Quantitative CT characterization of pediatric lung development using routine clinical imaging.

BACKGROUND: The use of quantitative CT analysis in children is limited by lack of normal values of lung parenchymal attenuation. These characteristics are important because normal lung development yields significant parenchymal attenuation changes as children age. OBJECTIVE: To perform quantitative characterization of normal pediatric lung parenchymal X-ray CT attenuation under routine clinical conditions in order to establish a baseline comparison to that seen in pathological lung conditions. MATERIALS AND METHODS: We conducted a retrospective query of normal CT chest examinations in children ages 0-7 years from 2004 to 2014 using standard clinical protocol. During these examinations semi-automated lung parenchymal segmentation was performed to measure lung volume and mean lung attenuation. RESULTS: We analyzed 42 CT examinations in 39 children, ages 3 days to 83 months (mean ± standard deviation [SD] = 42 ± 27 months). Lung volume ranged 0.10-1.72 liters (L). Mean lung attenuation was much higher in children younger than 12 months, with values as high as -380 Hounsfield units (HU) in neonates (lung volume 0.10 L). Lung volume decreased to approximately -650 HU by age 2 years (lung volume 0.47 L), with subsequently slower exponential decrease toward a relatively constant value of -860 HU as age and lung volume increased. CONCLUSION: Normal lung parenchymal X-ray CT attenuation decreases with increasing lung volume and age; lung attenuation decreases rapidly in the first 2 years of age and more slowly thereafter. This change in normal lung attenuation should be taken into account as quantitative CT methods are translated to pediatric pulmonary imaging.

COMPARISON OF LUNG ATTENUATION AND HETEROGENEITY BETWEEN CATS WITH EXPERIMENTALLY INDUCED ALLERGIC ASTHMA, NATURALLY OCCURRING ASTHMA AND NORMAL CATS.

Airway remodeling is a prominent feature of feline allergic asthma but requires biopsy for characterization. Computed tomography (CT) has appeal as a minimally invasive diagnostic test. The purpose of this prospective case-control study was to compare indices of airway remodeling between cats with experimentally induced, spontaneous asthma and healthy unaffected cats using CT. We hypothesized that experimental and spontaneous feline asthma would have similar CT airway remodeling characteristics and that these would be significantly different in healthy cats. Experimentally induced asthmatic research cats (n = 5), spontaneously asthmatic pet cats (n = 6), and healthy research cats (n = 5) were scanned unrestrained using a 64-detector row CT scanner. Inspiratory breath-hold CT scans were also performed in experimentally induced asthmatic and healthy cats. Mean ± extent variation of lung attenuation for each cat was determined using an airway inspector software program and CT images were scored for lung heterogeneity by a board-certified veterinary radiologist who was unaware of cat group status. Groups were compared using one-way ANOVA (unrestrained scans) and the Student's t-test (anesthetized scans) with significance defined as P < 0.10. Experimentally asthmatic and spontaneously asthmatic cats had significantly (P = 0.028 and P = 0.073, respectively) increased lung attenuation compared to healthy cats. Heterogeneity scores were higher in experimentally induced asthmatic cat than in healthy cats. Objective quantification of lung heterogeneity and lung volume did not differ among the three groups (P = 0.311, P = 0.181, respectively). Findings supported our hypothesis. Inspiratory breath-hold anesthetized CT scans facilitated discrimination between asthmatic and healthy cats in comparison to unrestrained CT scans.

Prevalence of lung atelectasis in sedated dogs examined with computed tomography.

