ORAL ABSTRACTS: CONTRAST MECHANISMS 129

Table I

The NMR Relaxation Times of Muscles in Normal and Dystrophic Chicks1

Muscle T12 (ms) T22

Normal Dystrophic Normal

Pectoralis 506 + 12 559 + 14*"3 47 + 5 _ -

PLD 539 + 15 578 + 27h4 50 + 3 -

ALD 534 + 11 539 + 16 61+ 3 - - _

Biceps 526 t 16 567 5 17” 46 + 4

Dystrophic

58 + 5**

60 + 5>\* -

60 + 4

54 + 5*

56 + 4

58 + 3*

51 + 10

PAT

SMP

MLD

1. 2. 3. 4.

563 2 28 600 5 6" 52 + 4

523 + 26 573 + 49* 52 + 4

531 + 9 553 28 53 + 4 - - +

6 chicks each from normal and dystrophic lines were used. Mean + S.D. Significant at PC 0.01 Significant at PlO.05

PIXEL INTENSITY AND CONTRAST VALUES AS FUNCTIONS OF RELAXATION TIMES AND PULSE INTERVALS IN SEVERAL COMMERCIAL MR IMAGERS

David W. Anderson, Ph.D.; William S. Yamanashi, Ph.D.; John W. Ross-Duggan, M.D.; Patrick D. Lester, M.D.; Steven E. Harms, M.D.*; Wei Kom Chu, Ph.D.+; Richard A. Suss, M.D.++; Rajendra Shenoy, Ph.D.** and Kenneth Maravira, M.D.***

City of Faith Medical and Research Center, Tulsa, Oklahoma 74137-1270; *Baylor Hospital, Dallas, Texas; +University of Nebraska Medical Center, Omaha, Nebraska; ++Arlington Diagnostic and Treatment Center, Arlington, Texas; **N'MR System, Inc., Amityville, New York; ***University of Texas Health Science Center, Dallas, Texas

When a radiologist requests a patient scan with a given pulse sequence and pulse interval, he may expect that the image contrast obtained from his scanner is the same as that obtained from any other scanner. If there is a difference, is it significant? In order to answer these inquiries, investigators in several medical centers have participated in a study of images of a relaxation time phantom. The phantom has several chambers filled with paramagnetic solutions in various concentrations so that relaxation times cover the typical tissue Tl and T2 ranges. Spin echo and inversion recovery images were compared with respect to pixel intensity and contrast values as functions of relaxation time Tl and T2, and pulse intervals TE and TI with TR held constant. Imagers used are: Picker MR VISTA 2055 at O.ST, Technicare Teslacon at 0.6T. General Electric Signa at 1.5T. FONAR 3000 Beta at 0.3T and Siemens Magnetom at 0.3TS. Experimental data were compared with theoretical plots of pixel and contrast values derived from the Bloch equations. Since Tl varies with magnetic field, the computed pixel values were obtained using Tl values initially measured with a pulse spectrometer at 10 MHz and those obtained from extrapolation using Bottomley's equation relating Tl and the B field. Deviation from the theoretical Bloch (exponential-like) behavior in different commercial imagers were observed. We suggest that some standardization of parameters such as RF pulse width, attenuation, contour, gradient pulse on-time, etc. be agreed upon so that Tl and T2 dependence would be more uniform for different scanners.

References

P.A. Bottomley, T.H. Foster, R.E. Argersinger, L.M. Pfeifer, Medical Physics 2, 425-448 (1984). P.A. Hardy, M.J. Bronskill, R.M. Henkelman, Med. Phys. 12, 581-585 (1985). F.W. Wehrli, J.R. McFall, T.H. Newton in Advanced Imaging Techniques, ed. T.H. Newton, Clavadel Press, New York, pp. 81-117, 1985.

W.S. Yamanashi, D.W. Anderson, P.D. Lester, et al, Physiol. Chem. Phys. -- Med. NMRE, 81-100 (1985).

§data from Diasonic 0.5T unit are also included.