Ultrafast Magnetic Resonance Imaging Technique Research Articles

2D ultra-fast MRI of granular dispersion by a liquid jet

This paper illustrates the application of ultra-fast magnetic resonance imaging (MRI) as a noninvasive tool to study the dispersion of a dry, static granular bed by the injection of a liquid. Spatial distributions of undispersed grains (poppy seeds) and injected water were independently imaged at sub-millimetre resolution in 2D with ultra-fast MRI techniques. A liquid jet was observed above the bottom injection orifice, complementing optical imaging. Co-registration of the grains and water images enables the interaction of the static grains and of the liquid jet to be observed for the first time in situ . This visualization of the dispersion process can be used to identify optimal process parameters for a fast and uniform dispersion and to validate quantitatively numerical granular-fluid simulations [1].

In vitro quantitative 1H and 19F nuclear magnetic resonance spectroscopy and imaging studies of fluvastatin™ in Lescol® XL tablets in a USP-IV dissolution cell

Swellable polymeric matrices are key systems in the controlled drug release area. Currently, the vast majority of research is still focused on polymer swelling dynamics. This study represents the first quantitative multi-nuclear ( 1 H and 19 F) fast magnetic resonance imaging study of the complete dissolution process of a commercial (Lescol® XL) tablet, whose formulation is based on the hydroxypropyl methylcellulose (HPMC) polymer under in vitro conditions in a standard USP-IV (United States Pharmacopeia apparatus IV) flow-through cell that is incorporated into high field superconducting magnetic resonance spectrometer. Quantitative RARE 1 H magnetic resonance imaging (MRI) and 19 F nuclear magnetic resonance (NMR) spectroscopy and imaging methods have been used to give information on: (i) dissolution media uptake and hydrodynamics; (ii) active pharmaceutical ingredient (API) mobilisation and dissolution; (iii) matrix swelling and dissolution and (iv) media activity within the swelling matrix. In order to better reflect the in vivo conditions, the bio-relevant media Simulated Gastric Fluid (SGF) and Fasted State Simulated Intestinal Fluid (FaSSIF) were used. A newly developed quantitative ultra-fast MRI technique was applied and the results clearly show the transport dynamics of media penetration and hydrodynamics along with the polymer swelling processes. The drug dissolution and mobility inside the gel matrix was characterised, in parallel to the 1 H measurements, by 19 F NMR spectroscopy and MRI, and the drug release profile in the bulk solution was recorded offline by UV spectrometer. We found that NMR spectroscopy and 1D-MRI can be uniquely used to monitor the drug dissolution/mobilisation process within the gel layer, and the results from 19 F NMR spectra indicate that in the gel layer, the physical mobility of the drug changes from “dissolved immobilised drug” to “dissolved mobilised drug”.

Hydrodynamics in two-phase flow within porous media

Ultra-fast magnetic resonance imaging techniques are used to image liquid distribution in two and three dimensions during air-water co-current down flow through a fixed bed of cylindrical porous pellets of length and diameter 3 mm, packed within a 43 mm internal diameter column in both the trickle- and pulsing-flow regimes. The data acquisition times used were 20 and 280 ms, giving 2-D and 3-D spatial resolutions of 1.4 mm x 2.8 mm and 3.75 mm x 3.75 mm x 1.87 mm, respectively. This work reports images of local pulsing events within the bed occurring during the trickle-to-pulse flow transition. The evolution of the local instabilities is studied as a function of increasing liquid velocity at constant gas velocity.

Fetal shoulder measurements by fast and ultrafast MRI techniques.

The purpose of this study was to evaluate magnetic resonance imaging (MRI) of fetal shoulder measurements of fetuses with suspected macrosomia. The actual fetal shoulder measurements made immediately after birth were compared with measurements obtained by fast and ultrafast MRI techniques antepartum. Eight singleton diabetic pregnant mothers underwent MRI examination with fast imaging in steady-state precession (TrueFISP) and spin-echo (SE) and gradient-echo (GE) echo-planar (EPI) sequences to show the fetal shoulder width. The actual shoulder width was measured immediately postpartum by a neonatologist. There was a statistically significant correlation between the MRI measurements and the actual shoulder width (P < 0.001 - P < 0.05) for all sequences. TrueFISP (r = 0.98, P < 0.001) was superior to EPI sequences (r = 0.88, P < 0.01 for SE EPI and r = 0.80, P < 0.05 for GE EPI). The images of all three sequences used were free of major motion artifacts. Fast and ultrafast sequences seem to be reliable for fetal shoulder measurements and the TrueFISP was the most accurate sequence compared to SE and GE echo-planar sequences. J. Magn. Reson. Imaging 2001;13:938-942.

Magnetic Resonance Imaging of the Fetal and Neonatal Central Nervous System

After completing this article, readers should be able to: 1. Compare and contrast magnetic resonance technology with computed tomography and ultrasonography. 2. Delineate the primary clinical uses of magnetic resonance spectroscopy, perfusion magnetic resonance, functional magnetic resonance imaging, and diffusion imaging. 3. Describe the primary uses of magnetic resonance imaging in congenital and developmental abnormalities, neurovascular disease, trauma, infections, inflammatory processes, and metabolic and neurodegenerative disorders. Magnetic resonance (MR) is one of several neuroimaging technologies used to diagnose fetal and neonatal central nervous system (CNS) abnormalities. It can aid in differentiating static from progressive encephalopathies and in diagnosing such conditions as congenital and developmental abnormalities, trauma, neurovascular disease, infections and inflammatory processes, and metabolic and neurodegenerative disorders. Although it also is helpful in diagnosing neoplastic processes, which are rare but important causes of progressive encephalopathy, these presentations are not considered in this article. MR, which employs magnetic fields and radiowaves, is a less invasive imaging technology than ultrasonography (US), computed tomography (CT), and nuclear medicine (NM), but it is more expensive. In contrast to the other modalities, which derive their signals from single parameters, the MR signal is derived exponentially from multiple parameters (eg, T1, T2, proton density, T2*, proton flow, proton relaxation enhancement, chemical shift, and molecular diffusion). MR also employs many more basic imaging techniques than other modalities, including spin echo, inversion recovery, gradient echo, and chemical shift imaging methods. Advancing MR capabilities have improved its sensitivity, specificity, and efficiency, particularly compared with US, CT, and NM. Among these advanced capabilities are the flow-attenuated inversion recovery technique (FLAIR), fat suppression short inversion time-inversion recovery imaging, and magnetization transfer imaging for increased structural resolution. Fast and ultrafast MR imaging techniques (fast spin echo, fast gradient echo, echo planar imaging) have reduced imaging times, improved structural resolution, and provided functional imaging. Specific applications …

Clinical applications and techniques of echo-planar imaging

The ultrafast magnetic resonance imaging technique known as echo-planar imaging has undergone considerable technical improvements in recent years. It is currently being evaluated at only a few institutions worldwide. Although EPI, invented by P. Mansfield in 1977, is the oldest fast MRI technique, it is still not widely available on clinical scanners. Only 20–30 EPI scanners exist worldwide, compared to about 7000 conventional MRI scanners. The main reason why EPI has not emerged from the scientific prototype niche is its high demands on hardware and software. However, the time is now coming when EPI is entering the clinical stage. We describe the common EPI sequence types, show clinical results, and describe the contrast in the measured images.