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Tractography refers to the in vivo reconstruction of fiber bundles, e.g., in brain, via the analysis of anisotropic diffusion patterns measured by diffusion weighted magnetic resonance imaging (DWI). The data provides a probabilistic model of local diffusion which was shown to correlate with the underlying fibrous structure under certain assumptions. Deterministic tractography suffers from uncertainties at kissing and crossing fibers, at different levels depending on the diffusion model employed (e.g., DTI, HARDI), yet it is easy to interpret and use in clinic. In this study, a novel generic algorithm, split and merge tractography (SMT), is proposed that provides a real-time, interactive and reliability ranked assessment of potential pathways, communicating the true information content of the data without sacrificing the usability of tractography. Specifically, SMT takes in a precomputed set of tracts and the diffusion data (e.g., DTI, HARDI) as its input, generates a set of short (reliable) tracts via splitting at unreliable points and forms quasi-random clusters of short tracts by means of which the space of short tract clusters, representing complete tracts, is sampled. A histogram of thus formed clusters is built in an efficient way and used for real-time, interactive assessment of pathways. The current implementation uses DTI and fourth-order Runge-Kutta integration based streamline tractography as its input. The method is qualitatively assessed on phantom DTI data and real DTI data. Phantom experiments demonstrated that SMT is capable of highlighting the problematic regions and suggesting pathways that are completely overseen by input streamline tractography. Real data experiment results correlate well with known anatomy and also demonstrate that the reliability ranking can efficiently suppress the erroneous tracts interactively. The method is compared to a recent method that also pursues a similar approach, yet in a global optimization based framework. The comparative study on real DTI data revealed the lower computational load of SMT and a better correlation with known anatomy.

Introduction: The purpose of this study was to determine the normative apparent diffusion coefficient (ADC) values at 3T using high b-value (3000 s/mm(2)) diffusion-weighted images (DWI) and compare the signal characteristics of the high b value with standard b-value (1000 s/mm(2)) DWI., Methods: Institutional review board approval was obtained for this prospective study which included 20 volunteers (10 M, 10 F, mean age: 38.7+/-14.9) without any known clinical disease or radiological findings. All brain examinations were performed with 3T MR by using similar parameters of b1000 and b3000 DWI sequences. DWI and ADC maps were obtained. Signal intensity, noise, signal to noise ratio (SNR), contrast to noise (CNR), contrast ratio (CR), and ADC values of bilateral posterior limb of internal capsule, frontal white matter, parietal gray matter, pons, thalamus, splenium of corpus callosum were measured on b1000 and b3000 DW images., Results: In all anatomic locations, MR signal intensity, SNR and ADC values of b3000 images were significantly lower than MR signal intensity, SNR and ADC values of b1000 images (p<0.001). The CNR and CR values at the posterior limb of internal capsule and pons were significantly increased on b3000 images (p<0.001) and decreased in the other regions measured., Conclusion: The ADC values calculated from standard b-value DWI were significantly higher than those calculated from high b-value DWI. These results agree with the previous studies. In the regions where CNR values increase with high b value, b3000 DWI images may provide additional clinical information.

The aim of this study was to assess the feasibility of diffusion tensor imaging (DTI) of the prostate and to determine normative fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of healthy prostate with a 3-Tesla magnetic resonance imaging (MRI) system. Thirty volunteers with a mean age of 28 (25-35) years were scanned with a 3-Tesla MRI (Intera Achieva; Philips, The Netherlands) system using a six-channel phased array coil. Initially, T2-weighted turbo spin-echo (TSE) axial images of the prostate were obtained. In two subjects, a millimetric hypointense signal change was detected in the peripheral zones on T2-weighted TSE images. These two subjects were excluded from the study. DTI with single-shot echo-planar imaging (ssEPI) was performed in the remaining 28 subjects. ADC and FA values were measured using the manufacturer supplied software by positioning 9-pixel ROIs on each zone. Differences between parameters of the central and peripheral zones were assessed. Mean ADC value of the central (1.220 +/- 0.271 x 10(-3) mm(2)/s) was found to be significantly lower when compared with the peripheral gland (1.610 +/- 0.347 x 10(-3) mm(2)/s) (P < 0.01). Mean FA of the central gland was significantly higher (0.26), compared with the peripheral gland (0.16) (P < 0.01). This study shows the feasibility of prostate DTI with a 3-Tesla MR system and the normative FA and ADC values of peripheral and central zones of the normal prostate. The results are compatible with the microstructural organization of the gland. [ABSTRACT FROM AUTHOR]