Applications of positron emission tomography in the newborn nursery

Abnormal Nutritive Sucking as an Indicator of Neonatal Brain Injury

A term neonate is born with the ability to suck; this neuronal network is already formed and functional by 28 weeks gestational age and continues to evolve into adulthood. Because of the necessity of acquiring nutrition, the complexity of the neuronal network needed to suck, and neuroplasticity in infancy, the skill of sucking has the unique ability to give insight into areas of the brain that may be damaged either during or before birth. Interpretation of the behaviors during sucking shows promise in guiding therapies and how to potentially repair the damage early in life, when neuroplasticity is high. Sucking requires coordinated suck-swallow-breathe actions and is classified into two basic types, nutritive and non-nutritive. Each type of suck has particular characteristics that can be measured and used to learn about the infant's neuronal circuitry. Basic sucking and swallowing are present in embryos and further develop to incorporate breathing ex utero. Due to the rhythmic nature of the suck-swallow-breathe process, these motor functions are controlled by central pattern generators. The coordination of swallowing, breathing, and sucking is an enormously complex sensorimotor process. Because of this complexity, brain injury before birth can have an effect on these sucking patterns. Clinical assessments allow evaluators to score the oral-motor pattern, however, they remain ultimately subjective. Thus, clinicians are in need of objective measures to identify the specific area of deficit in the sucking pattern of each infant to tailor therapies to their specific needs. Therapeutic approaches involve pacifiers, cheek/chin support, tactile, oral kinesthetic, auditory, vestibular, and/or visual sensorimotor inputs. These therapies are performed to train the infant to suck appropriately using these subjective assessments along with the experience of the therapist (usually a speech therapist), but newer, more objective measures are coming along. Recent studies have correlated pathological sucking patterns with neuroimaging data to get a map of the affected brain regions to better inform therapies. The purpose of this review is to provide a broad scope synopsis of the research field of infant nutritive and non-nutritive feeding, their underlying neurophysiology, and relationship of abnormal activity with brain injury in preterm and term infants.

Dynamic TSPO-PET for assessing early effects of cerebral hypoxia and resuscitation in new born pigs

INTRODUCTION

Inflammation associated with microglial activation may be an early prognostic indicator of perinatal hypoxic ischemic injury, where translocator protein (TSPO) is a known inflammatory biomarker. This piglet study used dynamic TSPO-PET with [¹⁸F]GE180 to evaluate if microglial activation after global perinatal hypoxic injury could be detected.

METHODS

New born anesthetized pigs (n = 14) underwent hypoxia with fraction of inspired oxygen (FiO₂)0.08 until base excess -20 mmol/L and/or a mean arterial blood pressure decrease to 20 mm Hg, followed by resuscitation with FiO₂ 0.21 or 1.0. Three piglets served as controls and one had intracranial injection of lipopolysaccharide (LPS). Whole body [¹⁸F]GE180 Positron emission tomography-computed tomography (PET-CT) was performed repeatedly up to 32 h after hypoxia and resuscitation. Volumes of interest were traced in the basal ganglia, cerebellum and liver using MRI as anatomic correlation. Standardized uptake values (SUVs) were measured at baseline and four time-points, quantifying microglial activity over time. Statistical analysis used Mann Whitney- and Wilcoxon rank test with significance value set to p < 0.05.

RESULTS

At baseline (n = 5), mean SUVs ±1 standard deviation were 0.43 ± 0.10 and 1.71 ± 0.62 in brain and liver respectively without significant increase after hypoxia at the four time-points (n = 5-13/time point). Succeeding LPS injection, SUV increased 80% from baseline values.

CONCLUSIONS

Cerebral inflammatory response caused by severe asphyxia was not possible to detect with [¹⁸F]GE180 PET CT the first 32 h after hypoxia and only sparse hepatic uptake was revealed.

ADVANCES IN KNOWLEDGE

Early microglial activation as indicator of perinatal hypoxic ischemic injury was not detectable by TSPO-PET with [¹⁸F]GE180.

