Low-dose, dynamic, expiratory thin-section CT of the lungs using a spiral CT scanner

Idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common fibrosing lung disease. It is associated with a very poor prognosis. Treatments can delay the progression of IPF, so early diagnosis is fundamental. Radiologists play a fundamental role in the evaluation and accurate diagnosis of IPF. Identifying the characteristic patterns of IPF on high-resolution computed tomography (HRCT) is key in the process of multidisciplinary diagnosis, often obviating the need for surgical lung biopsies. This review describes and illustrates the clinical and imaging findings in IPF in the context of the most recent international guidelines, as well as the differential diagnosis and the role of HRCT in follow-up and assessment of complications.

Ultralow Dose Dynamic Expiratory Computed Tomography for Evaluation of Tracheomalacia

OBJECTIVE

The aim of this study was to determine the average effective radiation dose and feasibility of ultralow dose dynamic expiratory computed tomography (CT) for evaluation of tracheomalacia (ULD) and to evaluate factors that impact image quality.

METHODS

This is a retrospective study of 64 consecutive patients from September to October 2016 for the evaluation of tracheomalacia. All studies were performed with routine inspiration chest CT followed by ULD z(kilovoltage peak (kVp) 80, 100, or 120 and fixed milliamperage 10) or typical dose CT (TD) (kVp 100 or 120 with automated milliamperage) dynamic expiration CT. Image quality was considered diagnostic if the trachea area could be accurately measured for tracheomalacia assessment, and diagnostic studies were graded fair, good, or excellent. Scan length, image quality, and effective radiation dose were compared for ULD versus TD and ULD at 100 kVp versus ULD at 80 kVp. For ULD studies, patient factors were compared across image quality.

RESULTS

The ULD had a mean effective radiation dose of 0.08 mSv, with all studies of diagnostic image quality. The ULD showed 95% reduction in effective radiation dose (P < 0.001), 14% significant reduction in scan length (P = 0.029), and qualitatively decreased image quality compared w2 ith TD (P < 0.001). The ULD at 100 kVp had significantly better image quality compared with ULD at 80 kVp (P = 0.041) with higher effective radiation dose (0.09 vs 0.05 mSv) (P < 0.001). Body mass index significantly impacted image quality for all ULD studies but not for ULD at 80 or 100 kVp.

CONCLUSION

For evaluation of tracheomalacia, ULD showed low effective radiation dose less than 0.1 mSv and maintained diagnostic image quality.

Imaging of Small Airways Diseases

Small airways disease, or bronchiolitis, encompasses many conditions that result in bronchiolar inflammation and/or fibrosis. Bronchioles are distal airways within secondary pulmonary lobules that are only visible on imaging when abnormal. High-resolution computed tomography plays an important role in diagnosing small airways disease. The predominant direct high-resolution computed tomography sign of bronchiolitis includes centrilobular nodules, whereas air trapping is the main indirect finding. This article reviews bronchiolar anatomy, discusses the differential diagnosis for cellular and constrictive bronchiolitis with a focus on key imaging features, and discusses how to distinguish important mimics.

CT Imaging of Interstitial Lung Diseases

Until today, computed tomography (CT) is the most important and valuable radiological modality to detect, analyze, and diagnose diffuse interstitial lung diseases (DILD), based on the unsurpassed morphological detail provided by high-resolution CT technique.

In the past decade, there has been a shift from an isolated histopathological diagnosis to a multidisciplinary acquired diagnosis consensus that is nowadays regarded to provide the highest level of diagnostic accuracy in patients with diffuse interstitial lung diseases. The 2002 ATS/ERS statement on classification of idiopathic interstitial pneumonias assigned a central role to high-resolution CT (HRCT) in the diagnostic workup of idiopathic interstitial pneumonias (ATS/ERS consensus classification 2002). The more recent 2013 ERS/ATS statement reinforced that combined clinical data (presentation, exposures, smoking status, associated diseases, lung function, and laboratory findings) and radiological findings are essential for a multidisciplinary diagnosis (Travis et al., Am J Respir Crit Care Med 188(6):733–748, 2013).

