Technical Note: Real‐time 3D MRI in the presence of motion for MRI‐guided radiotherapy: 3D Dynamic keyhole imaging with super‐resolution

Abstract

Purpose The purpose of this study was to present real‐time three‐dimensional (3D) magnetic resonance imaging (MRI) in the presence of motion for MRI‐guided radiotherapy (MRgRT) using dynamic keyhole imaging for high‐temporal acquisition and super‐resolution generative (SRG) model for high‐spatial reconstruction. Method We propose a unique real‐time 3D MRI technique by combining a data sharing technique (3D dynamic keyhole imaging) with a SRG model using cascaded deep learning technique. 3D dynamic keyhole imaging utilizes the data sharing mechanism by combining keyhole central k‐space data acquired in real‐time with high‐spatial, high‐temporal resolution prior peripheral k‐space data at various motion positions prepared by the SRG model. The efficacy of the 3D dynamic keyhole imaging with super‐resolution (SR_dKeyhole) was compared to the ground‐truth super‐resolution images with the original full k‐space data. It was also compared with the zero‐filling reconstruction (zero‐filling), conventional keyhole reconstruction with low‐spatial high‐temporal prior data (LR_cKeyhole), and conventional keyhole reconstruction with super‐resolution prior data (SR_cKeyhole). Results High‐spatial, high‐temporal resolution 3D MRI datasets (1.5 × 1.5 × 6 mm3) were generated from low‐spatial, high‐temporal resolution 3D MRI datasets (6 × 6 × 6 mm3) using the cascaded deep learning SRG framework (<100 ms/volume). 3D dynamic keyhole imaging with the SRG model provided high‐spatial, high‐temporal resolution images (1.5 × 1.5 × 6 mm3, 455 ms) with the highest similarity to the ground‐truth SR images without any noticeable artifacts. Structural similarity indices (SSIM) of the reconstructed 3D MRI to the original SR 3D MRI were 0.65, 0.66, 0.86, and 0.89 for zero‐filling, LR_cKeyhole, SR_cKeyhole, and SR_dKeyhole, respectively (1 for identical image). In addition, average value of image relative error (IRE) of the reconstructed 3D MRI to the original SR 3D MRI were 0.169, 0.191, 0.079, and 0.067 for zero‐filling, LR_cKeyhole, SR_cKeyhole, and SR_dKeyhole, respectively (0 for identical image). Conclusions We demonstrated that high‐spatial, high‐temporal resolution 3D MRI was feasible by combing 3D dynamic keyhole imaging with a SRG model in terms of image quality and imaging time. The proposed technique can be utilized for real‐time 3D MRgRT.

Novel Technique to Measure Pulse Wave Velocity in Brain Vessels Using a Fast Simultaneous Multi-Slice Excitation Magnetic Resonance Sequence

“…For the cerebral-artery PWV measurement, an SMS technique, which was previously introduced for fast-imaging [ 20 , 21 ], was combined with a keyhole technique that consisted of only a few K-space center lines [ 22 , 23 ]. At first, for the simultaneous acquisition of an image for two different locations, the SINC-shaped radio-frequency pulse was modulated with a cosine function which was the same as the conventional SMS method [ 20 ].…”

“…For the keyhole acquisition and reconstruction of an image with resolution 256 × 256, a K-space dataset of 256 lines along the phase-encoding direction (one of spatial frequency axes) is necessary, which can be referred to as the reference K-space dataset in the keyhole technique; multiple datasets with a few K-space center lines were acquired for fast imaging [ 22 , 23 ]. In this study, a 3-line K-space dataset was acquired and shared the other peripheral K-space lines with the reference K-space dataset in reconstruction ( Figure 1 ).…”

Real‐Time Magnetic Resonance Imaging

“…The geometry of transcranial high‐intensity focused ultrasound (HIFU) therapy devices restrict the number of receive coils that can be positioned around the head, and undersampled stack‐of‐spiral and stack‐of‐stars EPI thermometry acquisitions 40,43 have been developed for volumetric brain coverage with 75‐msec temporal resolution (13 fps). 3D dynamic keyhole imaging has generated high spatiotemporal resolution (1.5×1.5×6 mm 3 with 455 msec temporal resolution, 2 fps) imaging for dynamic guidance of radiotherapy 137 . This work utilizes a super‐resolution generative model for high spatial reconstruction from low‐spatial and high‐temporal resolution images.…”

Evaluating dose constraints for radiation induced liver damage following magnetic resonance image guided Stereotactic Body radiotherapy

“…Diagnostic magnetic resonance imaging (MRI) is the preferred imaging technique for liver imaging due to its high level of soft tissue contrast, multiple sequences, and liver specific contrast agents compared to computed tomography (CT) [11]. MRI-guided radiotherapy (MRgRT) offers real time image guidance during gated treatment delivery [12]. This permits tracking the tumor volume during radiotherapy, allowing precise delivery of radiation dose and reduction of margin when expanding from the gross tumor volume (GTV).…”