 carriers, lower Aβ42, higher CSF t-tau, and p-tau/Aβ42 ratio than the iNPH/FBB- group (24/31, 77.4%), while the two groups did not differ in imaging characteristics. The iNPH/FBB- group had a higher percentage of tap responders and showed a greater improvement in gait scores after the tap test than the iNPH/FBB+ group (group-tap test effect interaction, p=0.035). A multivariable logistic regression analysis showed that amyloid positivity on PET scans (OR 0.03, p=0.029) and CSF p-tau (OR 0.87, p=0.044) were independently associated with the positive tap test response. Among 21 tap responders in the iNPH/FBB- group, 14 patients received shunt surgery and 12/14 (85.7%) patients showed symptom improvement. Our findings suggest that amyloid PET scans can help determine which iNPH patients will benefit from shunt surgery by discriminating concomitant AD.

The use of positron emission tomography (pet) in the diagnosis of neurodegenerative diseases of the elderly

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Contextualizing the use of oncologic imaging within treatment phases: imaging trends and modality preferences, 2000-2014.

In the present study, we retrospectively evaluated the use of tomographic imaging in adult cancer patients to clarify how recent growth plateaus in the use of tomographic imaging in the United States might have affected oncologic imaging during the same period. At a U.S. academic cancer centre, 12,059 patients with dates of death from January 2000 through December 2014 were identified. Imaging was restricted to brain and body computed tomography (ct), brain and body magnetic resonance (mr), and body positron-emission tomography (pet) with and without superimposed ct. Trends during the staging (1 year after diagnosis), monitoring (18-6 months before death), and end-of-life (final 6 months before death) phases were analyzed. Comparing the 2005-2009 with the 2010-2014 period, mean intensity of pet imaging increased 21% during staging (p = 0.0000) and 27% during end of life (p = 0.0019). In the monitoring phase, mean intensity for ct brain, ct body, and mr body imaging decreased by 26% (p = 0.0133), 11% (p = 0.0118), and 26% (p = 0.0008), respectively. Aggregate mean intensity of imaging increased in the 13%-27% range every 3 months from 18 months before death to death, reaching 1.43 images in the final 3 months of life. Patients diagnosed in the final 18 months of life had an average of 1 additional image during both the 3 months after diagnosis (p = 0.0000) and the final 3 months before death (p = 0.0000). Imaging increased as temporal proximity to death decreased, and patients diagnosed near death received more staging imaging, suggesting that imaging guidelines should consider imaging intensity within the context of treatment phase. Despite the development, by multiple organizations, of appropriateness criteria to reduce imaging utilization, aggregate per-patient imaging showed insignificant changes. Simultaneous fluctuations in the intensity of imaging by modality suggest recent changes in the modalities preferred by providers.

Do myocardial PET–MR and PET–CT FDG images provide comparable information?

IntroductionAlthough positron emission tomography PET–MR imaging is emerging into clinical practice, many aspects of this imaging technique such as attenuation correction have yet to be validated for myocardial imaging. Thus, it is uncertain whether PET–MR FDG images provide clinical information which is comparable to PET–CT FDG images. The study goal was to systematically compare relative myocardial FDG concentrations obtained from cardiac PET–MR images to those derived from same day PET–CT images. MethodsMyocardial FDG images of 27 patients undergoing PET–CT imaging, followed by PET–MR imaging 42 ± 13 minutes later as part of a prospective oncology study were analyzed. Mean segmental standardized uptake measurements (SUVmean) were obtained in each of the 17 standard myocardial segments and normalized to the brightest segment. ResultsNormalized segmental SUVmean values did not differ significantly between the PET–MR and PET–CT images (mean difference 0.002, P = .826). The specific segment was a marginally significant predictor of the differences (P = .057), with the largest difference in the anteroseptal basal segment. ConclusionsPET–MR, vis-à-vis PET–CT, does not significantly raise segmental uptake relative to the brightest segment, suggesting that PET–MR can be used similarly to PET–CT for applications where relative uptake is important.

