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Digitale Medien

An apparatus for glancing incidence ion beam polishing and characterization of surfaces to angstrom-scale root-mean-square roughness (1996)

Wissing, M. ; Holzwarth, M. ; Simeonova, D. S. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 67 (1996), S. 4314-4320

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: An instrument is described which combines a glancing incidence ion beam erosion system with a scanning tunneling and an atomic force microscope. This instrument allows the ion beam polishing and surface topographic characterization of conducting and insulating, crystalline, polycrystalline, and amorphous samples under ultrahigh vacuum conditions. As an illustration of the capability of the instrument and the polishing technique, we present results demonstrating a fivefold improvement in rms roughness of a polycrystalline Cr film and a fivefold reduction in rms roughness of a vicinal, initially mechanically polished CaF2 (111) sample. The final rms roughness of the latter sample of 0.12±0.04 nm measured over the bandwidth of 10–500 nm is just 75% of the Ca–F interlayer spacing for the (111) surface orientation. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1147532

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Digitale Medien

Hepatic MR imaging: comparison of RARE derived sequences with conventional sequences for detection and characterization of focal liver lesions (1996)

Reimer, P. ; Rummeny, E. J. ; Wissing, M. ; [weitere]

Springer

Abdominal imaging 21 (1996), S. 427-432

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ISSN: 1432-0509

Schlagwort(e): Key words: MRI—Hepatic imaging—RARE—Detection—Characterization.

Quelle: Springer Online Journal Archives 1860-2000

Thema: Medizin

Notizen: Abstract. Background: We compared two T2-weighted turbo spin echo (TSE) sequences with a T2-weighted conventional SE (CSE) sequence to determine whether sequences derived from rapid acquisition with relaxation enhancement such as TSE could replace CSE for the detection and subsequent characterization of focal liver lesions. Methods: A total of 55 consecutive patients with 107 liver lesions underwent magnetic resonance imaging examinations at 1.5 Tesla, with a constant imaging protocol. TSE pulse sequences were acquired with eight echo trains (repetition time [TR], 4718 ms; echo time [TE], 90 ms; acquisition time [TA], 4.03 min; and a symmetric k-space ordering scheme) and 11 echo trains (TR, 4200 ms; TE, 140 ms; TA, 4.40 min; and an asymmetric k-space ordering scheme) and compared with CSE (TR, 2300 ms; TE, 45/90 ms; TA, 9.53 min). Images were analyzed qualitatively by scoring image quality and artifacts and counting focal liver lesions by independent reading with consensus obtained for discrepancies. Quantitative analysis was performed by measuring signal-to-noise (S/N), contrast-to-noise (C/N), and tumor–liver signal intensity (T/L) ratios. Results: T2-weighted TSE sequences provided better subjective image quality and reduced artifacts as compared with the T2-weighted CSE sequence. CSE and TSE sequences exhibited no statistically significant differences in liver S/N, lesion–liver C/N (CSE TE, 90 ms: 18.6 ± 14.0; TSE TE, 90 ms: 16.5 ± 12.9) and the detectability of focal liver lesions. Heavily T2-weighted TSE with a TE of 140 ms allowed correct characterization of focal liver lesions based on a T/L ratio of 3.0 in 84% of patients. Conclusions: T2-weighted TSE sequences are as suited as CSE for the detection (TE, 90 ms), and appear to be superior for the characterization (TE, 140 ms), of focal hepatic lesions. Whether a single sequence, such as a double-echo TSE or a single-echo TSE sequence with a TE between 110 and 120 ms, might perform both functions as well or better than CSE is unknown. However, because of time savings, TSE eventually may be preferred over CSE.