Age and gender dependence of liver diffusion parameters and the evidence of intravoxel incoherent motion modelling of perfusion component is constrained by diffusion component

Abstract

ObjectivesTo establish reference values for middle aged subjects and investigate age and gender dependence of liver diffusion MRI parameters.MethodsThe IVIM type of liver diffusion scan was based on a single-shot spin-echo type echo-planar sequence using a 1.5-T magnet with 16 b-values. DDVD (diffusion-derived vessel density) was the signal difference between b=0 and b=2 s/mm2 images after removing visible vessels. IVIM analysis was performed with full-fitting and segmented-fitting, and with threshold b-value of 60 or 200 s/mm2, and fitting started from b=2 s/mm2. 32 men (age range: 25-71 years) and 26 men (age: 22-69 years) had DDVD and IVIM analysis respectively, while 36 women (age: 20-71 years) had DDVD and IVIM analysis.ResultsDDVD had an age-related reduction noted for women. IVIM results of full fitting had good agreement with segmented fitting with threshold b of 60 s/mm2 results, but less so with results of threshold b of 200 s/mm2. As age increases, female subjects’ Dslow measure had significant reduction, and PF and Dfast measure had significant increase. For the age group of 40-55 years, DDVD, Dslow, PF, and Dfast were 12.27±3.90, 1.072±0.067 (10−3mm2/s), 0.141±0.025, 61.0±14.0 (10−3mm2/s), and 13.4±3.6, 1.069±0.074 mm2/s, 0.119±0.014, 57.1±13.2 mm2/s, for men and women, respectively.ConclusionDDVD measure suggest that aging may be associated with reduction in liver perfusion. Lower Dslow measurement can lead to artificial higher PF and Dfast measurement, providing the evidence of IVIM modeling of perfusion component is constrained by diffusion component.

Mutual constraining of slow component and fast component measures: some observations in liver IVIM imaging

“…However, the observed PF and D fast results gave contradictory results compared with DDVD and known vessel physiology of the liver aging, with both PF and D fast measures showed age-dependent elevation. This was observed when we used segmentation fitting or full fitting, and observed when we performed bi-exponential decay fitting included or excluded b=0 data (3). We concluded that the quantification of both PF and D fast is constrained by D slow , i.e., lower D slow leads to higher PF and D fast measurements, even PF and D fast did not increase or even declined.…”

“…Recently we reported that, for the liver, IVIM modeling of the perfusion component is constrained by the diffusion component, and a reduced D slow measure leads to artificially higher PF and D fast measures (3). In this study of 26 male volunteers (age: 22-69 years) and 36 female volunteers (age: 20-71 years), we demonstrated an age-dependent liver D slow decline, which is expected to be caused by an agedependent iron deposition increase, an age-dependent fat deposition increase, and also a reduction of vasculature in the healthy aging livers.…”

“…We use the data from Huang et al's study (3), and we only choose those of very clean and good quality, i.e., those had two good quality IVIM scans and we were able to use the mean values from these two scans, which included 17 healthy men and 27 healthy women. We assume age of the subjects is the initial independent variable, and physiologically aging causes both D slow and PF to decrease (3). We make a plot to study the relationship between D slow and PF (Figure 3A).…”

Observed paradoxical perfusion fraction elevation in steatotic liver: An example of intravoxel incoherent motion modeling of the perfusion component constrained by the diffusion component

“…However, in NMR in Biomedicine we recently published that, at least for the liver, IVIM modeling of the perfusion component is constrained by the diffusion component, and a reduced D slow measure leads to artificially higher PF and D fast measures. 1 Our results may have important implications for interpreting previously published literature on IVIM and for designing future IVIM studies. For one example, many previous works have reported that liver steatosis is associated with an increased PF.…”

“…In a study evaluating IVIM measure of liver fibrosis, we reported a Pearson correlation coefficient r of 0.865 between PF and D fast . 19 Although it is more difficult to measure D fast precisely, 18,20 the point mentioned above is also likely to have implications for interpreting D fast results, as a reduced D slow measure can lead to an artificially higher D fast measure as well 1 .…”