To investigate intravoxel incoherent motion (IVIM) tensor imaging of the in vivo human heart and elucidate whether the estimation of IVIM tensors is affected by the complexity of pseudo-diffusion components in myocardium. Methods: The cardiac IVIM data of 10 healthy subjects were acquired using a diffusion weighted spin-echo echo-planar imaging sequence along 6 gradient directions with 10 b values (0~400 s/mm 2). The IVIM data of left ventricle myocardium were fitted to the IVIM tensor model. The complexity of myocardial pseudo-diffusion components was reduced through exclusion of low b values (0 and 5 s/mm 2) from the IVIM curve-fitting analysis. The fractional anisotropy, mean fraction/mean diffusivity, and Westin measurements of pseudo-diffusion tensors (f p and D*) and selfdiffusion tensor (D), as well as the angle between the main eigenvector of f p (or D*) and that of D, were computed and compared before and after excluding low b values. Results: The fractional anisotropy values of f p and D* without low b value participation were significantly higher (P < .001) than those with low b value participation, but an opposite trend was found for the mean fraction/diffusivity values. Besides, after removing low b values, the angle between the main eigenvector of f p (or D*) and that of D became small, and both f p and D* tensors presented significant decrease of spherical components and significant increase of linear components. Conclusion: The presence of multiple pseudo-diffusion components in myocardium indeed influences the estimation of IVIM tensors. The IVIM tensor model needs to be further improved to account for the complexity of myocardial microcirculatory network and blood flow.

PURPOSE: To distinguish hepatocellular carcinoma (HCC) from other types of hepatic lesions with the adaptive multi-exponential IVIM model. METHODS: 94 hepatic focal lesions, including 38 HCC, 16 metastasis, 12 focal nodular hyperplasia, 13 cholangiocarcinoma, and 15 hemangioma, were examined in this study. Diffusion-weighted images were acquired with 13 b values (b = 0, 3, …, 500 s/mm2) to measure the adaptive multi-exponential IVIM parameters, namely, pure diffusion coefficient (D), diffusion fraction (fd), pseudo-diffusion coefficient (Di*) and perfusion-related diffusion fraction (fi) of the ith perfusion component. Comparison of the parameters of and their diagnostic performance was determined using Mann-Whitney U test, independent-sample t test, one-way analysis of variance, Z test and receiver-operating characteristic analysis. RESULTS: D, D1* and D2* presented significantly difference between HCCs and other hepatic lesions, whereas fd, f1 and f2 did not show statistical differences. In the differential diagnosis of HCCs from other hepatic lesions, D2* (AUC, 0.927) provided best diagnostic performance among all parameters. Additionally, the number of exponential terms in the model was also an important indicator for distinguishing HCCs from other hepatic lesions. In the benign and malignant analysis, D gave the greatest AUC values, 0.895 or 0.853, for differentiation between malignant and benign lesions with three or two exponential terms. Most parameters were not significantly different between hypovascular and hypervascular lesions. For multiple comparisons, significant differences of D, D1* or D2* were found between certain lesion types. CONCLUSION: The adaptive multi-exponential IVIM model was useful and reliable to distinguish HCC from other hepatic lesions.

Background Preoperative chemotherapy is becoming standard therapy for liver metastasis from colorectal cancer, so early assessment of treatment response is crucial to make a reasonable therapeutic regimen and avoid overtreatment, especially for patients with severe side effects. The role of three non-mono-exponential diffusion models, such as the kurtosis model, the stretched exponential model and the statistical model, were explored in this study to early assess the response to chemotherapy in patients with liver metastasis from colorectal cancer. Methods Thirty-three patients diagnosed as colorectal liver metastasis were evaluated in this study. Diffusion-weighted images with b values (0, 200, 500, 1000, 1500, 2000 s/mm 2 ) were acquired at 3.0 T. The parameters ( ADC k , K, DDC,α, D s and σ ) were derived from three non-mono-exponential models (the kurtosis, stretched exponential and statistical models) as well as their corresponding percentage changes before and after chemotherapy. The difference in above parameters between the response and non-response groups were analyzed with independent-samples T-test (normality) and Mann–Whitney U-test (non-normality). Meanwhile, receiver operating characteristic curve (ROC) analyses were performed to assess the response to chemotherapy. Results Significantly lower values of K (the kurtosis coefficient derived from the kurtosis model) and σ (the width of diffusion coefficient distribution in the statistical model) ( P < 0.05) were observed in the respond group before treatment, as well as higher Δ K and Δ σ values ( P < 0.05) after the first cycle of chemotherapy were also found compared with the non-respond group. ROC analyses showed the K value acquired before treatment had the highest diagnostic performance (0.746) in distinguishing responders from non-responders. Furthermore, the high sensitivity (100%) and accuracy (76.3%) from the K value before treatment was found in assessing the response of colorectal liver metastasis to chemotherapy. Conclusions The non-mono-exponential diffusion models may be able to predict early response to chemotherapy in patients with colorectal liver metastasis.

