How many patients should be scanned to achieve in-vivo precision for a validity study?

• A. 20 patients scanned twice
• B. 30 patients scanned twice
• C. 15 patients scanned three times
• D. 40 patients scanned once

Answer: (B)

To achieve in-vivo precision for a validity study in bone densitometry, the recommendation is to scan 30 patients twice. This approach provides a robust dataset that can effectively assess the reproducibility of the results, which is crucial in establishing the accuracy and reliability of the bone density measurements.

Scanning each patient multiple times allows for the calculation of variability within results and helps ensure that any differences in measurements are statistically significant rather than due to random error. By choosing to scan 30 patients, the study includes a sufficient sample size that improves the statistical power of the analysis, allowing for more reliable conclusions about the precision of the imaging technique.

In contrast, scanning fewer patients or fewer times would not yield enough data to draw meaningful conclusions about the consistency of the measurements. A higher number of scans creates a stronger analysis for determining reproducibility, which is a critical aspect of any validity study in medical imaging. Thus, scanning 30 patients gives the best combination of patient population and repeated measurements to achieve necessary precision standards.