The traditional HRCT consisted of discontinuous 1 mm high-resolution axial slices. The primary focus was on visual pattern analysis demanding for the highest possible spatial resolution. Because of the intrinsic high structural contrast of the lung, it has been possible to substantially reduce dose without losing diagnostic information. This development has been supported by new detection and reconstruction techniques. Not only detection of subtle disease and visual comparison of disease stage but also disease classification and quantification nowadays take advantage of continuous volumetric data acquisition provided by multidetector row (MD) CT technique. The following book chapter will focus on acquisition technique with special emphasis on dose and reconstruction, advantages, and new diagnostic options of volumetric MDCT technique for interstitial lung diseases. Based on evidence from the literature, certain diseases will be covered more specifically, but it has to be noted that for the pattern analysis of the various interstitial lung diseases, the plethora of other publications and books is recommended.

American Thoracic Society-European Respiratory Society Classification of the Idiopathic Interstitial Pneumonias: Advances in Knowledge since 2002

In the updated American Thoracic Society-European Respiratory Society classification of the idiopathic interstitial pneumonias (IIPs), the major entities have been preserved and grouped into (a) "chronic fibrosing IIPs" (idiopathic pulmonary fibrosis and idiopathic nonspecific interstitial pneumonia), (b) "smoking-related IIPs" (respiratory bronchiolitis-associated interstitial lung disease and desquamative interstitial pneumonia), (c) "acute or subacute IIPs" (cryptogenic organizing pneumonia and acute interstitial pneumonia), and (d) "rare IIPs" (lymphoid interstitial pneumonia and idiopathic pleuroparenchymal fibroelastosis). Furthermore, it has been acknowledged that a final diagnosis is not always achievable, and the category "unclassifiable IIP" has been proposed. The diagnostic interpretation of the IIPs is often challenging because other diseases with a known etiology (most notably, connective tissue disease and hypersensitivity pneumonitis) may show similar morphologic patterns. Indeed, more emphasis has been given to the integration of clinical, computed tomographic (CT), and pathologic findings for multidisciplinary diagnosis. Typical CT-based morphologic patterns are associated with the IIPs, and radiologists play an important role in diagnosis and characterization. Optimal CT quality and a systematic approach are both pivotal for evaluation of IIP. Interobserver variation for the various patterns encountered in the IIPs is an issue. It is important for radiologists to understand the longitudinal behavior of IIPs at serial CT examinations, especially for providing a framework for cases that are unclassifiable or in which a histologic diagnosis cannot be obtained.

Imaging of small airways disease and chronic obstructive pulmonary disease

CT is a useful tool for identification of small airways diseases, and it can be used to classify these entities into inflammatory and constrictive bronchiolitis. Inflammatory forms of bronchiolitis include cellular bronchiolitis (usually caused by infection or aspiration), respiratory bronchiolitis, panbronchiolitis, and follicular bronchiolitis. Constrictive bronchiolitis may be caused by previous infection, toxic inhalation, collagen vascular disease, or transplantation. CT also helps categorize chronic obstructive pulmonary disease into emphysema predominant and airway predominant forms.

Obliterative Bronchiolitis

Obliterative bronchiolitis (OB) is a condition characterized by inflammation and fibrosis of the bronchiolar walls resulting in narrowing or obliteration of the bronchiolar lumen. The most common causes are childhood lower respiratory tract infection, hematopoietic stem cell or lung and heart-lung transplantation, and toxic fume inhalation. The most frequent clinical manifestations are progressive dyspnea and dry cough. Pulmonary function tests demonstrate airflow obstruction and air trapping. Radiographic manifestations include reduction of the peripheral vascular markings, increased lung lucency, and overinflation. The chest radiograph, however, is often normal. High-resolution CT is currently the imaging modality of choice in the assessment of patients with suspected or proven OB. The characteristic findings on high-resolution CT consist of areas of decreased attenuation and vascularity (mosaic perfusion pattern) on inspiratory scans and air trapping on expiratory scans. Other CT findings of OB include bronchiectasis and bronchiolectasis, bronchial wall thickening, small centrilobular nodules, and three-in-bud opacities. Recent studies suggest that hyperpolarized ³He-enhanced magnetic resonance imaging may allow earlier recognition of obstructive airway disease and therefore may be useful in the diagnosis and follow-up of patients with OB.

