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Liver: Segment-specific Analysis of B1 Field Homogeneity at 3.0-T MR Imaging with Single-Source versus Dual-Source Parallel Radiofrequency Excitation.
MedLine Citation:
PMID:  22929333     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Purpose:To measure B(1) field distribution in different liver segments with and without dual transmission and to quantify the contrast-to-noise ratio (CNR) between normal liver tissue and segmental venous vessels on standard clinical 3.0-T liver magnetic resonance (MR) images.Materials and Methods:This prospective study was approved by the local ethics committee. All subjects gave written informed consent. Six patients with liver lesions and nine healthy volunteers were included. Average hepatic B(1) field values in all Couinaud liver segments were assessed by using actual flip-angle imaging (first and second repetition times msec/echo time msec: 72, 192/2.2; transmission angle: 60°) for both single and dual transmission in a 3.0-T MR imaging unit that allowed both transmission modes. Additionally, two-dimensional T1-weighted gradient-echo (repetition time msec/echo time msec, 180/2.3; transmission angle, 55°) and T2-weighted single-shot fast spin-echo images (1501/80) were acquired. Average CNR between liver parenchyma and segmental veins were measured in each segment. Two-sided paired Student t tests were used for statistical evaluation. Two blinded radiologists independently identified lesions in images from acquisitions in both transmission modes.Results:Mean flip angles achieved with conventional single transmission were 44%-53% of the nominal value in segments II-IV and 67% and 63% of the nominal value in segments VI and VII, respectively, and were less than 77% in all segments. Mean actual flip angles measured for dual transmission were between 82% and 100% of the nominal value in all segments. T1-weighted single-transmission images exhibited areas of low B(1) field strength with reduced image contrast. T2-weighted single-transmission images displayed significantly reduced signal intensity but nearly unchanged contrast weighting in these areas. On T1-weighted dual-transmission images, the two readers detected 22 and 14 additional lesions that they did not identify on the single-transmission images. On the dual-transmission T2-weighted images, they detected 11 and five additional lesions, respectively.Conclusion:Dual transmission can generate a B(1) field with significantly improved homogeneity over all liver segments at a field strength of 3.0 T.© RSNA, 2012Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112715/-/DC1.
Authors:
Shila Pazahr; Michael Alexander Fischer; Natalie Chuck; Roger Luechinger; Fritz Schick; Daniel Nanz; Andreas Boss
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-8-28
Journal Detail:
Title:  Radiology     Volume:  -     ISSN:  1527-1315     ISO Abbreviation:  Radiology     Publication Date:  2012 Aug 
Date Detail:
Created Date:  2012-8-29     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0401260     Medline TA:  Radiology     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Department of Diagnostic and Interventional Radiology, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland; Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
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