Oh Boy! The doctor wants to do a cath using biplane. Maybe he wants to conserve contrast. That’s not a bad thing, you know? Or maybe, he’s just in a hurry. Whatever the reason, we don’t do a lot of biplane cardiac caths. So a lot of us are unfamiliar with the concept. It’s not that difficult to understand (once someone explains it!) Let me give it a try.
Biplane imaging is all about centering the patient in both the AP and Lateral planes. This is a concept known in IR as “ISOCENTER”. There are a lot of people under the impression that isocenter means centering the table. There’s a little more to it than that.
ISOCENTER is the process of putting the part of interest (the heart) in the center of both the AP and lateral planes. The heart will be a few centimeters (4-5) above the tabletop, so centering the table itself will throw the centering off by just enough to make the task difficult.
Think of a wheel on a bicycle. There’s the outer tire and the center core (axle). Think of the patient as the center core and the outer tire as the path of the tube. This is the A plane. Anywhere the tube goes, the core is in the center of the circle. The trick is to make sure the heart is at the core.
Now, add a second plane at right angles to the first. The same principles apply. Keeping the heart as the core of the second plane means the heart will be in the center of the circle. If the heart is in the center of both planes, it is comparable to a sphere, such as the earth. Any point on the surface of the sphere (the earth) is aligned with the center of the earth. So imagine a sphere around your patient, with each tube and detector moving along the surface and the heart at the center. Even when the two circles aren’t at right angles, the heart should still be at the center of the circles.
Now…the trick! Before you begin the procedure, center the heart in both planes. Center in the lateral plane (B) by changing the table height. When the table height is set so the heart is in the center, don’t move it (or make tiny adjustments). Center the heart in the AP plane by moving the tabletop as usual. As you angle the tubes, you may need to adjust the centering slightly, but it should remain close to perfect. Just remember:
If you need to adjust the AP plane, change the tabletop. If you need to adjust the B (lateral) plane, change the table height.
That’s the trick...center the lateral plane using the table height before you begin the procedure. Your adjustments during the case will be slight, if you need them at all.
It may take a little practice or it may click the first time you try it. Either way, I think you will come to the same conclusion. It’s not that difficult once you get it!