Monitoring of Smoking-induced Emphysema with CT in a Lung Cancer Screening Setting: Detection of Real Increase in Extent of Emphysema

PURPOSE

To retrospectively establish the minimum increase in emphysema score (ES) required for detection of real increased extent of emphysema with 95% confidence by using multi-detector row computed tomography (CT) in a lung cancer screening setting.

MATERIALS AND METHODS

The study was a substudy of the NELSON project that was approved by the Dutch Ministry of Health and the ethics committee of each participating hospital, with patient informed consent. For this substudy, original approval and informed consent allowed use of data for future research. Among 1684 men screened with low-dose multi-detector row CT (30 mAs, 16 detector rows, 0.75-mm section thickness) between April 2004 and March 2005, only participants who underwent repeat multi-detector row CT with the same scanner after 3 months because of an indeterminate pulmonary nodule were included. Extent of emphysema was considered to remain stable in this short period. Extent of low-attenuation areas representing emphysema was computed for repeat and baseline scans as percentage of lung volume below three attenuation threshold values (-910 HU, -930 HU, -950 HU). Limits of agreement were determined with Bland-Altman approach; upper limits were used to deduce the minimum increase in ES required for detecting increased extent of emphysema with 95% probability. Factors influencing the limits of agreement were determined.

RESULTS

In total, 157 men (mean age, 60 years) were included in the study. Limits of agreement for differences in total lung volume between repeat and baseline scans were -13.4% to +12.6% at -910 HU, -4.7% to +4.2% at -930 HU, and -1.3% to +1.1% at -950 HU. Differences in ES showed weak to moderate correlation with variation in level of inspiration (r=0.20-0.49, P<.05). Scanner calibration could be excluded as a factor contributing to variation in ES.

CONCLUSION

Increase in ES required to detect increased extent of smoking-related emphysema with 95% probability varies between 1.1% of total lung volume at -950 HU and 12.6% at -910 HU for low-dose multi-detector row CT. Clinical trial registration no. ISRCTN63545820.

Challenges in pulmonary fibrosis. 1: Use of high resolution CT scanning of the lung for the evaluation of patients with idiopathic interstitial pneumonias

High resolution CT (HRCT) scanning has contributed significantly to the evaluation of patients with interstitial lung disease and is particularly useful in the diagnosis of idiopathic pulmonary fibrosis (IPF). The characteristic radiographic features of the idiopathic interstitial pneumonias on HRCT scans have been increasingly analysed and are now fairly well described. Based on current data, HRCT scanning can provide a confident, highly specific diagnosis of IPF in many patients with diffuse lung disease. This article reviews an organised approach to HRCT scanning and identifies the features that allow an accurate diagnosis of the idiopathic interstitial pneumonias to be made. The role of surgical lung biopsy is discussed in the diagnosis of cases when a definite HRCT diagnosis cannot be made.

Relapsing Polychondritis: Prevalence of Expiratory CT Airway Abnormalities

PURPOSE

To retrospectively determine the prevalence of expiratory computed tomographic (CT) abnormalities, including malacia and air trapping, in patients with relapsing polychondritis and to retrospectively determine the frequency with which expiratory abnormalities are accompanied by inspiratory abnormalities on CT scans.