IMPLICATIONS FOR PATIENT CARE

TSPO-PET with [¹⁸F]GE180 might not be suitable for early detection of perinatal hypoxic ischemic brain injury.

Neonatal brain resting-state functional connectivity imaging modalities

Infancy is the most critical period in human brain development. Studies demonstrate that subtle brain abnormalities during this state of life may greatly affect the developmental processes of the newborn infants. One of the rapidly developing methods for early characterization of abnormal brain development is functional connectivity of the brain at rest. While the majority of resting-state studies have been conducted using magnetic resonance imaging (MRI), there is clear evidence that resting-state functional connectivity (rs-FC) can also be evaluated using other imaging modalities. The aim of this review is to compare the advantages and limitations of different modalities used for the mapping of infants' brain functional connectivity at rest. In addition, we introduce photoacoustic tomography, a novel functional neuroimaging modality, as a complementary modality for functional mapping of infants' brain.

Nuclear medicine of the cerebellum

Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) with different radiotracers enable regional evaluation of blood flow and glucose metabolism, of receptors and transporters of several molecules, and of abnormal deposition of peptides and proteins in the brain. The cerebellum has been used as a reference region for different radiotracers in several disease conditions. Whole-brain voxel-wise analysis is not affected by a priori knowledge bias and should be preferred. SPECT and PET have contributed to establishing the cerebellum role in motion, cognition, and emotion control in physiologic and pathophysiologic conditions. The basic abnormal imaging findings include decreased or increased uptake of flow or metabolism tracers in the cerebellum alone or as part of a network. Decreased uptake is generally observed in primary structural damage of the cerebellum, but can also represent a distant effect of cerebral damage (crossed diaschisis). Increased uptake can be observed in Freidreich ataxia, inflammatory or immune-mediated diseases of the cerebellum, and in status epilepticus. The possibility is also recognized that primary structural damage of the cerebellum might determine distance effects on other brain structures (reversed diaschisis). So far, SPECT and PET have been predominantly used in clinical studies to investigate cerebellar changes in neurologic and psychiatric diseases and in connection with pharmacologic, transcranial magnetic stimulation, deep-brain stimulation, or surgical treatments.

Relevance of urinary S100B protein levels as a short-term prognostic biomarker in asphyxiated infants treated with hypothermia

The initial diagnosis of neonatal hypoxic-ischemic encephalopathy is based on nervous system clinical manifestations. The use of biomarkers to monitor brain injury and evaluate neuroprotective effects allows early intervention and treatment. This study was designed to determine the short-term prognostic significance of urinary S100B calcium-binding protein (S100B) in asphyxiated newborns treated with hypothermia.An observational prospective study was conducted over a period of 5 years in 31 newborns with hypoxic-ischemic encephalopathy who received therapeutic hypothermia. The patients were divided into 2 groups: Group A (13 newborns with a normal neurological examination before discharge) and Group B (18 newborns who died during admission or had an abnormal neurologic examination before discharge). Urinary S100B was the main variable, serum S100B and neuron-specific enolase (NSE) were considered as secondary variables, and all of them were assessed on the first 3 days of life. The newborns were subsequently divided into groups with normal and abnormal electrophysiological and imaging findings.Mean urinary S100B levels were significantly higher in group B than group A on day 1 (10.58 ± 14.82 vs 4.65 ± 9.16 μg/L, P = .031) and day 2 (5.16 ± 7.63 vs 0.88 ± 2.53, P = .002). The optimal cutoff for urinary S100B on day 1 was >1.11 μg/L of (sensitivity, 100%; specificity 60%) for the prediction of neonatal death and < 0.66 μg/L (sensitivity 83% and specificity 70%) for the prediction of a normal neurological examination before discharge. It was not possible to calculate cutoffs with a similar accuracy for serum S100B or NSE. Urinary S100B on day 1 was higher in patients with abnormal magnetic resonance imaging findings (7.89 ± 8.09 vs 4.49 ± 9.14, P = .039) and abnormal positron emission tomography findings (8.60 ± 9.29 vs 4.30 ± 8.28, P = .038). There were no significant differences in S100B levels between patients with normal and abnormal electroencephalography results.Urinary S100B measured in the first days of life can predict neonatal death and short-term prognosis in asphyxiated newborns treated with hypothermia. The method is convenient, noninvasive, and has a higher sensitivity and specificity than measurement of serum S100B or NSE.

