Metal Protocol

The axial T1 scan through the pelvis (FOV = 30 cm.) raises the SNR. This gain is partially outweighed by a concomitant increase in the matrix. In addition, the wide FOV magnifies inhomogeneities in the magnetic field. With all other parameters adjusted for comparison, note the marked reduction in artifact on the T1 axial through the prosthetic hip on the left (FOV = 18 cm.).

Large FOV encompassing the whole pelvis

Smaller FOV limited to the right hip: Notice the marked reduction in the area of susceptibility around the hip prosthesis.

Use fast / turbo STIR:

STIR is a robust way of fat-suppressing, relatively unaffected by inhomogenities in the magnetic field. This sequence would probably improve increasing the NEX to 2.

Never use GRE:

FSE or fast/turbo STIR are relative tolerant to the presence of metal. SE follows in order. GRE should always be avoided.

Use Contrast:

Contrast increases the SNR without any drawbacks. Even without fat-suppression the findings will come to light if there is a pre-contrast image for comparison. The scan to the left is with contrast material.


pre-contrast	post-contrast

What else can we do?

Increase the BW to 32 KHz for a 16 cm FOV, and 62 KHz for a 30 cm FOV. An increase in receiver bandwidth results in less artifact, including chemical-shift and magnetic susceptibility. Further a higher Bw will result in shorter interecho spacing, decreasing the TE for echoes at the end of the train. Lower TE values for peripheral echoes increases the signal of these peripheral echoes, and results in reduced blur.

Since one of the parameters modified in the "metal protocol" is the ETL - as indicated below - a concomitant increase in Bw will also indirectly be beneficial in reducing blur.

Increase the matrix to reduce intravoxel dephasing.

Increase the ETL to 16 for T2 weighted images.

T1 FSE with reduced ETL (3). It's important to compensate by increasing the TE values to 20 msec.