Fourier decomposition pulmonary MRI using a variable flip angle balanced steady-state free precession technique.
OBJECTIVE
Fourier decomposition (FD) is a noninvasive method for assessing ventilation and perfusion-related information in the lungs. However, the technique has a low signal-to-noise ratio (SNR) in the lung parenchyma. We present an approach to increase the SNR in both morphological and functional images.


METHODS
The data used to create functional FD images are usually acquired using a standard balanced steady-state free precession (bSSFP) sequence. In the standard sequence, the possible range of the flip angle is restricted due to specific absorption rate (SAR) limitations. Thus, using a variable flip angle approach as an optimization is possible. This was validated using measurements from a phantom and six healthy volunteers.


RESULTS
The SNR in both the morphological and functional FD images was increased by 32%, while the SAR restrictions were kept unchanged. Furthermore, due to the higher SNR, the effective resolution of the functional images was increased visibly. The variable flip angle approach did not introduce any new transient artifacts, and blurring artifacts were minimized.


CONCLUSIONS
Both a gain in SNR and an effective resolution gain in functional lung images can be obtained using the FD method in conjunction with a variable flip angle optimized bSSFP sequence.
Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Heidelberg, Germany.
D M R
DM
Corteville
Å
Å
Kjïrstad
T
T
Henzler
F G
FG
Zöllner
L R
LR
Schad
D000328:Adult; D016477:Artifacts; D003198:Computer Simulation; D005583:Fourier Analysis; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008168:Lung / Q000033:anatomy & histology* / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D012016:Reference Values; D059629:Signal-To-Noise Ratio; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*; D051598:Whole Body Imaging / Q000295:instrumentation / Q000379:methods*
Fourier decomposition; SNR optimization; balanced steady-state free precession (bSSFP); non-contrast-enhanced lung MRI; variable flip angles