MATERIALS AND METHODS

Institutional review board approval was obtained, and informed consent was not required for this retrospective HIPAA-compliant study. A computerized hospital information system was used to identify all patients with clinically diagnosed or biopsy-proved relapsing polychondritis who were referred for CT airway imaging during a 17-month period. The study cohort comprised 18 patients (15 women, three men; mean age, 47 years; age range, 20-71 years). Multidetector helical CT was performed in all patients by using a standard protocol, which included end-inspiratory and dynamic expiratory volumetric imaging. Two observers who were blinded to the original scan interpretations simultaneously reviewed CT scans. Findings were recorded in consensus. Dynamic expiratory CT scans were assessed for malacia that involved the trachea and main bronchi (reduction in cross-sectional area of more than 50%) and for air trapping (failure of lung parenchyma to increase in attenuation during expiration). Air trapping was visually classified according to pattern and extent (lobular, segmental, lobar, or whole lung). Inspiratory CT scans were evaluated for tracheal and bronchial stenosis (>25% luminal diameter narrowing compared with a corresponding uninvolved segment), wall thickening (>2 mm), and calcification.

RESULTS

Expiratory CT abnormalities were present in 17 (94%) of 18 patients and included malacia in 13 patients (72%) and air trapping in 17 patients (94%). Inspiratory CT abnormalities were found in eight (47%) of 17 patients who had expiratory CT abnormalities. Calcification of the airway walls was present in seven (39%) of 18 patients. All patients who had inspiratory CT abnormalities demonstrated expiratory CT abnormalities.

CONCLUSION

Expiratory CT abnormalities were present in the majority of patients with relapsing polychondritis who were referred for airway imaging, yet only half of these patients demonstrated abnormalities on routine inspiratory CT scans. Thus, dynamic expiratory CT should be a standard component of imaging assessment in patients with relapsing polychondritis.

Assessment of lung function in children by cross-sectional imaging: techniques and clinical applications

Imaging techniques are indispensable for diagnosis and follow-up of paediatric pulmonary diseases. In the past, interest was focused on morphological aspects of pulmonary tissue. With the development of novel CT and MRI techniques, functional pulmonary imaging became available. In this review, the new techniques of cross-sectional functional imaging of the lung are presented and the value of these methods for investigating paediatric pulmonary diseases and their potential clinical applications are discussed.

High-resolution CT of the lung: patterns of disease and differential diagnoses

High-resolution CT (HRCT) of the lung is a powerful tool for the investigation of patients with acute or chronic respiratory symptoms or diffuse parenchymal lung disease. Detailed knowledge of normal pulmonary anatomy and an understanding of how normal anatomy is altered in disease states are required to appreciate fully HRCT findings in patients with pulmonary disease. Detailed knowledge of the technical aspects of HRCT examinations is required for optimal image quality. With the proper foundation, a pattern approach to HRCT interpretation may then be used successfully to provide accurate and reproducible interpretation.

Frequency and Severity of Air Trapping at Dynamic Expiratory CT in Patients with Tracheobronchomalacia

OBJECTIVE

The purpose of this study was to compare the frequency and severity of air trapping in patients with and without tracheobronchomalacia using dynamic expiratory volumetric CT.

MATERIALS AND METHODS

The study group consisted of 20 subjects, including 10 patients with bronchoscopically proven tracheobronchomalacia and 10 control subjects of similar ages without tracheobronchomalacia. All 20 subjects underwent MDCT performed at the end of deep inspiration and during dynamic expiration. The images were analyzed at three lung levels, and the extent of air trapping was assessed visually using a 5-point scale. For each subject, a total air-trapping score was derived by summing the values for the three lung levels (possible range, 0-12). Statistical analysis was performed using the Mann-Whitney U test.

RESULTS

In the tracheobronchomalacia group, 10 (100%) of 10 patients showed air trapping, with a median score of 5 (range, 2-12). In the control group, six (60%) of 10 subjects showed air trapping, with a median score of 2 (range, 0-3). The median total air-trapping score was significantly higher (p < 0.001) for the tracheobronchomalacia group compared with the control group. Excessive central airway collapse (expiratory reduction in cross-sectional area of > 50%) was seen on CT scans in all tracheobronchomalacia patients but in none of the control subjects.

CONCLUSION

Air trapping was observed with a higher frequency and greater severity in patients with tracheobronchomalacia than in a control group of patients of similar ages without tracheobronchomalacia.