A 3D MR-acquisition scheme for nonrigid bulk motion correction in simultaneous PET-MR

PURPOSE

Positron emission tomography (PET) is a highly sensitive medical imaging technique commonly used to detect and assess tumor lesions. Magnetic resonance imaging (MRI) provides high resolution anatomical images with different contrasts and a range of additional information important for cancer diagnosis. Recently, simultaneous PET-MR systems have been released with the promise to provide complementary information from both modalities in a single examination. Due to long scan times, subject nonrigid bulk motion, i.e., changes of the patient's position on the scanner table leading to nonrigid changes of the patient's anatomy, during data acquisition can negatively impair image quality and tracer uptake quantification. A 3D MR-acquisition scheme is proposed to detect and correct for nonrigid bulk motion in simultaneously acquired PET-MR data.

METHODS

A respiratory navigated three dimensional (3D) MR-acquisition with Radial Phase Encoding (RPE) is used to obtain T1- and T2-weighted data with an isotropic resolution of 1.5 mm. Healthy volunteers are asked to move the abdomen two to three times during data acquisition resulting in overall 19 movements at arbitrary time points. The acquisition scheme is used to retrospectively reconstruct dynamic 3D MR images with different temporal resolutions. Nonrigid bulk motion is detected and corrected in this image data. A simultaneous PET acquisition is simulated and the effect of motion correction is assessed on image quality and standardized uptake values (SUV) for lesions with different diameters.

RESULTS

Six respiratory gated 3D data sets with T1- and T2-weighted contrast have been obtained in healthy volunteers. All bulk motion shifts have successfully been detected and motion fields describing the transformation between the different motion states could be obtained with an accuracy of 1.71 ± 0.29 mm. The PET simulation showed errors of up to 67% in measured SUV due to bulk motion which could be reduced to less than 10% with the proposed motion compensation approach.

CONCLUSIONS

A MR acquisition scheme which yields both high resolution 3D anatomical data and highly accurate nonrigid motion information without an increase in scan time is presented. The proposed method leads to a strong improvement in both MR and PET image quality and ensures an accurate assessment of tracer uptake.

Assessing the early changes of cerebral glucose metabolism via dynamic (18)FDG-PET/CT during cardiac arrest

To study the changes of cerebral glucose metabolism (CGM) during the phase of return of spontaneous circulation (ROSC) after cardiac arrest (CA), we used 18-fluorodeoxyglucose-positron emission tomography/computed tomography ((18)FDG-PET/CT) to measure the CGM changes in six beagle canine models. After the baseline (18)FDG-PET/CT was recorded, ventricular fibrillation (VF) was induced for 6 min, followed by close-chest cardiopulmonary resuscitation (CPR) in conjunction with intravenous (IV) administration of epinephrine and external defibrillator shocks until ROSC was achieved, within 30 min. The (18)FDG was recorded prior to intravenous administration at 0 h (baseline), and at 4, 24, and 48 h after CA with ROSC. We evaluated the expression of two key control factors in canine CGM, hexokinase I (HXK I) and HXK II, by immunohistochemistry at the four above mentioned time points. Electrically induced VF of 6 min duration was successfully induced in the dogs. Resuscitation was then performed to maintain blood pressure stability. Serial (18)FDG-PET/CT scans found that the CGM decreased at 4 h after ROSC and remained lower than the baseline even at 48 h. The expression of HXK I and II levels were consistent with the changes in CGM. These data from our present work showed that (18)FDG-PET/CT imaging can be used to detect decreased CGM during CA and was consistent with the results of CMRgl. Furthermore, there were also concomitant changes in the expression of HXK I and HXK II. The decrease in CGM may be an early sign of hyperacute global cerebral ischemia.

