Browsing by Subject "4D-MRI"
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Item Open Access Development and Optimization of Four-dimensional Magnetic Resonance Imaging (4D-MRI) for Radiation Therapy(2016) Liu, YilinA tenet of modern radiotherapy (RT) is to identify the treatment target accurately, following which the high-dose treatment volume may be expanded into the surrounding tissues in order to create the clinical and planning target volumes. Respiratory motion can induce errors in target volume delineation and dose delivery in radiation therapy for thoracic and abdominal cancers. Historically, radiotherapy treatment planning in the thoracic and abdominal regions has used 2D or 3D images acquired under uncoached free-breathing conditions, irrespective of whether the target tumor is moving or not. Once the gross target volume has been delineated, standard margins are commonly added in order to account for motion. However, the generic margins do not usually take the target motion trajectory into consideration. That may lead to under- or over-estimate motion with subsequent risk of missing the target during treatment or irradiating excessive normal tissue. That introduces systematic errors into treatment planning and delivery. In clinical practice, four-dimensional (4D) imaging has been popular in For RT motion management. It provides temporal information about tumor and organ at risk motion, and it permits patient-specific treatment planning. The most common contemporary imaging technique for identifying tumor motion is 4D computed tomography (4D-CT). However, CT has poor soft tissue contrast and it induce ionizing radiation hazard. In the last decade, 4D magnetic resonance imaging (4D-MRI) has become an emerging tool to image respiratory motion, especially in the abdomen, because of the superior soft-tissue contrast. Recently, several 4D-MRI techniques have been proposed, including prospective and retrospective approaches. Nevertheless, 4D-MRI techniques are faced with several challenges: 1) suboptimal and inconsistent tumor contrast with large inter-patient variation; 2) relatively low temporal-spatial resolution; 3) it lacks a reliable respiratory surrogate. In this research work, novel 4D-MRI techniques applying MRI weightings that was not used in existing 4D-MRI techniques, including T2/T1-weighted, T2-weighted and Diffusion-weighted MRI were investigated. A result-driven phase retrospective sorting method was proposed, and it was applied to image space as well as k-space of MR imaging. Novel image-based respiratory surrogates were developed, improved and evaluated.
Item Open Access Robust 4D-MRI Sorting with Reduced Artifacts Based on Anatomic Feature Matching(2018) Yang, ZiPurpose: Motion artifacts induced by breathing variations are common in 4D-MRI
images. This study aims to reduce the motion artifacts by developing a novel, robust 4DMRI
sorting method based on anatomic feature matching, which is applicable in both
cine and sequential acquisition.
Method: The proposed method uses the diaphragm as the anatomic feature to guide the
sorting of 4D-MRI images. Initially, both abdominal 2D sagittal cine MRI images and
axial MRI images (in both axial cine and sequential scanning modes) were acquired. The
sagittal cine MRI images were divided into 10 phases as ground truth. Next, the phase of
each axial MRI image is determined by matching the diaphragm position in the
intersection plane between the axial MRI and the ground truth cine MRI. Then, those
matched phases axial MRI images were sorted into 10-phase bins identical to the ground
truth cine images. Finally, 10-phase 4D-MRI were reconstructed from these sorted axial
MRI images. The accuracy of reconstructed 4D-MRI data was evaluated in a simulation
study using the 4D eXtended Cardiac Torso (XCAT) digital phantom with a sphere
tumor in the liver. The effects of breathing signal, including both regular (cosine
function) and irregular (patient data), on reconstruction accuracy were investigated by
calculating total relative error (TRE) of the 4D volumes, Volume-Percent-Difference
(VPD) and Center-of-Mass-Shift(COMS) of the simulated tumor between the
reconstructed and the ground truth images.
Results: In both scanning modes, reconstructed 4D-MRI images matched well with the
ground truth except minimal motion artifacts. The averaged TRE of the 4D volume, VPD
and COMS of the EOE phase in both scanning modes were 0.32%/1.20%/±0.05𝑚𝑚 for
regular breathing, and 1.13%/4.26%/±0.21𝑚𝑚 for patient irregular breathing,
respectively.
Conclusion: The preliminary results illustrated the robustness of the new 4D-MRI
sorting method based on anatomic feature matching. This method improved image
quality with reduced motion artifacts in the resulting reconstructed 4D MRI is applicable
for axial MR images acquired using both cine and sequential scanning modes.