Cystic Fibrosis
Fenretinide inhibits vitamin A formation from β-carotene and regulates carotenoid levels in mice
Biochim Biophys Acta Mol Cell Biol Lipids. 2021 Nov 4:159070. doi: 10.1016/j.bbalip.2021.159070. Online ahead of print.
ABSTRACT
N-[4-hydroxyphenyl]retinamide, commonly known as fenretinide, a synthetic retinoid with pleiotropic benefits for human health, is currently utilized in clinical trials for cancer, cystic fibrosis, and COVID-19. However, fenretinide reduces plasma vitamin A levels by interacting with retinol-binding protein 4 (RBP4), which often results in reversible night blindness in patients. Cell culture and in vitro studies show that fenretinide binds and inhibits the activity of β-carotene oxygenase 1 (BCO1), the enzyme responsible for endogenous vitamin A formation. Whether fenretinide inhibits vitamin A synthesis in mammals, however, remains unknown. The goal of this study was to determine if the inhibition of BCO1 by fenretinide affects vitamin A formation in mice fed β-carotene. Our results show that wild-type mice treated with fenretinide for ten days had a reduction in tissue vitamin A stores accompanied by a two-fold increase in β-carotene in plasma (P < 0.01) and several tissues. These effects persisted in RBP4-deficient mice and were independent of changes in intestinal β-carotene absorption, suggesting that fenretinide inhibits vitamin A synthesis in mice. Using BCO1-/- and BCO2-/- mice we also show that fenretinide regulates intestinal carotenoid and vitamin E uptake by activating vitamin A signaling during short-term vitamin A deficiency. This study provides a deeper understanding of the impact of fenretinide on vitamin A, carotenoid, and vitamin E homeostasis, which is crucial for the pharmacological utilization of this retinoid.
PMID:34742949 | DOI:10.1016/j.bbalip.2021.159070
Mental status changes during elexacaftor/tezacaftor / ivacaftor therapy
J Cyst Fibros. 2021 Nov 3:S1569-1993(21)02104-4. doi: 10.1016/j.jcf.2021.10.002. Online ahead of print.
ABSTRACT
Elexacaftor/tezacaftor/ivacaftor (ELX/TEZ/IVA, Trikafta) is the newest Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) modulator drug approved by the Food and Drug Administration. Post-marketing reports with earlier CFTR modulators suggest these medications can impact mood, and in clinical trials an adverse effect of headache was reported with all currently approved CFTR modulators. However, there are no other documented reports of mental status changes during clinical trials or in post-marketing reports with elexacaftor/tezacaftor/ivacaftor. In this case series, we describe 6 patients who reported "mental fogginess" or other mental status changes shortly after initiation of this drug. The mechanism of this patient-reported side effect is still unclear. All patients noticed a change within the first 3 months of therapy. The management differed in each case, with all four cystic fibrosis (CF) care teams utilizing a patient-centered decision-making approach to address this concern.
PMID:34742667 | DOI:10.1016/j.jcf.2021.10.002
Chronic respiratory diseases other than asthma in children: the COVID-19 tsunami
Ital J Pediatr. 2021 Nov 6;47(1):220. doi: 10.1186/s13052-021-01155-9.
ABSTRACT
Coronavirus disease 2019 (COVID-19) affects all components of the respiratory system, including the neuromuscular breathing apparatus, conducting and respiratory airways, pulmonary vascular endothelium, and pulmonary blood flow. In contrast to other respiratory viruses, children have less severe symptoms when infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A minority of children experience a post-infectious inflammatory syndrome, the pathology and long-term outcomes of which are poorly understood. The reason for the lower burden of symptomatic disease in children is not yet clear, but several pathophysiological characteristics are postulated. The SARS-CoV-2 pandemic has brought distinct challenges to the care of children globally. Proper recommendations have been proposed for a range of non-asthmatic respiratory disorders in children, including primary ciliary dyskinesia and cystic fibrosis. These recommendations involve the continuation of the treatment during this period and ways to maintain stability. School closures, loss of follow-up visit attendance, and loss of other protective systems for children are the indirect outcomes of measures to mitigate the COVID-19 pandemic. Moreover, COVID-19 has reshaped the delivery of respiratory care in children, with non-urgent and elective procedures being postponed, and distancing imperatives have led to rapid scaling of telemedicine. The pandemic has seen an unprecedented reorientation in clinical trial research towards COVID-19 and a disruption in other trials worldwide, which will have long-lasting effects on medical science. In this narrative review, we sought to outline the most recent findings on the direct and indirect effects of SARS-CoV-2 pandemic on pediatric respiratory chronic diseases other than asthma, by critically revising the most recent literature on the subject.
