[18F]fluorodeoxyglucose uptake in neonatal acute lung injury measured by positron emission tomography

A longitudinal study of FDG-PET in Crohn disease patients receiving granulocyte/monocyte apheresis therapy

BACKGROUND AIMS

Endoscopy is the gold standard for the diagnosis and follow-up of patients with Crohn disease (CD). However, a less invasive approach is now being sought for the management of these patients. The objective of this study was to examine whether (18)F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) might be relevant for monitoring the disease activity in CD patients undergoing granulocyte/monocyte apheresis (GMA).

METHODS

This study was conducted in 12 patients with CD who were receiving treatment with 10 once-a-week GMA sessions with the Adacolumn. The response to treatment was monitored by measuring standard laboratory variables, Crohn's Disease Activity Index (CDAI) score, International Organization for the Study of Inflammatory Bowel Diseases (IOIBD) score, and regional and global bowel uptakes on FDG-PET.

RESULTS

In 6 of the 12 patients, significant improvement of the CDAI was observed after the final session of GMA. The patients who showed clinical response to GMA had a decrease in the regional and global bowel uptakes on FDG-PET, whereas those who did not respond showed no change. In the patients who responded to the GMA, the decrease in regional bowel uptake on FDG-PET in each disease area of the same patient varied in parallel. There was a significant correlation between decrease in the global bowel uptake on FDG-PET and improvement of the CDAI and IOIBD scores.

CONCLUSIONS

The longitudinal changes in FDG-PET uptakes are of potential clinical interest for assessing the regional and global bowel disease activity in CD patients undergoing GMA therapy.

Monitoring Lung Volumes During Mechanical Ventilation

Respiratory inductive plethysmography (RIP) is a non-invasive method of measuring change in lung volume which is well-established as a monitor of tidal ventilation and thus respiratory patterns in sleep medicine. As RIP is leak independent, can measure end-expiratory lung volume as well as tidal volume and is applicable to both the ventilated and spontaneously breathing patient, there has been a recent interest in its use as a bedside tool in the intensive care unit.

Positron emission tomography: a tool for better understanding of ventilator-induced and acute lung injury

PURPOSE OF REVIEW

PET has recently gained traction among several groups of investigators as an imaging tool to study lung pathophysiology in vivo noninvasively on a regional basis. This review aims to present the major findings of PET studies on acute lung injury (ALI) and ventilator-induced lung injury (VILI) with a perspective relevant to the physiologist-intensivist.

RECENT FINDINGS

Using various tracers, PET has been used to investigate the relationship between the distributions of pulmonary perfusion, ventilation and aeration, and the effect of positive end-expiratory pressure, recruitment maneuvers, prone positioning, and endotoxin on these distributions in ALI. More recently, PET with 2-[18F]fluoro-2-deoxy-D-glucose has been used to measure regional neutrophil metabolic activation in ALI and VILI. Because gas exchange impairment and inflammation are two hallmarks of ALI and VILI, these studies have provided significant insights into the pathophysiology of these conditions.

SUMMARY

PET is a versatile imaging tool for physiologic investigation. By imaging the regional effects of interventions commonly performed in critically ill patients with ALI, PET has improved our understanding of the mechanism by which such interventions can exert their positive or negative effects as well as of the pathophysiology of ALI and VILI.

