Rapid measurement of intravoxel incoherent motion (IVIM) derived perfusion fraction for clinical magnetic resonance imaging

Objective This study aimed to investigate the reliability of intravoxel incoherent motion (IVIM) model derived parameters D and f and their dependence on b value distributions with a rapid three b value acquisition protocol. Materials and methods Diffusion models for brain, kidney, and liver were assessed for bias, error, and reproducibility for the estimated IVIM parameters using b values 0 and 1000, and a b value between 200 and 900, at signal-to-noise ratios (SNR) 40, 55, and 80. Relative errors were used to estimate optimal b value distributions for each tissue scenario. Sixteen volunteers underwent brain DW-MRI, for which bias and coefficient of variation were determined in the grey matter. Results Bias had a large influence in the estimation of D and f for the low-perfused brain model, particularly at lower b values, with the same trends being confirmed by in vivo imaging. Significant differences were demonstrated in vivo for estimation of D (P = 0.029) and f (P < 0.001) with [300,1000] and [500,1000] distributions. The effect of bias was considerably lower for the high-perfused models. The optimal b value distributions were estimated to be brain500,1000, kidney300,1000, and liver200,1000. Conclusion IVIM parameters can be estimated using a rapid DW-MRI protocol, where the optimal b value distribution depends on tissue characteristics and compromise between bias and variability

Quantitative liver MRI combining phase contrast imaging, elastography, and DWI: assessment of reproducibility and postprandial effect at 3.0 T.

To quantify short-term reproducibility (in fasting conditions) and postprandial changes after a meal in portal vein (PV) flow parameters measured with phase contrast (PC) imaging, liver diffusion parameters measured with multiple b value diffusion-weighted imaging (DWI) and liver stiffness (LS) measured with MR elastography (MRE) in healthy volunteers and patients with liver disease at 3.0 T.In this IRB-approved prospective study, 30 subjects (11 healthy volunteers and 19 liver disease patients; 23 males, 7 females; mean age 46.5 y) were enrolled. Imaging included 2D PC imaging, multiple b value DWI and MRE. Subjects were initially scanned twice in fasting state to assess short-term parameter reproducibility, and then scanned 20 min. after a liquid meal. PV flow/velocity, LS, liver true diffusion coefficient (D), pseudodiffusion coefficient (D*), perfusion fraction (PF) and apparent diffusion coefficient (ADC) were measured in fasting and postprandial conditions. Short-term reproducibility was assessed in fasting conditions by measuring coefficients of variation (CV) and Bland-Altman limits of agreement. Differences in MR metrics before and after caloric intake and between healthy volunteers and liver disease patients were assessed.PV flow parameters, D, ADC and LS showed good to excellent short-term reproducibility in fasting state (CV <16%), while PF and D* showed acceptable and poor reproducibility (CV = 20.4% and 51.6%, respectively). PV flow parameters and LS were significantly higher (p<0.04) in postprandial state while liver diffusion parameters showed no significant change (p>0.2). LS was significantly higher in liver disease patients compared to healthy volunteers both in fasting and postprandial conditions (p<0.001). Changes in LS were significantly correlated with changes in PV flow (Spearman rho = 0.48, p = 0.013).Caloric intake had no/minimal/large impact on diffusion/stiffness/portal vein flow, respectively. PC MRI and MRE but not DWI should be performed in controlled fasting state

DCE-MRI of the liver: reconstruction of the arterial input function using a low dose pre-bolus contrast injection.

To assess the quality of the arterial input function (AIF) reconstructed using a dedicated pre-bolus low-dose contrast material injection imaged with a high temporal resolution and the resulting estimated liver perfusion parameters.In this IRB-approved prospective study, 24 DCE-MRI examinations were performed in 21 patients with liver disease (M/F 17/4, mean age 56 y). The examination consisted of 1.3 mL and 0.05 mmol/kg of gadobenate dimeglumine for pre-bolus and main bolus acquisitions, respectively. The concentration-curve of the abdominal aorta in the pre-bolus acquisition was used to reconstruct the AIF. AIF quality and shape parameters obtained with pre-bolus and main bolus acquisitions and the resulting estimated hepatic perfusion parameters obtained with a dual-input single compartment model were compared between the 2 methods. Test-retest reproducibility of perfusion parameters were assessed in three patients.The quality of the pre-bolus AIF curve was significantly better than that of main bolus AIF. Shape parameters peak concentration, area under the time activity curve of gadolinium contrast at 60 s and upslope of pre-bolus AIF were all significantly higher, while full width at half maximum was significantly lower than shape parameters of main bolus AIF. Improved liver perfusion parameter reproducibility was observed using pre-bolus acquisition [coefficient of variation (CV) of 4.2%-38.7% for pre-bolus vs. 12.1-71.4% for main bolus] with the exception of distribution volume (CV of 23.6% for pre-bolus vs. 15.8% for main bolus). The CVs between pre-bolus and main bolus for the perfusion parameters were lower than 14%.The AIF reconstructed with pre-bolus low dose contrast injection displays better quality and shape parameters and enables improved liver perfusion parameter reproducibility, although the resulting liver perfusion parameters demonstrated no clinically significant differences between pre-bolus and main bolus acquisitions

Changes in liver stiffness after a liquid meal (ΔLS*) correlated to changes in portal vein flow (ΔPV Flow*) in healthy volunteers (blue diamonds) and patients (red squares).