Beta-amyloid deposition and cognitive function in patients with major depressive disorder with different subtypes of mild cognitive impairment: 18F-florbetapir (AV-45/Amyvid) PET study

The objective of this study was to evaluate the amyloid burden, as assessed by (18)F-florbetapir (AV-45/Amyvid) positron emission tomography PET, in patients with major depressive disorder (MDD) with different subtypes of mild cognitive impairment (MCI) and the relationship between amyloid burden and cognition in MDD patients. The study included 55 MDD patients without dementia and 21 healthy control subjects (HCs) who were assessed using a comprehensive cognitive test battery and (18)F-florbetapir PET imaging. The standardized uptake value ratios (SUVR) in eight cortical regions using the whole cerebellum as reference region were determined and voxel-wise comparisons between the HC and MDD groups were performed. Vascular risk factors, serum homocysteine level and the apolipoprotein E (ApoE) genotype were also determined. Among the 55 MDD patients, 22 (40.0%) had MCI, 12 (21.8%) non-amnestic MCI (naMCI) and 10 (18.2%) amnestic MCI (aMCI). The MDD patients with aMCI had the highest relative (18)F-florbetapir uptake in all cortical regions, and a significant difference in relative (18)F-florbetapir uptake was found in the parietal region as compared with that in naMCI subjects (P < 0.05) and HCs (P < 0.01). Voxel-wise analyses revealed significantly increased relative (18)F-florbetapir uptake in the MDD patients with aMCI and naMCI in the frontal, parietal, temporal and occipital areas (P < 0.005). The global cortical SUVR was significantly negatively correlated with MMSE score (r = -0.342, P = 0.010) and memory function (r = -0.328, P = 0.015). The negative correlation between the global SUVR and memory in the MDD patients remained significant in multiple regression analyses that included age, educational level, ApoE genotype, and depression severity (β = -3.607, t = -2.874, P = 0.006). We found preliminary evidence of brain beta-amyloid deposition in MDD patients with different subtypes of MCI. Our findings in MDD patients support the hypothesis that a higher amyloid burden is associated with a poorer memory performance. We also observed a high prevalence of MCI among elderly depressed patients, and depressed patients with MCI exhibited heterogeneously elevated (18)F-florbetapir retention as compared with depressed patients without MCI. The higher amyloid burden in the aMCI patients suggests that these patients may also be more likely to develop Alzheimer's disease than other patients diagnosed with major depression.

Picosecond Time Resolved Studies of Photon Transport Inside Scintillators

The traveling time of scintillation photons from the ionization track to the photodetector varies from photon to photon. For scintillators used in (time-of-flight) positron emission tomography (TOF-)PET systems the resulting optical transit time-spread can have a significant influence on the timing resolution. Using a femtosecond pulsed diode laser in combination with a fast imaging streak camera we measured this time-spread on the picosecond time scale for both polished and etched Ca co-doped and non co-doped LSO:Ce and LYSO:Ce crystals of $3 \times 3 \times 5 ~\hbox{mm}^3$ , $3 \times 3 \times 10 ~\hbox{mm}^3$ , and $3 \times 3 \times 20 ~\hbox{mm}^3$ in size. Measurements were performed with the crystals wrapped on 5 of their sides in 1 to 4 layers of 0.1 mm thick white reflecting Teflon tape (PTFE). Optical photons can migrate through Teflon tape for some time before they re-enter the crystal. This Teflon time-spread was measured as well. The roughness of the crystal surfaces were determined using a surface profiler. In addition to experiments, the optical transit time-spread was obtained by means of ray-tracing software and compared to experimental data. In addition, an analytical model about optical transit time-spreads was derived.

Positron kinetics in an idealized PET environment.

The kinetic theory of non-relativistic positrons in an idealized positron emission tomography PET environment is developed by solving the Boltzmann equation, allowing for coherent and incoherent elastic, inelastic, ionizing and annihilating collisions through positronium formation. An analytic expression is obtained for the positronium formation rate, as a function of distance from a spherical source, in terms of the solutions of the general kinetic eigenvalue problem. Numerical estimates of the positron range - a fundamental limitation on the accuracy of PET, are given for positrons in a model of liquid water, a surrogate for human tissue. Comparisons are made with the ‘gas-phase’ assumption used in current models in which coherent scattering is suppressed. Our results show that this assumption leads to an error of the order of a factor of approximately 2, emphasizing the need to accurately account for the structure of the medium in PET simulations.