State-of-the-art MR Imaging for Thoracic Diseases

Abstract

Since thoracic MR imaging was first used in a clinical setting, it has been suggested that MR imaging has limited clinical utility for thoracic diseases, especially lung diseases, in comparison with x-ray CT and positron emission tomography (PET)/CT. However, in many countries and states and for specific indications, MR imaging has recently become practicable. In addition, recently developed pulmonary MR imaging with ultra-short TE (UTE) and zero TE (ZTE) has enhanced the utility of MR imaging for thoracic diseases in routine clinical practice. Furthermore, MR imaging has been introduced as being capable of assessing pulmonary function. It should be borne in mind, however, that these applications have so far been academically and clinically used only for healthy volunteers, but not for patients with various pulmonary diseases in Japan or other countries. In 2020, the Fleischner Society published a new report, which provides consensus expert opinions regarding appropriate clinical indications of pulmonary MR imaging for not only oncologic but also pulmonary diseases. This review article presents a brief history of MR imaging for thoracic diseases regarding its technical aspects and major clinical indications in Japan 1) in terms of what is currently available, 2) promising but requiring further validation or evaluation, and 3) developments warranting research investigations in preclinical or patient studies. State-of-the-art MR imaging can non-invasively visualize lung structural and functional abnormalities without ionizing radiation and thus provide an alternative to CT. MR imaging is considered as a tool for providing unique information. Moreover, prospective, randomized, and multi-center trials should be conducted to directly compare MR imaging with conventional methods to determine whether the former has equal or superior clinical relevance. The results of these trials together with continued improvements are expected to update or modify recommendations for the use of MRI in near future.

Keywords: lung; magnetic resonance imaging; mediastinum; thorax.

Fig. 1

64-year-old male with a solid nodule with 13-mm-long axis diameter and diagnosed as invasive adenocarcinoma (From left to right: standard-dose CT, low-dose CT, and pulmonary MR imaging with UTE). Standard- and low-dose CTs and pulmonary MR imaging with UTE clearly show a solid nodule with a 13-mm-long axis diameter in the right upper lobe. (Reproduced, with permission, from reference No. 45) UTE, ultra-short TE.

Fig. 2

60-year-old male with part-solid nodule with 15-mm-long axis diameter and diagnosed as invasive adenocarcinoma (From left to right: standard-dose CT, low-dose CT, and pulmonary MR imaging with UTE). Standard- and low-dose CTs and pulmonary MR imaging with UTE clearly show a part-solid nodule with a 15-mm-long axis diameter in the right upper lobe. (Reproduced, with permission, from reference No. 45) UTE, ultra-short TE.

Fig. 3

48-year-old male with ground-glass nodule, 5-mm-long axis diameter, and followed up for over 1 year (From left to right: standard-dose CT, low-dose CT, and pulmonary MR imaging with UTE). Standard- and low-dose CTs and pulmonary MR imaging with UTE clearly show a ground-glass nodule with a 5-mm-long diameter in the right middle lobe. (Reproduced, with permission, from reference No. 45) UTE, ultra-short TE.

Fig. 4

Images in 82-year-old man with invasive adenocarcinoma in right upper lobe. a: Thin-section CT scan with 1-mm-thick sections (left), pulmonary MRI scan with ultrashort echo time at 110 msec and 1-mm-thick sections (middle), and fluorine 18 FDG PET/CT scan with 2.5-mm-thick sections (right). CT and MRI scans show solid nodule with notch. This nodule demonstrates high FDG uptake on PET/CT scan. CT and MRI scans also show bullae and emphysematous lung surrounding tumor. b: Dynamic first-pass contrast material-enhanced perfusion gradient-echo MRI scans obtained with a 3-T system demonstrate well-enhanced nodule (arrows) in right upper lobe. This nodule shows enhancement from lung parenchymal phase and is well enhanced at systemic circulation phase. t is the time after injection of gadolinium-based contrast agent followed by saline chaser. (Reproduced, with permission, from reference No. 2) FDG, fluorodeoxyglucose.

