Brain Fluid Clearance After Traumatic Brain Injury Measured Using Dynamic Positron Emission Tomography

Brain fluid clearance by pathways including the recently described paravascular glymphatic system is a critical homeostatic mechanism by which metabolic products, toxins, and other wastes are removed from the brain. Brain fluid clearance may be especially important after traumatic brain injury (TBI), when blood, neuronal debris, inflammatory cells, and other substances can be released and/or deposited. Using a non-invasive dynamic positron emission tomography (PET) method that models the rate at which an intravenously injected radiolabeled molecule (in this case 11C-flumazenil) is cleared from ventricular cerebrospinal fluid (CSF), we estimated the overall efficiency of brain fluid clearance in humans who had experienced complicated-mild or moderate TBI 3-6 months before neuroimaging (n = 7) as compared to healthy controls (n = 9). While there was no significant difference in ventricular clearance between TBI subjects and controls, there was a significant group difference in dependence of ventricular clearance upon tracer delivery/blood flow to the ventricles. Specifically, in controls, ventricular clearance was highly, linearly dependent upon blood flow to the ventricle, but this relation was disrupted in TBI subjects. When accounting for blood flow and group-specific alterations in blood flow, ventricular clearance was slightly (non-significantly) increased in TBI subjects as compared to controls. Current results contrast with past studies showing reduced glymphatic function after TBI and are consistent with possible differential effects of TBI on glymphatic versus non-glymphatic clearance mechanisms. Further study using multi-modal methods capable of assessing and disentangling blood flow and different aspects of fluid clearance is needed to clarify clearance alterations after TBI.

The Clinical Utility of Gallium-68-DOTATATE Positron Emission Tomography Scanning in Medullary Thyroid Cancer

OBJECTIVE

Somatostatin receptor (SST) functional imaging with positron emission tomography (PET)/computed tomography (CT) has broadened the diagnostic and staging capabilities for medullary thyroid cancer (MTC). Gallium-68 (68Ga)-DOTA-conjugated peptide (Tyr3)-octreotate (DOTATATE) is a radiotracer with a high affinity for type 2 SSTs expressed in several, but not all, MTCs. The utility of 68Ga-DOTATATE PET/CT and 18fluorine-labeled fluoro-2-deoxy-D-glucose (18F-FDG)-PET/CT imaging in predicting MTC prognosis is also unknown.

METHODS

In this single-center retrospective study, 103 of patients with MTC underwent assessment of SST2 and SST5 immunohistochemistry (IHC). A subgroup of 37 patients received 68Ga-DOTATATE PET/CT imaging, and 13 received contemporaneous 18F-FDG-PET/CT imaging. The maximum standardized uptake value (SUV), mean SUV, metabolic tumor volume, and total lesion activity (TLA) were assessed.

RESULTS

Forty-two patients (41%) demonstrated positive expression of SST2, and 45 (44%) had a positive SST5 IHC result. Seventeen patients (17%) expressed both SST2 and SST5. No survival advantage was identified with SST2 or SST5 IHC positivity. No correlation was noted between the maximum SUV, mean SUV, metabolic tumor volume, or TLA and SST2 and/or SST5 expression by IHC. Shorter survival was associated with a TLA of >20 (P = .04). A RET-negative status also appeared to have shorter survival, although this may be because the small numbers did not reach statistical significance (P = .12).

CONCLUSION

Assessment of TLA from 68Ga-DOTATATE PET/CT may predict survival. SST2 IHC was not correlated with 68Ga-DOTATATE avidity. Metastatic disease may be optimally assessed by concurrent 18F-FDG and 68Ga-DOTATATE imaging.

Cerebral Glucose Metabolism in Patients with Chronic Disorders of Consciousness

OBJECTIVE

To measure regional cerebral metabolic rate of glucose (CMRGlu) in patients with chronic disorders of consciousness (DOCs) using 18F-fluorodeoxyglucose positron emission tomography (FDG-PET).

METHODS

This retrospective cohort study examined 50 patients (mean age: 40.9 ± 20.1 years) with traumatic brain injury (TBI)-induced chronic DOCs [minimally conscious state (MCS)+, n = 20; MCS-, n = 15 and vegetative state (VS), n = 15]. We measured FDG-PET-based CMRGlu values in 12 regions of both brain hemispheres and compared those among MCS+, MCS - and VS patients.

RESULTS

In both hemispheres, the regional CMRGlu reduced with consciousness deterioration in 11 of 12 regions (91.7%). In seven right hemisphere regions, CMRGlu values were markedly higher in MCS+ patients than in MCS- patients. Furthermore, CMRGlu was suggestively higher in the left occipital region in MCS- patients than in VS patients.

CONCLUSION

Functional preservation in the left occipital region in patients with chronic DOCs might reflect an awareness of external environments, whereas extensive functional preservation in the right cerebral hemisphere might reflect communication motivation.