PMID:34742332 | DOI:10.1186/s13052-021-01155-9
Role for animal models in understanding essential fatty acid deficiency in cystic fibrosis
Cell Mol Life Sci. 2021 Nov 5. doi: 10.1007/s00018-021-04014-2. Online ahead of print.
ABSTRACT
Essential fatty acid deficiency has been observed in most patients with Cystic Fibrosis (CF); however, pancreatic supplementation does not restore the deficiency, suggesting a different pathology independent of the pancreas. At this time, the underlying pathological mechanisms are largely unknown. Essential fatty acids are obtained from the diet and processed by organs including the liver and intestine, two organs significantly impacted by mutations in the cystic fibrosis transmembrane conductance regulator gene (Cftr). There are several CF animal models in a variety of species that have been developed to investigate molecular mechanisms associated with the CF phenotype. Specifically, global and systemic mutations in Cftr which mimic genotypic changes identified in CF patients have been generated in mice, rats, sheep, pigs and ferrets. These mutations produce CFTR proteins with a gating defect, trafficking defect, or an absent or inactive CFTR channel. Essential fatty acids are critical to CFTR function, with a bidirectional relationship between CFTR and essential fatty acids proposed. Currently, there are limited analyses on the essential fatty acid status in most of these animal models. Of interest, in the mouse model, essential fatty acid status is dependent on the genotype and resultant phenotype of the mouse. Future investigations should identify an optimal animal model that has most of the phenotypic changes associated with CF including the essential fatty acid deficiencies, which can be used in the development of therapeutics.
PMID:34741185 | DOI:10.1007/s00018-021-04014-2
Treating nontuberculous mycobacteria in children with cystic fibrosis: a multicentre retrospective study
Arch Dis Child. 2021 Nov 5:archdischild-2021-322177. doi: 10.1136/archdischild-2021-322177. Online ahead of print.
ABSTRACT
BACKGROUND: Respiratory infection with nontuberculous mycobacteria (NTM) in children with cystic fibrosis (CF) has increased in prevalence. The condition is difficult to diagnose and treatments are complex with limited evidence to guide practice. This study describes the approaches to diagnosis, management and consequences of treatment in a multicentre cohort of children with CF in the UK.
METHODS: Retrospective data were collected from 11 CF specialist centres from patients less than 17 years old, treated for NTM infection between 2006 and 2017. Descriptive statistics were used to describe the clinical characteristics of children treated. Treatment regimens, adverse events and success of treatment, with respect to lung function and culture conversion, were evaluated.
RESULTS: Data from 70 patients treated for NTM pulmonary disease were collated (60 Mycobacterium abscessus complex (MABSC); 10 M. avium complex (MAC)). Older age and previous diagnosis of allergic bronchopulmonary aspergillosis were all significantly associated with NTM. There was a wide variance in drug choice and side effects were reported with all agents. NTM eradication occurred in 80% of patients with MAC and 48% with MABSC, with variable outcomes on lung function.
CONCLUSIONS: Diagnosis and treatment of NTM infection in children with CF is challenging. Treatment success is not guaranteed, particularly for MABSC. Large clinical trials are urgently required to evaluate treatment regimes and their suitability and efficacy in children.