Regulation of lipopolysaccharide-induced increases in neutrophil glucose uptake

The pathogenesis of many lung diseases involves neutrophilic inflammation. Neutrophil functions, in turn, are critically dependent on glucose uptake and glycolysis to supply the necessary energy to meet these functions. In this study, we determined the effects of p38 mitogen-activated protein kinase and hypoxia-inducible factor (HIF)-1, as well as their potential interaction, on the expression of membrane glucose transporters and on glucose uptake in murine neutrophils. Neutrophils were harvested and purified from C57BL/6 mice and stimulated with lipopolysaccharide (LPS) in the presence or absence of specific p38 and HIF-1 inhibitors. Glucose uptake was measured as the rate of [3H]deoxyglucose (DG) uptake. We identified GLUT-1 in mouse neutrophils, but neither GLUT-3 nor GLUT-4 were detected using Western blot analysis, even after LPS stimulation. LPS stimulation did not increase GLUT-1 protein levels but did cause translocation of GLUT-1 from the cell interior to the cell surface, together with a dose-dependent increase in [3H]DG uptake, indicating that glucose uptake is regulated in these cells. LPS also activated both p38 and the HIF-1 pathway. Inhibitors of p38 and HIF-1 blocked GLUT-1 translocation and [3H]DG uptake. These data suggest that LPS-induced increases in neutrophil glucose uptake are mediated by GLUT-1 translocation to the cell surface in response to sequential activation of neutrophil p38 and HIF-1alpha in neutrophils. Given that neutrophil function and glucose metabolism are closely linked, control of the latter may represent a new target to ameliorate the deleterious effects of neutrophils on the lungs.

FDG-PET imaging of pulmonary inflammation in healthy volunteers after airway instillation of endotoxin

Recent studies indicate that a focal, limited, inflammatory response can be safely elicited after direct bronchial instillation of small doses of endotoxin into a single lung segment. Because the radiotracer [18F]fluorodeoxyglucose ([18F]FDG) is taken up at accelerated rates within inflamed tissues, we hypothesized that we could detect and quantify this regional inflammatory response with positron emission tomography (PET). We imaged 18 normal volunteers in a dose-escalation study with 3 endotoxin dosing groups ( n = 6 in each group): 1 ng/kg, 2 ng/kg, and 4 ng/kg. Endotoxin was instilled by bronchoscopy into a segment of the right middle lobe, with imaging performed ∼24 h later, followed by bronchoalveolar lavage (BAL). A “subtraction imaging analysis” was performed in the highest dose cohort to identify the area of inflammation, using the preendotoxin scan as a baseline. BAL neutrophil counts were significantly higher in the highest dose group compared with the other two groups (1,413 ± 625 vs. 511 ± 396 and 395 ± 400 cells/mm3; P < 0.05). Autoradiography performed on cells harvested by BAL showed specific [3H]deoxyglucose ([3H]DG) uptake limited to neutrophils. In vitro [3H]DG uptake in BAL neutrophils in the 4 ng/kg dose group (but not in the 2 ng/kg group) was statistically greater than in peripheral blood neutrophils obtained before endotoxin instillation. The rate of [18F]FDG uptake was greatest in the 4 ng/kg group, with a consistent, statistically significant increase in the rate of uptake after endotoxin instillation compared with baseline. We conclude that the inflammatory response to low-dose endotoxin in a single lung segment can be visualized and quantified by imaging with FDG-PET.

Molecular imaging of lung glucose uptake after endotoxin in mice

Positron emission tomographic imaging after administration of the glucose analog fluorine-18 fluorodeoxyglucose ([18F]FDG) may be useful to study neutrophilic inflammation of the lungs. In this study, we sought to determine the specificity of the increase in lung [18F]FDG uptake after intraperitoneal endotoxin (Etx) for neutrophil influx into mouse lungs and to determine the regulation of glucose uptake after Etx by Toll-like receptors (TLRs) and TNF-α. Lung tissue radioactivity measurements by imaging were validated against counts in a gamma well counter. Glucose uptake was quantified as the [18F]FDG tissue-to-blood radioactivity ratio (TBR) after validating this measure against the “gold standard” measure of glucose uptake, the “net influx rate constant.” TBR measurements were made in a control group (no intervention), a group administered Etx, and a group administered Etx plus an additional agent (e.g., vinblastine) or Etx administered to a mutant mouse strain. The glucose uptake measurements were compared with measurements of myeloperoxidase. Increases in TBR after Etx were significantly but not completely eliminated by neutrophil depletion with vinblastine. Increases in TBR after Etx were consistent with signaling via either TLR-4 or TLR-2 (the latter probably secondary to peptidoglycan contaminants in Etx preparation) and were decreased by drug inhibition of TLR-4 but not by inhibition of TNF-α. Thus molecular imaging can be used to noninvasively monitor biological effects of Etx on lungs in mice, and changes in lung glucose uptake can be used to monitor effects of anti-inflammatory agents. Such imaging capacity provides a powerful new paradigm for translational “mouse-to-human” pulmonary research.

