People who get shot don't usually have the opportunity to choose the type of bullet -- unless the wound is self-inflicted, of course. But the kind of bullet involved may be important in figuring out whether the bit of metal will wreak havoc in an MRI's magnetic field.
As the authors of a write: "Few studies exist for magnetic resonance imaging (MRI) issues and ballistics, and there are no studies addressing movement, heating, and artifacts associated with ballistics at 3-tesla (T). Movement because of magnetic field interactions and radiofrequency (RF)-induced heating of retained bullets may injure nearby critical structures. Artifacts may also interfere with the diagnostic use of MRI."
So , of the University of California San Francisco, and colleagues collected 32 different bullets and seven types of shotgun pellets from the San Francisco Police Department, and used 1.5-, 3-, and 7-Tesla MRIs to measure translational attraction and torque. They tested five bullets for "magnetic field interactions, RF-induced heating, and the generation of artifacts at 3-T."
Their findings? "Ballistics made of lead with copper or alloy jackets appear to be safe with respect to MRI-related movement at 1.5-, 3-, and 7-T static magnetic fields, whereas ballistics containing steel may pose a danger if near critical body structures because of strong magnetic field interactions. Temperature increases of selected ballistics during 3-T MRI was not clinically significant, even for the ferromagnetic projectiles. Finally, ballistics containing steel generated larger artifacts when compared with ballistics made of lead with copper and alloy jackets and may impair the diagnostic use of MRI."
In other words, avoid using an MRI if you suspect a steel bullet -- say, an armor-piercing bullet with stainless steel cores, or steel shotgun pellet -- was involved in a past injury. After all, many implants are verboten in an MRI because they contain metal.
"Anytime someone has an implant of any type, and a bullet would be considered a type of implant, you need to determine what the safety profile is of that before you put them in the scanner," one of the authors, Russell Dedini, MD, of the University of California, when discussing the preliminary results in 2012.
Maybe bullets are a kind of "nontherapeutic implant?"
For an example of a "magic bullet," see a recent post. Then, read more of Ivan Oransky's blog posts.