2003 AUR Memorial Award. Dynamic expiratory volumetric CT imaging of the central airways: comparison of standard-dose and low-dose techniques

RATIONALE AND OBJECTIVES

Investigators in this study compared standard-dose and low-dose inspiratory and expiratory computed tomographic (CT) images with regard to their usefulness for measuring the tracheal lumen in patients with or without tracheobronchomalacia (TBM). MATERIALS AND METHODS; Hospital records were reviewed to identify 10 consecutive patients with bronchoscopically proved TBM and 10 control subjects without TBM who underwent paired volumetric inspiratory and dynamic expiratory examinations with multisection CT. A low-dose (40-80 mA) technique was used for dynamic expiratory CT in 14 (70%) of the 20 subjects, and a standard dose (240-280 mA) was used in the remaining six (30%). All images were reviewed in a randomized, blinded fashion by two observers, who measured the tracheal lumen to determine the presence of TBM by consensus. The degree of confidence in measuring the tracheal lumen was graded on a four-point scale from 0(no confidence) to 3 (highest level of confidence), also by consensus of the two observers. Statistical analysis for differences in confidence level was performed with the Mann-Whitney U test. The image noise level was assessed by measuring the standard deviation of the presternal soft tissue, and statistical analysis for differences in noise level was performed with the t test.

RESULTS

The level of confidence in tracheal lumen measurement was high, regardless of respiratory phase and dose (inspiratory mean, 2.9; median, 3; range, 2-3; expiratory low-dose mean, 2.6; median, 3; range, 2-3; expiratory standard-dose mean, 2.8; median, 3; range, 2-3). There was no significant difference in confidence level between standard- and low-dose techniques (P = .53). Excessive central airway collapse (expiratory reduction in cross-sectional diameter, > 50%) was seen in all 10 patients with TBM and in none of the control subjects.

CONCLUSION

The acquisition of paired inspiratory and dynamic expiratory images with multisection helical CT is a promising method for diagnosing TBM. The low-dose technique performs as well as the standard-dose technique for the dynamic expiratory phase, with a similar degree of confidence for measuring the tracheal lumen.

Acute rejection following lung transplantation: limitations in accuracy of thin-section CT for diagnosis

PURPOSE

To evaluate the sensitivity, specificity, predictive values, and accuracy of thin-section computed tomography (CT) for the diagnosis of acute rejection following lung transplantation and to determine whether any individual CT abnormalities are associated with histopathologically proved acute rejection.

MATERIALS AND METHODS

Thin-section CT studies from 64 lung transplant recipients were retrospectively reviewed. CT studies were temporally correlated with various grades of biopsy-proved acute rejection (n = 34); 30 other CT studies were from a control group with no histopathologic evidence of acute rejection. Acute rejection was diagnosed as present or absent, and the diagnostic was calculated.

RESULTS

The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of CT for the diagnosis of acute rejection were as follows: 35%, 73%, 60%, 50%, 53%, respectively. No individual CT finding was significantly associated with acute rejection. The sensitivity of CT for the detection of various grades of acute rejection was 17% for grade A1, 50% for grade A2, and 20% for grade A3. The combination of volume loss and septal thickening, with or without pleural effusion, was never seen in the absence of acute rejection.

CONCLUSION

Thin-section CT has limited accuracy for the diagnosis of acute rejection following lung transplantation, and no individual CT finding is significantly associated with this diagnosis.

Small airways diseases: detection and insights with computed tomography

Diseases affecting the small airways are difficult to detect by traditional diagnostic tests. Widespread involvement is needed before symptoms and abnormalities on pulmonary function testing or chest radiography become apparent. Obstruction of the bronchioles may be detected indirectly by computed tomography (CT) because regional under-ventilation results in reduced perfusion which in turn is shown as a mosaic attenuation pattern of the lung parenchyma. When there is inflammation of the bronchioles with accompanying exudate, the airways may become directly visible on CT, for example in cases of diffuse panbronchiolitis. Quantification of the various morphological features of small airways disease is possible from CT images and this increased precision has aided investigations of structure/function relationships. An understanding of the pathology and microscopic distribution of disease in relation to the airways allows some prediction of the likely computed tomography appearances in this wide spectrum of conditions, and thus helps to refine the differential diagnosis.