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Evaluation of a subject specific dual-transmit approach for improving B1 field homogeneity in cardiovascular magnetic resonance at 3T.

Krishnamurthy R, Pednekar A, Kouwenhoven M, Cheong B, Muthupillai R - J Cardiovasc Magn Reson (2013)

Bottom Line: Local RF shimming across the region encompassed by the heart increased the mean flip angle (μ) in that area (88.5 ± 15.2% vs. 81.2 ± 13.3%; P = 0.0014), reduced the B1 field variation by 42.2 ± 13%, and significantly improved the percentage of voxels closer to μ (39% and 82% more voxels were closer to ± 10% and ± 5% of μ, respectively) when compared with no RF shimming.With or without RF shimming, cardiac B1 field homogeneity does not depend on body type, as characterized by BMI, BSA, and AP/RL.For all body types studied, cardiac B1 field homogeneity was significantly improved by performing local RF shimming with 2 independent RF-transmit channels.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiology, Texas Heart Institute at St, Luke's Episcopal Hospital, 6720 Bertner Avenue, Houston, TX 77030, USA.

ABSTRACT

Background: Radiofrequency (RF) shading artifacts degrade image quality while performing cardiovascular magnetic resonance (CMR) at higher field strengths. In this article, we sought to evaluate the effect of local RF (B1 field) shimming by using a dual-source-transmit RF system for cardiac cine imaging and to systematically evaluate the effect of subject body type on the B1 field with and without local RF shimming.

Methods: We obtained cardiac images from 37 subjects (including 11 patients) by using dual-transmit 3T CMR. B1 maps with and without subject-specific local RF shimming (exploiting the independent control of transmit amplitude and phase of the 2 RF transmitters) were obtained. Metrics quantifying B1 field homogeneity were calculated and compared with subject body habitus.

Results: Local RF shimming across the region encompassed by the heart increased the mean flip angle (μ) in that area (88.5 ± 15.2% vs. 81.2 ± 13.3%; P = 0.0014), reduced the B1 field variation by 42.2 ± 13%, and significantly improved the percentage of voxels closer to μ (39% and 82% more voxels were closer to ± 10% and ± 5% of μ, respectively) when compared with no RF shimming. B1 homogeneity was independent of subject body type (body surface area [BSA], body mass index [BMI] or anterior-posterior/right-left patient width ratio [AP/RL]). Subject specific RF (B1) shimming with a dual-transmit system improved local RF homogeneity across all body types.

Conclusion: With or without RF shimming, cardiac B1 field homogeneity does not depend on body type, as characterized by BMI, BSA, and AP/RL. For all body types studied, cardiac B1 field homogeneity was significantly improved by performing local RF shimming with 2 independent RF-transmit channels. This finding indicates the need for subject-specific RF shimming.

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Variation of the mean percentage flip angle with subject body habitus. The variation of μ with body mass index (A), body surface area (B), and anterior-posterior/right-left (AP/RL) ratio (C) is shown. Because no clear pattern of variation can be discerned, the mean flip angle does not appear to depend on body type. RF, radiofrequency; W/o, without.
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Figure 3: Variation of the mean percentage flip angle with subject body habitus. The variation of μ with body mass index (A), body surface area (B), and anterior-posterior/right-left (AP/RL) ratio (C) is shown. Because no clear pattern of variation can be discerned, the mean flip angle does not appear to depend on body type. RF, radiofrequency; W/o, without.

Mentions: 2. The data were analyzed to see whether there was any observable dependence between the mean flip angle and the subject body type. No particular relationship was observed between these variables, either with or without local RF shimming (Figure 3). Also, analysis of the mean flip angle and the height and weight of all the subjects did not reveal any significant interrelationship among these variables (not shown).


Evaluation of a subject specific dual-transmit approach for improving B1 field homogeneity in cardiovascular magnetic resonance at 3T.

Krishnamurthy R, Pednekar A, Kouwenhoven M, Cheong B, Muthupillai R - J Cardiovasc Magn Reson (2013)

Variation of the mean percentage flip angle with subject body habitus. The variation of μ with body mass index (A), body surface area (B), and anterior-posterior/right-left (AP/RL) ratio (C) is shown. Because no clear pattern of variation can be discerned, the mean flip angle does not appear to depend on body type. RF, radiofrequency; W/o, without.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750927&req=5

Figure 3: Variation of the mean percentage flip angle with subject body habitus. The variation of μ with body mass index (A), body surface area (B), and anterior-posterior/right-left (AP/RL) ratio (C) is shown. Because no clear pattern of variation can be discerned, the mean flip angle does not appear to depend on body type. RF, radiofrequency; W/o, without.
Mentions: 2. The data were analyzed to see whether there was any observable dependence between the mean flip angle and the subject body type. No particular relationship was observed between these variables, either with or without local RF shimming (Figure 3). Also, analysis of the mean flip angle and the height and weight of all the subjects did not reveal any significant interrelationship among these variables (not shown).

Bottom Line: Local RF shimming across the region encompassed by the heart increased the mean flip angle (μ) in that area (88.5 ± 15.2% vs. 81.2 ± 13.3%; P = 0.0014), reduced the B1 field variation by 42.2 ± 13%, and significantly improved the percentage of voxels closer to μ (39% and 82% more voxels were closer to ± 10% and ± 5% of μ, respectively) when compared with no RF shimming.With or without RF shimming, cardiac B1 field homogeneity does not depend on body type, as characterized by BMI, BSA, and AP/RL.For all body types studied, cardiac B1 field homogeneity was significantly improved by performing local RF shimming with 2 independent RF-transmit channels.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiology, Texas Heart Institute at St, Luke's Episcopal Hospital, 6720 Bertner Avenue, Houston, TX 77030, USA.

ABSTRACT

Background: Radiofrequency (RF) shading artifacts degrade image quality while performing cardiovascular magnetic resonance (CMR) at higher field strengths. In this article, we sought to evaluate the effect of local RF (B1 field) shimming by using a dual-source-transmit RF system for cardiac cine imaging and to systematically evaluate the effect of subject body type on the B1 field with and without local RF shimming.

Methods: We obtained cardiac images from 37 subjects (including 11 patients) by using dual-transmit 3T CMR. B1 maps with and without subject-specific local RF shimming (exploiting the independent control of transmit amplitude and phase of the 2 RF transmitters) were obtained. Metrics quantifying B1 field homogeneity were calculated and compared with subject body habitus.

Results: Local RF shimming across the region encompassed by the heart increased the mean flip angle (μ) in that area (88.5 ± 15.2% vs. 81.2 ± 13.3%; P = 0.0014), reduced the B1 field variation by 42.2 ± 13%, and significantly improved the percentage of voxels closer to μ (39% and 82% more voxels were closer to ± 10% and ± 5% of μ, respectively) when compared with no RF shimming. B1 homogeneity was independent of subject body type (body surface area [BSA], body mass index [BMI] or anterior-posterior/right-left patient width ratio [AP/RL]). Subject specific RF (B1) shimming with a dual-transmit system improved local RF homogeneity across all body types.

Conclusion: With or without RF shimming, cardiac B1 field homogeneity does not depend on body type, as characterized by BMI, BSA, and AP/RL. For all body types studied, cardiac B1 field homogeneity was significantly improved by performing local RF shimming with 2 independent RF-transmit channels. This finding indicates the need for subject-specific RF shimming.

Show MeSH
Related in: MedlinePlus