Measurement accuracy of sonographic sector scanners

Discrepancies identified in anatomic size measurements in clinical obstetric sonographic studies prompted a study of the accuracy of measurements obtained from sonographic mechanical sector scanners. There were large variations in equipment calibration of the size of the sector scan angle among six clinical sonographic units from four manufacturers, causing transverse measurements to vary from 47% (high) to 9% (low), compared with the true size of a cylindrical plastic phantom. Depth measurements, parallel to the direction of sound penetration, are only velocity dependent and were accurate to within 6%. Transverse size measurements made using mechanical sector scanners should be suspect unless the calibration has been checked using a phantom test object.