FIG

In FIGS. 2-9, N is a vector representation of the nuclei of radioactive material 16 shown in FIG. 1. Nuclear vector N is depicted in a three dimensional graphical environment conventionally represented by X, Y and Z axes. The Z axis is defined as the external magnetic field B.sub.o vector produced by cylindrical magnet 18.

Nuclear vector N of radioactive material 16 possessing a magnetic moment will align along, and precess around, the external magnetic field vector B.sub.o or Z axis as represented in FIG. 2. The frequency of nuclear precession is the Larmor frequency. The radio-frequency (RF) coil 22 is tuned to the Larmor frequency of the radioactive nuclei N using the Larmor equation (.omega.=.gamma.. multidot.B.sub.o). For example, .gamma. for technetium 99 m is 9.5808781 Mhz/Tesla; .gamma. for U 235 is 0.76635 Mhz/Tesla; and . gamma. for tritium is 45.412125 Mhz/Tesla.

To initiate the production of beam 12 technician 26 prompts the appropriately tuned RF coil 22 to emit an RF pulse P, the frequency of which is matched to the Larmor frequency of the precessing nuclei. This matched RF pulse is absorbed by the precessing nuclei N as is shown in FIG. 3.

Larmor Frequency

Absorption of the RF pulse by the nuclei N results in the nuclei N tipping away from the external magnetic field vector B.sub.o. The degree to which the nuclei N flip out of the external magnetic field vector B.sub.o is referred to as the flip angle .theta. and is dependent upon the strength and duration of the RF pulse. A flip angle .theta. of 90.degree. results in nuclei revolving in the X-Y plane. This absorption of the tuned RF pulse P by nuclei N in FIG. 3 resulting in a flip angle .theta. of 90.degree. and subsequent revolution of the nuclei N in the X-Y plane is depicted in FIG. 4.

Once nuclear vector N has been flipped into the X-Y plane the nuclei spontaneously lose coherence into individual nucleus n', individual nucleus n", individual nucleus n'" and individual nucleus n"" by T2 or spin-spin relaxation as depicted in FIG. 5.

To restore the coherence of individual nucleus n', individual nucleus n", individual nucleus n'" and individual nucleus n"" the conventional MRI device of the nuclear decay laser 10 is prompted by either the operator 26 or through automatic programming of the MRI device to apply a 180.degree. refocusing RF pulse P' which is absorbed by individual nucleus n', individual nucleus n", individual nucleus n'" and individual nucleus n"" as shown in FIG. 6.

The 180.degree. refocusing pulse can be performed through conventional MRI spin echo techniques. Nuclear coherence can also be achieved by conventional MRI gradient echo techniques.

This absorption of the 180.degree. refocusing pulse or gradient echo technology results in coherent nuclei N revolving in the X-Y plane as depicted in FIG. 7.

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