Three‐dimensional oxygen‐enhanced MRI of the human lung at 1.5T with ultra‐fast balanced steady‐state free precession

Abstract

Purpose: To assess the feasibility of 3D oxygen-enhanced (OE) MRI of the lung at 1.5T using multi-volumetric ultra-fast balanced steady-state free precession (ufSSFP) acquisitions. Methods: Isotropic imaging of the lung for OE-MRI was performed with an adapted 3D ufSSFP sequence using five breathhold acquisitions ranging from functional residual capacity to tidal inspiration under both normoxic (room air) and hyperoxic (100% O 2 ) gas conditions. For each O 2 concentration, a sponge model (which captures the parenchymal signal intensity variation as a function of the lung volume) was fitted to the acquired multivolumetric datasets after semiautomatic lung segmentation and deformable image registration. From the retrieved model parameters, 3D oxygen-enhancement maps were calculated. Results: For OE ufSSFP imaging, the maximum parenchymal signal is observed for flip angles around 23 under both normoxic and hyperoxic conditions. It is found that the sponge model accurately describes parenchymal signal at different breathing positions, thereby mitigating the confounding bias in the estimated oxygen enhancement from residual density modulations. From the model, an average lung oxygen enhancement of 7.0% 6 0.3% was found in the healthy volunteers, and the oxygenenhancement maps indicate a ventral to dorsal gravitation-related gradient. Conclusion:The study demonstrates the feasibility of wholelung OE-MRI from multi-volumetric ufSSFP in healthy volunteers.

The effect of flow on blood oxygen level dependent (R*2) MRI of orthotopic lung tumors

“…Most studies of human lung have focused on chronic obstructive pulmonary disorder and asthma, thereby examining the lung itself . Indeed, oxygen‐enhanced MRI of the lung is becoming increasingly popular …”

Signal enhancement ratio imaging of the lung parenchyma with ultra‐fast steady‐state free precession MRI at 1.5T

“…Image postprocessing was identical for ufSSFP and VIBE, and essentially similar to previous works . Signal preservation by image registration was analyzed by comparing the whole‐lung signal before and after image registration.…”

“…Finally, SER images were calculated voxelwise (at positionx ) from the signal intensity before [SI pre ðx Þ] and after [SI post ðx Þ contrast agent administration, respectively, using SERðx Þ5 SI post ðxÞ2SI pre ðxÞ SI pre ðx Þ Image postprocessing was identical for ufSSFP and VIBE, and essentially similar to previous works. 19,20 Signal preservation by image registration was analyzed by comparing the whole-lung signal before and after image registration. A schematic summary of the proposed method is shown in Supporting Fig.…”

“…In contrast, balanced steady‐state free precession (bSSFP) offers the highest SNR per unit of time among all MRI sequences . Banding artifacts that typically compromise the image quality of bSSFP in the chest have been recently mitigated by the development of an ultra‐fast SSFP imaging approach (ufSSFP); a variant of bSSFP with ultrashort repetition times, which has already demonstrated potential for morphological and functional assessment of the lungs . Due to their mixed contrast behavior driven by the T 2 /T 1 relaxation time ratio, bSSFP sequences are frequently regarded as being rather insensitive to gadolinium‐based contrast agents, although their potential use after contrast administration has been demonstrated and advised .…”

“…16 Banding artifacts that typically compromise the image quality of bSSFP in the chest have been recently mitigated by the development of an ultra-fast SSFP imaging approach (ufSSFP) 17 ; a variant of bSSFP with ultrashort repetition times, which has already demonstrated potential for morphological and functional assessment of the lungs. 8,[18][19][20] Due to their mixed contrast behavior driven by the T 2 /T 1 relaxation time ratio, 21 bSSFP sequences are frequently regarded as being rather insensitive to gadolinium-based contrast agents, although their potential use after contrast administration has been demonstrated and advised. 22,23 From the theory, 16 the signal enhancement for SSFP after contrast administration is expected to be higher for tissue with long T 1 and short T 2 , such as the lung (T 1 /T 2 1375/66 [ms/ms] at 1.5T), 24 as compared to the blood (T 1 /T 2 1300/300) and fluids with comparable T 1 /T 2 .…”