The current status and further prospects for lung magnetic resonance imaging in pediatric radiology

Abstract

Lung MRI makes it possible to replace up to 90% of CT examinations with radiation-free magnetic resonance diagnostics of the lungs without suffering any diagnostic loss. The individual radiation exposure can thus be relevantly reduced. This applies in particular to children who repeatedly require sectional imaging of the lung, e.g., in tumor surveillance or in chronic lung diseases such as cystic fibrosis. In this paper we discuss various factors that favor the establishment of lung MRI in the clinical setting. Among the many sequences proposed for lung imaging, respiration-triggered T2-W turbo spin-echo (TSE) sequences have been established as a good standard for children. Additional sequences are mostly dispensable. The most important pulmonary findings are demonstrated here in the form of a detailed pictorial essay. T1-weighted gradient echo sequences with ultrashort echo time are a new option. These sequences anticipate signal loss in the lung and deliver CT-like images with high spatial resolution. When using self-gated T1-W ultrashort echo time 3-D sequences that acquire iso-voxel geometry in the sub-millimeter range, secondary reconstructions are possible.

Keywords: Children; Lung; Magnetic resonance imaging; Ultrashort echo time.

Fig. 1

Normal, good-quality lung MR in a 9-year-old girl (axial T2-weighted turbo spin-echo respiratory-triggered examination, parameters in Table 1). The arteries and bronchi are of equal width and have a dark lumen as well as a delicate signal-rich wall. The veins are predominantly bright, their walls indistinct. There is no relevant cardiac or breathing artifact

Fig. 2

Coronal time-resolved lung MR angiography in a 4-day-old boy with congenital pulmonary airway malformation of the right lung (MR parameters in Table 2). With a temporal resolution of 2–3 s, during the first pass of the contrast medium it is possible to distinguish the non-capillarized signal-free cystic lesion (arrowheads) from the normally contrast-enhancing lung tissue

Fig. 3

Bronchopneumonia on lung MR in a 10-year-old girl (axial T2-weighted turbo spin echo, parameters in Table 2). There is alveolar exudation and infiltration in bronchopneumonia in the right lower lobe (arrow) and, to a lesser extent, in the left lower lobe (arrowheads)

Fig. 4

Pneumonia on lung MR in a 5-year-old girl (axial T2-weighted turbo spin echo, parameters in Table 2). There is almost complete alveolar infiltration in the right lower lobe (arrow) caused by lobar pneumonia. Note pleural effusion with fibrinous septation (arrowheads)

Fig. 5

Lobar pneumonia with an abscess on lung MR in a 3-year-old girl (MR parameters in Tables 2 and 3). a On axial T2-weighted turbo spin-echo image, the abscess is not clearly distinguishable from the surrounding inflammatory tissue. It only demarcates itself by ventral air accumulation (arrow). b In axial T1-W gradient echo sequence after contrast medium administration, the abscess (arrows) is clearly distinguishable from the inflammatory area. Note that the administration of a contrast agent for lung examinations is almost only necessary for this indication. c Apparent diffusion coefficient (ADC) map from the axial diffusion-weighted imaging sequence: The low ADC values (arrow) prove the purulent content within the cave

Fig. 6

Lung MR in a 16-year-old girl with severe combined immunodeficiency. Axial T2-weighted turbo spin-echo image (MR parameters, Table 2) shows an inflammatory myofibroblastic tumor (arrow) in the right middle lobe

Fig. 7

MRI of lung tuberculosis in a 1-year-old boy (MR parameters, Table 2). a Coronal T2-weighted turbo spin-echo image shows an infiltrate (arrow) in the right upper lobe. Note also the 3-mm nodular infiltrates (arrowhead) in the right lung. b Coronal T2-weighted turbo spin-echo image shows swelling of hilar lymph nodes (arrows) and evidence of central peribronchial infiltrations. c Coronal reformat of a low-dose contrast-enhanced CT for comparison

Fig. 8

MRI of tuberculosis in a 12-year-old girl. Coronal T2-weighted turbo spin-echo image (MR parameters in Table 2) demonstrates that in older children, the tuberculous infiltrates (arrows) are often multi-focal and look similar to bronchopneumonia

