Olivier Chevallier1,2, Nan Zhou3, Jean-Pierre Cercueil2, Jian He3, Romaric Loffroy2, Yì Xiáng J Wáng1. 1. Department of Imaging and Interventional Radiology, Faculty of Medicine, The Chinese University of Hong Kong, New Territories, Hong Kong SAR. 2. Department of Vascular and Interventional Radiology, Image-Guided Therapy Center, François-Mitterrand University Hospital, Dijon Cedex, France. 3. Department of Radiology, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing, China.
Abstract
OBJECTIVES: To determine whether bi- or tri-exponential models, and full or segmented fittings, better fit the intravoxel incoherent motion (IVIM) imaging signal of healthy livers. METHODS: Diffusion-weighted images were acquired with a 3 T scanner using a respiratory-triggered echo-planar sequence and 16 b-values (0-800 s/mm2 ). Eighteen healthy volunteers had their livers scanned twice in the same session, and then once in another session. Liver parenchyma region-of-interest-based measurements were processed with bi-exponential and tri-exponential models, with both full fitting and segmented fitting (threshold b-value = 200 s/mm2 ). RESULTS: With the signal of all scans averaged, bi-exponential model full fitting showed Dslow = 1.14 × 10-3 mm2 /s, Dfast = 193.6 × 10-3 mm2 /s, and perfusion fraction (PF) = 16.9%, and segmented fitting showed Dslow = 0.98 × 10-3 mm2 /s, Dfast = 42.2 × 10-3 mm2 /s, and PF = 23.3%. IVIM parameters derived from the tri-exponential model were similar for full fitting and segmented fitting, with slow (D'slow = 0.98 × 10-3 mm2 /s; F'slow = 76.4 or 76.6%), fast (D'fast = 15.1 or 15.4 × 10-3 mm2 /s; F'fast = 11.8 or 11.7%) and very fast (D'Vfast = 445.0 or 448.8 × 10-3 mm2 /s; F'Vfast = 11.8 or 11.7%) diffusion compartments. The tri-exponential model provided an overall better fit than the bi-exponential model. For the bi-exponential model, full fitting provided a better fit at very low and low b-values compared with segmented fitting, with the latter tending to underestimate Dfast ; however, the segmented method demonstrated lower error in signal prediction for high b-values. Compared with full fitting, tri-exponential segmented fitting offered better scan-rescan reproducibility. CONCLUSION: For healthy liver, tri-exponential modeling is preferred to bi-exponential modeling. For the bi-exponential model, segmented fitting underestimates Dfast , but offers a more accurate estimation of Dslow .
OBJECTIVES: To determine whether bi- or tri-exponential models, and full or segmented fittings, better fit the intravoxel incoherent motion (IVIM) imaging signal of healthy livers. METHODS: Diffusion-weighted images were acquired with a 3 T scanner using a respiratory-triggered echo-planar sequence and 16 b-values (0-800 s/mm2 ). Eighteen healthy volunteers had their livers scanned twice in the same session, and then once in another session. Liver parenchyma region-of-interest-based measurements were processed with bi-exponential and tri-exponential models, with both full fitting and segmented fitting (threshold b-value = 200 s/mm2 ). RESULTS: With the signal of all scans averaged, bi-exponential model full fitting showed Dslow = 1.14 × 10-3 mm2 /s, Dfast = 193.6 × 10-3 mm2 /s, and perfusion fraction (PF) = 16.9%, and segmented fitting showed Dslow = 0.98 × 10-3 mm2 /s, Dfast = 42.2 × 10-3 mm2 /s, and PF = 23.3%. IVIM parameters derived from the tri-exponential model were similar for full fitting and segmented fitting, with slow (D'slow = 0.98 × 10-3 mm2 /s; F'slow = 76.4 or 76.6%), fast (D'fast = 15.1 or 15.4 × 10-3 mm2 /s; F'fast = 11.8 or 11.7%) and very fast (D'Vfast = 445.0 or 448.8 × 10-3 mm2 /s; F'Vfast = 11.8 or 11.7%) diffusion compartments. The tri-exponential model provided an overall better fit than the bi-exponential model. For the bi-exponential model, full fitting provided a better fit at very low and low b-values compared with segmented fitting, with the latter tending to underestimate Dfast ; however, the segmented method demonstrated lower error in signal prediction for high b-values. Compared with full fitting, tri-exponential segmented fitting offered better scan-rescan reproducibility. CONCLUSION: For healthy liver, tri-exponential modeling is preferred to bi-exponential modeling. For the bi-exponential model, segmented fitting underestimates Dfast , but offers a more accurate estimation of Dslow .
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