Background Non‐monoexponential diffusion models are being used increasingly for the characterization and curative effect evaluation of hepatocellular carcinoma (HCC). But the fitting quality of the models and the repeatability of their parameters have not been assessed for HCC. Purpose To evaluate kurtosis, stretched exponential, and statistical models for diffusion‐weighted imaging (DWI) of HCC, using b‐values up to 2000 s/mm2, in terms of fitting quality and repeatability. Study Type Prospective. Population Eighteen patients with HCC. Field Strength/Sequence Conventional and DW images (b = 0, 200, 500, 1000, 1500, 2000 s/mm2) were acquired at 3.0T. Assessment The parameters of the kurtosis, stretched exponential, and statistical models were calculated on regions of interest (ROIs) of each lesion. Statistical Tests The fitting quality was evaluated through comparing the fitting residuals produced on the average data of ROI between different models using a paired t‐test or Wilcoxon rank‐sum test. Repeatability of the fitted parameters at the median values on the voxelwise data of ROI was assessed using the within coefficient of variation (WCV), the intraclass correlation coefficient (ICC), and the 95% Bland–Altman limits of agreements (BA‐LA). The repeatability was divided into four levels: excellent, good, acceptable, and poor, referring to the values of ICC and WCV. Results Among three models, the stretched exponential model provided the best fit to HCC (P < 0.05), whereas the statistical model produced the largest fitting residuals (P < 0.05). The repeatability of K from the kurtosis model was excellent (ICC 0.915; WCV 8.79%), while the distributed diffusion coefficient (DDC) from the stretched model was just acceptable (ICC 0.477; WCV 27.83%). The repeatability was good for other diffusion‐related parameters. Data Conclusion Considering the model fit and repeatability, the kurtosis and stretched exponential models are the preferred models for the description of the DW signals of HCC with respect to the statistical model. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:297–304.

Background Intravoxel incoherent motion (IVIM) tensor imaging is a promising technique for diagnosis and monitoring of cardiovascular diseases. Knowledge about measurement repeatability, however, remains limited. Purpose To evaluate short‐term repeatability of IVIM tensor imaging in normal in vivo human hearts. Study Type Prospective. Population Ten healthy subjects without history of heart diseases. Field Strength/Sequence Balanced steady‐state free‐precession cine sequence and single‐shot spin‐echo echo planar IVIM tensor imaging sequence (9 b‐values, 0–400 seconds/mm2 and six diffusion‐encoding directions) at 3.0 T. Assessment Subjects were scanned twice with an interval of 15 minutes, leaving the scanner between studies. The signal‐to‐noise ratio (SNR) was evaluated in anterior, lateral, septal, and inferior segments of the left ventricle wall. Fractional anisotropy (FA), mean diffusivity (MD), mean fraction (MF), and helix angle (HA) in the four segments were independently measured by five radiologists. Statistical Tests IVIM tensor indexes were compared between observers using a one‐way analysis of variance or between scans using a paired t‐test (normal data) or a Wilcoxon rank‐sum test (non‐normal data). Interobserver agreement and test–retest repeatability were assessed using the intraclass correlation coefficient (ICC), within‐subject coefficient of variation (WCV), and Bland–Altman limits of agreements. Results SNR of inferior segment was significantly lower than the other three segments, and inferior segment was therefore excluded from repeatability analysis. Interobserver repeatability was excellent for all IVIM tensor indexes (ICC: 0.886–0.972; WCV: 0.62%–4.22%). Test–retest repeatability was excellent for MD of the self‐diffusion tensor (D) and MF of the perfusion fraction tensor (fp) (ICC: 0.803–0.888; WCV: 1.42%–9.51%) and moderate for FA and MD of the pseudo‐diffusion tensor (D*) (ICC: 0.487–0.532; WCV: 6.98%–10.89%). FA of D and fp and HA of D presented good test–retest repeatability (ICC: 0.732–0.788; WCV: 3.28%–8.71%). Data Conclusion The D and fp indexes exhibited satisfactory repeatability, but further efforts were needed to improve repeatability of D* indexes. Level of Evidence 2 Technical Efficacy Stage 1