Quantitative T2 in the occipital lobe: The role of the CPMG refocusing rate

✍ Scribed by Bojana Stefanovic; John G. Sled; G. Bruce Pike

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 267 KB
• Volume: 18
• Category: Article
• ISSN: 1053-1807
• DOI: 10.1002/jmri.10360

✦ Synopsis

Abstract

Purpose

To investigate the dependence of occipital gray and white matter T~2~ on the Carr‐Purcell‐Meiboom‐Gill (CPMG) refocusing interval, thereby testing the basis of a novel functional magnetic resonance imaging (fMRI) method for blood volume quantification, and addressing recent questions surrounding T~2~ contrast in the occipital lobe.

Materials and Methods

A CPMG sequence with 1 × 1 × 5 mm^3^ resolution was used to quantify T~2~ in a single axial slice at the midlevel of the occipital lobe in 23 healthy adult volunteers. Refocusing intervals of 8, 11, and 22 msec were compared. A Bayesian classifier was used to classify a 1 × 1 × 1 mm^3^ T~1~‐weighted three‐dimensional data set into gray matter, white matter, and cerebrospinal fluid, with an average 95% a posteriori probability used as the threshold for inclusion into a tissue‐specific region of interest (ROI).

Results

The usual T~2~ contrast between the gray and white matter (i.e., T~2__GM__~ > T~2__WM__~) was observed, with a highly significant effect of tissue type on the estimated T~2~ (P < 10^−5^). The observed T~2~ gradually decreased with increasing refocusing interval, for a decrease of 3.3 ± 1.5 msec in gray matter and 3.0 ± 1.5 msec in white matter between the 8 and 22 msec refocusing interval acquisitions.

Conclusion

The observed T~2~ shortening is consistent with the effect of the dramatic decrease in T~2~ of partly deoxygenated blood on this range of refocusing rates. J. Magn. Reson. Imaging 2003;18:302–309. © 2003 Wiley‐Liss, Inc.