Effects of diffusional kurtosis imaging parameters

Authors: Issei Fukunaga Masaaki Hori Yoshitaka Masutani Nozomi Hamasaki Shuji Sato Yuriko Suzuki Fumitaka Kumagai Masatsugu Kosuge Haruyoshi Hoshito Koji Kamagata Keigo Shimoji Atsushi Nakanishi Shigeki Aoki Atsushi Senoo

Publish Date: 2013/03/28

Volume: 6, Issue: 2, Pages: 343-348

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Abstract

Diffusional kurtosis imaging DKI is a new technique based on nonGaussian water diffusion analysis However the original DKI protocol six b values and 30 motionprobing gradient MPG directions requires more than 10 min of scanning time which is too long for daily clinical use We aimed to find suitable b value MPG direction and diffusion time settings for faster DKI Four normal healthy subjects participated in the study All DKI data sets were acquired on a clinical 3TMRI scanner Philips Medical Systems with use of three protocols of 0–7500 s/mm2 b values 6–32 MPG directions and 23–80 ms diffusion time There was a remarkable difference in the standard deviation SD of the mean DK values in the number of MPG directions The mean DK values were significantly higher in the posterior limb of the internal capsule p = 0003 r = 0924 and thalamus p = 0005 r = 0903 whereas the mean DK values of the cerebrospinal fluid CSF p = 0001 r = −0976 were significantly lower when we used a longer diffusion time Our results indicate that the SD of the mean DK values was higher in 15 MPG directions than in 20 MPG directions and more Because the mean DK values of the CSF were significantly lower when we used longer diffusion times we expect longer diffusion times to be useful for DKI We propose the following imaging parameters for clinical use 0 1000 and 2000 s/mm2 b values 20 MPG directions Δ/δ 453/133 msIn the technique known as diffusionweighted imaging DWI the diffusion of water through biological tissue provides image contrast that depends on the Brownian motion of water molecules This technique was introduced into clinical practice in the 1990s 1 2 3 DWI can be used with echo planar imaging through which it is possible to detect cerebral ischemia with imaging times ranging from a few seconds to 2 min 4 Diffusion tensor imaging is a magnetic resonance imaging MRI technique enabling in vivo examination of white matter WM anisotropy in the human brain Diffusion anisotropy is a parameter derived from the directional distribution of diffusivity and the degrees of anisotropy have been shown to correlate with microstructural changes in neural tissues 5Diffusional kurtosis imaging DKI has been highlighted as a new technique based on nonGaussian water diffusion analysis 5 It is assumed that water diffusion in biological tissues is restricted The nonGaussian behavior of water molecules may provide useful information related to tissue structure and pathophysiology 2 Many studies have been conducted with DKI for evaluation of cerebral infarction glioma multiple sclerosis MS Parkinson disease attentiondeficit hyperactive disorder and others 6 7 8 9 10 11 It is important to use DKI as a clinical tool for investigation of the imaging parameters in the healthy brain In the DKI approach it is desirable to acquire DKI datasets with multiple b value to minimize the fitting errors However the original protocol six b values and 30 motionprobing gradient MPG directions 5 requires more than 10 min of scanning time which is regarded as being too long for daily clinical use Moreover to date few reports have been conducted on the imaging parameters of DKI 12 13 compared with those of diffusion tensor imaging and DWI 14 15 16Because the original DKI protocol six b values and 30 MPG directions takes too much time for daily clinical use we sought DKI settings that result in faster scans We examined the influence of various b values MPG directions and diffusion times on measurements of the mean DKFour normal healthy subjects age range 21–24 years mean age 225 years participated in the study This study was approved by the institutional review board of our hospital Written informed consent was obtained from all participants and their relatives All DKI data were acquired on a clinical 3TMRI scanner Philips Medical Systems Best The Netherlands with use of three study protocols as follows

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