Teng-Yi Huang

T2 measurement of the human myocardium using a T2-prepared transient-state TrueFISP sequence.

A fast and motion‐insensitive technique suitable for myocardial BOLD contrast imaging is presented. The method, termed T2‐TrueFISP, combines T2 magnetization preparation with steady‐state free precession (SSFP) imaging for T2 relaxation mapping of the myocardium in healthy volunteers. The T2 contrast‐to‐noise ratio (CNR) was optimized with the use of transient‐state TrueFISP readout and half‐Fourier readout with linear phase encoding. Single‐slice myocardial T2‐weighted image was obtained within one heartbeat, and a single slice T2 map of the myocardium was obtained in under 5–7 s. A respiratory navigator‐gating method was incorporated for serial measurements and signal averaging, with the subjects breathing freely. The mean myocardial T2 relaxation time measured in 12 healthy volunteers was 54 ± 5.7 ms. Regional variations of T2 values across the myocardium were 7%. Temporal variations across serial T2 measurements in a transmural region covering ∼0.5 cc of the left ventricular (LV) wall were 3.6% without signal averaging (number of excitations (NEX) = 1) and 1.7% with signal averaging (NEX = 10). According to our preliminary results, the T2‐TrueFISP method is expected to provide a robust and sensitive tool for clinical application of myocardial BOLD contrast imaging. Magn Reson Med 57:960–966, 2007.

Functional MRI Using Regularized Parallel Imaging Acquisition

Parallel MRI techniques reconstruct full‐FOV images from undersampled k‐space data by using the uncorrelated information from RF array coil elements. One disadvantage of parallel MRI is that the image signal‐to‐noise ratio (SNR) is degraded because of the reduced data samples and the spatially correlated nature of multiple RF receivers. Regularization has been proposed to mitigate the SNR loss originating due to the latter reason. Since it is necessary to utilize static prior to regularization, the dynamic contrast‐to‐noise ratio (CNR) in parallel MRI will be affected. In this paper we investigate the CNR of regularized sensitivity encoding (SENSE) acquisitions. We propose to implement regularized parallel MRI acquisitions in functional MRI (fMRI) experiments by incorporating the prior from combined segmented echo‐planar imaging (EPI) acquisition into SENSE reconstructions. We investigated the impact of regularization on the CNR by performing parametric simulations at various BOLD contrasts, acceleration rates, and sizes of the active brain areas. As quantified by receiver operating characteristic (ROC) analysis, the simulations suggest that the detection power of SENSE fMRI can be improved by regularized reconstructions, compared to unregularized reconstructions. Human motor and visual fMRI data acquired at different field strengths and array coils also demonstrate that regularized SENSE improves the detection of functionally active brain regions. Magn Reson Med 54:343–353, 2005.

PROPELLER-EPI with parallel imaging using a circularly symmetric phased-array RF coil at 3.0 T : Application to high-resolution diffusion tensor imaging

A technique integrating multishot periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) and parallel imaging is presented for diffusion echo‐planar imaging (EPI) at high spatial resolution. The method combines the advantages of parallel imaging to achieve accelerated sampling along the phase‐encoding direction, and PROPELLER acquisition to further decrease the echo train length (ETL) in EPI. With an eight‐element circularly symmetric RF coil, a parallel acceleration factor of 4 was applied such that, when combined with PROPELLER acquisition, a reduction of geometric distortions by a factor substantially greater than 4 was achieved. The resulting phantom and human brain images acquired with a 256 × 256 matrix and an ETL of only 16 were visually identical in shape to those acquired using the fast spin‐echo (FSE) technique, even without field‐map corrections. It is concluded that parallel PROPELLER‐EPI is an effective technique that can substantially reduce susceptibility‐induced geometric distortions at high field strength. Magn Reson Med, 2006.

Inter-Strain Differences in Default Mode Network: A Resting State fMRI Study on Spontaneously Hypertensive Rat and Wistar Kyoto Rat.

Genetic divergences among mammalian strains are presented phenotypically in various aspects of physical appearance such as body shape and facial features. Yet how genetic diversity is expressed in brain function still remains unclear. Functional connectivity has been shown to be a valuable approach in characterizing the relationship between brain functions and behaviors. Alterations in the brain default mode network (DMN) have been found in human neuropsychological disorders. In this study we selected the spontaneously hypertensive rat (SHR) and the Wistar Kyoto rat (WKY), two inbred rat strains with close genetic origins, to investigate variations in the DMN. Our results showed that the major DMN differences are the activities in hippocampal area and caudate putamen region. This may be correlated to the hyperactive behavior of the SHR strain. Advanced animal model studies on variations in the DMN may have potential to shed new light on translational medicine, especially with regard to neuropsychological disorders.

