Novel MRI Technologies for Structural and Functional Imaging of Tissues with Ultra-short T₂ Values

Conventional MRI has several limitations such as long scan durations, motion artifacts, very loud acoustic noise, signal loss due to short relaxation times, and RF induced heating of electrically conducting objects. The goals of this work are to evaluate and improve the state-of-the-art methods for MRI of tissue with short T₂, to prove the feasibility of in vivo Concurrent Excitation and Acquisition, and to introduce simultaneous electroglottography measurement during functional lung MRI

Novel MRI Technologies for Structural and Functional Imaging of Tissues with Ultra-short T2 Values

Conventional MRI has several limitations such as long scan durations, motion artifacts, very high acoustic noise levels, signal loss due to short relaxation times, and RF induced heating of electrically conducting objects. The goals of this thesis are to evaluate state-of-the-art methods for MRI of tissue with short relaxation times, to prove the feasibility of CEA in a clinical MRI system, and to introduce a new electrophysiological measurement unit applied simultaneously with lung MRI

In vivo MRI with Concurrent Excitation and Acquisition using Automated Active Analog Cancellation

Magnetic resonance imaging (MRI) provides excellent cross-sectional images of the soft tissues in patients. Unfortunately, MRI is intrinsically slow, it exposes patients to severe acoustic noise levels, and is limited in the visualization of certain tissues such as bone. These limitations are partly caused by the timing structure of the MRI exam which first generates the MR signal by a strong radio-frequency excitation and later acquires the weak MRI signal. Concurrent excitation and acquisition (CEA) can overcome these limitations, but is extremely challenging due to the huge intensity difference between transmit and receive signal (up to 100 dB). To suppress the strong transmit signals during signal reception, a fully automated analog cancellation unit was designed. On a 3 Tesla clinical MRI system we achieved an on-resonance analog isolation of 90 dB between the transmit and receive path, so that CEA images of the head and the extremities could be acquired with an acquisition efficiency of higher than 90% at sound pressure levels close to background noise. CEA with analog cancellation might provide new opportunities for MRI in tissues with very short T2 relaxation times, and it offers a silent and time-efficient MRI acquisition

Differences of respiratory kinematics in female and male singers – A comparative study using dynamic magnetic resonance imaging

Breath control is an important factor for singing voice production, but pedagogic descriptions of how a beneficial movement pattern should be performed vary widely and the underlying physiological processes are not understood in detail. Differences in respiratory movements during singing might be related to the sex of the singer. To study sex-related differences in respiratory kinematics during phonation, 12 singers (six male and six female) trained in the Western classical singing tradition were imaged with dynamic magnetic resonance imaging. Singers were asked to sustain phonation at five different pitches and loudness conditions, and cross-sectional images of the lung were acquired. In each dynamic image frame the distances between anatomical landmarks were measured to quantify the movements of the respiratory apparatus. No major difference between male and female singers was found for the general respiratory kinematics of the thorax and the diaphragm during sustained phonation. However when compared to sole breathing, male singers significantly increased their thoracic movements for singing. This behavior could not be observed in female singers. The presented data support the hypothesis that professional singers follow sex-specific breathing strategies. This finding may be important in a pedagogical context where the biological sex of singer and student differ and should be further investigated in a larger cohort

Respiratory dynamics in phonation and breathing-A real-time MRI study.

The respiratory system is a central part of voice production, but for phonation neither the underlying functional relations between diaphragm (DPH) and rib cage (RC), nor differences to normal breathing are yet understood. This study aims to compare respiratory dynamics in phonation and breathing via dynamic MRI of the lung. Images of the breathing apparatus of 6 professional singers were captured in a 1.5T MRI system in supine position during vital capacity breathing and maximal long sustained phonation at 3 different pitches and loudness conditions. In a dynamic series of cross-sectional images of the lung, distances between characteristic anatomical landmarks were measured. During exhalation in normal breathing the diaphragm and rib cage moved synchronously to reduce lung volume, but during phonation different functional units could be identified, which support phonation by facilitating the control of subglottic pressure

Sub-millisecond 2D MRI of the vocal fold oscillation using single-point imaging with rapid encoding

Objective!#!The slow spatial encoding of MRI has precluded its application to rapid physiologic motion in the past. The purpose of this study is to introduce a new fast acquisition method and to demonstrate feasibility of encoding rapid two-dimensional motion of human vocal folds with sub-millisecond resolution.!##!Method!#!In our previous work, we achieved high temporal resolution by applying a rapidly switched phase encoding gradient along the direction of motion. In this work, we extend phase encoding to the second image direction by using single-point imaging with rapid encoding (SPIRE) to image the two-dimensional vocal fold oscillation in the coronal view. Image data were gated using electroglottography (EGG) and motion corrected. An iterative reconstruction with a total variation (TV) constraint was used and the sequence was also simulated using a motion phantom.!##!Results!#!Dynamic images of the vocal folds during phonation at pitches of 150 and 165 Hz were acquired in two volunteers and the periodic motion of the vocal folds at a temporal resolution of about 600 µs was shown. The simulations emphasize the necessity of SPIRE for two-dimensional motion encoding.!##!Discussion!#!SPIRE is a new MRI method to image rapidly oscillating structures and for the first time provides dynamic images of the vocal folds oscillations in the coronal plane

Ultra-short T2 components imaging of the whole brain using 3D dual-echo UTE MRI with rosette k-space pattern.

