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  • Open Access

Does moving away from the center frequency resonance benefit or hurt the valvular structure evaluation? A study of on and off peak resonance

  • 1,
  • 1,
  • 1,
  • 1,
  • 1 and
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Journal of Cardiovascular Magnetic Resonance200911 (Suppl 1) :T4

https://doi.org/10.1186/1532-429X-11-S1-T4

  • Published:

Keywords

  • Mitral Valve
  • Imaging Parameter
  • Structure Evaluation
  • Mitral Valve Leaflet
  • Valvular Regurgitation

Introduction

Cardiac MRI (CMR) is the diagnostic modality of choice for ventricular volumes and function. The qualitative and quantitative valve function by CMR is performed by SSFP and phase contrast imaging respectively. However, often times the valve and subvalvular morphologic details are not clearly visualized in a reproducible fashion limiting the complete interrogation of the heart.

Hypothesis

We propose that adjusting the center frequency resonance (CFR) as determined by the MRI interface for each sequence may, counterintuitively, produce optimal images for valve definition. By adjusting the center frequency manually to 'off' resonance, we hypothesize that CFR can exaggerate the susceptibility around the valves, making the valves easier to visualize.

Methods

We scanned two healthy subjects without prior knowledge of their cardiac valvular structure or function. The imaging protocol was limited to the mitral valve and was performed on a 1.5 T GE HD Excite (Milwaukee, WI), 8 channel cardiac array coil; using the SSFP sequence. The imaging parameters were: matrix: 224/224; averages: 1; TR 3.285 (heart rate based); TE 1.42; Tdel, temporal resolution: 27 msec. (See Table 1.)

Table 1

Subject 1

Series

Resonance frequency (Hertz)

Transmit gain

R1 gain

R2 gain

Tuning method

Peak CFR

63868605

117

13

15

A

30° off Peak CFR

63868577

117

13

15

M

60° off Peak CFR

63858341

117

13

15

M

90 ° off Peak CFR

63868585

117

13

15

M

Subject 2

Series

Resonance frequency (Hertz)

Transmit gain

R1 gain

R2 gain

Tuning method

Peak CFR

63868553

128

13

15

A

30° off Peak CFR

63868536

128

13

15

M

60° off Peak CFR

63868505

128

13

15

M

90 ° off Peak CFR

63868474

128

13

15

M

Results

The specific results are summarized in Table 2. The incremental offset of the CFR, otherwise maintaining imaging parameters, allowed improved delineation of the mitral valve leaflet, and its subvalvular apparati. Despite better visualization of the valves, the measured thickness of the valves decreased when compared to the peak CFR valve measurements (approximately 5 to 12% decline in Subject A and 17 to 26% decline in subject B). We believe that this is related to the better image quality from the off resonance peak. (See Figures 1, 2, 3.)

Table 2

Mitral valve leaflet measurements

Image

S1 mitral leaflet (mm)

S3 mitral leaflet (mm)

Difference between each degree offset

    

S1/S3

Comparison to Peak CFR

Subject A

Peak CFR

2.1

2.2

  
 

30° off peak CFR

2.0

2.1

0.1/0.1

0/30 degree

 

60° off peak CFR

2.0

1.9

0.1/0.3

0/60 degree

 

90° off peak CFR

2.0

1.8

0.1/0.4

0/90 degree

Subject B

Peak CFR

2.9

2.9

  
 

30° off peak CFR

2.4

2.4

0.5/0.5

0/30 degree

 

60° off peak CFR

2.2

2.4

0.7/0.5

0/60 degree

 

90° off peak CFR

2.1

2.2

0.8/0.7

0/90 degree

Figure 1

Figure 2

Figure 3

Conclusion

Off resonance CFR may assist in the diagnosis of valvular abnormalities otherwise not seen clearly with routine CMR settings which utilize on peak CFR imaging. This method for valve evaluation may be beneficial when valvular and subvalvular structure evaluation is the main aim of the imaging. Unfortunately, as the frequency is shifted, the chamber flow is exaggerated therefore leading to exaggeration of valvular regurgitation or stenosis jets. Therefore the valvular jets should only be interrogated on routine SSFP imaging parameters ('On' Peak Center Frequency).

Authors’ Affiliations

(1)
Allegheny General Hopital, Pittsburgh, PA, USA

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