PMID:34740877 | DOI:10.1136/archdischild-2021-322177
The Immunomodulatory Effects of Macrolide Antibiotics in Respiratory Disease
Pulm Pharmacol Ther. 2021 Nov 2:102095. doi: 10.1016/j.pupt.2021.102095. Online ahead of print.
ABSTRACT
Macrolide antibiotics are well known for their antibacterial properties, but extensive research in the context of inflammatory lung disease has revealed that they also have powerful immunomodulatory properties. It has been demonstrated that these drugs are therapeutically beneficial in various lung diseases, with evidence they significantly reduce exacerbations in patients with COPD, asthma, bronchiectasis and cystic fibrosis. The efficacy demonstrated in patients infected with macrolide tolerant organisms such as Pseudomonas aeruginosa supports the concept that their efficacy is at least partly related to immunomodulatory rather than antibacterial effects. Inconsistent data and an incomplete understanding of their mechanisms of action hampers the use of macrolide antibiotics as immunomodulatory therapies. Macrolides recently demonstrated no clinically relevant immunomodulatory effects in the context of COVID-19 infection. This review provides an overview of macrolide antibiotics and discusses their immunomodulatory effects and mechanisms of action in the context of inflammatory lung disease.
PMID:34740749 | DOI:10.1016/j.pupt.2021.102095
Frequency of allele variations in the CFTR gene in a Mexican population
BMC Med Genomics. 2021 Nov 5;14(1):262. doi: 10.1186/s12920-021-01111-w.
ABSTRACT
BACKGROUND: Cystic fibrosis (CF) is an autosomal recessive disorder caused by pathogenic variants in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CF variants incidence is highly variable and even undetermined in some countries like Mexico.
METHODS: In this study, the allele frequencies of 361 variants in the CFTR gene were investigated in 1455 Mexicans without a CF or CFTR-related disorders (CFTR-RD) diagnosis. We also performed a statistical comparative analysis against allele frequencies of different populations to measure genetic differences in the prevalence of CFTR variants.
RESULTS: In the vast majority of cases, the allele frequencies of this cohort were comparable to those found in other populations. However, some variants displayed significant differences in their allele frequencies when compared with European and African populations.
CONCLUSIONS: This study provides information about CFTR variants to predict the prevalence of CF in Mexico and uncover other unknown but frequent pathogenic variants in the country. Additionally, other CFTR-RD variants have also been studied using population data of the same CFTR variants. Studies like this could help develop a regional molecular diagnostic screen to optimize the medical care of CF patients.
PMID:34740355 | DOI:10.1186/s12920-021-01111-w
Perspectives on the translation of in-vitro studies to precision medicine in Cystic Fibrosis
EBioMedicine. 2021 Oct 28;73:103660. doi: 10.1016/j.ebiom.2021.103660. Online ahead of print.
ABSTRACT
Recent strides towards precision medicine in Cystic Fibrosis (CF) have been made possible by patient-derived in-vitro assays with the potential to predict clinical response to small molecule-based therapies. Here, we discuss the status of primary and stem-cell derived tissues used to evaluate the preclinical efficacy of CFTR modulators highlighting both their potential and limitations. Validation of these assays requires correlation of in-vitro responses to in-vivo measures of clinical biomarkers of disease outcomes. While initial efforts have shown some success, this translation requires methodologies that are sensitive enough to capture treatment responses in a CF population that now predominantly has mild lung disease. Future development of in-vitro and in-vivo biomarkers will facilitate the generation of new therapeutics particularly for those patients with rare mutations where clinical trials are not feasible so that in the future every CF patient will have access to effective targeted therapies.
PMID:34740114 | DOI:10.1016/j.ebiom.2021.103660
Therapeutic education and cystic fibrosis
Rev Med Liege. 2021 Nov;76(11):794-798.
