MRI of pulmonary nodules: technique and diagnostic value

Abstract

Chest wall invasion by a tumour and mediastinal masses are known to benefit from the superior soft tissue contrast of magnetic resonance imaging (MRI). However, helical computed tomography (CT) (i.e. with multiple row detector systems) remains the modality of choice to detect and follow lesions of the lung parenchyma. Since minimizing radiation exposure plays a minor role in oncologic patients, there are only few routine indications for which MRI of lung parenchyma is preferred to CT. This includes whole body MR imaging for staging or scientific studies with frequent follow-up examinations. MR-based lung imaging in this context was always considered as a weak point. Depending on the sequence technique and imaging conditions (i.e. ability to hold breath) the threshold for lung nodule detection with MRI using 1.5 T systems was estimated to be above 3-4 mm. The feasibility of lung MRI at 0.3-0.5 T and 3.0 T systems has been demonstrated. The clinical value of time-resolved lung nodule perfusion analysis cannot yet be determined, although the combination of perfusion characteristics with morphologic criteria contributes to estimate the integrity of a solitary lesion.

Figure 1

An example demonstrating the limitations of MRI for the detection of small lung nodules: (a,d) Small pulmonary metastases of a malignant melanoma in a 62-year-old patient (5 mm slices of a standard helical CT scan). (b,e) MRI of the corresponding positions at the same time; (c,e) the follow-up MRI after 3 months (the contrast-enhanced transverse 3D-GRE (VIBE) images were obtained as part of a whole body study; TR/TE 3.15/1.38 ms, TA 20 s, +FA 8°, FOV 350×400 mm, slices 72/4 mm). The clearly visible 3 mm nodule in the left lower lobe ((a) and (b); marked with an arrow on (a)) grew to a diameter of 5 mm within 3 months (c). Another 3 mm nodule in the lateral right middle lobe (marked with an arrow on (d)) is hardly visible on the corresponding MRI due to cardiac pulsation, but becomes clearer in the follow up study after growing to 4–5 mm (f).

Figure 2

A 67-year-old female patient with pulmonary metastases of a colorectal carcinoma. (a,b) Adjacent slices from a helical CT scan (Siemens Volume Zoom, 120 kVp, 70 mAs, 3 mm slice thickness). The images show a solid 1.4 cm nodule in the right upper lung lobe and two adjacent 0.7 and 0.9 cm nodules in the left upper lobe (lesions marked by circles on the CT images; histologic proof was obtained by wedge resection). (c,d) MR scans (Siemens Magnetom Avanto). Contrast-enhanced 3D-GRE (VIBE; on the left a single 4 mm slice, on the right an 8 mm MIP reconstruction; TR/TE 3.15/1.38 ms, TA 20 s, FA 8°, FOV 350 × 400 mm, slices 72/4 mm). (e) SS-GRE (TrueFISP; TR/TE 290.3/1.2 ms, TA 56 s, FA 80°, FOV 276 × 340 mm, slices 128/4 mm). (f) T2-weighted single-shot half-Fourier FSE (HASTE; TR/TE 550/30 ms, TA 16 s, FA 180°, FOV 309 × 450 mm, slices 35/6mm). All images were acquired using the breath-hold technique except for SS-GRE (free breathing); note the differences in chest wall configuration and nodule position.