Exercise increases myocardial free fatty acid oxidation in subjects with metabolic dysfunction-associated fatty liver disease

BACKGROUND AND AIMS

Metabolic dysfunction-associated fatty liver disease (MAFLD) is associated with dyslipidemia and may promote cardiac lipotoxicity. Myocardial free fatty acids (FFA) oxidation (MO_FFA) is normal in pre-diabetes, but reduced in heart failure. We hypothesized that during exercise MO_FFA, very low-density lipoprotein triglycerides (VLDL-TG) secretion, hepatic FFA utilization, and lactate production differ among obese subjects with and without MAFLD.

METHODS

Nine obese subjects with MAFLD and 8 matched subjects without MAFLD (Control) without a history of heart failure and cardiovascular disease were compared before and after 90-min exercise at 50% Peak oxygen consumption. Basal and exercise induced cardiac and hepatic FFA oxidation, uptake and re-esterification and VLDL-TG secretion were measured using [¹¹C]palmitate positron-emission tomography and [1-¹⁴C]VLDL-TG.

RESULTS

In the heart, increased MO_FFA was observed after exercise in MAFLD, whereas MO_FFA decreased in Control (basal vs exercise, MAFLD: 4.1 (0.8) vs 4.8 (0.8) μmol·100 ml^-1 min^-1; Control: 4.9 (1.8) vs 4.0 (1.1); μmol·100 ml^-1 min^-1, mean (SD), p < 0.048). Hepatic FFA fluxes were significantly lower in MAFLD than Control and increased ≈ two-fold in both groups. VLDL-TG secretion was 50% greater in MAFLD at rest and similarly suppressed during exercise. Plasma lactate increased significantly less in MAFLD than Control during exercise.

CONCLUSIONS

Using robust tracer-techniques we found that obese subjects with MAFLD do not downregulate MO_FFA during exercise compared to Control, possibly due to diminished lactate supply. Hepatic FFA fluxes are significantly lower in MAFLD than Control, but increase similarly with exercise. VLDL-TG export remains greater in MAFLD compared to Control. Basal and post-exercise myocardial and hepatic FFA, VLDL-TG and lactate metabolism is abnormal in subjects with MAFLD compared to Control.

Positron Emission Tomography in Pediatric Neurodegenerative Disorders

Application of molecular neuroimaging using positron emission tomographic techniques to assess pediatric neurodegenerative disorders has been limited, unlike in adults where positron emission tomography has contributed to clinical diagnosis, monitoring of neurodegenerative disease progression, and assessment of novel therapeutic approaches. Yet, there is a huge unexplored potential of molecular imaging to improve our understanding of the pathophysiology of neurodegenerative disorders in children and provide radiological biomarkers that can be applied clinically. The obstacles in performing PET scans on children include sedation, radiation exposure, and access but, as will be illustrated, these barriers can be easily overcome. This review summarizes findings from PET studies that have been performed over the past three decades on children with various neurodegenerative disorders, including the neuronal ceroid lipofuscinoses, juvenile Huntington disease, Wilson disease, Niemann-Pick disease type C, Dravet syndrome, dystonia, mitochondrial disorders, inborn errors of metabolism, lysosomal storage diseases, dysmyelinating disorders, Rett syndrome, neurotransmitter disorders, glucose transporter Glut 1 deficiency, and Lesch-Nyhan disease. Because positron emission tomographic scans have often been clinically useful and have contributed to the management of these disorders, we suggest that the time has come for glucose metabolism positron emission tomographic scans to be reimbursed by insurance carriers for children with neurodegenerative disorders, and not restricted only to epilepsy surgery evaluation.

A Systematic Review of Positron Emission Tomography of Tau, Amyloid Beta, and Neuroinflammation in Chronic Traumatic Encephalopathy: The Evidence To Date

Chronic traumatic encephalopathy (CTE) is associated with pathological changes, yet detecting these changes during life has proven elusive. Positron emission tomography (PET) offers the potential for identifying such pathology. Few studies have been completed to date and their approaches and results have been diverse. It was the objective of this review to systematically examine relevant research using ligands for PET that bind to identified pathology in CTE. We focused on identification of patterns of binding and addressing gaps in knowledge of PET imaging for CTE. A comprehensive literature search was conducted. Data used were published on or before May 22, 2017. As the extant literature is limited, any peer-reviewed article assessing military, contact sports athletes, or professional fighters was considered for inclusion. The main outcomes were regional binding to brain regions identified through control comparisons or through clinical metrics (e.g., standardized uptake volume ratios). A total of 1207 papers were identified for review, of which six met inclusion criteria. Meta-analyses were planned but were deemed inappropriate given the small number of studies identified. Methodological concerns in these initial papers included small sample sizes, lack of a control comparison, use of nonstandard statistical procedures to quantify data, and interpretation of potentially off-target binding areas. Across studies, the hippocampi, amygdalae, and midbrain had reasonably consistent increased uptake. Evidence for increased uptake in cortical regions was less consistent. The evidence suggests that the field of PET imaging in those at risk for CTE remains nascent. As the field evolves to include more stringent studies, ligands for PET may prove an important tool in identifying CTE in vivo.

