(453) VDP comparison between spiral with post-acquisition denoising and cartesian acquisition for 19F lung MRI

Background: MRI of the lung with fluorinated gases has been shown to be effective at characterizing disease severity in people with CF (PwCF) [1]. A major limitation of current ¹⁹F MRI with conventional sequences is the required scan time. A shorter acquisition time could enable the application of ¹⁹F lung MRI to pediatric patients who are unable to perform breath-holds. In this study we explore the feasibility of spiral ¹⁹F imaging that achieves a 0.45 second full lung volume scan, enabling free-breathing acquisitions. Post-acquisition denoising [2] is applied to recover signal to noise ratio (SNR).

Methods: Five PwCF were recruited and underwent ¹⁹F lung MR imaging in a multinuclear capable Siemens Prisma 3.0T scanner (Siemens Medical Systems, Erlangen, Germany) and a custom 8-channel ¹⁹F-tuned chest coil (ScanMed, Inc., Omaha NE). For the cartesian ¹⁹F acquisition, acquisition was taken during breath holds at inspiration lasting 18 seconds with a 3D VIBE sequence. Between the breath holds, two expiration-inspiration cycles were performed during which a four-arm 19F spiral sequence was obtained 12 times during the breaths. Each repetition lasted 0.45 seconds. Additionally, 1H MRI GRE VIBE images were acquired during a 15 second inspiration breath hold. The 5^th breath hold acquisition and its corresponding spiral acquisition was used to measure SNR and VDP.

The anatomical scans were registered to the ¹⁹F scans and masks were drawn to cover the whole thoracic lung cavity. Ventilation defect percentage (VDP) was measured as regions in the lung with 19F signal lower than the 95^th percentile signal intensity of the most posterior slice which lies outside the lungs. SNR was calculated as the ratio between the mean signal inside the lung at the highest signal coronal slice over the standard deviation of the most posterior slice values.

Results: Imaging was well tolerated by subjects. The results are reported as mean ± standard deviation. The SNR of the Cartesian acquisition images was 13.65±2.49and 4.69±0.32 for the initial spiral sequence prior to denoising. Denoising successfully increased the SNR of ¹⁹F signal by an average factor of 39.55±12.47, thus leading to a significant improvement in SNR (p=0.002 Paired t-test). VDP also systematically increased by 6.74±3.12%. The increase in VDP by the spiral method was observed to increase and correlate with the breath hold VDP with a R² score of 0.847 (Figure 1).

Conclusions: Denoising of spiral ¹⁹F has been shown to increase SNR substantially, and the short time of acquisition (0.45 s) has the potential for free breathing acquisition. VDP calculated from free breathing spiral was systematically higher but correlated (R² 0.847) to the VDP calculated from cartesian 3D VIBE.

Acknowledgements:

References: [1] Goralski JL, Chung SH, Glass TM, Ceppe AS, Akinnagbe-Zusterzeel EO, Trimble AT, Boucher RC, Soher BJ, Charles HC, Donaldson SH, Lee YZ. Dynamic perfluorinated gas MRI reveals abnormal ventilation despite normal FEV1 in cystic fibrosis. JCI insight. 2020 Jan 30;5(2).

[2] Huynh KM, Chang WT, Chung SH, Chen Y, Lee Y, Yap PT. Noise Mapping and Removal in Complex-Valued Multi-Channel MRI via Optimal Shrinkage of Singular Values. In International Conference on Medical Image Computing and Computer-Assisted Intervention 2021 Sep 27 (pp. 191-200). Springer, Cham.