Optimization of TI values in inversion-recovery MR sequences for the depiction of fine structures within gray and white matter: separation of globus pallidus interna and externa.
OBJECTIVE
The authors' purpose was to search the inversion time (TI) values that enable the best differentiation of fine structures in gray matter (gray-gray differentiation).


METHODS
Seven healthy adult volunteers with no history of neurologic disease or head trauma were recruited and gave their informed consent. The subjects consisted of two men and five women ranging in age from 25 to 38 years, with a mean age of 28 years +/- 5. The subjects were imaged with a turbo spin-echo inversion-recovery sequence. This sequence was performed in the axial plane at the level of the basal ganglia with the following parameters: repetition time, 3,200 msec; echo time, 15 msec; three signals acquired; echo train, seven; section thickness, 3 mm; matrix size, 256 x 256; and field of view, 180 mm. The tested values were TI = 100, 200, 300, 400, and 500 msec. Region-of interest measurements were performed at the following anatomic structures and represent gray-gray and white-white differentiations, respectively: globus pallidus externa versus globus pallidus interna, and optic radiation versus surrounding white matter.


RESULTS
The maximum contrast index value occurred at TI = 400 msec for globus pallidus externa versus globus pallidus interna (P < .05) With the contrast-to-noise ratio, no significant difference in gray-gray differentiation was observed among the various TIs. The minimum signal-to-noise ratio of the gray matter occurred at TI = 400 msec (P < .05). A subjective evaluation revealed an overall superiority of gray-matter differentiation with TI = 400 msec.


CONCLUSIONS
A TI of 400 msec was the most suitable for this purpose.
Nakamura
Hisao
H
Department of Radiology, Kyoto Prefectural University of Medicine, 465 Kajiicho, Kawaramachi Hirokoji, Kamigyoku, Kyoto 602-8566, Japan.
Yamada
Kei
K
Kizu
Osamu
O
Ito
Hirotoshi
H
Nishimura
Tsunehiko
T
D000328:Adult; D005260:Female; D005917:Globus Pallidus / Q000033:anatomy & histology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male