Malignant hepatic tumors: short-term reproducibility of apparent diffusion coefficients with breath-hold and respiratory-triggered diffusion-weighted MR imaging.

PURPOSE

To prospectively evaluate the reproducibility of apparent diffusion coefficient (ADC) measurement in malignant hepatic tumors and to examine the influence of imaging methods, lesion location, and lesion size on the reproducibility of ADC measurement.

MATERIALS AND METHODS

The institutional review board approved the study protocol, and informed consent was obtained. Forty-nine patients underwent both breath-hold and respiratory-triggered diffusion-weighted (DW) magnetic resonance imaging on a 1.5-T system twice. Two independent readers measured the ADC of the largest malignant hepatic tumor for each patient on each image sets. Mean ADCs were compared between repeated acquisitions and imaging techniques by using the paired t test. Reproducibility of the ADC measurement and interobsever agreement were determined by using 95% Bland-Altman limits of agreement and intraclass correlation coefficients (ICCs). The effects of the imaging technique, lesion location, and lesion size on the reproducibility of the ADC measurements were assessed by comparing ICCs by using the z test.

RESULTS

There were no significant differences in the mean ADC between repeated acquisitions for breath-hold ([1.266-1.275] x 10(-3) mm(2)/sec vs [1.285-1.290] x 10(-3) mm(2)/sec; P = .572-.634) or respiratory-triggered ([1.487-1.502] x 10(-3) mm(2)/sec vs [1.421-1.441] x 10(-3) mm(2)/sec; P = .073-.091) DW MR imaging. The mean ADCs measured by using the respiratory-triggered method ([1.421-1.502] x 10(-3) mm(2)/sec) were significantly higher than those measured by using the breath-hold method ([1.266-1.290] x 10(-3) mm(2)/sec) (P < or = .001). The 95% limits of agreement between ADCs measured on repeated DW images were 28.7%-31.3% of the mean, and those between ADCs measured by two readers were 14.6%-22.5% of the mean. ADC measurement of malignant hepatic tumors tended to be more reproducible for right-lobe than for left-lobe lesions and for larger rather than smaller lesions.

CONCLUSION

Changes in ADCs of less than approximately 30% fall into the range of measurement error. Imaging technique significantly affected ADCs of malignant hepatic tumors. Lesion location and size are potentially influential on the reproducibility of ADC measurement.