|Quoting francoflier (Reply 7):|
It's a cool new bit of tech, but Doc, what is the usefulness of a video MRI?
First of all, as a research tool it is useful. Second, it can be used to watch organs at work. As the resolution improves, we might be able to catch heart valves in action, track fluid flows (which can be done with short-pulses and diffusion-weighted imaging), follow labeled contrast agents (C-13, gadolinium) through arteries looking for obstructions, etc.
At present, there are only two imaging modalities that can be used to generate real-time video images: ultrasound and fluoroscopy.
Ultrasound has a number of limitations. While it can track fluid flow and relative motion (toward or away from the probe) and generate real-time images, it is a poor choice for certain types of imaging (brain [because it's surrounded by bone], perfusion studies, bone, etc.). It also works poorly in the obese patient. While it can generate 3-D images in real-time due to advances in scanning technology and computer reconstruction, fidelity . Ultrasound is fantastic for pregnancy and cardiac studies because it involves no ionizing radiation (like X-rays or gamma rays) and it can generate very good 3-D images when used in a newer scanning mode, but it's also difficult to interpret and operator-dependent. This video shows how ultrasound can be used to image the heart: http://www.youtube.com/watch?v=4vBJoWP-zBM
Fluoroscopy is basically video X-ray. This is a video of fluoroscopy (suggest you mute sound to eliminate boring music): http://www.youtube.com/watch?v=q0cKhkJk30A.
Fluoroscopy cannot generate 3-D images and is limited because it can only image radiopaque structures (those that are opaque to X-ray). So, for example, if you want to image swallowing, you need to have the patient swallow a barium-laced substrate. If you want to image coronary blood flow, you need to snake a catheter into the coronary circulation (which is a very invasive procedure) and inject the tracer that way. The other problem with fluoroscopy is that it uses X-rays, which are ionizing radiation, and the dose is much higher than that for a single film.
There is some research into using high-speed volumetric CT
as a video imaging modality, but this research is hampered by the excessive radiation doses delivered to the patients and so until much more sensitive detectors can be developed, this modality will probably be stalled in development.
So video MRI
will enable us to image entire volumes in four dimensions (three space, one time) without the need for radiopaque tracers (although contrast agents might still be useful in some studies) or ionizing radiation. MRI
magnets are expensive to purchase and to operate (think bizjet). They require liquid helium cooling, magnetic shielding, and lots of electricity, which is why even a short scan will run you over $1000, but they are very useful for a lot of different types of imaging that were once essentially impossible to obtain.