Flip angle optimization for balanced SSFP: Cardiac cine imaging following the application of standard extracellular contrast agent (gadobutrol)

Abstract

Purpose: To investigate the effect of the flip angle (FA) on the blood-myocardium contrast and to define the FA leading to highest image quality in contrast-enhanced balanced steady-state free precession (bSSFP) images. bSSFP images provide excellent contrast between myocardium and blood with high signal-to-noise and contrast-to-noise ratios (SNR, CNR). In clinical practice, bSSFP images are typically acquired following the injection of extracellular contrast agents (ECAs), although ECAs decrease the blood-myocardium contrast. Materials and Methods: First, a theoretical optimization was performed to determine the FA that maximizes CNR in bSSFP imaging 2-20 minutes after application of ECA. Second signal-ratios, contrast, SNR, and CNR were assessed in vivo in 25 patients in bSSFP images at 1.5T acquired before (FA 5 508) and 10-15 minutes after (FAs 5 508, 808, 908, 1008) application of a double-dose contrast agent. Image quality was assessed by two readers. Results: Simulations yielded FAs in the range of 85-1008 for optimal CNR in contrast-enhanced images. In vivo comparison of conventionally acquired cine images (FA 508) showed an increase in CNR between blood and myocardium by 57% in diastole and 78% in systole in adapted contrast-enhanced bSSFP images (FA 1008). Contrast-enhanced images with an FA of 1008 were rated highest in image quality assessment. Conclusion: By means of FA adaptation a similar blood-myocardium contrast can be achieved in contrast-enhanced bSSFP as in unenhanced bSSFP imaging with an increase in CNR. 1 Cardiac functional assessment is typically performed based on bright-blood cine images. Most commonly a steady-state free precession sequence with balanced gradients (bSSFP) is used for this purpose. 2 Balanced SSFP sequences are employed due to their high signal-to-noise ratio (SNR) and high blood-myocardium contrast-to-noise ratio (CNR), and are currently considered the method of choice for assessing cardiac function at 1.5T. 3,4Image contrast in bSSFP sequences depends primarily on the T 2 /T 1 ratio of the relaxation times, but the signal intensities are also influenced by inflow and out-of-slice effects.5 Furthermore, the signal intensity also varies with the applied flip angle (FA), which is typically set in the range of 50-608. 6 As the T 2 /T 1 ratio is high for blood and low for myocardium, there is a high contrast between blood and myocardium, which not only enables automatic myocardial segmentation but is also essential for the application of sophisticated image postprocessing, eg, strain analysis with feature-tracking software. 7-9Although extracellular contrast agents decrease the blood-myocardium interface contrast in bSSFP images, 10 in clinical practice bSSFP images are typically acquired followingView this article online at wileyonlinelibrary.com.

The effects of flip angle and gadolinium contrast agent on single breath-hold compressed sensing cardiac magnetic resonance cine for biventricular global strain assessment

“…Notably, this compensation effect was apparent in parameters such as GRS-LAX and GCS values of the left ventricle, as well as GRS-LAX and GLS values of the right ventricle. While previous studies have recommended a flip angle of 100 degrees, we opted for a lower value of 70 degrees ( 35 ). This decision was made to strike a balance between the initially low flip angle of 45 degrees and the potential risk of exceeding the specific absorption rate (SAR) limit associated with larger flip angles in obesity participants ( 27 ).…”