Accuracy and repeatability of QRAPMASTER and MRF-vFA.

Our purpose is to evaluate bias and repeatability of the quantitative MRI sequences QRAPMASTER, based on steady-state imaging, and variable Flip Angle MRF (MRF-VFA), based on the transient response. Both techniques are assessed with a standardized phantom and five volunteers on 1.5 T and 3 T clinical scanners.

From signal-based to comprehensive magnetic resonance imaging.

We present and evaluate a new insight into magnetic resonance imaging (MRI). It is based on the algebraic description of the magnetization during the transient response-including intrinsic magnetic resonance parameters such as longitudinal and transverse relaxation times (T, T) and proton density (PD) and experimental conditions such as radiofrequency field (B) and constant/homogeneous magnetic field (B) from associated scanners. We exploit the correspondence among three different elements: the signal evolution as a result of a repetitive sequence of blocks of radiofrequency excitation pulses and encoding gradients, the continuous Bloch equations and the mathematical description of a sequence as a linear system.

Implementation and validation of ASL perfusion measurements for population imaging.

Purpose: Pseudocontinuous arterial spin labeling (pCASL) allows for noninvasive measurement of regional cerebral blood flow (CBF), which has the potential to serve as biomarker for neurodegenerative and cardiovascular diseases. This work aimed to implement and validate pCASL on the dedicated MRI system within the population-based Rotterdam Study, which was installed in 2005 and for which software and hardware configurations have remained fixed.

Methods: Imaging was performed on two 1.

K-space trajectories in 3D-GRASE sequence for high resolution structural imaging.

Purpose: To propose and evaluate new k-space trajectories for 3D-GRASE to improve scan time over 3D-FSE/TSE for high resolution structural imaging.

Methods: Five different Cartesian k-space trajectories were developed and evaluated. They combine ideas of existing k-space trajectories for 3D-GRASE and 3D-FSE/TSE.

Cloud-processed 4D CMR flow imaging for pulmonary flow quantification.

Objectives: In this study, we evaluated a cloud-based platform for cardiac magnetic resonance (CMR) four-dimensional (4D) flow imaging, with fully integrated correction for eddy currents, Maxwell phase effects, and gradient field non-linearity, to quantify forward flow, regurgitation, and peak systolic velocity over the pulmonary artery.

Methods: We prospectively recruited 52 adult patients during one-year period from July 2014. The 4D flow and planar (2D) phase-contrast (PC) were acquired during same scanning session, but 4D flow was scanned after injection of a gadolinium-based contrast agent.

Acoustic noise reduction in MRI using Silent Scan: an initial experience.

Purpose: Acoustic noise during magnetic resonance imaging (MRI) is the main source for patient discomfort and leads to verbal communication problems, difficulties in sedation, and hearing impairment. Silent Scan technology uses less changes in gradient excitation levels, which is directly related to noise levels. Here, we report our preliminary experience with this technique in neuroimaging with regard to subjective and objective noise levels and image quality.

Small-tip-angle spokes pulse design using interleaved greedy and local optimization methods.

Current spokes pulse design methods can be grouped into methods based either on sparse approximation or on iterative local (gradient descent-based) optimization of the transverse-plane spatial frequency locations visited by the spokes. These two classes of methods have complementary strengths and weaknesses: sparse approximation-based methods perform an efficient search over a large swath of candidate spatial frequency locations but most are incompatible with off-resonance compensation, multifrequency designs, and target phase relaxation, while local methods can accommodate off-resonance and target phase relaxation but are sensitive to initialization and suboptimal local cost function minima. This article introduces a method that interleaves local iterations, which optimize the radiofrequency pulses, target phase patterns, and spatial frequency locations, with a greedy method to choose new locations.

Nonuniform and multidimensional Shinnar-Le Roux RF pulse design method.

The Shinnar-Le Roux (SLR) radiofrequency (RF) pulse design algorithm is widely used for designing slice-selective RF pulses due to its intuitiveness, optimality, and speed. SLR is limited, however, in that it is only capable of designing one-dimensional pulses played along constant gradients. We present a nonuniform SLR RF pulse design framework that extends most of the capabilities of classical SLR to nonuniform gradient trajectories and multiple dimensions.

Fast radiofrequency flip angle calibration by Bloch-Siegert shift.

In a recent work, we presented a novel method for B 1+ field mapping based on the Bloch-Siegert shift. Here, we apply this method to automated fast radiofrequency transmit gain calibration. Two off-resonance radiofrequency pulses were added to a slice-selective spin echo sequence.

Local specific absorption rate in high-pass birdcage and transverse electromagnetic body coils for multiple human body models in clinical landmark positions at 3T.