Positron emission tomography in the investigation of pediatric inflammatory bowel disease

BACKGROUND

Endoscopic and radiologic studies are frequently required in inflammatory bowel disease (IBD) to determine disease activity, extent of disease, and delineating disease type. Positron emission tomography (PET) using fluorine-18-fluoro-deoxyglucose to identify metabolically active tissues may offer a simple noninvasive alternative to conventional studies in identification and localization of active intestinal inflammation in children with IBD. The aim of this study was to assess the value of PET in identifying active intestinal inflammation compared with conventional endoscopic and radiologic studies, including small bowel follow-through and colonoscopy.

METHODS

Sixty-five children were enrolled in the study. This included 55 children (mean age, 13.3 yr; range, 7-18 yr; 20 girls) with newly diagnosed IBD (37) or symptoms suggestive of recurrent disease (18) and 10 children with recurrent abdominal pain (mean age, 12.7 yr; range, 8-15 yr; 7 girls) who were studied with PET, and the results were compared with small bowel follow-through with pneumocolon and/or colonoscopy. Thirty-eight patients had Crohn's disease (17 ileal, 12 ileocolic, 5 pancolonic, 3 left-sided disease, 1 right-sided disease), and 17 had ulcerative colitis (15 pan-colitis, 2 left-sided colitis). Mean time interval between PET and other studies was 30 +/- 17.6 days.

RESULTS

PET correctly identified active inflammatory disease in 80% of children with IBD (81.5% with Crohn's disease; 76.4% with ulcerative colitis) and correctly showed no evidence of inflammation in children with recurrent abdominal pain. Gluorine-18-fluoro-deoxyglucose accumulated at sites that corresponded with active disease at colonoscopy in 83.8% of patients and with small bowel follow-through with pneumocolon 75.0% of the time.

CONCLUSION

This study suggests that PET offers a noninvasive tool for identifying and localizing active intestinal inflammation in children with IBD. PET may not be able to replace conventional studies; however, it may be useful when conventional studies cannot be performed or fail to be completed.

Positive end-expiratory pressure above lower inflection point minimizes influx of activated neutrophils into lung*

OBJECTIVES

To compare the effects of low vs. high tidal volume (Vt) with three positive end-expiratory pressure (PEEP) strategies on activated neutrophil influx into the lung.

DESIGN

Prospective, randomized controlled animal study.

SETTING

Animal laboratory in a university hospital.

SUBJECTS

Newborn piglets.

INTERVENTIONS

Surfactant-depleted piglets were randomized in littermate pairs; to PEEP of either 0 (zero end-expiratory pressure [ZEEP]; n = 6), 8 cm H2O (PEEP 8; n = 5), or 1 cm H2O above the lower inflection point (LIP) (PEEP>LIP; n = 6). Within each pair piglets were randomized to a low VT (5-7 mL/kg) or high VT strategy (17-19 mL/kg). After 4 hrs of mechanical ventilation, 18-fluorodeoxyglucose (18FDG) was injected and positron emission tomography scanning was performed.

MEASUREMENTS AND MAIN RESULTS

VT and PEEP changes on influx constants of 18FDG were assessed by analysis of variance. A within-litter comparison of Vt was nonsignificant (p = .50). A between-litter comparison, ordered in linear trend rank, from ZEEP, to PEEP 8, to PEEP>LIP, showed a strong effect of PEEP on influx constant (p = .019).

