CT arthrography of the human knee to measure cartilage quality with low radiation dose

Objective: Recently, CT arthrography (CTa) was introduced as a non-destructive technique to quantitatively measure cartilage quality in human knees. This study investigated whether this is also possible using lower radiation dose CT protocols. Furthermore, we studied the ability of (lower radiation) CTa to distinguish between local sulphated glycosaminoglycan (sGAG) content differences. Design: Of ten human cadaveric knee joints, six CT scans using different radiation doses (81.33-8.13 mGy) were acquired after intra-articular ioxaglate injection. The capability of CTa to measure overall cartilage quality was determined in seven anatomical regions of interest (ROIs), using equilibrium partitioning of an ionic contrast agent using (EPIC)-microCT (μCT) as reference standard for sGAG content. To test the capability of CTa to spatially distinguish between local differences in sGAG content, we calculated the percentage of pixels incorrectly predicted as having high or low sGAG content by the different CTa protocols. Results: Low radiation dose CTa correlated well with EPIC-μCT in large ROIs (R = 0.78; R2= 0.61; P < 0.0001). CTa can also distinguish between high and low sGAG content within a single slice. However, the percentage of incorrectly predicted quality pixels increases (from 35% to 41%) when less radiation is used. This makes is hard or even impossible to differentiate between spatial differences in sGAG content in the lowest radiation scans. Conclusions: CTa acquired using low radiation exposure, comparable to a regular knee CT, is able to measure overall cartilage quality. Spatial sGAG distribution can also be determined using CTa, however for this purpose a higher radiation dose is necessary. Nevertheless, radiation dose reduction makes CTa suitable for quantitative analysis of cartilage in clinical research.

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