ABSTRACT
Therapeutic education is defined as all the tools taught to patients with the aim of improving their compliance to treatments. In a chronic disease, such as cystic fibrosis, this education should be done during the first months of child's life with the collaboration of parents and then gradually given to children from the age of 6 until they are autonomous in the management of their treatment during adolescence. The tools used for therapeutic education should be playful, varied and adapted to the child's development, while respecting a standard for competences. In this article, we will define the main approaches of therapeutic education in patients with cystic fibrosis.
PMID:34738752
Overweight and Cystic Fibrosis: An Unexpected Challenge
Pediatr Pulmonol. 2021 Nov 5. doi: 10.1002/ppul.25748. Online ahead of print.
ABSTRACT
Achieving a healthy weight balance has been a central focus of care for people who have cystic fibrosis (CF). Over the years, the emphasis has primarily been on promoting weight gain in order to optimize pulmonary outcomes. With continued improvements in CF care, including highly effective CF modulator available for many people, the CF community is now experiencing a new challenge: addressing the concern that some people are gaining weight excessively. While at this time, we do not know to what extent overweight and obesity will affect health outcomes for people with CF, it is likely that excessive weight gain may have negative health impacts similar to those seen in the general population. In this paper, we review the history of nutritional guidelines for people with CF, as well as more recent trends toward overweight and obesity for some. A multidisciplinary approach is needed to collaboratively start the oftentimes difficult conversation regarding excessive weight gain, and to identify resources to help people achieve and maintain a healthy weight through diet, exercise, and behavioral modification. This article is protected by copyright. All rights reserved.
PMID:34738328 | DOI:10.1002/ppul.25748
Effects of a Partially Supervised Conditioning Program in Cystic Fibrosis: An International Multicenter Randomized Controlled Trial (ACTIVATE-CF)
Am J Respir Crit Care Med. 2021 Nov 4. doi: 10.1164/rccm.202106-1419OC. Online ahead of print.
ABSTRACT
Rationale: The long-term effects of vigorous physical activity (PA) on lung function in cystic fibrosis are unclear. Objectives: To evaluate effects of a 12-month partially supervised PA intervention using motivational feedback. Methods: In a parallel arm multicenter randomized controlled trial (ACTIVATE-CF), relatively inactive patients aged ≥12 years were randomly assigned (1:1 ratio) to an intervention group or control group. The intervention group consented to add 3 hours of vigorous PA per week, while the control group was asked not to change their PA behavior. Primary endpoint was change in percent predicted forced expiratory volume in 1s (ΔFEV1) at 6 months. Secondary endpoints included PA, exercise capacity, exercise motives, time to first exacerbation and exacerbation rates, quality of life, anxiety, depression, and stress, and blood glucose control. Data were analyzed using mixed linear models. Measurements and Main Results: 117 patients (40% of target sample size) were randomized to an intervention (n=60) or control group (n=57). After 6 months, ΔFEV1 was significantly higher in the control group compared to the intervention group (2.70% predicted, 95% CI 0.13 to 5.26; p=0.04). The intervention group reported increased vigorous PA compared with the control group at each study visit, had higher exercise capacity at 6 and 12 months, and higher PA at 12 months. No effects were seen in other secondary outcomes. Conclusions: ACTIVATE-CF increased vigorous PA and exercise capacity, with effects carried over for the subsequent 6 months, but resulted in better FEV1 in the control group. Clinical trial registration available at www.clinicaltrials.gov, ID: NCT01744561.
PMID:34735776 | DOI:10.1164/rccm.202106-1419OC
Utility of Cough Provocation Tests in Chronic Cough and Respiratory Diseases: A Comprehensive Review and Introduction of New Reference Ranges for the Capsaicin Test
Allergy Asthma Immunol Res. 2021 Nov;13(6):833-849. doi: 10.4168/aair.2021.13.6.833.
