Influence of k-space trajectory corrections on proton density mapping with ultrashort echo time imaging: Application for imaging of short T2 components in white matter

Background Magnetic resonance imaging (MRI) of the pulmonary parenchyma is generally hampered by multiple challenges related to patient respiratory- and circulation-related motion, low proton density and extremely fast signal decay due to the structure of the lungs evolved for gas exchange. Methods Systematic literature database research as well as annual participation in conferences dedicated to pulmonary MRI for more than the past 20 years by at least one member of the author team. Results and Conclusion The problem of motion has been addressed in the past by developments such as triggering, gating and parallel imaging. The second problem has, in part, turned out to be an advantage in those diseases that lead to an increase in lung substance and thus an increase in signal relative to the background. To reduce signal decay, ultrashort echo time (UTE) methods were developed to minimize the time between excitation and readout. Having been postulated a while ago, improved hardware and software now open up the possibility of achieving echo times shorter than 200 µs, increasing lung signal significantly by forestalling signal decay and more effectively using the few protons available. Such UTE techniques may not only improve structural imaging of the lung but also enhance functional imaging, including ventilation and perfusion imaging as well as quantitative parameter mapping. Because of accelerating progress in this field of lung MRI, the review at hand seeks to introduce some technical properties as well as to summarize the growing data from applications in humans and disease, which promise that UTE MRI will play an important role in the morphological and functional assessment of the lung in the near future. Key Points: Citation Format

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Exponential subtraction in 3D ultrashort echo time imaging to visualize short T2 tissues in tibia

Acta Radiologica ◽

10.1177/0284185119877797 ◽

2019 ◽

Vol 61 (6) ◽

pp. 760-767

Author(s):

Sha Li ◽

Xinrui Huang ◽

Guozhen Li ◽

Yibao Zhang ◽

Zhaotong Li ◽

...

Keyword(s):

Cortical Bone ◽

Three Dimensional ◽

Regions Of Interest ◽

Observer Agreement ◽

Exponential Factor ◽

Ultrashort Echo Time ◽

Short T2 ◽

Exponential Factors ◽

Echo Time ◽

Dual Echo

Background Short T2 tissues can be directly visualized by dual-echo ultrashort echo time imaging with weighted subtraction. As a type of post-processing method, exponential subtraction of ultrashort echo time images with an optimal exponential factor is expected to provide improved positive short T2 contrast. Purpose To test the feasibility and effectiveness of exponential subtraction in three-dimensional ultrashort echo time imaging and to determine the optimal exponential factor. Material and Methods A dual-echo three-dimensional ultrashort echo time sequence was implemented on a 3-T MRI system. Exponential subtraction was performed on dual three-dimensional ultrashort echo time images of the tibia of seven healthy volunteers with exponential factors in the range of 1.00–3.00 in increments of 0.01. The regions of interest, including cortical bone, marrow, and muscle, were depicted on subtracted images of different exponential factors. Contrast-to-noise ratio values were calculated from these regions of interest and then used to assess the optimal exponential factor. To determine intra-observer agreement regarding region of interest selection, paired intra-observer measurements of regions of interest in all direct subtraction images were conducted with a one-week interval and the paired measurements were assessed using Bland–Altman analysis and paired-samples t-test. Results Cortical bone can be better visualized by using exponential subtraction in three-dimensional ultrashort echo time imaging; the suggested optimal exponential factor is 1.99–2.03 in the tibia. Paired measurements showed excellent intra-observer agreement. Conclusion It is feasible to visualize cortical bone of the tibia using exponential subtraction in three-dimensional ultrashort echo time imaging. Compared with weighted subtraction images, exponential subtraction images with an optimal exponential factor provide enhanced visualization of short T2 tissues.

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A pilot study of short T2* measurements with ultrashort echo time imaging at 0.35 T

BioMedical Engineering OnLine ◽

10.1186/s12938-018-0505-5 ◽

2018 ◽

Vol 17 (1) ◽

Cited By ~ 2

Author(s):

Xiuyuan Chen ◽

Bensheng Qiu

Keyword(s):

Pilot Study ◽

Ultrashort Echo Time ◽

Short T2 ◽

Echo Time

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Detecting Articular Cartilage and Meniscus Deformation Effects Using Magnetization Transfer Ultrashort Echo Time (MT-UTE) Modeling during Mechanical Load Application: Ex Vivo Feasibility Study

Cartilage ◽

10.1177/1947603520976771 ◽

2020 ◽

pp. 194760352097677

Author(s):

Saeed Jerban ◽

Akhil Kasibhatla ◽

Yajun Ma ◽

Mei Wu ◽

Yanjun Chen ◽

...

Keyword(s):

Articular Cartilage ◽

Mechanical Load ◽

Ex Vivo ◽

Magnetization Transfer ◽

Knee Joints ◽

Loading Conditions ◽

Ultrashort Echo Time ◽

Short T2 ◽

Echo Time ◽

Magnetic Resonance Imaging Mri

Objective Ultrashort echo time (UTE) magnetic resonance imaging (MRI) sequences have improved imaging of short T2 musculoskeletal (MSK) tissues. UTE-MRI combined with magnetization transfer modeling (UTE-MT) has demonstrated robust assessment of MSK tissues. This study aimed to investigate the variation of UTE-MT measures under mechanical loading in tibiofemoral cartilage and meniscus of cadaveric knee joints. Design Fourteen knee joints from young ( n = 8, 42 ± 12 years old) and elderly ( n = 6, 89 ± 4 years old) donors were scanned on a 3-T scanner under 3 loading conditions: load = 300 N (Load1), load = 500 N (Load2), and load = 0 N (Unload). UTE-MT sequences were performed at each loading condition. Macromolecular proton fraction (MMF) was calculated from UTE-MT modeling. Wilcoxon rank sum test was used to examine the MRI data differences between loading conditions. Results For young donors, MMF increased in all grouped regions of interest (meniscus [M], femoral articular cartilage [FAC], tibial articular cartilage [TAC], articular cartilage regions covered by meniscus [AC-MC], and articular cartilage regions uncovered by meniscus [AC-UC]) when the load increased from 300 to 500 N. The increases in MMF were significant for M (13.3%, P < 0.01) and AC-MC (9.2%, P = 0.04). MMF decreased in all studied regions after unloading, which was significant only for AC-MC (−8.9%, P = 0.01). For elderly donors, MRI parameters did not show significant changes by loading or unloading. Conclusion This study highlights the potential of the UTE-MT modeling combined with knee loading in differentiating between normal and abnormal knees. Average tissue deformation effects were likely higher and more uniformly distributed in the joints of young donors compared with elderly donors.

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