Measurement Accuracy

Measurement Accuracy
 
Small errors in measurements can lead to large errors in calculated results.  Measurement accuracy is dependent upon the resolution of the image and following standard measurement techniques.  The transducer that will provide the best resolution for the measurement should be selected.  Use the highest frequency possible that will allow visualization of the structure to be measured.  The focal point should be located at the structure to be measured.  The display should be maximized (magnified using zoom, depth, width) so only the area of interest is visualized.  Timing measurements should be done under higher sweep speeds.  Consistent settings and probes should be used for similar measurements between patients and between studies of the same patients.  Do not change settings or change probes and expect that the measurements will be equally accurate.  Measurements of length or area of a cardiac structure should be made on the inside edge or leading edge to leading edge technique.  When measuring slopes, use two points as far apart as possible.  Use the ECG for locating mechanical end-diastolic and end-systolic phases. The doppler angle may be off more than 20 degrees which will induce an error greater than 5%.  While the Doppler in one plane may appear to be correct, in another plane it can be off more than 20 degrees.  Therefore, clinical interpretation is important. If your measurements do not fit the clinical picture, search for views or angles that may indicate that your measurements are not accurate.    
Accuracy Factors
Resolution
Focal Point
Display Size
Sweep Speed
Consistency
Leading Edge Technique
Slope Points
ECG utilization