Abstract
ObjectivesTo investigate transient signal loss on diffusion weighted images (DWI) and overestimation of apparent diffusion coefficient (ADC) in parotid glands using single shot echoplanar DWI (EPDWI).Materials and MethodsThis study enrolled 6 healthy subjects and 7 patients receiving radiotherapy. All participants received dynamic EPDWI with a total of 8 repetitions. Imaging quality of DWI was evaluated. Probability of severe overestimation of ADC (soADC), defined by an ADC ratio more than 1.2, was calculated. Error on T2WI, DWI, and ADC was computed. Statistical analysis included paired Student t testing and Mann-Whitney U test. A P value less than 0.05 was considered statistically significant.ResultsTransient signal loss was visually detected on some excitations of DWI but not on T2WI or mean DWI. soADC occurred randomly among 8 excitations and 3 directions of diffusion encoding gradients. Probability of soADC was significantly higher in radiotherapy group (42.86%) than in healthy group (24.39%). The mean error percentage decreased as the number of excitations increased on all images, and, it was smallest on T2WI, followed by DWI and ADC in an increasing order.ConclusionsTransient signal loss on DWI was successfully detected by dynamic EPDWI. The signal loss on DWI and overestimation of ADC could be partially remedied by increasing the number of excitations.
Highlights
Over the last two decades, diffusion-weighted imaging (DWI) has been increasingly applied to characterize the diffusivity of tissue in head and neck by measuring apparent diffusion coefficient (ADC)
Transient signal loss was visually detected on some excitations of DWI but not on T2WI or mean DWI. severe overestimation of ADC (soADC) occurred randomly among 8 excitations and 3 directions of diffusion encoding gradients
Probability of soADC was significantly higher in radiotherapy group (42.86%) than in healthy group (24.39%)
Summary
Over the last two decades, diffusion-weighted imaging (DWI) has been increasingly applied to characterize the diffusivity of tissue in head and neck by measuring apparent diffusion coefficient (ADC). There is a wide variation regarding ADC measurements in head and neck. Taking parotid glands as an example, the ADC measured in different studies varies widely from as low as 0.28 × 10–3 mm2/s [4] to as high as 2.46 × 10–3 mm2/s [5] in healthy subjects. Such a wide range of ADC has exceeded the difference of ADC among different tumors and the change of ADC before and after treatment of tumors. Direct comparison of parotid ADC in different study groups becomes difficult due to several technical factors that cause the discrepancy in parotid ADC measurements, including strength and number of diffusion gradients (b values) [6], pulse sequences [7, 8], and acceleration factors [7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