<p>There was a significant correlation between ΔLS vs. ΔPV Flow (Spearman rho = 0.48, p = 0.013 for all subjects; rho = 0.51 p = 0.05 for fibrosis patients, and rho = 0.41, p = 0.21 for healthy volunteers). *Δ computed as 100*(postprandial-fasting)/fasting.</p

Image processing demonstrated in a 30 year-old healthy volunteer.

<p>Top row demonstrates the region of interest placement in the portal vein (PV) on the phase contrast magnitude and phase images obtained in fasting and postprandial conditions. PV flow and velocity values were 21.15 ml/s/2.7 cm/s (fasting) and 31.1 ml/s/17.8 cm/s (postprandial). Middle row demonstrates the region of interest placement in the right hepatic lobe on the diffusion images (for b = 15) and plots for bi-exponential fitting in fasting (true diffusion coefficient D, pseudodiffusion coefficient D* and perfusion fraction PF of 1.3×10⁻³ mm²/s, 57×10⁻³ mm²/s and 22%) and postprandial conditions (1.1×10⁻³ mm²/s, 171×10⁻³ mm²/s, 19%). Bottom row shows the gradient echo MRE reference image (left) and liver stiffness (LS) maps in fasting and postprandial conditions (LS was 1.9 and 1.9 kPa in fasting and postprandial conditions, respectively).</p

Hepatocellular carcinoma: IVIM diffusion quantification for prediction of tumor necrosis compared to enhancement ratios

Purpose: To correlate intra voxel incoherent motion (IVIM) diffusion parameters of liver parenchyma and hepatocellular carcinoma (HCC) with degree of liver/tumor enhancement and necrosis; and to assess the diagnostic performance of diffusion parameters vs. enhancement ratios (ER) for prediction of complete tumor necrosis. Patients and methods: In this IRB approved HIPAA compliant study, we included 46 patients with HCC who underwent IVIM diffusion-weighted (DW) MRI in addition to routine sequences at 3.0 T. True diffusion coefficient (D), pseudo-diffusion coefficient (D*), perfusion fraction (PF) and apparent diffusion coefficient (ADC) were quantified in tumors and liver parenchyma. Tumor ER were calculated using contrast-enhanced imaging, and degree of tumor necrosis was assessed using post-contrast image subtraction. IVIM parameters and ER were compared between HCC and background liver and between necrotic and viable tumor components. ROC analysis for prediction of complete tumor necrosis was performed. Results: 79 HCCs were assessed (mean size 2.5 cm). D, PF and ADC were significantly higher in HCC vs. liver (p  0.95, p < 0.002). Conclusion: D has a reasonable diagnostic performance for predicting complete tumor necrosis, however lower than that of contrast-enhanced imaging. Keywords: Hepatocellular carcinoma, Diffusion, Perfusion, Necrosi

Sequence parameters of the cine phase contrast, DWI and MR elastography (MRE) sequences obtained at 3.0 T in fasting and postprandial states.

<p>Sequence parameters of the cine phase contrast, DWI and MR elastography (MRE) sequences obtained at 3.0 T in fasting and postprandial states.</p

Study design.

<p>All subjects were scanned twice after 6 hours of fasting to assess short-term reproducibility of MRI metrics (subjects were removed from the MRI system and re-imaged). Subjects were then scanned again in postprandial conditions, 20 min. after a 700 kcal liquid meal.</p

Postprandial changes in phase contrast metrics (PV flow, PV velocity), DWI metrics (liver D, D*, PF and ADC) and liver stiffness (LS) measured in 30 subjects (expressed in mean ± SD).

<p>PV: portal vein, PV flow (ml/s), PV velocity (cm/s), D (true diffusion coefficient, ×10⁻³ mm²/s), D* (pseudodiffusion coefficient, ×10⁻³ mm²/s), PF (perfusion fraction, %), ADC (apparent diffusion coefficient, ×10⁻³ mm²/s), liver stiffness (liver stiffness, kPa).</p><p>**First fasting measurement.</p><p>***Paired Wilcoxon test.</p><p>****Calculated as 100*(postprandial-fasting)/fasting.</p><p>****LS calculated in 27 subjects.</p

Diagram depicting calculated AIF (arterial input function) parameters (A).

<p>An example is shown in a 67-year-old patient with HCV (same patient as in Fig. 1). Pre-bolus AIF (B) and main bolus AIF (C). Pre-bolus AIF demonstrates higher peak concentration, upslope and AUC60, shorter TTP and smaller FWHM (values are given on the figures).</p