MRI proves clinical value in lung cancer

MR imaging has failed to assume the same importance as CT in the radiological evaluation of lung cancer. It is usually considered as an alternative modality when CT findings are inconclusive or as a primary modality in cases of contraindication to iodinated contrast media.1 Key reasons for the limited role of MRI relate to technical limitations, including longer scan times, inferior spatial resolution, and low signal of the lung parenchyma.2,3 Unfavorable signal characteristics are due to the lungs' low proton density and high magnetic susceptibility.4 MR offers several benefits over CT for assessing lung cancer, however. Its contrast media have lower toxicity than contrast used in CT scans, the examination involves no ionizing radiation, and resulting images provide much better soft-tissue contrast. MR also offers a variety of contrast options (T1 weighting, T2 weighting, fat saturation, etc.), which in practice facilitates differentiation of pathologic tissue growth.2 The modality allows imaging in any desired plane without further need for image processing. Contrast-enhanced MR angiography has also proved valuable for evaluating the thoracic vascular system, allowing noninvasive assessments of tumor invasion.2,5 Continuous improvements in MR hardware, including high-performance gradient systems and new pulse sequences, are counteracting the modality's technical drawbacks. Improved triggering options and pulse sequence techniques, for example, reduce cardiac and/or respiratory motion artifacts. Use of fast MR sequences now enables the entire thorax to be imaged during a single breath-hold.3,6,7 Application of long-term averaging to conventional turbo spin-echo MRI produces high image quality with reduced motion artifacts.8 Single-shot pulse sequences, such as half-Fourier single-shot turbo spin-echo (HASTE),6 further decrease susceptibility to cardiac or respiratory motion, reducing scan times to below one second per image. Problems arising from T2*-related signal loss can be reduced by using short echo times, which allow improved visualization of lung parenchyma.6 Results can be improved by applying parallel imaging techniques.9