What action should be taken if a phantom falls outside the +/- 1.5% Shewhart limit?

• A. Ignore the results
• B. Repeat the scan
• C. Calibrate the machine immediately
• D. Change the phantom used

Answer: (B)

When a phantom falls outside the +/- 1.5% Shewhart control limits, the appropriate action is to repeat the scan. This decision is grounded in the principles of quality control in diagnostic imaging. The Shewhart control charts are used to monitor the stability and performance of imaging systems, including bone densitometry machines.

The purpose of repeating the scan is to confirm whether the initial out-of-range result was a true indication of a problem with the machine or if it was due to other transient factors, such as a random error or an issue with the setup of the phantom. By repeating the scan, technicians can collect additional data to determine the reliability of the findings, which is essential for ensuring accurate and precise measurements in bone density assessments.

If the repeated scan still shows values outside the established limits, further actions, such as calibration or maintenance of the equipment, may indeed need to be considered, but the immediate next step is to confirm the results with another trial. This approach reinforces the commitment to maintaining high standards in imaging protocols, ultimately ensuring patient safety and accurate diagnoses.