Self-gated PROPELLER-encoded cine cardiac imaging

This study uses the k-space center over-sampling property of PROPELLER encoding to detect cardiac and respiratory motion using raw k-space data. Using the motion information, cine cardiac imaging is self-gated. The data acquisition process requires neither electrocardiography triggering nor patient breath-holding. Using physiology motion information, this post-processing method rearranges the k-space data into groups corresponding to cardiac and respiratory phases. The PROPELLER blades of the same groups are combined to produce cine high-resolution images. This approach reduces the potential discrepancy of the k-space data and the motion-related artifacts in the reconstructed image because all blades in a group are acquired at consistent cardiac and respiratory phases. The study concludes that self-gated cine cardiac imaging is feasible using PROPELLER encoding. It is a potentially practical tool for cine cardiac imaging.

Resting‐State Functional Magnetic Resonance Imaging: The Impact of Regression Analysis

To investigate the impact of regression methods on resting‐state functional magnetic resonance imaging (rsfMRI). During rsfMRI preprocessing, regression analysis is considered effective for reducing the interference of physiological noise on the signal time course. However, it is unclear whether the regression method benefits rsfMRI analysis.

Optimization of PROPELLER reconstruction for free-breathing T1-weighted cardiac imaging.

PURPOSE Clinical cardiac MR imaging techniques generally require patients to hold their breath during the scanning process to minimize respiratory motion-related artifacts. However, some patients cannot hold their breath because of illness or limited breath-hold capacity. This study aims to optimize the PROPELLER reconstruction for free-breathing myocardial T1-weighted imaging. METHODS Eight healthy volunteers (8 men; mean age 26.4 years) participated in this study after providing institutionally approved consent. The PROPELLER encoding method can reconstruct a low-resolution image from every blade because of k-space center oversampling. This study investigated the feasibility of extracting a respiratory trace from the PROPELLER blades by implementing a fully automatic region of interest selection and introducing a best template index to account for the property of the human respiration cycle. RESULTS Results demonstrated that the proposed algorithm significantly improves the contrast-to-noise ratio and the image sharpness (p < 0.05). CONCLUSIONS The PROPELLER method is expected to provide a robust tool for clinical application in free-breathing myocardial T1-weighted imaging. It could greatly facilitate the acquisition procedures during such a routine examination.

Simultaneous Temperature and Magnetization Transfer (MT) Monitoring During High-Intensity Focused Ultrasound (HIFU) Treatment: Preliminary Investigation on Ex Vivo Porcine Muscle

To measure temperature change and magnetization transfer ratio (MTR) simultaneously during high‐intensity focused ultrasound (HIFU) treatment.

Temporal correlation-based dynamic contrast-enhanced MR imaging improves assessment of complex pulmonary circulation in congenital heart disease†

A temporal correlation (TC) mapping method is proposed to help bolus chasing during dynamic contrast‐enhanced (DCE) MRI of complex pulmonary circulation (CPC) in patients with congenital heart disease. DCE‐MRI was performed on five healthy male subjects (23–24 years old) and 25 patients (nine males and 16 females, 0.25–44 years old), and TC maps were generated by performing pixel‐based computation of cross‐correlations to the pulmonary artery with a series of time shifts in all subjects. Qualitative and quantitative evaluations were performed in comparison with original DCE images. TC maps exhibited a better signal‐to‐noise ratio (SNR) by factors of 4.3 and 1.3 in the lung parenchyma, pulmonary veins, and superior artery/vein; a better intraparenchymal contrast‐to‐noise ratio (CNR) by factors of 1.5–5.4; and a significantly higher conspicuity in all regions except the pulmonary arteries when graded with a five‐point score. TC maps evaluated by two experienced clinicians significantly added relevant information (P < 0.001), and in some cases affected the final diagnosis. We conclude that TC maps facilitate bolus chasing for DCE‐MRI by reducing recirculation effects and interframe fluctuations, and hence complements morphological imaging of CPC in patients with complex congenital heart disease. Magn Reson Med, 2006.

Correction of geometric distortion in Propeller echo planar imaging using a modified reversed gradient approach.

OBJECTIVE This study investigates the application of a modified reversed gradient algorithm to the Propeller-EPI imaging method (periodically rotated overlapping parallel lines with enhanced reconstruction based on echo-planar imaging readout) for corrections of geometric distortions due to the EPI readout. MATERIALS AND METHODS Propeller-EPI acquisition was executed with 360-degree rotational coverage of the k-space, from which the image pairs with opposite phase-encoding gradient polarities were extracted for reversed gradient geometric and intensity corrections. The spatial displacements obtained on a pixel-by-pixel basis were fitted using a two-dimensional polynomial followed by low-pass filtering to assure correction reliability in low-signal regions. Single-shot EPI images were obtained on a phantom, whereas high spatial resolution T2-weighted and diffusion tensor Propeller-EPI data were acquired in vivo from healthy subjects at 3.0 Tesla, to demonstrate the effectiveness of the proposed algorithm. RESULTS Phantom images show success of the smoothed displacement map concept in providing improvements of the geometric corrections at low-signal regions. Human brain images demonstrate prominently superior reconstruction quality of Propeller-EPI images with modified reversed gradient corrections as compared with those obtained without corrections, as evidenced from verification against the distortion-free fast spin-echo images at the same level. CONCLUSIONS The modified reversed gradient method is an effective approach to obtain high-resolution Propeller-EPI images with substantially reduced artifacts.