Purpose: To use electromagnetic (EM) simulations to study the effects of body type, landmark position, and radiofrequency (RF) body coil type on peak local specific absorption rate (SAR) in 3T magnetic resonance imaging (MRI).

Materials And Methods: Numerically computed peak local SAR for four human body models (HBMs) in three landmark positions (head, heart, pelvic) were compared for a high-pass birdcage and a transverse electromagnetic 3T body coil. Local SAR values were normalized to the IEC whole-body average SAR limit of 2.

B1 mapping by Bloch-Siegert shift.

A novel method for amplitude of radiofrequency field (B1+) mapping based on the Bloch-Siegert shift is presented. Unlike conventionally applied double-angle or other signal magnitude-based methods, it encodes the B(1) information into signal phase, resulting in important advantages in terms of acquisition speed, accuracy, and robustness. The Bloch-Siegert frequency shift is caused by irradiating with an off-resonance radiofrequency pulse following conventional spin excitation.

Combined optoacoustic/ultrasound system for tomographic absorption measurements: possibilities and limitations.

In this paper, we present the OPUS (optoacoustic plus ultrasound) system, which is a combination of a wavelength-tunable pulsed optical parametrical oscillator (OPO) laser with a commercial ultrasound (US) scanner. Optoacoustic (OA) or, synonymously, photoacoustic (PA) imaging is a spectroscopic technique to measure optical absorption in semitransparent solids and liquids. The measured signal is an acoustical pressure wave, which represents the absorption of pulsed optical radiation.

Spiral imaging artifact reduction: a comparison of two k-trajectory measurement methods.

Purpose: To compare an external sensor-based k-space calibration technique with a routine precalibration method for quantification of method accuracy and reduction of spiral imaging artifacts to obtain improved image quality.

Materials And Methods: Recently, magnetic field monitoring (MFM) has been introduced as a new calibration technique of gradient field-related imperfections. External sensors are placed near the observed object to measure magnetic field variations during image acquisition.

Design of phase-modulated broadband refocusing pulses.

Broadband linear-phase refocusing pulses were designed with the Shinnar-Le Roux (SLR) transformation and verified experimentally. The design works in several steps: initially, a linear-phase B polynomial is created with the Parks-McClellan/Remez exchange algorithm. The complementary A polynomial required for the SLR transformation is generated with the Hilbert transformation, yielding the minimum-phase response.

Importance of bone-conducted sound transmission on patient hearing in the MR scanner.

Purpose: to evaluate the influence of bone-conduction in the MR environment compared to a standardized acoustic environment.

Materials And Methods: Acoustic noise is an unwanted side effect of MRI that is commonly tackled with passive hearing protection. In an MR scanner, however, with the patient completely surrounded by the MR sounds and in close contact with the vibrating MR table and gantry, bone-conduction may increase subjective sound levels, restricting the efficacy of passive protection that reduces air-conducted noise only.

Monitoring tissue coagulation during thermoablative treatment by using a novel magnetic resonance imaging contrast agent.

Introduction: We tested the feasibility of using a novel contrast agent, MS-325, as a marker of coagulating tissue during thermoablative treatment.

Materials And Methods: In vivo, we created coagulated lesions in porcine muscle tissue under 3 different conditions: MS-325 (n = 5), gadolinium-DTPA (n = 5), or no contrast agent (n = 9) present during laser thermoablation. At the same time, we performed continuous T1-weighted magnetic resonance imaging at 1.

Use of fast spin echo for phase shift magnetic resonance thermometry.

Purpose: To propose a modified fast spin echo (FSE) magnetic resonance imaging sequence for MR thermometry, employing the proton resonance frequency (PRF) shift by means of MR phase maps. Despite their obvious advantages of speed and high signal-to-noise ratio (SNR), FSE sequences have not until now been used for this purpose due to the restraints imposed by the Carr-Purcell-Meiboom-Gill (CPMG) conditions.

Materials And Methods: The new FSE combines a new phase modulation scheme that maintains magnetization that ordinarily is destroyed under CPMG conditions, while employing conventional FSE gradient waveforms.

Efficacy of passive acoustic screening: implications for the design of imager and MR-suite.

Purpose: To investigate the efficacy of passive acoustic screening in the magnetic resonance (MR) environment by reducing direct and indirect MR-related acoustic noise, both from the patient's and health worker's perspective.

Materials And Methods: Direct acoustic noise refers to sound originating from the inner and outer shrouds of the MR imager, and indirect noise to acoustic reflections from the walls of the MR suite. Sound measurements were obtained inside the magnet bore (patient position) and at the entrance of the MR imager (health worker position).