Magnetic Resonance Imaging Astounding

The MRI magnet and patient table The operator’s console

Most MR magnets are Superconductors Liquid helium is the primary cryogen Boiling 1 atm: °F (-268.9°C, 4 o K) Once ramped up, MR magnets remain on all the time

Housed in an 18 wheeler, mobile MR machines use permanent or resistance coil magnets.

Damadian’s apparatus 1972 patent did not describe imaging Lauterbur built the first imaging machine, but Damadian made The first for human imaging.

Hydrogen: 55-60% of the body is water 2/3 of water is hydrogen An MRI scan of the head and brain Created from imaging hydrogen

A spinning, charged particle, such as a hydrogen proton, has a magnetic north and south pole. It will align to an external magnetic field like a compass needle aligns to the earth’s magnetosphere North South

Magnetic poles of H are randomly oriented in the human body

Aligned to the MRI magnet roughly half spin up, and half spin down Opposing spins cancel each other’s force Unpaired spinning protons create a net magnetization vector

The protons that are used to create the MR signal are the unpaired ones In a sample of 20 million protons, about 7 are usable.

Hydrogen protons in the patient’s body do not align fully parallel to the magnetic field. They precess (wobble). The rate of precession is called the larmor frequency. It is 42.5 MHz at one tesla

RF energy 42.5 MHz is in the range of radio frequencies A H proton will absorb RF when it has the same frequency. It resonates. 90 o flip

180 o flip RF energy

When the RF is turned off, the proton returns to alignment with the MRI magnet. It relaxes. As it does it gives off the energy it absorbed from the RF in a process called free Induction decay (FID)

The net magnetization vector scans coils of wire, inducing a flow of electrical current which is the MR signal.

Z X Y Gradient coils vary the magnetic field strength thoughout the x, y, z planes causing every H proton to precess at a different frequency MHz

The net magnetization vector scans coils of wire, inducing a flow of electrical current which is the MR signal.

QD Head Speeder Surface Coils

Functional MRI fMRI Is that the truth, the whole truth, and nothing but the truth?

Computed Tomography (CT) Magnetic Resonance Imaging (MRI) Cardiovascular Interventional Technology (CIT) Radiologic Science Advanced Registry Modalities Mammography