BACKGROUND: Computed tomography (CT) scanning of the lung is known to be a valuable tool when investigating lung pathology of the dog. During CT-scan the dog needs to be immobilized and general anesthesia has historically been considered as gold standard although being a more expensive and time-consuming alternative to sedation. Today, modern high speed multidetector CT-scanners offer new possibilities for sedation as an alternative. Both anesthesia and sedation can cause lung atelectasis, and this can be problematic when reading the CT-images since it potentially can masque or mimic lung pathology leading to misdiagnosis. The objective of this prospective analytic study was to investigate the prevalence of lung atelectasis and changes in lung attenuation over time in dogs that receive intravenous sedation and positioned in sternal recumbency. RESULTS: 20 dogs without known lung pathology underwent three consecutive CT-scans of the lung; the first scan was initiated as soon as the dog was sufficiently sedated, the second scan approximately 5 min after the first one and the last scan after the dog's orthopaedic scan was completed. The dogs received intravenous sedation in a combination of dexmedetomidine and butorphanol and were kept positioned in a strict sternal recumbency during sedation and exam. Each lung lobe was individually examined in an axial plane and measurements of dorsal, ventral, and mean lung attenuation were made. Atelectasis or areas with poorly aerated lung tissue were not detected as all parts of the lobes were normally aerated at all three scans. A statistically significant increase in lung attenuation between the first and the second scan (P = 0.03) and between the first and the third scan (P = 0.0004) was seen in the ventral part of the lobes. CONCLUSIONS: This study indicates that CT-examination of the lungs can be performed on sedated dogs that are kept in a sternal recumbency without development of atelectasis. It also suggests that there is an early correlation between time and increase in lung attenuation.

Normal lung attenuation distribution and lung volume on computed tomography in a Chinese population.

Backgroud and objectives: Although lung attenuation distribution and lung volume on computed tomography (CT) have been widely used in evaluating COPD and interstitial lung disease, there are only a few studies regarding the normal range of these indices, especially in Chinese subjects. We aimed to describe the normal range of lung attenuation distribution and lung volume based on CT. Methods: Subjects with normal lung function and basically normal chest CT findings (derivation group) at Ruijin Hospital, Shanghai (from January 2010 to June 2014) were included according to inclusion and exclusion criteria. The range of the percentage of lung volume occupied by low attenuation areas (LAA%), percentile of the histogram of attenuation values (Perc n), and total lung volume were analyzed. Relationships of these measures with demographic variables were evaluated. Participants who underwent chest CT examination for disease screening and had basically normal CT findings served as an external validation group. Results: The number of subjects in the derivation group and external validation groups were 564 and 1,787, respectively. Mean total lung volumes were 4,468±1,271 mL and 4,668±1,192 mL, and median LAA%(-950 HU) was 0.19 (0.03-0.43) and 0.17 (0.01-0.41), in the derivation and external validation groups, respectively. Reference equations for lung volume and attenuation distribution (LAA% using -1,000-210 HU, Perc 1 to Perc 98) were generated: Lung volume (mL) = -1.015 *10^4+605.3*Sex (1= male, 0= female)+92.61*Height (cm) -12.99*Weight (kg) ±1766; LAA% (-950 HU)=[0.2027+0.05926*Sex (1= male, 0= female) -4.111*10^-3*Weight (kg) +4.924*10^-3*Height (cm) +8.504*10^-4*Age]^7.341-0.05; Upper limit of normal range: [0.2027+0.05926*Sex-4.111*10^-3*Weight+4.924*10^-3*Height+8.504*10^-4*Age+0.1993]^7.341-0.05. Conclusion: This large population-based retrospective study demonstrated the normal range of LAA%, Perc n, and total lung volume measured on CT scans among subjects with normal lung function and CT findings. Reference equations are provided.

A systematic approach to interpretation of heterogeneous lung attenuation on computed tomography of the chest.

Computed tomography (CT) chest is widely used as an adjunct to clinical examination and pulmonary function tests in the evaluation of unexplained dyspnoea. In such patients, heterogeneous lung attenuation is a common finding on CT. Heterogeneous lungs can be caused by varying regional aeration, varying regional perfusion, and ground glass opacities (GGO) representing airspace or interstitial pathology. It does not serve the referring clinicians or the patients well if the radiology report simply mentions the heterogeneity of the lungs without due analysis of the cause of heterogeneity and a meaningful differential diagnosis. Therefore, it is imperative for the radiologist and the treating pulmonologist to have an in-depth understanding of the pathogenesis of pulmonary heterogeneity. This, in conjunction with clinical data, can narrow the differential diagnosis or, at times, lead to specific diagnoses. The purpose of this review is to familiarize readers with the CT representation of heterogeneities in aeration and perfusion of the lung, relate patterns of GGO to underlying pathology, and provide illustrative case studies highlighting the radiological approach to heterogeneous lungs.