In the previous video, we covered using Marquees to create regions of interest or areas of interest. In this video, we are going to use the Lasso tool so we are able to trace around a region of interest. So I will select the Lasso tool and we want to make sure it's the regular Lasso tool, since we are going to manually trace around this vessel. If you are working with me open HE_ NORMAL20x.TIF found in your Chapter 10 Exercise Folder. What you are seeing is a hematoxylin and eosin stained coronary vessel. We want to make sure that any measurements we perform are on the correct measurement scale. So we go to Analysis > Set Measurement Scale and select the 20x Calibration.
Now we can always use the Info panel to monitor what calibration setting we have selected. Now with this image, one area that you might want to manually trace around would be the boundary between the adventitia, here this lighter pink color, and the cardio myocytes. This would be very difficult to do in an automated way, so you will have to use some sort of manual tool to actually place the selection. By using the Lasso tool, we have to press our button down and just start tracing. Now we have to hold the button down at all times and we just manually go around the area and here, I am using a mouse as I am drawing, a track path would definitely work out better. Now if I were to let go right now, Photoshop would automatically close the selection. Once you start using this tool you are in it for the entire trace, you can't stop half way through or let go off the mouse or else it will be automatically connect the two ends of a line.
In this case, I am close enough. I am going to let go over the mouse and it closed the boundary and now we have our margin and selection around the adventitia of the coronary vessel. This case, I want to open up the Measurement Log. I will go to Window > Measurement Log. Before I hit Record Measurements, even though I have the correct calibration selected, I want to make sure I have the right data points selected. Now 20x Boxes while I use it for boxes previously, in this case, I am going to use it for an area and that's still an appropriate data point set to use.
I can come down, hit Record Measurements. There is my label, the document, the fact that was our selection versus a count or a ruler, it's in microns and I have an area in microns, the perimeter and the height and the width of a bounding box, not the maximum height or the maximum width and that's an important cautionary tale because that height is from this top, all the way down to this bottom and the width is from right here, all the way across to here where it matches up with this point.
So if there was a square bounding box around the region of interest, this is the height and width of that bounding box. Now if you need fine detail and the region of interest is not too large, you can use the Lasso tool but there is two other Lasso tools. They are more automated, they are easier and quicker to use and I will be demonstrating them in the next two videos.
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