A clinical study of autologous bone marrow mononuclear cells for cerebral palsy patients: a new frontier

Cerebral palsy is a nonprogressive heterogeneous group of neurological disorders with a growing rate of prevalence. Recently, cellular therapy is emerging as a potential novel treatment strategy for cerebral palsy. The various mechanisms by which cellular therapy works include neuroprotection, immunomodulation, neurorestoration, and neurogenesis. We conducted an open label, nonrandomized study on 40 cases of cerebral palsy with an aim of evaluating the benefit of cellular therapy in combination with rehabilitation. These cases were administered autologous bone marrow mononuclear cells intrathecally. The follow-up was carried out at 1 week, 3 months, and 6 months after the intervention. Adverse events of the treatment were also monitored in this duration. Overall, at six months, 95% of patients showed improvements. The study population was further divided into diplegic, quadriplegic, and miscellaneous group of cerebral palsy. On statistical analysis, a significant association was established between the symptomatic improvements and cell therapy in diplegic and quadriplegic cerebral palsy. PET-CT scan done in 6 patients showed metabolic improvements in areas of the brain correlating to clinical improvements. The results of this study demonstrate that cellular therapy may accelerate the development, reduce disability, and improve the quality of life of patients with cerebral palsy.

Evaluation of mild hypothermia therapy for neonatal hypoxic-ischaemic encephalopathy on brain energy metabolism using 18F-fluorodeoxyglucose positron emission computed tomography

It remains unclear whether mild hypothermia affects energy metabolism in the brain tissue of newborns with hypoxic-ischaemic encephalopathy (HIE). The current study aimed to investigate the effect of mild hypothermia on energy metabolism in neonatal HIE and assess brain energy metabolism using position emission tomography/computed tomography (PET/CT) scanning. The mean standardised uptake values of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) were used to determine the glucose metabolic rate in various brain anatomical regions, including the thalamus, basal ganglia and the frontal, parietal and occipital lobes. The rate of glucose metabolism significantly improved following treatment with mild hypothermia therapy and conventional therapy (P<0.001). Prior to the treatment, no significant differences were identified between the groups (P>0.05). Following treatment, the rate of glucose metabolism was significantly improved in the mild hypothermia therapy group compared with that in the conventional therapy group (P<0.001). Thus, these results indicate that mild hypothermia therapy effectively promotes the recovery of patients with neonatal HIE. ¹⁸F-FDG PET/CT scanning may be used to provide reference values for the assessment of energetic metabolism in patients with neonatal HIE.

Nanomedicine in cerebral palsy

Cerebral palsy is a chronic childhood disorder that can have diverse etiologies. Injury to the developing brain that occurs either in utero or soon after birth can result in the motor, sensory, and cognitive deficits seen in cerebral palsy. Although the etiologies for cerebral palsy are variable, neuroinflammation plays a key role in the pathophysiology of the brain injury irrespective of the etiology. Currently, there is no effective cure for cerebral palsy. Nanomedicine offers a new frontier in the development of therapies for prevention and treatment of brain injury resulting in cerebral palsy. Nanomaterials such as dendrimers provide opportunities for the targeted delivery of multiple drugs that can mitigate several pathways involved in injury and can be delivered specifically to the cells that are responsible for neuroinflammation and injury. These materials also offer the opportunity to deliver agents that would promote repair and regeneration in the brain, resulting not only in attenuation of injury, but also enabling normal growth. In this review, the current advances in nanotechnology for treatment of brain injury are discussed with specific relevance to cerebral palsy. Future directions that would facilitate clinical translation in neonates and children are also addressed.

