Parallel Imaging with RASER using Multiband Frequency-modulated Excitation Pulses

The many advantages of the recently proposed RASER sequence have been demonstrated. Hence, RASER holds great promises for functional MRI (fMRI), particularly for studies of the orbital-frontal cortex and other brain regions near air cavities, which cause distortion and signal loss in conventional EPI methods. However, the single-shot RASER sequence implemented so far inherently presents a set of temporal and spatial limitations that hinders it feasibility and full potential for fMRI applications. It is believed that parallel imaging will help overcome such restrictions. In this work, the RASER acquisition and reconstruction scheme is extended for parallel imaging using tailored pulses for simultaneous multi-band excitation

Exploring synchrony and chaos of parahydrogen-pumped two-compartment radio-frequency amplification by stimulated emission of radiation

A nuclear-spin-based RASER (radio-frequency amplification by stimulated emission of radiation) is an ideal experimental system to explore nonlinear interaction phenomena of nuclear spins coupled via virtual photons to a resonator. This is due to the RASER being stable for several hours, allowing for extended observation of these phenomena. Nonlinear phenomena in multimode RASERs range from mode oscillations in synchrony, frequency shifts, frequency combs, period doublings, and even chaos. These phenomena are observed in a parahydrogen-pumped two-compartment proton RASER. In two independently pumped compartments, the separation in frequency space between the two RASER modes is precisely controlled with a magnetic field gradient. By controlling the mode separation, we can select the type of nonlinear phenomena observed. A key finding is that the ranges of mode separation where chaos and synchrony occur are very close together. The experimental results are supported by numerical simulations, based on two-mode RASER equations

Myocardial perfusion imaging by cardiac magnetic resonance

Cardiovascular magnetic resonance (CMR) has been shown to provide high quality data on cardiac and valvular function, perfusion, viability, blood flow, and potentially, on cardiac metabolism as well. Several of these CMR applications (eg, function and viability assessment) matured during the past years and are now established components of a cardiac workup. Perfusion-CMR is close to this status and is already a major contributor to cardiac examinations in a growing number of expert centers. Large multicenter perfusion-CMR trials comparing the diagnostic performance of CMR with other techniques were recently reported yielding areas under the receiver-operator-characteristics curve as a high as 0.85 for coronary artery disease detection (MR-IMPACT). Anticipating a growing role for perfusion-CMR in cardiology in the near future, this article discusses the principles of perfusion-CMR and its integration into the workup of patient with coronary artery disease (CAD). In addition to a functional study, this integration is mainly composed of a perfusion-CMR part, followed by a viability assessment by late enhancement CMR techniques. The principal characteristics of these CMR techniques are compared with those of single photon emission computed tomography (SPECT) and positron emission tomography (PET). After introduction into principles and techniques of perfusion-CMR, some open questions in perfusion-CMR and challenges for the future are addressed. Finally, newer CMR applications are shortly mentioned utilizing hyperpolarized carbon-13 compounds in experimental models for quantification of myocardial perfusion and for real-time assessment of metabolic pathways in postischemic myocardium. (J Nucl Cardiol 2006;13: 841-54.

Arterial spin labeling using spatio-temporal encoding readout for robust perfusion imaging in inhomogenous magnetic fields

Purpose: To evaluate the feasibility of spatio-temporal encoding (SPEN) readout for pseudo-continuous ASL (pCASL) in brain, and its robustness to susceptibility artifacts as introduced by aneurysm clips. Methods: A 2D self-refocused T-2*-compensated hybrid SPEN scheme, with super-resolution reconstruction was implemented on a 1.5T Philips system. Q (=BWchirp*T-chirp) was varied and, the aneurysm clip-induced artifact was evaluated in phantom (label-images) as well as in vivo (perfusion-weighted signal (PWS)-maps and temporal SNR (tSNR)). In vivo results were compared to gradient-echo EPI (GE-EPI) and spin-echo EPI (SE-EPI). The dependence of tSNR on TR was evaluated separately for SPEN and SE-EPI. SPEN with Q similar to 75 encodes with the same off-resonance robustness as EPI. Results: The clip-induced artifact with SPEN decreased with increase in Q, and was smaller compared to SE-EPI and GE-EPI in vivo. tSNR decreased with Q and the tSNR of GE-EPI and SE-EPI corresponded to SPEN with a Q-value of approximately similar to 85 and similar to 108, respectively. In addition, SPEN perfusion images showed a higher tSNR (p 75) compared to SE-EPI and GE-EPI. However, the SPEN chirp-pulse saturates incoming blood, thereby reducing pCASL labeling efficiency of the next acquisition for short TRs. Future developments are needed to enable 3D scanning.Radiolog

Prediction of stroke risk in patients with transient ischemic attack: ABCD score and its derived scores

Transient Ischemic Attack (TIA) is a high-risk signal of acute ischemic cerebrovascular disease, indicates a significant increase in the risk of ischemic stroke, especially within 7 days. Risk assessment and stratification are important in patient with TIA. A variety of simple prediction scales were developed based on the risk factors for stroke in patients with TIA, such as the California scale, ABCD scale, and ABCD2 scale. Among them, the ABCD scale score is used most commonly, but as its application becomes more and more common, the defects of this scale are also increasingly apparent. In recent years, some derived scales of ABCD score were introduced in order to improve the sensitivity and specificity of prediction. This article reviews the evolution, contents, characteristics, and predictive value of the ABCD score and its derived scales in the prediction of the stroke risk in patients with TIA