Respiratory triggered diffusion-weighted imaging with a single diffusion sensitising gradient to reduce image acquisition time - A feasibility study in the workup of hepatocellular carcinoma.

Abstract

PURPOSE\nWe evaluated respiratory triggered unidirectional single-shot echo-planar imaging (u-SSEPI) as a time-saving measure in diffusion imaging of the upper abdomen. Specifically, we compared the ADC values obtained from unidirectional DWI (u-SSEPI) and routine DWI (4t-SSEPI) and also the diagnostic accuracies of unidirectional and routine DWI sequences in the identification of focal liver lesions in the setting of chronic liver disease (CLD).\n\n\nMATERIALS AND METHODS\nThis prospective, IRB approved study, included 48 patients of CLD who underwent-DCE-MRI on a 1.5\u202fT scanner for hepatocellular carcinoma (HCC) workup. In addition to 4t-SSEPI, u-SSEPI was acquired with the diffusion sensitising gradient being applied in only one direction; keeping all other parameters same as 4t-SSEPI. Two blinded radiologists evaluated the DWI studies for image quality and detection of liver lesions. A composite gold standard was established using DCE-MRI, follow-up imaging and patient clinical details. The apparent diffusion coefficients (ADCs) of the liver, spleen and the lesions were compared between the two sequences. ROC analysis evaluated the diagnostic accuracy of ADC from both the sequences in identifying HCC.\n\n\nRESULTS\nEighty-eight lesions were identified using the composite gold standard. u-SSEPI resulted in 3 times faster image acquisition. No statistically significant differences were demonstrated between the unidirectional and routine DWI sequences for image quality parameters and lesion detection rates. Lesion wise comparison of the ADC values from both the sequences was not statistically different (p\u202f=\u202f0.8) with a coefficient of variation\u202f=\u202f12-14 %. The Bland- Altman plots and the Passing-Bablock regression analysis demonstrated a systematic and proportional bias between the ADC values obtained. The AUC of the ROC curve, however, was 0.63-observer1; 0.62-oobserver2 for routine DWI and 0.65; 0.62 for unidirectional DWI when ADC was used to identify HCC (the AUCs were not statistically different (p\u202f=\u202f 0.6-0.8)).\n\n\nCONCLUSION\nNo significant differences were demonstrated in the diagnostic accuracies of unidirectional and routine DWI in the diagnosis of HCC. Unidirectional diffusion may be further evaluated in other organs where diffusion is isotropic, especially in respiratory triggered sequences where the imaging time dividend is significant.