ABSTRACT
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.
Subject(s)
Carcinoma, Hepatocellular/diagnostic imaging , Diffusion Magnetic Resonance Imaging , Liver Neoplasms/diagnostic imaging , Adult , Aged , Algorithms , Female , Humans , Image Interpretation, Computer-Assisted , Image Processing, Computer-Assisted , Male , Middle Aged , Observer Variation , Prospective Studies , Reproducibility of Results , Signal-To-Noise RatioABSTRACT
The objective of this work was to fit the degradation model proposed by Orskov & McDonald (1979) to data of an in situ degradability trial. Neutral detergent fiber degradations (NDF) of coast cross grass (Cynodon dactylon x Cynodon nlemfunensis) were submitted to twelve cutting ages (30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330 and 360 days) in a complete block design. At each cutting age, NDF degradation was investigated using nine incubation times (0, 3, 6, 12, 24, 48, 72, 96 and 120 hours) in a split-plot design, taking cutting age as main plots and incubation time as subplots. Each plot comprised a non-lactating cow with a permanent ruminal fistula. Variances of the parameter estimates were also obtained, as well as expressions for the estimation of confidence intervals for parameters in the model. A good fit of the model to the data of neutral detergent fiber degradability in the most cutting ages was found. The cutting ages of the coast cross grass influenced the degradability of different fractions, benefiting early stages. In advanced cutting ages the parameters estimates were less precise.
Objetivou-se com este trabalho ajustar o modelo de degradação proposto por Orskov & McDonald (1979) aos dados de um experimento de degradabilidade in situ. Foi avaliada a degradação da fibra em detergente neutro (FDN) da gramínea Coast Cross (Cynodon dactylon x Cynodon nlemfunensis) submetida a doze idades de corte (30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330 e 360 dias) em um delineamento em blocos casualizados. Em cada idade de corte a degradação da FDN foi avaliada em nove tempos de incubação (0, 3, 6, 12, 24, 48, 72, 96 e 120 horas) em um esquema de parcela subdividida, com as idades de corte na parcela e os tempos de incubação na subparcela. Cada parcela foi constituída por uma vaca não-lactante com fístula ruminal permanente. O ajuste do modelo foi avaliado através da interpretação biológica dos parâmetros, coeficiente de determinação, quadrado médio do resíduo e teste de aderência (lack of fit). As variâncias dos estimadores dos parâmetros também foram obtidas por meio da matriz de covariância dos parâmetros fornecendo expressões para estimação do intervalo de confiança dos parâmetros do modelo. O modelo se ajustou bem aos dados de degradabilidade da fibra em detergente neutro na maioria das idades de corte. As idades de corte da gramínea Coast Cross influenciaram a degradabilidade das diferentes frações, favorecendo os cortes mais precoces. Nas idades de corte avançadas as estimativas dos parâmetros foram menos precisas.