Fig. 9

Hamartoma on lung MR in a 16-year-old girl (coronal T2-weighted-turbo spin echo, MR parameters in Table 2). Image shows a hamartoma (arrow) in the right upper lobe. The lesion was an incidental finding on a chest radiograph taken because of a cough. On MR, the nodule presents homogeneous hyperintensity

Fig. 10

Multifocal mesenchymal hamartoma on lung MR in a 1-year-old boy. Axial fat-suppressed T2-weighted-turbo spin-echo image (MR parameters in Table 2) shows a multifocal mesenchymal hamartoma of the right thoracic wall with a large intrapulmonary portion in a newborn. The tumor originates primarily from the ribs (arrowheads), but manifests intrapulmonally. Blood-liquid levels (arrow) are a typical sign of associated aneurysmal bone cysts

Fig. 11

Pulmonary papillomatosis on lung MR in a 5-year-old girl. Axial T2-weighted turbo spin-echo image (MR parameters in Table 2) shows the typical manifestation of pulmonary papillomatosis, with round nodules that are solid or cystic and have a wall of varying thickness (arrows). They can grow to several centimeters and then lead to air-filled cavities, with significant destruction of the parenchyma

Fig. 12

Axial lung MR in an 11-year-old boy with Ewing sarcoma and lung metastases (MR parameters in Table 2). a T2-weighted turbo spin-echo (TSE) image shows a 15-mm metastasis (arrow) in left upper lobe. b Fat-suppressed T2-weighted TSE image shows a 3-mm metastasis (arrow) in the right lower lobe. At MRI, metastases are just as easy to detect as they are at CT — they usually show a slightly brighter signal than that of vessels. This is especially true in heavily T2-weighted fat-suppressed sequences. c For comparison, axial CT image shows the same 3-mm metastasis (arrow) as the MR image in (b)

Fig. 13

Rhabdomyosarcoma on lung MR in a 14-year-old girl. Coronal T2-weighted turbo spin-echo image (MR parameters in Table 2) shows partially cystic, partially necrotic metastases (arrows) from rhabdomyosarcoma

Fig. 14

Lung MR in a 2.5-year-old boy with pleuropulmonary blastoma in DICER-1 syndrome. Coronal fat-suppressed T2-weighted turbo spin-echo image (MR parameters in Table 2) shows a partially cystic, partially solid tumor filling the entire left hemithorax

Fig. 15

Pulmonary sequestration on lung MR in a 6-month-old boy. a Axial T2-weighted turbo spin-echo MR image (parameters in Table 2) identifies the supradiaphragmal lesion on the left (arrow) as a pulmonary sequestration by the low-signal vessels. b Coronal MR angiography proves the diagnosis by demonstrating the atypical arterial supply and venous drainage (arrow)

Fig. 16

Pulmonary vascular malformation in a 9-year-old boy. a Axial T2-weighted turbo spin-echo MR (parameters in Table 2) shows multiple arteriovenous shunts (arrow). b Identical representation (arrow) in matching axial contrast-enhanced CT

Fig. 17

Lung MR in a 9-year-old girl with cystic fibrosis. Axial T2-weighted turbo spin-echo image (parameters in Table 2) shows multiple bronchiectases (arrow) in the right middle lobe. The bronchiectases are recognizable from the larger diameter and the thickened bronchial wall in contrast to the signal-free arteries

Fig. 18

Lung MR in a 14-year-old girl with cystic fibrosis. a, b T2-weighted turbo spin-echo axial (a) and coronal (b) images show multiple bronchiectases among scarred strands, infiltrations and mucus plugging in the upper and middle lobes (arrow in a). Pulmonary scarring leads to thoracic asymmetry. Smaller pneumonic infiltrates (arrows in b) can be seen. Various scoring systems have been published and correlate well with the modified Bhalla CT score and the Chrispin–Norman score

Fig. 19

Lung MR in an 11-year-old boy with cystic fibrosis and aspergillomas within bronchiectasis. a Axial T2-weighted turbo spin-echo MR image (parameters in Table 2) shows aspergillomas in preformed cavities (arrow). They can be diagnosed specifically on MR by the increased iron content. They show low signal at T2 weighting. However, confusion with air in the bronchiectases is possible. b A low-dose axial CT image shows that the bronchiectases are filled with echogenic aspergillomas of high density (arrow)

