Academy of Chiropractic’s

Doctor's PI Program

#97

 From the Desk of:

 Mark Studin DC, FASBE (C), DAAPM, DAAMLP


"MRI STIR Views,
An Essential Protocol"

 

"The role of the STIR sequence in detection of recurrences in the post-surgical follow-up was also evaluated. The STIR sequence, designed to suppress signal from fat, also enhances the signal from tissue with long T1 and Trelaxation times, such as neoplastic and inflammatory tissue" (Golfieri, Baddely, Pringle, & Souhami, 1990, http://bjr.birjournals.org/cgi/content/abstract/63/748/251).

"(STIR) Also called Short Tau (t) (inversion timeInversion RecoverySTIR is a fat suppression technique with an inversion time TI = T1 ln2 where the signal of fat is zero (T1 is the spin lattice relaxation time of the component that should be suppressed). To distinguish two tissue components with this technique, the T1 values must be different. Fluid Attenuation Inversion Recovery (FLAIR) is a similar technique to suppress water.

Inversion recovery doubles the distance spins will recover, allowing more time for 
T1 differences. A 180° preparation pulse inverts the net magnetization to the negative longitudinal magnetization prior to the 90° excitation pulse. This specialized application of the inversion recovery sequence set the inversion time (TI) of the sequence at 0.69 times the T1 of fat. The T1 of fat at 1.5 Tesla is approximately 250 with a null point of 170 ms while at 0.5 Tesla its 215 with a 148 ms null point. At the moment of excitation, about 120 to 170 ms after the 180° inversion pulse (depending of the magnetic field) the magnetization of the fat signal has just risen to zero from its original, negative, value and no fat signal is available to be flipped into the transverse plane.

When deciding on the optimal 
T1 time, factors to be considered include not only the main field strength, but also the tissue to be suppressed and the anatomy. In comparison to a conventional spin echo where tissues with a short T1 are bright due to faster recovery, fat signal is reversed or darkened. Because body fluids have both a long T1 and a long T2, it is evident that STIR offers the possibility of extremely sensitive detection of body fluid. This is of course, only true for stationary fluid such as edema, as the MRI signal of flowing fluids is governed by other factors" 
(Magnetic Resonance -  Technology Information Portal, n.d., http://www.mr-tip.com/serv1.php?type=db1&dbs=Short%20T1%20Inversion%20Recovery).


According to Robert Peyster MD, DABR, CAQ-NR, Neuroradiologist (Columbia University, Downstate University, Massachusetts General-Harvard, published 63 times...Get the picture?!), a STIR view is essential to best visualize the vertebrate, spinal cord and soft tissue as ligaments. Once the fat is suppressed, pathology will be more readily visualized, thereby making the STIR view critical in a conclusive diagnosis.

When ordering MRI’s, order a STIR view for all regions of the spine. If your MRI company doesn’t have the protocols, they are ancient and you need to find one that has up to date equipment. Most, if not all, MRI machines can do STIR views. It’s not the machine, it’s the software of the machine.

The MRI Spine Interpretation Course teaches STIR in Module 5 with examples, pictures and details directly from myself and Dr. Peyster who co-authored the program. 



References:

1.  Golfieri, R., Baddeley, H., Pringle, J. S. & Souhami, R. (1990). The role of the STIR sequence in magnetic resonance imaging examination of bone tumours. British Journal of Radiology, 63, 251-256. Retrieved from  http://bjr.birjournals.org/cgi/content/abstract/63/748/251


2.  Magnetic Resonance - Technology Information Portal. (n.d.). Short T1 inversion recovery. Retrieved from http://www.mr-tip.com/serv1.php?type=db1&dbs=Short%20T1%20Inversion%20Recovery