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Download powerpoint Fig 4. The relationship between f and rCBV is shown for conventional biexponential fitting left panel and for simplified linear fitting of 7 nonzero b-values right panel.
The correlation coefficient r for each relationship is also provided. Time to reconstruct a complete perfusion fraction dataset for a single patient was approximately 2 minutes for flinear compared with 36 Simplified model for fbiexponential.
Discussion Our results demonstrate that clinically relevant perfusion information can be obtained using a simplified IVIM methodology based on linear asymptotic fitting of as few as 2 nonzero b-values.
We validated this method for 2 commonly encountered clinical scenarios: Perfusion maps constructed using the simplified fitting procedure were qualitatively similar to those obtained with conventional biexponential fitting.
As expected, reducing the number of b-values in the estimation of flinear came at a cost of reduced accuracy in the resulting perfusion maps compared with full biexponential fitting. However, clinically meaningful differences in the perfusion fraction between high- and low-grade tumors and Simplified model ischemic and healthy brain tissue were observed independent of the choice of model and number of b-values used in the fit.
For both gliomas and strokes, flinear underestimated fbiexponential when only 2 nonzero b-values were used. In addition, reducing the number of b-values resulted in increased variability lower R2 in the estimated perfusion fraction.
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This variability may be more problematic in the evaluation of strokes than in tumors because the large perfusion fraction observed in high-grade gliomas would be easier to detect than the small differences in the perfusion fraction between ischemic and normal brain tissue.
On the basis of these results and the data presented in Table 2we propose a recommended minimum of 4 nonzero b-values for clinical application of the simplified IVIM procedure. The simplified linear fitting procedure has been applied in other organ systems.
With respect to gliomas, results using simplified linear fitting are in agreement with prior studies using conventional IVIM methods, 618 suggesting that the perfusion fraction obtained by either fitting procedure is valuable in the preoperative evaluation of tumor grade.
Interestingly, a recent study did not show a significant association between IVIM and conventional DSC perfusion parameters, 34 while the present study and another study with partial subject overlap 6 showed only a moderate correlation.
Our results are consistent with the hypothesis that IVIM parameters may contain slightly different information than classically defined perfusion measurements, as has been previously postulated on theoretical grounds. The weighting of the IVIM perfusion fraction toward the capillary network is supported by immunohistochemical measurements of microvessel density in animal models.
For example, a recent study found that the IVIM perfusion fraction was prognostic for 2-year survival in a small cohort of patients with gliomas.
The ability to rapidly obtain simultaneous diffusion and perfusion information using a simplified linear fitting procedure may prove useful in the setting of acute stroke. Beyond obvious advantages such as lack of dependence on gadolinium administration or estimation of an arterial input function, the local nature of IVIM perfusion measurements may make them more sensitive to flow from leptomeningeal collaterals, which is a known challenge for other MR perfusion methods.
Our study has several limitations. Further evaluation at multiple institutions using a variety of hardware configurations is required to demonstrate the broader applicability of the simplified IVIM methodology for brain imaging.
Finally, while it appears that IVIM provides clinically valuable information regarding the cerebral microcirculation, the underlying physiologic interpretation of IVIM perfusion parameters requires further study.
Decreasing the number of b-values comes at a cost of reduced accuracy in the resulting perfusion maps, and we have proposed a recommended minimum of 4 nonzero b-values when applying linear fitting for quantitative evaluation of clinical pathology.
The reduced acquisition times and simple postprocessing requirements of this technique may facilitate more widespread adoption of IVIM for brain imaging in clinical and research settings.
GE National Football League advisory board. Swiss National Science Foundation C. Federau received support from the Swiss National Science Foundation. Related abstract previously presented at: Indicates open access to non-subscribers at www.ASimpleModel uses video-driven instruction with financial templates and notes available for download to teach financial modeling in a simple and effective way.
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BACKGROUND AND PURPOSE: Despite a recent resurgence, intravoxel incoherent motion MRI faces practical challenges, including limited SNR and demanding acquisition and postprocessing requirements. A simplified approach using linear fitting of a subset of higher b-values has seen success in other organ systems.
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