ABSTRACT
Cough provocation tests (CPTs) are an objective measurement of the sensitivity of the cough reflex arc. However, they are not established in clinical practice because a large variability of response in healthy subjects limits their diagnostic value. There is a paucity of studies that have investigated CPT reference ranges in healthy subjects. This systematic review describes the variability of the responses to CPTs in healthy subjects and factors that influence it. A new analysis of 134 healthy subjects was conducted to create reference ranges for single-breath capsaicin CPT by calculating the interquartile ranges for the provocative concentration of capsaicin to induce 2 and 5 coughs. Female subjects had a more sensitive cough reflex than male counterparts. The ability of CPTs to distinguish various respiratory diseases from healthy subjects was also reviewed. Cough sensitivity was consistently heightened in the following groups: unselected patients with chronic, refractory, or recurrent cough, unexplained chronic cough, gastro-esophageal reflux-associated cough, cough-variant asthma, lower airway symptoms induced by chemical irritants, and fibrotic interstitial lung diseases. In the following groups, hypersensitivity of the cough reflex was present in those individuals whose symptom profile was predominated by cough: asthma, chronic obstructive pulmonary disease (COPD), bronchiectasis, and sarcoidosis. In the following conditions, patients usually cough in order to expectorate mucus from their airways, not because of a hypersensitive cough reflex arc: productive cough, asthma, upper airway cough syndrome, COPD, bronchiectasis, cystic fibrosis, and chronic respiratory infections. CPTs have the potential to identify patients with chronic respiratory symptoms due to cough reflex hypersensitivity, thereby providing a targeted approach for therapy.
PMID:34734503 | DOI:10.4168/aair.2021.13.6.833
Characteristics of new adult users of mepolizumab with asthma in the USA
BMJ Open Respir Res. 2021 Nov;8(1):e001003. doi: 10.1136/bmjresp-2021-001003.
ABSTRACT
BACKGROUND: In the USA, over 25 million people have asthma; 5%-10% of cases are severe. Mepolizumab (Nucala) is an interleukin-5 antagonist monoclonal antibody; it was approved by the FDA in 2015 as add-on maintenance treatment of severe asthma for patients aged ≥12 years with an eosinophilic phenotype.
OBJECTIVES: (1) Describe baseline demographic and clinical characteristics of new US adult mepolizumab users 2015-2019, (2) describe asthma medication use in the 12 months preceding initiation of and concomitant with mepolizumab and (3) assess mepolizumab adherence, persistence and discontinuation patterns in 12 months postinitiation.
METHODS: We conducted a new-user observational cohort study using data from Aetna, a CVS Health Company, HealthCore (Anthem), Harvard Pilgrim Healthcare, and IBM MarketScan Research Databases. Curated administrative claims data in the FDA Sentinel System common data model format and publicly available Sentinel analytical tools were used to query the databases. We included adults who initiated mepolizumab in 2015-2019 with an asthma diagnosis in the preceding 12 months and no evidence of cystic fibrosis. We examined age, sex, comorbid conditions, asthma medication use and severe asthma exacerbations.
RESULTS: We identified 3496 adults (mean age 54.2 years, SD 12.5 years) who initiated mepolizumab. In the 12 months before mepolizumab initiation, 22% had received inhaled corticosteroids, 46% had inhaled corticosteroid/long-acting beta agonists, 72.6% had leukotriene antagonists, 38% had long-acting muscarinic antagonist, 18% had omalizumab,<1% had reslizumab, dupilumab or benralizumab. In the previous 12 months, 70% had a diagnosis of allergic rhinitis, 32% had chronic obstructive pulmonary disease, 17% eosinophilia and 3% eosinophilic granulomatosis with polyangiitis. Further, 56% had an asthma-related ambulatory visit, 73%≥1 course of oral corticosteroids lasting 3-27 days, 10% an asthma-related emergency department visit and 22% an asthma-related hospitalisation. In the 12 months following initiation, the mean proportion of days covered was 70%, and reductions in the average mean dispensings of rescue oral corticosteriods (35%) and omalizumab (61%) were observed.
CONCLUSIONS: Adults with asthma treated with mepolizumab had varying levels of healthcare utilisation and we observed evidence of mepolizumab use in patients without severe asthma.