PURPOSE: This study aimed to develop a new 3D dual-echo rosette k-space trajectory, specifically designed for UTE MRI applications. The imaging of the ultra-short transverse relaxation time (uT2 ) of brain was acquired to test the performance of the proposed UTE sequence. THEORY AND METHODS: The rosette trajectory was developed based on rotations of a "petal-like" pattern in the kx -ky plane, with oscillated extensions in the kz -direction for 3D coverage. Five healthy volunteers underwent 10 dual-echo 3D rosette UTE scans with various TEs. Dual-exponential complex model fitting was performed on the magnitude data to separate uT2 signals, with the output of uT2 fraction, uT2 value, and long-T2 value. RESULTS: The 3D rosette dual-echo UTE sequence showed better performance than a 3D radial UTE acquisition. More significant signal intensity decay in white matter than gray matter was observed along with the TEs. The white matter regions had higher uT2 fraction values than gray matter (10.9% ± 1.9% vs. 5.7% ± 2.4%). The uT2 value was approximately 0.10 ms in white matter . CONCLUSION: The higher uT2 fraction value in white matter compared to gray matter demonstrated the ability of the proposed sequence to capture rapidly decaying signals

Multi-parameter Analytical Method for B1 and SNR Analysis (MAMBA): An open source RF coil design tool

In Magnetic Resonance Imaging (MRI), radio frequency (RF) coils of different forms and shapes are used to maximize signal-to-noise ratio (SNR). RF coils are designed for clinical applications and have dimensions comparable with the target body part to be imaged, and they perform best when loaded by human tissue majority of which have conductivity values higher than 0.5 S/m. However, they are not properly tuned and matched for samples having low conductivity such as solid samples with low water content. Moreover, for samples with low filling factor and low conductivity, the noise in MRI is dominated by RF coil losses. In this case, RF coil design can be optimized to improve image SNR. Here, a new software tool (Multi-parameter Analytical Method for B1 and SNR Analysis) MAMBA is presented to design and compare volume coils of birdcage, solenoid, and loop-gap design for these samples. The input parameters of the tool are the sample properties, the coil design and the hardware properties, of which a relative SNR is determined. For that, a figure of merit is calculated from the coil sensitivity, applied resonant frequency and the resistive losses of sample, coil and capacitive components. The tool was tested in an ancient Egyptian mummy head which represents an extreme case of MRI with short T2*. Two optimized birdcage coils were designed using MAMBA, constructed and compared to a commercial transmit receive head coil. Calculated relative SNR values are in good agreement with the measurements

Table_1_Differences of respiratory kinematics in female and male singers – A comparative study using dynamic magnetic resonance imaging.DOCX

Breath control is an important factor for singing voice production, but pedagogic descriptions of how a beneficial movement pattern should be performed vary widely and the underlying physiological processes are not understood in detail. Differences in respiratory movements during singing might be related to the sex of the singer. To study sex-related differences in respiratory kinematics during phonation, 12 singers (six male and six female) trained in the Western classical singing tradition were imaged with dynamic magnetic resonance imaging. Singers were asked to sustain phonation at five different pitches and loudness conditions, and cross-sectional images of the lung were acquired. In each dynamic image frame the distances between anatomical landmarks were measured to quantify the movements of the respiratory apparatus. No major difference between male and female singers was found for the general respiratory kinematics of the thorax and the diaphragm during sustained phonation. However when compared to sole breathing, male singers significantly increased their thoracic movements for singing. This behavior could not be observed in female singers. The presented data support the hypothesis that professional singers follow sex-specific breathing strategies. This finding may be important in a pedagogical context where the biological sex of singer and student differ and should be further investigated in a larger cohort.</p

Video_1_Differences of respiratory kinematics in female and male singers – A comparative study using dynamic magnetic resonance imaging.mp4

Breath control is an important factor for singing voice production, but pedagogic descriptions of how a beneficial movement pattern should be performed vary widely and the underlying physiological processes are not understood in detail. Differences in respiratory movements during singing might be related to the sex of the singer. To study sex-related differences in respiratory kinematics during phonation, 12 singers (six male and six female) trained in the Western classical singing tradition were imaged with dynamic magnetic resonance imaging. Singers were asked to sustain phonation at five different pitches and loudness conditions, and cross-sectional images of the lung were acquired. In each dynamic image frame the distances between anatomical landmarks were measured to quantify the movements of the respiratory apparatus. No major difference between male and female singers was found for the general respiratory kinematics of the thorax and the diaphragm during sustained phonation. However when compared to sole breathing, male singers significantly increased their thoracic movements for singing. This behavior could not be observed in female singers. The presented data support the hypothesis that professional singers follow sex-specific breathing strategies. This finding may be important in a pedagogical context where the biological sex of singer and student differ and should be further investigated in a larger cohort.</p