Ultrasound M-mode is defined as a motion versus time display of the B-mode ultrasound image along a chosen line. The motion is represented by the Y-axis and time is represented by the X-axis. Common applications for M-mode include looking at E point septal separation in cardiac scanning or calculating fetal heart rate for obstetrics. You can also use M-mode in lung ultrasound to evaluate for lung sliding and rule out pneumothorax.
Below is an example of how the M-mode (left side of screen) and B-mode (right side of screen) compare when looking at lung sliding. M-mode simply takes a “slice” of your B-mode image where the cursor line is placed and translates that “slice” over time. It ignores everything else on the B-mode scan except for where you have that cursor line. You can see on the Y-axis how the structures (subcutaneous tissue, muscle, and pleural line) correlate between the M-mode and B-mode images. You can also see the relative motion of these structures over time (X-axis).
Here are the steps to acquiring an M-mode Image:
- M-mode Step 1: Acquire 2D image and Center Structure of Image
- M-mode Step 2: Push the M-mode button to make the M-mode cursor line appear
- M-mode Step 3: Place the M-mode cursor line along the structure of interest
- M-mode Step 4: Push the M-mode button again to activate M-mode
- M-mode Step 5: Push the Freeze Button
- M-mode Step 6: Scroll to the desired image
- M-mode Step 7: Push the Measure Button
- M-mode Step 8: Measure Area of Interest