How to Measure Cobb Angle with CobbAngleApp on Apple Vision Pro: Detailed Guide

 

Using the CobbAngleApp on Apple Vision Pro makes measuring Cobb angles in X-ray images highly intuitive and precise, thanks to its advanced gesture-based interactions and immersive interface. Here is a detailed step-by-step guide to help you measure the Cobb angle accurately:

 

 1. Load an X-ray Image

   - Consent: Before loading the X-ray image, the app will prompt you to confirm that you have consent to use the patient’s X-ray for analysis. You will be asked to allow the app to access your photo library.

   - Select an Image: After providing consent, you will be guided to choose an X-ray image from your library. The selected image will be displayed in the immersive space of Vision Pro, allowing you to see it clearly as you proceed with the measurement.

 

 2. Identifying Key Points on the Vertebrae

   The Cobb angle is calculated based on the vertebral end plates at the extreme ends of the spinal curvature (most caudal and most cephalad vertebrae). You will mark four points:

 

   - P1 (First Point): Locate the left edge of the inferior end plate of the most caudal vertebra in the spinal curve.

   - P2 (Second Point): Locate the right edge of the same end plate. The app will automatically draw a line between P1 and P2.

   

   > The line P1-P2 represents the inferior end plate of the vertebra, which is the base for calculating the Cobb angle.

 

   - P3 (Third Point): Move upwards to the superior end plate of the most cephalad vertebra (the topmost vertebra in the curve) and mark the left edge of this end plate.

   - P4 (Fourth Point): Mark the right edge of the same superior end plate. The app will draw a line between P3 and P4.

 

 3. Drawing Perpendicular Vectors

   Once the four points are set (P1, P2, P3, and P4), the app will automatically calculate the midpoints of the lines P1-P2 and P3-P4. Two perpendicular lines will then be drawn:

   

   - A perpendicular line from the midpoint of P1-P2 will extend in both directions.

   - A perpendicular line from the midpoint of P3-P4 will also extend in both directions, but it will always be aligned to ensure it points towards the P1-P2 line, ensuring the measurement of the correct Cobb angle.

 

 4. Calculating the Cobb Angle

   - Real-Time Calculation: As the perpendicular lines are drawn, the app will calculate the Cobb angle in real-time. The Cobb angle is the angle formed by the intersection of these perpendicular lines.

   - Acute Angle Measurement: The app ensures that the acute angle (less than 90 degrees) between the perpendiculars is always calculated. The calculated Cobb angle will be displayed halfway between the two sets of points (P1-P2 and P3-P4) for easy viewing.

 

 5. Refining the Measurement

   - Draggable Points: If you need to adjust the positions of any of the points, simply drag the corresponding point (P1, P2, P3, or P4) to a more accurate location. The lines and the calculated angle will automatically update in real-time.

   - The points are equipped with larger, invisible hitboxes to make them easier to grab and move, ensuring precise placement over the vertebral edges.

 

 6. Reviewing the Results

   - Once the angle is calculated, you will see the Cobb angle in degrees displayed between the two sets of points. This value is updated dynamically as you adjust the points.

   - The app ensures that the angle displayed is easy to read and positioned clearly on the screen.

 

 7. Saving Your Measurement

   - After the measurement is complete, you can save a screenshot of the current image, including all lines, points, and the Cobb angle, by clicking the Save Screenshot button. The screenshot will be stored in your photo library.

   

 8. Resetting for a New Measurement

   - If you wish to measure a new curve or a new X-ray, you can reset the current measurement by pressing the Reset button. This will clear the selected points, lines, and the angle, allowing you to either select new points on the same image or load a new X-ray.

 

 9. Accessing Help

   - If you ever need guidance, simply click the Help button. This will open a detailed help window with step-by-step instructions on how to use the app and measure the Cobb angle accurately.

 

 Summary of Steps:

   1. Load an X-ray image.

   2. Mark P1 and P2 on the caudal vertebra’s inferior end plate.

   3. Mark P3 and P4 on the cephalad vertebra’s superior end plate.

   4. Let the app automatically draw perpendicular lines and calculate the Cobb angle in real-time.

   5. Adjust points as necessary to refine the measurement.

   6. Save or reset for a new measurement.