In‐phase zero TE musculoskeletal imaging

Abstract

Purpose To introduce a new method for in‐phase zero TE (ipZTE) musculoskeletal MR imaging. Methods ZTE is a 3D radial imaging method, which is sensitive to chemical shift off‐resonance signal interference, especially around fat–water tissue interfaces. The ipZTE method addresses this fat–water chemical shift artifact by acquiring each 3D radial spoke at least twice with varying readout gradient amplitude and hence varying effective sampling time. Using k‐space‐based chemical shift decomposition, the acquired data is then reconstructed into an in‐phase ZTE image and an out‐of‐phase disturbance. Results The ipZTE method was tested for knee, pelvis, brain, and whole‐body. The obtained images demonstrate exceptional soft‐tissue uniformity free from out‐of‐phase disturbances apparent in the original ZTE images. The chemical shift decomposition was found to improve SNR at the cost of reduced image resolution. Conclusion The ipZTE method can be used as an averaging mechanism to eliminate fat–water chemical shift artifacts and improve SNR. The method is expected to improve ZTE‐based musculoskeletal imaging and pseudo CT conversion as required for PET/MR attenuation correction and MR‐guided radiation therapy planning.

Motion corrected silent ZTE neuroimaging

“…Similarly, MERLIN could be extended to Looping Star 72 for quiet functional BOLD imaging, 73,74 and anatomical T 2 * and susceptibility weighted imaging. MERLIN could also find applications in other parts of the body where the unique aspect of short‐T 2 imaging could be used, such as bone or lung imaging 64,75 . Motion outside the brain is in many cases non‐rigid, which could be addressed by masking out an area where rigid body motion is expected, 76 or more generally using local autofocusing for non‐rigid body motion correction 77 …”

“…At ultra‐high field strengths, head motion can alter the susceptibility‐induced B 0 field inhomogeneities, and thus produce k‐space data with inconsistent phase and T 2 * decay when acquired with a non‐zero echo time 63 . Given a sufficiently short readout and TE = 0, this problem is largely avoided 64 …”

“…63 Given a sufficiently short readout and TE = 0, this problem is largely avoided. 64 The MERLIN motion correction framework was demonstrated for T 1 magnetization prepared ZTE but can be extended to other ZTE-based pulse sequences including other types of magnetization preparation such as T 2 , 52,65 magnetization transfer, 66 MRA, 67 diffusion, 68 and parameter mapping. 69 With native FLASH-type ZTE, further applications include variable FA T 1 mapping, 70 and PD-weighted ZTE for bone imaging 62 and synthetic CT conversion for PET/MR attenuation correction and radiation therapy planning.…”

“…MERLIN could also find applications in other parts of the body where the unique aspect of short-T 2 imaging could be used, such as bone or lung imaging. 64,75 Motion outside the brain is in many cases non-rigid, which could be addressed by masking out an area where rigid body motion is expected, 76 or more generally using local autofocusing for non-rigid body motion correction. 77 The auto-calibrated coil sensitivity mapping is essential in MERLIN, here extracted from an initial WASPI acquisition, but could be substituted for other methods such as PETRA and HYFI.…”

Zero-TE MRI: Potential Applications in the Oral Cavity and Oropharynx

“…As part of a comprehensive MRI examination, these techniques offer the possibility for ''one-stopshop'' head and neck imaging. Multiple centers are evaluating ZTE performance and utility relative to CT for clinical applications including craniofacial bone imaging, 3,8 pediatric and fetal imaging, [8][9][10] airway and lung imaging, [11][12][13][14] dental imaging, [15][16][17] cartilage imaging, [18][19][20] positron emission tomography attenuation correction, [21][22][23][24] radiation therapy planning, 25 and surgical navigation. [26][27][28]…”