Ultra-high resolution CT imaging of interstitial lung disease: impact of photon-counting CT in 112 patients.

OBJECTIVES: To compare lung parenchyma analysis on ultra-high resolution (UHR) images of a photon-counting CT (PCCT) scanner with that of high-resolution (HR) images of an energy-integrating detector CT (EID-CT). METHODS: A total of 112 patients with stable interstitial lung disease (ILD) were investigated (a) at T0 with HRCT on a 3rd-generation dual-source CT scanner; (b) at T1 with UHR on a PCCT scanner; (c) with a comparison of 1-mm-thick lung images. RESULTS: Despite a higher level of objective noise at T1 (74.1 ± 14.1 UH vs 38.1 ± 8.7 UH; p < 0.0001), higher qualitative scores were observed at T1 with (a) visualization of more distal bronchial divisions (median order; Q1-Q3) (T1: 10th division [9-10]; T0: 9th division [8-9]; p < 0.0001); (b) greater scores of sharpness of bronchial walls (p < 0.0001) and right major fissure (p < 0.0001). The scores of visualization of CT features of ILD were significantly superior at T1 (micronodules: p = 0.03; linear opacities, intralobular reticulation, bronchiectasis, bronchiolectasis, and honeycombing: p < 0.0001), leading to the reclassification of 4 patients with non-fibrotic ILD at T0, recognized with fibrotic ILD at T1. At T1, the mean (± SD) radiation dose (CTDI vol: 2.7 ± 0.5 mGy; DLP: 88.5 ± 21 mGy.cm) was significantly lower than that delivered at T0 (CTDI vol: 3.6 ± 0.9 mGy; DLP: 129.8 ± 31.7 mGy.cm) (p < 0.0001), corresponding to a mean reduction of 27% and 32% for the CTDIvol and DLP, respectively. CONCLUSIONS: The UHR scanning mode of PCCT allowed a more precise depiction of CT features of ILDs and reclassification of ILD patterns with significant radiation dose reduction. CLINICAL RELEVANCE STATEMENT: Evaluation of lung parenchymal structures with ultra-high-resolution makes subtle changes at the level of the secondary pulmonary lobules and lung microcirculation becoming visually accessible, opening new options for synergistic collaborations between highly-detailed morphology and artificial intelligence. KEY POINTS: • Photon-counting CT (PCCT) provides a more precise analysis of lung parenchymal structures and CT features of interstitial lung diseases (ILDs). • The UHR mode ensures a more precise delineation of fine fibrotic abnormalities with the potential of modifying the categorization of ILD patterns. • Better image quality at a lower radiation dose with PCCT opens new horizons for further dose reduction in noncontrast UHR examinations.

Ultra-High-Resolution Photon-Counting CT Imaging of the Chest: A New Era for Morphology and Function.

ABSTRACT: After a decade of preclinical testing, photon-counting computed tomography (PCCT) has now entered daily routine, enabling radiologists to start investigating thoracic disorders in unprecedented conditions. The improved spatial resolution of the ultra-high-resolution (UHR) scanning mode is a major step for the analysis of bronchopulmonary disorders, making abnormalities at the level of small anatomical structures such as secondary pulmonary lobules accessible to radiologists. Distal divisions of pulmonary and systemic vessels also benefit from UHR protocols as alterations of lung microcirculation were previously excluded from confident analysis with energy-integrating detector CT. Although noncontrast chest CT examinations were the initial target of UHR protocols, the clinical value of this mode is also applicable to chest CT angiographic examinations with improved morphological evaluation and higher-quality lung perfusion imaging. The clinical benefits of UHR have been evaluated in initial studies, allowing radiologists to foresee the field of future applications, all combining high diagnostic value and radiation dose reduction. The purpose of this article is to highlight the technological information relevant to daily practice and to review the current clinical applications in the field of chest imaging.

Machine Learning and Deep Neural Network Applications in the Thorax: Pulmonary Embolism, Chronic Thromboembolic Pulmonary Hypertension, Aorta, and Chronic Obstructive Pulmonary Disease.

The radiologic community is rapidly integrating a revolution that has not fully entered daily practice. It necessitates a close collaboration between computer scientists and radiologists to move from concepts to practical applications. This article reviews the current littérature on machine learning and deep neural network applications in the field of pulmonary embolism, chronic thromboembolic pulmonary hypertension, aorta, and chronic obstructive pulmonary disease.

Regional Distribution of Pulmonary Blood Volume with Dual-Energy Computed Tomography: Results in 42 Subjects.