PMID:34732517 | DOI:10.1136/bmjresp-2021-001003
CFTR modulators increase risk of acute pancreatitis in pancreatic insufficient patients with cystic fibrosis
J Cyst Fibros. 2021 Oct 31:S1569-1993(21)01415-6. doi: 10.1016/j.jcf.2021.09.010. Online ahead of print.
ABSTRACT
Patients with pancreatic insufficient cystic fibrosis rarely develop acute pancreatitis due to insufficient acinar reserve. We describe a series of five patients under the age of 18 (range 8-16 years) with pancreatic insufficient cystic fibrosis who developed a phenotype in keeping with acute pancreatitis following initiation of CFTR modulator therapy. This occurred at a median of 30 months following CFTR modulator initiation. 3/5 of these patients also developed pancreatic sufficiency or at least an intermediary pancreas status, indicated by fecal elastases above 100 μg/g. This series highlights a mostly unrecognized potential side effect of this therapy as well as the potential of CFTR modulator therapies to improve exocrine pancreatic function, even in adolescent patients.
PMID:34732308 | DOI:10.1016/j.jcf.2021.09.010
Obstructive sleep apnea in children and adolescents with cystic fibrosis and preserved lung function or mild impairment: a systematic review and meta-analysis of prevalence
Sleep Med. 2021 Oct 1;88:36-43. doi: 10.1016/j.sleep.2021.09.017. Online ahead of print.
ABSTRACT
OBJECTIVE/BACKGROUND: Sleep disorders in cystic fibrosis may be present before daytime clinical manifestations, regardless of lung function impairment, affecting quality of life and disease progression. This study investigated the prevalence of obstructive sleep apnea in children and adolescents with cystic fibrosis and preserved lung function or mild impairment, and evaluated its association with clinical variables.
METHODS: A systematic review with meta-analysis of prevalence was conducted, including observational studies with polysomnographies in patients with cystic fibrosis who presented mean lung function values > 60% predicted. The methodological quality of the studies was analyzed, and a meta-analysis was performed to assess the prevalence of obstructive sleep apnea.
RESULTS: Of the 2318 studies identified, 7 were included in the systematic review and 6 in the meta-analysis of prevalence. The confounding factors and strategies identified were the items with greatest weakness in the methodological quality assessment. Most studies were cross-sectional, and sample size ranged from 9 to 67 individuals. The most frequent criterion for defining obstructive sleep apnea was apnea-hypopnea index (AHI) > 1 per hour. The prevalence found ranged from 32.3 to 100% and the pooled prevalence was 65% (I2 = 53.4%), considering AHI>1, and 52% (I2 = 89.4%) for AHI>2 per hour. It was not possible to verify the association between obstructive sleep apnea and clinical variables.
CONCLUSIONS: A high prevalence of obstructive sleep apnea in children and adolescents with cystic fibrosis was found, regardless of age and lung function impairment, reinforcing the importance of investigating sleep-disordered breathing during clinical visits even when lung function is not yet compromised.
PMID:34731826 | DOI:10.1016/j.sleep.2021.09.017
Reply to: Contrast Enhanced Magnetic Resonance Imaging Does Not Detect a Progression in Lung Morphological Score in Preschool Children with Cystic Fibrosis
Am J Respir Crit Care Med. 2021 Nov 3. doi: 10.1164/rccm.202109-2050LE. Online ahead of print.
NO ABSTRACT
PMID:34731591 | DOI:10.1164/rccm.202109-2050LE
Contrast Enhanced Magnetic Resonance Imaging Does Not Detect a Progression in Lung Morphological Score in Preschool Children with Cystic Fibrosis
Am J Respir Crit Care Med. 2021 Nov 3. doi: 10.1164/rccm.202107-1747LE. Online ahead of print.
NO ABSTRACT
PMID:34731588 | DOI:10.1164/rccm.202107-1747LE
Toxic Epidermal Necrolysis Induced by Cystic Fibrosis Transmembrane Conductance Regulator modulators
Contact Dermatitis. 2021 Nov 3. doi: 10.1111/cod.14002. Online ahead of print.
