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Spine align images to root4/7/2023 ![]() To obtain ADC maps less sensitive to perfusion effects, while keeping a reasonable acquisition time and sufficient signal-to-noise ratio (SNR), the lowest acquired b-value for WB-DWI tends to lie in the range 50–100 s/mm 2 1, 8. In WB-DWI, two or three b-values are in general collected and followed by mono-exponential calculation of quantitative ADC maps 1. The b-value, set by the strength and timings of these gradients, makes the sequence sensitive to different scales of microscopic motion. This also hinders the integration of DWI data into workflows for large-scale analysis of multi-parametric oncology data, in which geometric alignment between input images are essential for automatic and correct tumor evaluation 5, 6, 7.ĭWI visualizes differences in water diffusivity by incorporating diffusion sensitizing gradients into the magnetic resonance (MR) sequence. This mismatch can lead to difficulties when segmenting and characterizing organs and lesions in DWI and apparent diffusion coefficient (ADC) data sets, manually and automatically 2, 3. One reason is that DWI data sets are typically affected by distortions and misalignments, meaning DWI and structural images acquired in the same scan session are not geometrically aligned. ![]() Widespread clinical use of WB-DWI has however been limited and the technique is primarily used in specialized centers. Usage areas span tumor detection, tumor characterization and therapy response assessment 3, 4. Whole-body diffusion-weighted imaging (WB-DWI) is increasingly being used in oncological applications and has proven a valuable diagnostic tool in cancers such as multiple myeloma, melanoma, lymphoma and metastatic disease, as well as in screening applications 1, 2. The b0- and b50-based distortion corrections had a very similar performance. Overall, the RPG distortion correction gave an improved geometric accuracy for WB-DWI data acquired at 1.5T and 3T. Visually, the distortion correction improved spine alignment at station borders, but introduced registration-based artefacts mainly for the spleen and kidneys. Small numerical differences between non-corrected and distortion corrected apparent diffusion coefficient (ADC) values were measured. Mutual information (MI) between low b-value DWI and structural data increased with distortion correction ( P < 0.05), while improvements in region of interest (ROI) based similarity metrics, comparing the position of incidental findings on DWI and structural data, were location dependent. DWI data was distortion corrected using the RPG method based on b = 0 s/mm 2 (b0) and b = 50 s/mm 2 (b50) DWI acquisitions. Multi-station DWI and structural magnetic resonance imaging (MRI) data of healthy controls were acquired at 1.5T (n = 20) and 3T (n = 20). ![]() In this work we assess the performance of the reverse polarity gradient (RPG) method for correction of WB-DWI geometric distortion. As such, DWI and structural images acquired in the same scan session are not geometrically aligned, leading to difficulties in e.g. Whole body diffusion-weighted imaging (WB-DWI) is increasingly used in oncological applications, but suffers from misalignments due to susceptibility-induced geometric distortion.
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