Qualitative and Quantitative Analyses: Image Evaluation and Interpretation
DW-MR images and their corresponding apparent diffusion coefficient (ADC) maps provide unique information that reflects tissue cellularity and organization. The b-value images and ADC maps can be assessed qualitatively, and by comparing the varying signal
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CONTENTS
SUMMARY 3.1
Introduction
33
3.2
Qualitative Assessment of DW-MR Images 34 3.2.1 DW-MR Images Acquired Using Different b-Values 34 3.2.1.1 T2 Shine-Through 35 3.2.1.2 Diffusion Anisotropy 36 3.2.2 ADC Maps 37 3.2.3 Principles of Image Interpretation Using DW-MRI and ADC Maps 39 3.3 3.3.1
Quantitative ADC Evaluation 41 Quantitative ADC Evaluation by Regions of Interests 41 3.3.1.1 Summary Statistics 41 3.3.1.2 Voxelwise Analysis 41 3.3.2 Software for ADC Calculation 42 3.3.3 Applying Quantitative ADC Values for Disease Characterization 42 3.3.4 Measurement Reproducibility 44 3.4 3.4.1 3.4.2 3.4.3
Image Display 44 Display of the b-Value DW-MR Images 44 Image Fusion 44 Diffusion-weighted Whole-body Imaging with Background Body Signal Suppression (DWIBS) 46
3.5
Conclusions 46
References
46
DW-MR images and their corresponding apparent diffusion coefficient (ADC) maps provide unique information that reflects tissue cellularity and organization. The b-value images and ADC maps can be assessed qualitatively, and by comparing the varying signal intensities and appearances of tissues on these images, it is possible to characterize tissues and diseases. However, the ADC maps can also provide quantitative measurements of tissue water diffusivity, which can be used not only for disease assessment, but also for the evaluation of disease response to treatment. In order to achieve optimal image interpretation, the DW-MR images and ADC maps should be displayed with conventional morphologic images to enable the best assessment to be made. A pragmatic approach to utilizing DW-MR images and ADC maps for disease assessment is discussed in this chapter.
3.1 Introduction
Dow-Mu Koh, MD, MRCP, FRCR Department of Diagnostic Radiology, Royal Marsden Hospital, Downs Road, Sutton, Surrey SM2 5PT, UK
Image interpretation of DW-MRI studies has a steep learning curve, and requires the radiologist to understand how and why the images are to be reviewed. There are some differences in the way one may look at DW-MR images compared with conventional morphological MR images. Firstly, whilst most conventional morphological MR images are only assessed visually, interpretation of DW-MR images can be performed qualitatively by visual assessment whilst quantitative assessment can be performed by analysing the apparent diffusion coefficient (ADC) maps.
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D. M. Koh
Secondly, because disease assessment is based on differential signal attenuation with increasing b-values on DW-MRI between tissues, it is often helpful to display images acquired using different b-values sideby-side to facilitate this evaluation. Thirdly, when applying DW-MRI for disease characterization, the quantitative ADC maps calculated from the DW-MR images should be interpreted in conjunction with the b-value images to avoid misinterpretation. Last, but not the least, using multi-planar reformats or fusion imaging with conventional morphological images can aid disease localization and assessment (Koh et al. 2008). In this chapter, we will discuss how to qualita
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