Long-T2 Suppression Pulses

Ultra-short echo time (UTE) and Zero Echo Time (ZTE) magnetic resonance imaging (MRI) allows for visualization of tissues with very short T2 relaxation times. This tissues, which include collagen-rich tissues such as tendons, ligaments and menisci, as well as calcifications, myelin, periosteum and cortical bone, are normally invisible with conventional MRI techniques.

Long-T2 species suppression is required for many UTE/ZTE applications to improve the contrast of short-T2 species. We have developed new long-T2 RF suppression pulses. This page provides descriptions and Matlab files for designing these pulses, as well as providing some sample pulses.

Larson PEZ, Gurney PT, Nayak K, Gold GE, Pauly JM, Nishimura DG. "Designing long-T2 suppression pulses for ultrashort echo time imaging." Magnetic Resonance in Medicine2006; 56: 94-103. PDF

Single-Band Pulses

These pulses contain a single spectral band for suppressing long-T2 species at the water proton resonance. They can be easily designed using the SLR pulse design algorithm as maximum-phase saturation pulses, as described in Pauly et al, Parameter relations for the Shinnar-Le Roux selective excitation pulse design algorithm (NMR imaging)IEEE Transactions on Medical Imaging 10:53-63 (1991).

The rf_tools Matlab toolbox for SLR RF pulse design is available at Stanford Radiological Science Laboratory Software. With this package, single-band pulses are designed with the command(:rf
= dzrf(Npoints, TBW, 'sat', 'max');) The pulses can be scaled to various lengths depending on the bandwidth required and/or T2 suppression desired.






 

 

Sample Single-Band Pulses

Normal UTE knee image


UTE knee images using a dual-band long-T2 suppression pulse


UTE knee images using a dual-band long-T2 suppression pulse

Single-band pulses (in a Matlab format MAT-file) with TBWs of 1.6, 2.0, 2.4 and 2.8

Dual-Band Pulses

These pulses contain two spectral bands for suppressing long-T2 species at both the fat and water proton resonances. They are created using the complex Parks-McClellan filter design algorithm.

Dual-Band Pulses

The sample pulses are in Matlab MAT-files, and are all in sample dualband.zip. In addition to the RF pulses, they include all inputs used in the design function.

  • 25 ms pulse with 85 Hz water suppression bandwidth, and 145 Hz fat suppression bandwidth centered at -255 Hz (dual-band pulse used in paper).
  • 20 ms pulse with 60 Hz water suppression bandwidth, and 120 Hz fat suppression bandwidth centered at -245 Hz.
  • 30 ms pulse with 60 Hz water suppression bandwidth, and 120 Hz fat suppression bandwidth centered at -240 Hz.
  • 30 ms pulse with 80 Hz water suppression bandwidth, and 120 Hz fat suppression bandwidth centered at -230 Hz.
  • 30 ms pulse with 100 Hz water suppression bandwidth, and 120 Hz fat suppression bandwidth centered at -240 Hz.

MATLAB Code

The Source Code (github) and download Package (matlabcentral) contains a Matlab function that designs maximum-phase dual-band RF pulses. The function includes usage details, which can be accessed through the Matlab help command. It requires additional MATLAB functions that are included in the archive, and also the rf_tools Matlab toolbox (available at Stanford Radiological Science Laboratory Software).

Other Resources

Some useful MR-related MATLAB resources:

Bloch Equation Simulator by Brian Hargreaves

Stanford Radiological Science Laboratory Software (includes rf_tools package)