CONCLUSIONS

PEEP set above the LIP on the inspiratory limb of the pressure-volume curve affords a stronger lung protection than VT strategy.

F-18 FDG PET/CT in Acute Respiratory Distress Syndrome: A Case Report

F-18 FDG PET/CT has become a useful technique in the evaluation of pulmonary lesions. We present a case of markedly increased and diffuse pulmonary F-18 FDG activity in a patient with acute respiratory distress syndrome (ARDS). High rates of glucose utilization by the inflammatory cells involved in the pathogenesis of ARDS might explain the increased pulmonary F-18 FDG uptake we observed. In the proper clinical setting, ARDS should be considered in the differential diagnosis of patients with diffusely increased F-18 FDG activity in the lungs.

Molecular imaging for pediatric lung diseases

Molecular imaging is a rapidly developing multidisciplinary field that combines advances in contrast agent development, instrumentation, and molecular/cell biology to follow cellular and sub-cellular events in intact organisms. Platforms for molecular imaging include radionuclide-based methods, optical methods, and magnetic resonance. To date, molecular imaging studies of the lungs have been used to monitor the effectiveness of gene transfer, neutrophilic inflammation, and cell trafficking. Eventually, the goal will be to translate these new techniques to clinical settings such as cystic fibrosis.

Pulmonary fluorodeoxyglucose uptake in infants of very low birth weight with and without intrauterine inflammation

OBJECTIVE

We compared early pulmonary (18)fluorodeoxyglucose ((18)FDG) uptake in infants who had very low birth weight with and without exposure to intrauterine inflammation by using positron emission tomography (PET). A secondary goal was to correlate (18)FDG uptake with later death or bronchopulmonary dysplasia.

METHODS

Within 72 hours of birth, 22 singleton infants between 25 and 30 weeks of gestation had a thoracic PET scan after intravenous (18)FDG. Influx constants (K(i)) for (18)FDG were determined. Placental histology assessed exposure to intrauterine inflammation.

RESULTS

Chorioamnionitis was found in 13 infants. Seven of these infants also had evidence of funisitis. No inflammation was detected in the remaining nine infants. Median (minimum, maximum) thoracic K(I) was 0.008 (0.006, 0.011) mL/min/mL in infants with funisitis, 0.006 (0.002, 0.008) in infants with chorioamnionitis only, and 0.006 (0.001, 0.015) in infants with no evidence of intrauterine inflammation (P=.16). No relation was found between K(i) and later death or bronchopulmonary dysplasia. Cord blood interleukin-6 was elevated in newborns with placental inflammation (P=.014).

CONCLUSION

Early thoracic PET scanning for metabolically active inflammatory cells does not differ between infants with and without exposure to intrauterine inflammation. Evidence of early intrapulmonary sequestration of inflammatory cells in some infants without chorioamnionitis points to the complex etiology of postnatal inflammation.

Absorbed dose to very low birth weight infants from 18F-fluorodeoxyglucose

The radiation absorbed dose to very low birth weight infants from 18F-fluorodeoxyglucose was investigated. Ten newborns undergoing clinical positron tomography lung imaging were included in this study. Two consecutive 45-min dynamic scans immediately following intravenous injection of fluorodeoxyglucose were acquired; the first was over the head, and the second was over the chest. Time-activity curves were generated for the brain, heart wall, lungs, and, when visible, the kidneys. The cumulated activity measurements obtained were for the entire organ masses; these masses were much smaller than the corresponding organ masses for the newborn mathematical model. Patient-specific dosimetry yielded average doses of 2.5 x 10(-1) mGy MBq(-1) for the brain, 6.8 x 10(-1) mGy MBq(-1) for the heart wall, 2.2 x 10(-1) mGy MBq(-1) for the kidneys, and 4.4 x 10(-1) mGy MBq(-1) for the lungs. The effective dose was estimated to be 2.1 x 10(-1) mSv MBq(-1), which is half that previously published for newborns but still an order of magnitude higher than that for adults.

