Estimation of pseudo-diffusion coefficient D* using different settings of low b-values in liver IVIM imaging

Meng-Chieh Liao^{1}, Cheng-Ping Chien^{1}, Shih-Han Hung^{1}, Feng-Mao Chiu^{2}, and Hsiao-Wen Chung^{1}

In this IRB
approved study, 4 subjects (M/F 3/1, mean age 22.79±0.78 y) underwent IVIM diffusion-weighted
imaging on a Philip 3T scanner using sixteen b values (0, 5, 10, 15, 20, 30,
40, 50, 60, 70, 80, 90, 100, 200, 400, 800s/mm^{2}) with navigator to
reduce influences from respiratory motion. Scanning parameters were as follow: FOV=340x340mm,
TE/TR=45/1092.1ms, thickness=7mm, matrix size=128x128, NEX=6. ROI (diameter 1cm)
was drawn on the right hepatic lobe (Fig.1), avoiding large hepatic vessels,
bile ducts, and cardiac motion artifacts. Signals as a function of b-value were
used to derive three parameters in IVIM equation by nonlinear least squared
(NLLS) fitting: $$$Sb= S0[(1-f) ∙ e^{-bD} + f ∙ e^{-bD^*}]$$$--[1], where Sb and S0
represent the signal magnitude at b-factor equals b and 0s/mm^{2}
respectively. Perfusion fraction is denoted by
f, D is the diffusion coefficient, and D* is the pseudo-diffusion coefficient
caused by perfusion. All data processing was carried out by self-designed
Matlab scripts.

Each subject
underwent the same scanning protocol twice, and two ROIs were selected from
each volunteer. Thus, four sets of data were obtained in each subject, making
the total number of data sixteen. Effects of low b-value settings were
evaluated by removing data points corresponding to specific b-values. Four schemes
were compared. First, all sixteen b-values were included (contained four very
low b-values which were b=0,5,10,15 s/mm^{2}); Second, b=5 s/mm^{2}
was eliminated (i.e., b=0,10,15 s/mm^{2} were included); Third, b=5 and
10 s/mm^{2} were eliminated (i.e., b=0,15 s/mm^{2} were included);
Last, b=15 s/mm^{2} was further eliminated (only b=0 s/mm^{2} preserved).

1. Le Bihan et al., Radiology, 161:401–407 (1986).

2. J.-P. Cercueil ·J.-M. Petit et al., Eur Radiol, 25:1541–1550 (2015).

Figure.1. Diffusion-weighted image with a ROI on the
right hepatic lobe ( b=100s/mm^{2})

Figure.2 Plots of Biexponential decay curve using
different number of very low b-value(red line contains four very low b values;
blue line contains three very low blues, and so on)

Figure.3 Fitting curves in the region of very low
b-value(b<20s/mm^{2})

Figure.4 Boxplot shows D* value in different number
of very low b values. D* value increases as selecting more number of very low b
values.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

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