RATIONALE AND OBJECTIVES: The noninvasive approach of lung perfusion generated from dual-energy computed tomography acquisitions has entered clinical practice. The purpose of this study was to analyze the regional distribution of iodine within distal portions of the pulmonary arterial bed on dual-source, dual-energy computed tomography examinations in a cohort of subjects without cardiopulmonary pathologies. MATERIALS AND METHODS: The study population included 42 patients without cardiorespiratory disease, enabling quantitative and qualitative analysis of pulmonary blood volume after administration of a 40% contrast agent. Qualitative analysis was based on visual assessment. Quantitative analysis was obtained after semiautomatic division of each lung into 18 areas. RESULTS: The iodine concentration did not significantly differ between the right (R) and left (L) lungs (P = .49), with a mean attenuation of 41.35 Hounsfield units (HU) and 41.14 HU, respectively. Three regional gradients of attenuation were observed between: (a) lung bases and apices (P < .001), linked to the conditions of examination (mean Δ: 6.23 in the R lung; 5.96 in the L lung); (b) posterior and anterior parts of the lung (P < .001) due to gravity (mean Δ: 11.92 in the R lung ; 15.93 in the L lung); and (c) medullary and cortical lung zones (P < .001) (mean Δ: 9.35 in the R lung ; 8.37 in the L lung). The intensity of dependent-nondependent (r = 0.42; P < .001) and corticomedullary (r = 0.58; P < .0001) gradients was correlated to the overall iodine concentration. CONCLUSION: Distribution of pulmonary blood volume is influenced by physiological gradients and scanning conditions.

Metal Artifact Reduction on Chest Computed Tomography Examinations: Comparison of the Iterative Metallic Artefact Reduction Algorithm and the Monoenergetic Approach.

OBJECTIVE: The aim of the study was to compare iterative metallic artefact reduction (iMAR) and monochromatic imaging on metal artifact reduction. MATERIALS AND METHODS: Follow-up of 29 occluded pulmonary arteriovenous malformations was obtained with dual-energy computed tomography with reconstruction of averaged images using filtered back projection (group 1), iMAR (group 2), and creation of high-energy monoenergetic images (group 3). Two types of coils had been used: (a) nickel only (group A, n = 18) and (b) nickel and platinum (group B, n = 11). RESULTS: Compared with group 1, groups 2 and 3 images showed significant reduction in artifact severity. Compared with group 3, group 2 images showed less artifacts on subjective (artifact severity score: P = 0.0118; score of visibility of surrounding structures: P = 0.0056) and objective (artifact attenuation: P < 0.0001) analyses. In group A, there was no significant difference in artifact severity between groups 2 and 3 images (P > 0.05). In group B, metal artifacts were only significantly reduced in group 2 images. CONCLUSIONS: Iterative metallic artefact reduction reduces metal artifacts more efficiently than monoenergetic imaging.

Lung perfusion characteristics in pulmonary arterial hypertension (PAH) and peripheral forms of chronic thromboembolic pulmonary hypertension (pCTEPH): Dual-energy CT experience in 31 patients.

PURPOSE: To compare lung perfusion in PAH and pCTEPH on dual-energy CT (DECT) examinations. MATERIALS AND METHODS: Thirty-one patients with PAH (group 1; n = 19) and pCTEPH (group 2; n = 12) underwent a dual-energy chest CTA with reconstruction of diagnostic and perfusion images. Perfusion alterations were analysed at a segmental level. V/Q scintigraphy was available in 22 patients (group 1: 13/19; group 2: 9/12). RESULTS: CT perfusion was abnormal in 52.6 % of group 1 patients and in 100 % of group 2 patients (p = 0.0051). The patterns of perfusion alteration significantly differed between the two groups (p < 0.0001): (1) in group 1, 96.6 % of segments with abnormal perfusion showed patchy defects; (2) in group 2, the most frequent abnormalities consisted of patchy (58.5 %) and PE-type (37.5 %) defects. Paired comparison of CT perfusion and scintigraphy showed concordant findings in 76.9 % of group 1 (10/13) and 100 % of group 2 (9/9) patients, with a predominant or an exclusive patchy pattern in group 1 and a mixed pattern of abnormalities in group 2. CONCLUSION: Lung perfusion alterations at DECT are less frequent and more homogeneous in PAH than in pCTEPH, with a high level of concordant findings with V/Q scintigraphy. KEY POINTS: • Depiction of chronic pulmonary embolism exclusively located on peripheral arteries is difficult. • The main differential diagnosis of pCTEPH is PAH. • The pattern of DECT perfusion changes can help differentiate PAH and pCETPH. • In PAH, almost all segments with abnormal perfusion showed patchy defects. • In pCTEPH, patchy and PE-type defects were the most frequent abnormalities.

Automated 3D Rendering of Ribs in 110 Polytrauma Patients: Strengths and Limitations.

RATIONALE AND OBJECTIVES: To evaluate the strengths and limitations of a rib-unfolding software in a polytrauma context. MATERIALS AND METHODS: Chest computed tomography (CT) examinations of 110 patients were reviewed for specific detection of rib fractures using: (1) transverse CT sections ± multiplanar reformattings (ie, the standard of reference), and (2) unfolded rib images reconstructed by the CT Bone Reading software with the possibility of rib analysis along their long axis and creation of standard orthogonal views in different orientations of any area suspected of fracture. RESULTS: The software provided complete reconstruction of the whole rib cage in 94 patients (85.5%) and partially incomplete reconstruction in 16 patients (14.5%). The percentage of ribs inadequately reconstructed was 1.5% (40 of 2640 ribs), mainly related to unfused epiphyses (13 of 40), costal hypoplasia (8 of 40), and vertebral fracture (6 of 40). The sensitivity and specificity in detecting rib fractures at a per-patient, per-rib, and per-costal arc level ranged from 0.73 to 0.84 and 0.99 to 1, respectively. At a costal arc level, the reader's misinterpretations accounted for 67% (4 of 6) of false-positive and 24% (20/84) of false-negative results, and interpretive difficulties were encountered for single-cortex fractures or fractures at the extremities of the costal shaft. CONCLUSIONS: An accurate diagnosis of rib fracture was achieved with the reading of unfolded rib images. In a polytrauma context, the evaluated system could facilitate rib analysis.