Measuring total and regional lung deposition using inhaled radiotracers

The delivery of an inhaled drug to the lungs can be measured by adding a gamma-emitting radiotracer to the formulation and using two-dimensional planar imaging or three-dimensional single photon emission computerized tomography (SPECT) to provide detailed information on lung deposition. The isotope most commonly used is the low energy (140 KeV) isotope, 99m technetium. Radiolabeling techniques have been successfully developed for use with nebulizers, pressurized metered dose inhalers (pMDIs), and dry powder inhaler formulations (DPI), and to investigate drug delivery to the respiratory tract for a variety of drug formulations and patient populations. However, for pMDIs and DPIs, the radiotracer is usually only physically associated with, rather than chemically bound, to the drug. Therefore, once deposited, the radiotracer may disassociate from the drug and cannot be used to track its subsequent fate; however, incorporation of a radiotracer directly into the drug molecule can overcome this. By using positron emitters such as 11carbon or 18fluorine it is possible to generate three-dimensional images of the drug in the lung using positron emission tomography (PET) scanning, which has a higher resolution and is more accurate than SPECT. Labeling drugs with PET emitters is more complex as the drug molecule must first be synthesized to contain the radioactive isotope before the drug is formulated for the inhaler. As with gamma-scintigraphy, PET scanning can be used to investigate physiological changes in the lung following therapeutic intervention, but as biological radiotracers are used, functional images (i.e., of the drug's uptake and metabolism) can also be obtained.

Measurement of protein flux with positron emission tomography in neonates

AIM

To determine whether abnormal transvascular protein flux can be measured with positron emission tomography (PET) in neonates with respiratory distress syndrome (RDS).

METHODS

Fourteen infants with normal gas exchange (non-RDS group) underwent one PET measurement and 12 infants with RDS (the RDS group) underwent two measurements of protein flux, as determined by the pulmonary transcapillary escape rate for 68Gallium labelled transferrin (PTCER).

RESULTS

The mean PTCER for the RDS infants (132 +/- 39 10(-4)/min) was significantly greater than that for infants without RDS (75 +/- 27 10(-4)/min). PTCER did not change between measurements in the infants with RDS, including five who received and responded to surfactant replacement between the two scans.

CONCLUSIONS

Increased transvascular flux of large molecular weight proteins complicates RDS in preterm infants. PET provides a tool with which to evaluate the processes that contribute to pulmonary dysfunction in neonates.

Heparin improves gas exchange during experimental acute lung injury in newborn piglets

Although intrapulmonary fibrin deposition is a pathognomonic feature of acute lung injury, it remains uncertain whether thrombin inhibitors affect clinically important outcomes. We hypothesized that both heparin and antithrombin (AT) concentrate improve gas exchange during experimental respiratory distress syndrome. We also tested whether combination therapy is more beneficial than monotherapy. Forty-eight newborn piglets were randomized within 12 litters to one of four groups in a factorial design: (1) AT; (2) heparin; (3) AT plus heparin; (4) untreated control animals. After lung lavage and 4 h of barovolutrauma, mechanical ventilation was continued for 24 h during which ventilator pressures and inspired oxygen were adjusted to maintain normal blood gases. The arterial/ alveolar oxygen tension ratio (a/A ratio) and the ventilator efficiency index (VEI) at 18 and 24 h were compared by repeated measures analysis of variance (ANOVA). In contrast to our hypothesis, only heparin improved gas exchange, and we found little evidence of an interaction with AT. The a/A ratio was 0.48 +/- 0.27 (mean +/- SD) in the presence of heparin versus 0.33 +/- 0.26 in its absence; p = 0.01. Corresponding VEI was 0.30 +/- 0.12 versus 0.25 +/- 0.14; p = 0.04. Hyaline membrane formation was also decreased in heparin-treated animals (p = 0.02).