Magnetic resonance imaging for lung cancer screen

Abstract

Lung cancer is the leading cause of cancer related death throughout the world. Lung cancer is an example of a disease for which a large percentage of the high-risk population can be easily identified via a smoking history. This has led to the investigation of lung cancer screening with low-dose helical/multi-detector CT. Evidences suggest that early detection of lung cancer allow more timely therapeutic intervention and thus a more favorable prognosis for the patient. The positive relationship of lesion size to likelihood of malignancy has been demonstrated previously, at least 99% of all nodules 4 mm or smaller are benign, while noncalcified nodules larger than 8 mm diameter bear a substantial risk of malignancy. In the recent years, the availability of high-performance gradient systems, in conjunction with phased-array receiver coils and optimized imaging sequences, has made MR imaging of the lung feasible. It can now be assumed a threshold size of 3-4 mm for detection of lung nodules with MRI under the optimal conditions of successful breath-holds with reliable gating or triggering. In these conditions, 90% of all 3-mm nodules can be correctly diagnosed and that nodules 5 mm and larger are detected with 100% sensitivity. Parallel imaging can significantly shorten the imaging acquisition time by utilizing the diversity of sensitivity profile of individual coil elements in multi-channel radiofrequency receive coil arrays or transmit/receive coil arrays to reduce the number of phase encoding steps required in imaging procedure. Compressed sensing technique accelerates imaging acquisition from dramatically undersampled data set by exploiting the sparsity of the images in an appropriate transform domain. With the combined imaging algorithm of parallel imaging and compressed sensing and advanced 32-channel or 64-channel RF hardware, overall imaging acceleration of 20 folds or higher can then be expected, ultimately achieve free-breathing and no ECG gating acquisitions in lung cancer MRI screening. Further development of protocols, more clinical trials and the use of advanced analysis tools will further evaluate the real significance of lung MRI.

Keywords: CT; Lung; MR; cancer; screening.

Figure 1

A 42-year-old male. T2 weighted HASTE MR axial (A) and coronal (B) imaging of the chest shows a nodule (arrows). It was also shown by CT (C, axial; D, coronal) and confirmed to be a bronchioalveolar carcinoma by surgery. HASTE, Half-Fourier Acquisition Single-Shot Turbo Spin-Echo.

Figure 2

A 72-year-old male. (A,B) T1 & T2 weighted MR screening of the chest; no abnormality was detected in 2005; (C,D) T1 & T2 weighted MR screening of the chest shows a nodule (arrow) in 2008. It was also shown by CT (E) and confirmed to be a bronchioalveolar carcinoma (stage I) by surgery.

Figure 3

An example demonstrates 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; TR/TE 3.15/1.38 ms, flip angle 8°, FOV 350 mm × 400 mm, slice thickness 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) [Reproduced with permission from reference (23)].

Figure 4

A 40-year-old woman with pulmonary hamartoma. (A) CT image shows low-attenuation spot (arrow) within nodule, suggesting lipoid tissue; (B,C) axial T1-weighted (B) and T2-weighted (C) MR images show hyperintense spots (arrows) within nodule. T2-weighted image (C) also shows hyper-intense matrix consistent with cartilaginous tissue [Reproduced with permission from reference (21)].