Abstract
BackgroundTo evaluate the feasibility of two-colour index maps containing combined diffusion and perfusion information from simplified intravoxel incoherent motion (IVIM) for liver lesion malignancy assessment.MethodsDiffusion-weighted data from a respiratory-gated 1.5-T magnetic resonance sequence were analysed in 109 patients with liver lesions. With three b values (0, 50, 800 s/mm2) estimated diffusion coefficient D′, perfusion fraction f′, and apparent diffusion coefficient (ADC) maps were calculated and analysed for regions of interest (ROIs). D′ and f′ cutoff values were determined by differentiating haemangiomas from other lesions and focal nodular hyperplasias from other lesions, respectively. Combined IDf index maps were generated with a voxel value set to 100, if both D′ and f′ voxel values were lower than their cutoff values (1,529.4 × 10-6 mm2/s and 114.4 × 10-3, respectively), otherwise to 0. Moreover, IADC index maps were generated from ADC cutoff value (1,338.5 × 10-6 mm2/s) obtained by differentiating benign from malignant lesions. Discriminatory power was assessed for both IDf and IADC. Index maps were displayed as two-colour overlays to b-800 images and visually assessed within the translucent hyperintense areas.ResultsFor IDf, the same diagnostic accuracy was achieved as for the combined use of parameters D′ and f′ (93.6%). Compared to IADC, IDf showed a higher diagnostic accuracy. Visual judgment of IDf yielded an accuracy (95.4%) similar to that of quantitative analysis (93.6%).ConclusionVoxel-wise combined two-colour index maps IDf provide similar diagnostic accuracy as ROI-based combination of estimated IVIM parameters D′ and f′ and are suitable for visual assessment of liver lesion malignancy.
Highlights
To evaluate the feasibility of two-colour index maps containing combined diffusion and perfusion information from simplified intravoxel incoherent motion (IVIM) for liver lesion malignancy assessment
While Diffusion-weighted imaging (DWI) acquired with a low b value (“black blood” images) provides high sensitivity for lesion detection [2, 3], the apparent diffusion coefficient (ADC) determined from at least two b values between 0 and 500–1000 s/mm2 is usually used for lesion characterisation [4, 5]
Of these 371 patients, 262 (70.6%) were excluded due to lack of a definitive diagnosis based on histology or typical imaging characteristics (n = 46), local treatment of the liver (n = 143), insufficient image quality caused by motion artifacts (n = 27) or pixel misalignments (n = 5), unfavourable lesion location as close to prior biopsy or drainage tracts or at the edge of the liver (n = 6), partial volume of an adjacent slice (n = 10), or difficulties to identify the lesions on DWI (n = 5)
Summary
To evaluate the feasibility of two-colour index maps containing combined diffusion and perfusion information from simplified intravoxel incoherent motion (IVIM) for liver lesion malignancy assessment. The true diffusion coefficient D, the pseudodiffusion coefficient D*, and the perfusion fraction f, reflecting the relative contribution of perfusion to the DWI signal, are often determined by fit algorithms [9]. These require a high number of b values and relatively long acquisition times. Simplified IVIM turned out to be valuable for liver lesion characterisation and assessment of therapy in clinical routine [3, 14,15,16,17,18,19,20]
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