NO ABSTRACT
PMID:34731505 | DOI:10.1111/cod.14002
Validation of a Spanish version of the Leicester Cough Questionnaire in cystic fibrosis
Chron Respir Dis. 2021 Jan-Dec;18:14799731211036903. doi: 10.1177/14799731211036903.
ABSTRACT
Cough is a main symptom in cystic fibrosis (CF). We aim to validate a Spanish version of the Leicester Cough Questionnaire (LCQ-Sp) to measure the impact of cough in CF bronchiectasis. A prospective longitudinal multicentre study was performed. Internal consistency and score changes over a 15-day period in stable state were assessed to analyse reliability. Concurrent validity was analysed by correlation with Saint George's Respiratory Questionnaire (SGRQ) and convergent validity by assessing the association with clinical variables. Changes in scores between stable state and the first exacerbation were assessed to analyse responsiveness. 132 patients (29.73 ± 10.52 years) were enrolled in four hospitals. Internal consistency was high for the total score and good for the three domains (Cronbach's α 0.81-0.93). The test-retest reliability showed an intraclass correlation coefficient of 0.86 for the total score. The correlation between LCQ-Sp and SGRQ scores was -0.74. The LCQ-Sp score negatively correlated with sputum volume, and the mean score decreased at the beginning of exacerbations (16.04±3.81 vs 13.91±4.29) with a large effect size. The LCQ-Sp is a reliable, repeatable and responsive instrument to assess the impact of cough in CF bronchiectasis and is responsive to change in the event of exacerbations.
PMID:34730449 | DOI:10.1177/14799731211036903
Improving hyperpolarized <sup>129</sup> Xe ADC mapping in pediatric and adult lungs with uncertainty propagation
NMR Biomed. 2021 Nov 2:e4639. doi: 10.1002/nbm.4639. Online ahead of print.
ABSTRACT
RATIONALE: Hyperpolarized (HP) 129 Xe-MRI provides non-invasive methods to quantify lung function and structure, with the 129 Xe apparent diffusion coefficient (ADC) being a well validated measure of alveolar airspace size. However, the experimental factors that impact the precision and accuracy of HP 129 Xe ADC measurements have not been rigorously investigated. Here, we introduce an analytical model to predict the experimental uncertainty of 129 Xe ADC estimates. Additionally, we report ADC dependence on age in healthy pediatric volunteers.
METHODS: An analytical expression for ADC uncertainty was derived from the Stejskal-Tanner equation and simplified Bloch equations appropriate for HP media. Parameters in the model were maximum b-value (bmax ), number of b-values (Nb ), number of phase encoding lines (Nph ), flip angle and the ADC itself. This model was validated by simulations and phantom experiments, and five fitting methods for calculating ADC were investigated. To examine the lower range for 129 Xe ADC, 32 healthy subjects (age 6-40 years) underwent diffusion-weighted 129 Xe MRI.
RESULTS: The analytical model provides a lower bound on ADC uncertainty and predicts that decreased signal-to-noise ratio yields increases in relative uncertainty ( ϵ ADC ) . As such, experimental parameters that impact non-equilibrium 129 Xe magnetization necessarily impact the resulting ϵ ADC . The values of diffusion encoding parameters (Nb and bmax ) that minimize ϵ ADC strongly depend on the underlying ADC value, resulting in a global minimum for ϵ ADC . Bayesian fitting outperformed other methods (error < 5%) for estimating ADC. The whole-lung mean 129 Xe ADC of healthy subjects increased with age at a rate of 1.75 × 10-4 cm2 /s/yr (p = 0.001).
CONCLUSIONS: HP 129 Xe diffusion MRI can be improved by minimizing the uncertainty of ADC measurements via uncertainty propagation. Doing so will improve experimental accuracy when measuring lung microstructure in vivo and should allow improved monitoring of regional disease progression and assessment of therapy response in a range of lung diseases.
PMID:34729838 | DOI:10.1002/nbm.4639