Diffusion-weighted magnetic resonance imaging for assessment of lung lesions: repeatability of the apparent diffusion coefficient measurement

To establish repeatability of apparent diffusion coefficients (ADCs) acquired from free-breathing diffusion-weighted magnetic resonance imaging (DW-MRI) in malignant lung lesions and investigate effects of lesion size, location and respiratory motion. Thirty-six malignant lung lesions (eight patients) were examined twice (1- to 5-h interval) using T1-weighted, T2-weighted and axial single-shot echo-planar DW-MRI (b = 100, 500, 800 s/mm(2)) during free-breathing. Regions of interest around target lesions on computed b = 800 s/mm(2) images by two independent observers yielded ADC values from maps (pixel-by-pixel fitting using all b values and a mono-exponential decay model). Intra- and inter-observer repeatability was assessed per lesion, per patient and by lesion size (> or < 2 cm) or location. ADCs were similar between observers (mean +/- SD, 1.15 +/- 0.28 x 10(-3) mm(2)/s, observer 1; 1.15 +/- 0.29 x 10(-3) mm(2)/s, observer 2). Intra-observer coefficients of variation of the mean [median] ADC per lesion and per patient were 11 % [11.4 %], 5.7 % [5.7 %] for observer 1 and 9.2 % [9.5 %], 3.9 % [4.7 %] for observer 2 respectively; inter-observer values were 8.9 % [9.3 %] (per lesion) and 3.0 % [3.7 %] (per patient). Inter-observer coefficient of variation (CoV) was greater for lesions < 2 cm (n = 20) compared with > 2 cm (n = 16) (10.8 % vs 6.5 % ADC(mean), 11.3 % vs 6.7 % ADC(median)) and for mid (n = 14) vs apical (n = 9) or lower zone (n = 13) lesions (13.9 %, 2.7 %, 3.8 % respectively ADC(mean); 14.2 %, 2.8 %, 4.7 % respectively ADC(median)). Free-breathing DW-MRI of whole lung achieves good intra- and inter-observer repeatability of ADC measurements in malignant lung tumours. aEuro cent Diffusion-weighted MRI of the lung can be satisfactorily acquired during free-breathing aEuro cent DW-MRI demonstrates high contrast between primary and metastatic lesions and normal lung aEuro cent Apparent diffusion coefficient (ADC) measurements in lung tumours are repeatable and reliable aEuro cent ADC offers potential in assessing response in lung metastases in clinical trials.