Interim PET Scans in Diffuse Large B-Cell Lymphoma: Is It Ready for Prime Time?

Prognostication of patients with diffuse large B-cell lymphoma (DLBCL) has improved in the past decade with a variety of clinical, morphologic, molecular, and radiographic methods. Comparable to data on the value of interim positron emission tomography (I-PET) in Hodgkin lymphoma, several retrospective and prospective studies are attempting to assess the value of I-PET scanning in DLBCL patients. In this review, we briefly describe and analyze the various prognostic methods in DLBCL with specific focus on the value of I-PET scanning in this disease. This is a timely analysis, as tailoring therapies based on prognosis at diagnosis are becoming of increased investigational interest.

(18)F-FDG PET scanning of abdominal aortic aneurysms and correlation with molecular characteristics: a systematic review

Purpose

The purpose of this study is to give an overview of studies investigating the role of fludeoxyglucose F18 (¹⁸F-FDG) positron emission tomography (PET) scanning in patients with aortic aneurysms with a focus on molecular characteristics of the aneurysm wall.

Methods

MEDLINE, EMBASE, and the Cochrane database were searched for relevant articles. After inclusion and exclusion, we selected 18 relevant articles reporting on ¹⁸F-FDG PET scanning of aortic aneurysms.

Results

The sample size of studies is limited, and there are no standardized imaging protocols and quantification methods. ¹⁸F-FDG PET scanning was shown to display molecular characteristics of the aortic wall. Different studies showed contradictory findings of aortic ¹⁸F-FDG uptake in aneurysm patients compared to controls.

Conclusions

Non-invasively determining molecular characteristics of aortic wall weakening might lead to better rupture and growth prediction. This might influence the decision of the surgeon between conservative and surgical treatment of aneurysms. To date, there is conflicted evidence regarding the use of ¹⁸F-FDG PET scanning to predict aneurysm rupture and growth. The role of ¹⁸F-FDG PET scanning in rupture risk prediction needs to be further investigated, and standardized imaging protocols and quantification methods need to be implemented.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-015-0153-8) contains supplementary material, which is available to authorized users.

Anxiety and depression: individual entities or two sides of the same coin?

Several factors have led to suggestions that anxiety and depression are actually the same disease: very frequently, they co-exist; there is an overlap of symptoms between the two conditions; a number of similar agents can be used to treat both mental states; the same neurotransmitters are involved in both anxiety and depressive disorders; and stress can predispose both. Selective serotonin reuptake inhibitors (SSRIs) have shown efficacy in a number of neuroses: depression; obsessive-compulsive disorder (OCD) and anxiety disorders (panic disorder [PD], social anxiety disorder [SAD], generalised anxiety disorder and post-traumatic stress disorder). Furthermore, other drugs, for example, tricyclic antidepressants and monoamine oxidase inhibitors, are effective in treating both depression and some anxiety disorders. Yet some drugs are only effective in anxiety, for example, benzodiazepines, and this suggests that the two states are actually different. Despite the broad range of conditions that are treated by SSRIs, a number of differences are clear when SSRIs are used in depressive and anxious states. When used in PD and OCD, the effective dose of the SSRI is often higher than when used to treat depression. Furthermore, SSRIs often work more slowly in patients with anxiety compared with those with depression. In order to assess which serotonergic pathways and mechanisms are involved in these conditions, tryptophan depletion tests can be performed. Tryptophan is the precursor to serotonin (5-HT), so if the SSRI treatment effects are dependent on an increase in synaptic 5-HT levels, depletion will result in a relapse in symptoms. However, if the SSRI treatment works through post-receptor events, then tryptophan depletion will have little effect on the individual's symptoms. In depression, tryptophan depletion induced relapse in patients treated and controlled on SSRIs, but not in those recovered on noradrenergic agents such as desipramine. In some anxious states (PD and SAD), our work has shown that relapse was also experienced following tryptophan depletion, indicating that the SSRIs are acting via increasing 5-HT levels at the synapse in these conditions. However, other studies have found no effect of the tryptophan depletion test. This suggests that in OCD, SSRIs act post-synaptically and therefore have a different mechanism of action in OCD patients compared with depressed patients. In summary, although most SSRIs are effective in the treatment of both depression and anxiety, differences in dose, time to onset of action and, in some cases, mechanism of action are evident when treating the two conditions.