Purpose To optimize the diffusion‐weighting b values and postprocessing pipeline for hybrid intravoxel incoherent motion diffusion kurtosis imaging in the head and neck region. Methods Optimized diffusion‐weighting b value sets ranging between 5 and 30 b values were constructed by optimizing the Cramér‐Rao lower bound of the hybrid intravoxel incoherent motion diffusion kurtosis imaging model. With this model, the perfusion fraction, pseudodiffusion coefficient, diffusion coefficient, and kurtosis were estimated. Sixteen volunteers were scanned with a reference b value set and 3 repeats of the optimized sets, of which 1 with volunteers swallowing on purpose. The effects of (1) b value optimization and number of b values, (2) registration type (none vs. intervolume vs. intra‐ and intervolume registration), and (3) manual swallowing artifact rejection on the parameter precision were assessed. Results The SD was higher in the reference set for perfusion fraction, diffusion coefficient, and kurtosis by a factor of 1.7, 1.5, and 2.3 compared to the optimized set, respectively. A smaller SD (factor 0.7) was seen in pseudodiffusion coefficient. The sets containing 15, 20, and 30 b values had comparable repeatability in all parameters, except pseudodiffusion coefficient, for which set size 30 was worse. Equal repeatability for the registration approaches was seen in all parameters of interest. Swallowing artifact rejection removed the bias when present. Conclusion To achieve optimal hybrid intravoxel incoherent motion diffusion kurtosis imaging in the head and neck region, b value optimization and swallowing artifact image rejection are beneficial. The optimized set of 15 b values yielded the optimal protocol efficiency, with a precision comparable to larger b value sets and a 50% reduction in scan time.
Perfusion MRI is promising for the assessment, prediction, and monitoring of radiation toxicity in organs at risk in head and neck cancer. Arterial spin labeling (ASL) may be an attractive alternative for conventional perfusion MRI, that does not require administration of contrast agents. However, currently, little is known about the characteristics and performance of ASL in healthy tissues in the head and neck region. Therefore, the purpose of this study was to optimize and evaluate multi-delay pseudo-continuous ASL (pCASL) for the head and neck region and to explore nominal values and measurement repeatability for the blood flow (BF), and transit time and T1 values needed for BF quantification in healthy tissues. Twenty healthy volunteers underwent a scan session containing 4 repeats of multidelay pCASL (Post-label delays (PLDs): 1000, 1632, 2479 ms). ROIs were defined in the parotid glands, submandibular glands, tonsils, and cerebellum (as reference). Nominal values of BF were calculated as the average over 4 repeats per volunteer. The repeatability Abbreviations ASL -Arterial Spin Labeling BF -Blood flow DCE -Dynamic Contrast Enhanced DSC -Dynamic susceptibility contrast pCASL -Pseudo-continuous arterial spin labeling PLD -Post labeling delay RC -Repeatability coefficient ROI -Region of interest SAR -Specific absorption rate SMG -Submandibular gland wCV -Within subject coefficient of variation wSD -Within subject standard deviation 3D-QALAS -3D multi-parametric quantification using an interleaved Look-Locker acquisition sequence with a T2 preparation pulse
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