Reversible lactic acidosis in a newborn with thiamine transporter-2 deficiency

Thiamine transporter-2 deficiency is a recessive disease caused by mutations in the SLC19A3 gene. Patients manifest acute episodes of encephalopathy; symmetric lesions in the cortex, basal ganglia, thalami or periaqueductal gray matter, and a dramatic response to biotin or thiamine. We report a 30-day-old patient with mutations in the SLC19A3 gene who presented with acute encephalopathy and increased level of lactate in the blood (8.6 mmol/L) and cerebrospinal fluid (7.12 mmol/L), a high excretion of α-ketoglutarate in the urine, and increased concentrations of the branched-chain amino acids leucine and isoleucine in the plasma. MRI detected bilateral and symmetric cortico-subcortical lesions involving the perirolandic area, bilateral putamina, and medial thalami. Some lesions showed low apparent diffusion coefficient values suggesting an acute evolution; others had high values likely to be subacute or chronic, most likely related to the perinatal period. After treatment with thiamine and biotin, irritability and opisthotonus disappeared, and the patient recovered consciousness. Biochemical disturbances also disappeared within 48 hours. After discontinuing biotin, the patient remained stable for 6 months on thiamine supplementation (20 mg/kg/day). The examination revealed subtle signs of neurologic sequelae, and MRI showed necrotic changes and volume loss in some affected areas. Our observations suggest that patients with thiamine transporter 2 deficiency may be vulnerable to metabolic decompensation during the perinatal period, when energy demands are high. Thiamine defects should be excluded in newborns and infants with lactic acidosis because prognosis largely depends on the time from diagnosis to thiamine supplementation.

Dynamic FDG PET for assessing early effects of cerebral hypoxia and resuscitation in new-born pigs

PURPOSE

Changes in cerebral glucose metabolism may be an early prognostic indicator of perinatal hypoxic-ischaemic injury. In this study dynamic ¹⁸F-FDG PET was used to evaluate cerebral glucose metabolism in piglets after global perinatal hypoxia and the impact of the resuscitation strategy using room air or hyperoxia.

METHODS

New-born piglets (n = 16) underwent 60 min of global hypoxia followed by 30 min of resuscitation with a fraction of inspired oxygen (FiO₂) of 0.21 or 1.0. Dynamic FDG PET, using a microPET system, was performed at baseline and repeated at the end of resuscitation under stabilized haemodynamic conditions. MRI at 3 T was performed for anatomic correlation. Global and regional cerebral metabolic rates of glucose (CMRgl) were assessed by Patlak analysis for the two time-points and resuscitation groups.

RESULTS

Global hypoxia was found to cause an immediate decrease in cerebral glucose metabolism from a baseline level (mean ± SD) of 21.2 ± 7.9 to 12.6 ± 4.7 μmol/min/ 100 g (p <0.01). The basal ganglia, cerebellum and cortex showed the greatest decrease in CMRgl but no significant differences in global or regional CMRgl between the resuscitation groups were found.

CONCLUSION

Dynamic FDG PET detected decreased cerebral glucose metabolism early after perinatal hypoxia in piglets. The decrease in CMRgl may indicate early changes of mild cerebral hypoxia-ischaemia. No significant effect of hyperoxic resuscitation on the degree of hypometabolism was found in this early phase after hypoxia. Cerebral FDG PET can provide new insights into mechanisms of perinatal hypoxic- ischaemic injury where early detection plays an important role in instituting therapy.

Umbilical cord blood mononuclear cell transplantation for neonatal hypoxic-ischemic encephalopathy

Despite recent advances in the treatment of neonatal hypoxic-ischemic encephalopathy (HIE) using therapeutic hypothermia, at least 30% of the cooled infants will die or have moderate/severe neurological disability. Umbilical cord blood cells (UCBCs), which are readily available at birth, have been shown to reduce sensorimotor and/or cognitive impairments in several models of brain damage, representing a promising option for the treatment of neurological diseases. In this review, we discuss recent preclinical studies that assessed the effects of UCBC transplantation in the Rice-Vannucci animal model of HIE. We also review the possible cell types and mechanisms involved in the therapeutic effect of UCBC transplantation, including neuroprotection, immunomodulation, and stimulation of neural plasticity and regeneration. In addition, we discuss how neuroimaging methods, such as bioluminescence imaging, nuclear-medicine imaging, or magnetic resonance imaging, could be used to evaluate the biodistribution of UCBCs in both preclinical and clinical studies.