Fig. 20

Interstitial lung disease in a 13-year-old girl. a Axial T2-weighted turbo spin-echo MR image (parameters in Table 2) shows pronounced interstitial pulmonary fibrosis in the right lower lobe as ground-glass signal increase (arrow). b On axial CT, interstitial fine granular consolidations can be detected (arrow). Fibrosis often cannot be diagnosed on MRI with sufficient certainty

Fig. 21

Interstitial lung disease in a 3-year-old boy. a Coronal T2-weighted turbo spin-echo MR image (parameters in Table 2) with 3-mm slice thickness at 3 T shows a diffuse ubiquitous fine granular pattern of interstitial lung disease. With a slice thickness of 5 mm, the fine granular interstitial process would hardly be recognizable if it affected the entire lung homogeneously. b Corresponding coronal CT image shows similar findings

Fig. 22

Mycoplasma infection in a 9-year-old boy. a Axial T2-weighted turbo spin-echo MR image (parameters in Table 2) shows local interstitial fluid collection from mycoplasma infection and interstitial reaction (arrow) in the right dorsal recess. b Axial CT shows corresponding findings (arrow)

Fig. 23

Interstitial edema (arrows) caused by lung toxicity in a 7-year-old girl. a Axial T2-weighted turbo spin-echo MR image (parameters in Table 2). b Corresponding axial CT image

Fig. 24

Diagnosis of neuroendocrine cell hyperplasia in an 8-month-old girl. a Axial T2-weighted turbo spin-echo MR image (parameters in Table 2) shows multisegmental interstitial ground-glass opacities in the right middle lobe and in Segment 5 of the left lung (arrows). The findings are not very pronounced. MR diagnosis of the condition should not yet be recommended in our experience. b Corresponding CT image shows subtle ground-glass opacities (arrows)

Fig. 25

Sarcoidosis Stage II in a 15-year-old girl. Lung MR (coronal T2-weighted turbo spin-echo image, parameters in Table 2) shows many small granulomas, especially in the right lung (arrow). This finding, in conjunction with hilar lymph node enlargement (arrowheads), is typical for sarcoidosis. A central signal reduction in the lymph nodes, which we could not observe in our patient, is also known to be characteristic. Please also note the low-signal granulomas in the spleen

Fig. 26

Emphysema of the left upper lobe in a 7-day-old boy on lung MRI (parameters in Table 2). a The upper-lobe emphysema is not clearly visible on coronal T2-W turbo spin-echo image (arrow). It is caused by a small single thoracic cyst with a diameter of 2 cm. b The over-inflation with the resulting capillary reduction (arrow) only becomes visible on the time-resolved coronal MR angiogram because of the lack of contrast enhancement of the left upper lobe. c Corresponding coronal CT image shows the left upper lobe over-inflation (arrow)

Fig. 27

Lung MR in a 15-year-old girl with cystic fibrosis. a–c Self-gated T1-weighted ultrashort echo time (UTE) 3-D gradient echo sequence in coronal (a) and axial (b) planes, and respiratory-triggered axial T2-weighted turbo spin echo (c) MR images show bronchiectasis (arrow) in the left upper lobe. The CT-like characteristics of the thin slices in the T1-W UTE sequence (0.86-mm isotropic voxels) only become apparent during scrolling. Therefore, movies showing the complete examination sequence are shown in the Online Supplementary Material to this article (Movies 1 and 2)

Fig. 28

Phase-resolved functional lung (PREFUL) MRI in a 13-year-old girl with cystic fibrosis. Coronal PREFUL MRI-derived regional ventilation (left column) and perfusion-weighted image (middle column) with ventilation defect percentage (VDP, blue), perfusion defect percentage (QDP, red) and ventilation/perfusion (VDP/QDP) maps (white, signifying matched ventilation-perfusion). The girl has typical heterogeneous areas of hypoperfusion (red) and hypoventilation (blue), which are predominantly matched on the VDP/QDP map (white), mainly because of mucus plugging and bronchial wall thickening in the central upper airways (arrows), as shown on the corresponding turbo inversion recovery magnitude image. Movies in the Online Supplementary Material show PREFUL MRI-derived regional ventilation over the whole ventilation cycle (Movie 3) and perfusion-weighted images during the whole cardiac cycle (Movie 4)