Table 4. Summary of conclusions and future recommendations.

Challenge	Effect	Recommendation
Gustatory stimulation	Gustatory stimulation increases ADC values significantly	Stimulating agents like lemon juice, high number of tablets or instantly bitten tablets of ascorbic acid that gives an immediate stimulation results in initial increase of ADC values and should be used. If using a stimulating agent giving an immediate stimulation, it is sufficient to perform only one DW-MRI scanning 30 seconds after stimulation
b-values	b-values below about 200 increases ADC. High b-values carries risk of bias towards lower ADC	If multiple low b-values are measured in addition to higher b-values a bi-exponential model should be used, for example IVIM. Alternatively, only b-values above 200 should be used with a mono-exponential model. If very high b-values are used, attention should be given to SNR to avoid measurement influenced by the noise-floor
ROI definition	There is no significant difference in mean ADC values between the four ROI selection methods	With no significant difference in mean ADC values between ROI selection methods, the only recommendation for choice of ROI selection method can be given from inter- and intra-reader agreement during ROI placement. The best inter- and intra-reader agreement can apparently be achieved using whole gland ROI selection methods
Irradiation of parotid glands	The ADC values are showing a significant increase after irradiation. There is no clear correlation between ADC changes and mean dose to the parotid glands. There is a slight negative correlation between changes in mean ADC pre-post RT values and time point of post treatment	Regarding post treatment timing of DW-MRI, it is recommended to perform it in the acute phase (0–10 days) or early phase (10–60 days) after RT where the radiation induced damage of salivary glands is most pronounced and the largest changes in mean ADC values are expected to occur

ADC, apparent diffusion coefficient; IVIM, intravoxel incoherent motion; SNR, signal-to-noise; ROI, region of interest.