Integrated intravoxel incoherent motion tensor and diffusion tensor brain MRI in a single fast acquisition

The acquisition of intravoxel incoherent motion (IVIM) data and diffusion tensor imaging (DTI) data from the brain can be integrated into a single measurement, which offers the possibility to determine orientation-dependent (tensorial) perfusion parameters in addition to established IVIM and DTI parameters. The purpose of this study was to evaluate the feasibility of such a protocol with a clinically feasible scan time below 6 min and to use a model-selection approach to find a set of DTI and IVIM tensor parameters that most adequately describes the acquired data. Diffusion-weighted images of the brain were acquired at 3 T in 20 elderly participants with cerebral small vessel disease using a multiband echoplanar imaging sequence with 15 b-values between 0 and 1000 s/mm² and six non-collinear diffusion gradient directions for each b-value. Seven different IVIM-diffusion models with 4 to 14 parameters were implemented, which modeled diffusion and pseudo-diffusion as scalar or tensor quantities. The models were compared with respect to their fitting performance based on the goodness of fit (sum of squared fit residuals, chi² ) and their Akaike weights (calculated from the corrected Akaike information criterion). Lowest chi² values were found using the model with the largest number of model parameters. However, significantly highest Akaike weights indicating the most appropriate models for the acquired data were found with a nine-parameter IVIM-DTI model (with isotropic perfusion modeling) in normal-appearing white matter (NAWM), and with an 11-parameter model (IVIM-DTI with additional pseudo-diffusion anisotropy) in white matter with hyperintensities (WMH) and in gray matter (GM). The latter model allowed for the additional calculation of the fractional anisotropy of the pseudo-diffusion tensor (with a median value of 0.45 in NAWM, 0.23 in WMH, and 0.36 in GM), which is not accessible with the usually performed IVIM acquisitions based on three orthogonal diffusion-gradient directions.

Role of intravoxel incoherent motion MRI in early assessment of the response of esophageal squamous cell carcinoma to chemoradiotherapy: A pilot study

BACKGROUND

Since definitive concurrent chemoradiotherapy (CRT) is standard therapy for inoperable esophageal squamous cell carcinoma (ESCC), early evaluation of treatment response is crucial for patients and would be useful in assessing response, especially in patients with severe side effects.

PURPOSE

To explore the feasibility of intravoxel incoherent motion (IVIM) MRI in the early assessment of treatment response to CRT.

STUDY TYPE

Prospective.

POPULATION

Twenty-three inoperable ESCC patients.

SEQUENCE

IVIM 3T MRI of nine b values (0, 25, 50, 75, 100, 150, 200, 500 and 800 s/mm² ) was performed at four timepoints: pre-CRT (within 5 days before CRT), mid-CRT (2-3 weeks after the start of CRT), end-CRT (within 5 days after the end of CRT), and post-CRT (1 month after the end of CRT).

ASSESSMENT

IVIM-based parameters and ADC were analyzed independently by two radiologists and treatment response was assessed by the Response Evaluation Criteria in Solid Tumors (RECIST).

STATISTICAL TESTS

Analyses of variance for repeated measurements were conducted to observe dynamic changes of IVIM-based parameters (D, f, and D*) and ADC during CRT. The parameters and their change percentages (Δ%) were compared between complete response (CR) and partial response (PR) by Mann-Whitney U-test. Diagnostic performance of parameters in predicting response was tested with receiver-operating characteristic curve analysis.

RESULTS

ADC, D, and f increased significantly during CRT (P < 0.001, < 0.001, and 0.001, respectively). ADC, f, Δ%ADC, and Δ%D at mid-CRT in CR group were significantly higher than those in the PR group (P = 0.002, 0.013, 0.005, and 0.011, respectively). D combined with f and ADC had highest area under curve (0.917) in identifying CR from PR.

DATA CONCLUSION

IVIM parameters proved useful in assessing response to definitive concurrent CRT for inoperable ESCC and combined with ADC at an early stage of treatment was a good predictor of response.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 4 J. MAGN. RESON. IMAGING 2018;48:349-358.