Fig. 5

Images in a 73-year-old patient with pathologically diagnosed N2 adenocarcinoma. a: STIR turbo SE image shows that primary lesion (medium arrow), subcarina lymph node (thick arrow), and right hilar lymph node (thin arrow) have high SI. Primary lesion in the right lower lobe is visible in the same axial plane. LSRs of lymph nodes were 0.75 (right hilar lymph node) and 0.78 (subcarina lymph node); LMRs were 1.7 (right hilar lymph node) and 1.9 (subcarina lymph node); and visual scores were 5. An accurate diagnosis of N2 disease was made. b: DW MR image shows that primary lesion (medium arrow), subcarina lymph node (thick arrow), and right hilar lymph node (thin arrow) have high SI. Primary lesion in the right lower lobe is visible in the same axial plane. ADCs of lymph nodes were 2.8×10^-3sec/mm²(right hilar lymph node) and 3.4×10^-3sec/mm²(subcarina lymph node), and visual scores were 5. An accurate diagnosis of N2 disease was made. c: FDG PET/CT image shows that primary lesion (medium arrow) and right hilar lymph node (thin arrow) have high uptake of FDG, and subcarina lymph node (thick arrow) has low uptake of FDG. Primary lesion in the right lower lobe is visible in the same axial plane. SUV_max of lymph nodes was 3.2 (right hilar lymph node) and 1.5 (subcarina lymph node), and visual scores were 5 (right hilar lymph node) and 2 (subcarina lymph node). An inaccurate diagnosis of N1 was made. (Reproduced, with permission, from reference No. 99) ADC, apparent diffusion coefficient; DW, diffusion-weighted; FDG, fluorodeoxyglucose; LMR, lymph node-to-muscle ratio; LSR, lesion-to-saline ratio; PET, positron emission tomography; SE, spin-echo; SI, signal intensity; STIR, short inversion time inversion recovery; SUV_max, maximum standardized uptake value.

Fig. 6

Images in a 72-year-old patient with pathologically diagnosed N1 adenocarcinoma. a: STIR turbo SE image shows that left hilar lymph node (arrow) has high SI. Primary lesion is not visible in the same axial plane. Thymic cyst can be seen in the anterior mediastinum. LSR of the lymph node was 0.70, LMR was 1.5, and visual score was 5. An accurate diagnosis of N1 disease was made. b: DW MR image shows that left hilar lymph node (arrow) has low SI. Primary lesion is not visible in the same axial plane. Thymic cyst can be seen as low SI in anterior mediastinum. ADC of the lymph node was 1.5×10^-3sec/mm², and visual score was 2. An inaccurate diagnosis of N0 was made. c: FDG PET/CT image shows that left hilar lymph node (arrow) has low uptake of FDG. Primary lesion is not visible in the same axial plane. Thymic cyst can be seen in the anterior mediastinum. SUV_max of the lymph node was 1.2, and visual score was 1. An inaccurate diagnosis of N0 disease was made. (Reproduced, with permission, from reference No. 99) ADC, apparent diffusion coefficient; DW, diffusion-weighted; FDG, fluorodeoxyglucose; LMR, lymph node-to-muscle ratio; LSR, lesion-to-spinal cord ratio; PET, positron emission tomography; SE, spin-echo; SI, signal intensity; STIR, short inversion time inversion recovery; SUV_max, maximum standardized uptake value.

Fig. 7

Images in 42-year-old woman with chronic pulmonary arterial hypertension from an atrial septal defect with pulmonary insufficiency.a: Coronal MR angiogram shows an enlarged pulmonary artery (arrow). b: Four-dimensional flow systolic phase path lines from emitter plane at pulmonary valve show rapid flow in red at the pulmonary trunk and turbulent (helical) flows in right and left (arrow) pulmonary arteries. c: Four-dimensional flow in diastolic phase shows lower velocity pulmonary insufficiency path lines in blue (arrow) from same emitter plane at pulmonary valve, with calculated regurgitant fraction of 28%. (Reproduced, with permission, from reference No. 2)