Impact of CT perfusion imaging on the assessment of peripheral chronic pulmonary thromboembolism: clinical experience in 62 patients.

PURPOSE: To evaluate the impact of CT perfusion imaging on the detection of peripheral chronic pulmonary embolisms (CPE). MATERIALS AND METHODS: 62 patients underwent a dual-energy chest CT angiographic examination with (a) reconstruction of diagnostic and perfusion images; (b) enabling depiction of vascular features of peripheral CPE on diagnostic images and perfusion defects (20 segments/patient; total: 1240 segments examined). The interpretation of diagnostic images was of two types: (a) standard (i.e., based on cross-sectional images alone) or (b) detailed (i.e., based on cross-sectional images and MIPs). RESULTS: The segment-based analysis showed (a) 1179 segments analyzable on both imaging modalities and 61 segments rated as nonanalyzable on perfusion images; (b) the percentage of diseased segments was increased by 7.2 % when perfusion imaging was compared to the detailed reading of diagnostic images, and by 26.6 % when compared to the standard reading of images. At a patient level, the extent of peripheral CPE was higher on perfusion imaging, with a greater impact when compared to the standard reading of diagnostic images (number of patients with a greater number of diseased segments: n = 45; 72.6 % of the study population). CONCLUSION: Perfusion imaging allows recognition of a greater extent of peripheral CPE compared to diagnostic imaging. KEY POINTS: • Dual-energy computed tomography generates standard diagnostic imaging and lung perfusion analysis. • Depiction of CPE on central arteries relies on standard diagnostic imaging. • Detection of peripheral CPE is improved by perfusion imaging.

New insights in thromboembolic disease.

This article highlights new areas of interest in the management of patients with acute pulmonary embolism, with the objective of alerting radiologists about necessary updates for daily practice.

Skeletal involvement in Langerhans cell histiocytosis.

UNLABELLED: Langerhans cell histiocytosis (LCH) represents a disorder characterised by an abnormal accumulation of histiocytes in miscellaneous tissues. The bone is commonly affected, especially the flat bones, the spine and the long bones. Some lesions in children such as a "vertebra plana" or a solitary lytic lesion of the skull may be suggestive for LCH, whereas others can be confused with a malignant tumour or osteomyelitis. This pictorial essay presents the main usual and unusual skeletal manifestations observed in LCH. TEACHING POINTS: • Osseous involvement in children with LCH is very similar to that seen in multiple myeloma. • A solitary lytic lesion of the cranial vault is a typical radiographic finding of LCH. • A vertebra plana appearance in the spine is another typical radiographic finding. • Extensive signal intensity changes within bone marrow on MRI are a helpful sign for the diagnosis. • In long bones, endosteal scalloping may be responsible for a "budding appearance".

Krypton ventilation imaging using dual-energy CT in chronic obstructive pulmonary disease patients: initial experience.

PURPOSE: To evaluate the tolerance and level of enhancement achievable after inhalation of stable krypton. MATERIALS AND METHODS: This study was approved by the institutional review board and the local ethics committee. Written informed consent was obtained from all subjects. The study was planned as a Fleming two-stage design, enabling one to assess the effectiveness of a newer treatment or technique on a small number of patients. At the end of each stage, the results are computed, and the trial can be stopped if the effectiveness is less than a minimum success rate or greater than an expected success rate. After informed consent was obtained, a total of 32 patients (ie, two successive series of 16 patients each) with severe emphysema underwent a dual-source, dual-energy chest computed tomographic (CT) examination after inhalation of a mixture of stable krypton (80%) and oxygen (20%), with reconstruction of diagnostic and ventilation images. For each patient, two regions of interest were selected on a diagnostic image, one in a region of severe emphysema (presumed to be poorly ventilated or not ventilated) and a second one in a region devoid of structural abnormalities (presumed to be normally ventilated), with measurements of attenuation values on the corresponding ventilation image. RESULTS: All examinations were successfully performed, without adverse effects. Differences in attenuation between normal lung and emphysematous areas were found in 28 patients (88%; 95% confidence interval: 71%, 96.5%). The maximal level of attenuation within normal lung was 18.5 HU. Krypton attenuation difference between normal and emphysematous lung was significant, with a median value of 51.8% (P < .001). CONCLUSION: The level of enhancement after inhalation of krypton and its excellent clinical tolerance makes this gas eligible for ventilation CT examinations.