MR relaxometry imaging. Work in progress.

Carlson, Joseph W.; Goldhaber, David M.; Brito, Anthony; Kaufman, L

doi:10.1148/radiology.184.3.1509044

Cited by 25 publications

(24 citation statements)

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“…We introduce here a novel method to distinguish between signal intensities produced by tissues containing activated probe from all other sources of signal intensity, which we have termed Delta relaxation enhanced MR (DREMR) (10). This approach finds its roots in field‐cycling relaxometry imaging methods used by Carlson et al (11) as a means to differentiate biological tissues. Carlson et al outfitted a 64 mT whole‐body MR with a pulsed electromagnet insert in order to modulate the strength of the main magnetic field during an imaging experiment.…”

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confidence: 99%

Delta relaxation enhanced MR: Improving activation‐specificity of molecular probes through R₁ dispersion imaging

Alford

Rutt

Scholl

et al. 2009

Magnetic Resonance in Med

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MR molecular imaging enables high-resolution, in vivo study of molecular processes frequently utilizing gadolinium-based probes that specifically bind to a particular biological molecule or tissue. While some MR probes are inactive when unbound and produce enhancement only after binding, the majority are less specific and cause enhancement in either state. Accumulation processes are then required to increase probe concentration in regions of the target molecule/tissue. Herein, a method is described for creating specificity for traditionally nonspecific probes. This method utilizes MR field-cycling methods to produce MRI contrast related to the dependence of R 1 upon magnetic field. It is shown that the partial derivative of R 1 with respect to magnetic field strength, R 1 , can be used as an unambiguous measure of probe binding. Molecular imaging is the in vivo study and measurement of biological processes at the molecular level (1). Popular molecular imaging modalities include positron emission tomography, single photon emission computed tomography, MRI, and optical imaging. These modalities rely on probes or tracers to enhance sites of target molecules or tissues through the complementary processes of accumulation and activation. Accumulation occurs when the local concentration of the probe is increased through metabolic uptake or molecular adhesion and is the principle mechanism for localized image enhancement in nuclear medicine. Many varieties of probe are also activatable, their behavior mediated by interaction with the target molecule. Probes demonstrating activation are variously called "sensing," "smart," or "activatable" probes. For the purposes of this study the term activatable will be used. Activatable probes are used in both optical imaging and MRI studies to improve the specificity of the probe (2). Ideally, activatable probes would produce no image enhancement in the inactivated state; however, to date these probes combined with conventional MRI have shown image intensity enhancement in both inactivated and activated states, with relatively modest signal intensity ratios between these two states. Herein we describe a means of obtaining increased specificity in MR molecular imaging by utilizing an auxiliary electromagnet to modify the strength of the main magnetic field as a function of time in an otherwise standard MRI scanner. Due to the unique response in relaxivity of activated contrast agents, this technique allows one to specifically identify the location of activated contrast agents within an MR image.Contrast-enhanced MRI can generally be categorized as either positive or negative contrast. In positive contrast, image intensity increases at sites of MR probe accumulation as a result of the dominating effect of a decreased longitudinal relaxation time (T 1 ). In negative contrast, image intensity decreases at sites of MR probe accumulation as a result of the dominating effect of a decreased transverse relaxation time (T 2 ) (3). In this article we focus on the application of the variable fi...

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confidence: 99%

Delta relaxation enhanced MR: Improving activation‐specificity of molecular probes through R₁ dispersion imaging

Alford

Rutt

Scholl

et al. 2009

Magnetic Resonance in Med

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“…Because nuclear relaxation processes are more strongly dependent on correlation times at low frequency than at high frequency, T 1 contrast is enhanced in low field (24,25). Our experiment is ideally suited to probing T 1 in microtesla fields.…”

Section: T1-contrast Imaging a Commonly Used Technique In Clinical Mrimentioning

confidence: 97%

Microtesla MRI with a superconducting quantum interference device

McDermott

Lee

Haken

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

151

130

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MRI scanners enable fast, noninvasive, and high-resolution imaging of organs and soft tissue. The images are reconstructed from NMR signals generated by nuclear spins that precess in a static magnetic field B 0 in the presence of magnetic field gradients. Most clinical MRI scanners operate at a magnetic field B0 ‫؍‬ 1.5 T, corresponding to a proton resonance frequency of 64 MHz. Because these systems rely on large superconducting magnets, they are costly and demanding of infrastructure. On the other hand, low-field imagers have the potential to be less expensive, less confining, and more mobile. The major obstacle is the intrinsically low sensitivity of the low-field NMR experiment. Here, we show that prepolarization of the nuclear spins and detection with a superconducting quantum interference device (SQUID) yield a signal that is independent of B 0, allowing acquisition of highresolution MRIs in microtesla fields. Reduction of the strength of the measurement field eliminates inhomogeneous broadening of the NMR lines, resulting in enhanced signal-to-noise ratio and spatial resolution for a fixed strength of the magnetic field gradients used to encode the image. We present high-resolution images of phantoms and other samples and T 1-weighted contrast images acquired in highly inhomogeneous magnetic fields of 132 T; here, T 1 is the spin-lattice relaxation time. These techniques could readily be adapted to existing multichannel SQUID systems used for magnetic source imaging of brain signals. Further potential applications include low-cost systems for tumor screening and imaging peripheral regions of the body. T he conventional MRI receiver coil operates on the principle of Faraday induction (1-4): the signal is therefore proportional to the product of sample magnetization and the frequency of nuclear spin precession. In the high-temperature limit, the thermal magnetization of the sample scales linearly with the magnetic field strength. Similarly, the nuclear precession frequency is proportional to the strength of the applied field. In the case of conventional detection, therefore, the NMR signal strength scales as B 0 2 . The quadratic dependence of NMR signal on magnetic field has fuelled the drive to higher field strengths in MRI scanners for the last two decades, despite the disadvantages of converging T 1 times and increased energy deposition at higher frequencies.At the same time, there has been continued interest in the development of MRI scanners that operate at low magnetic field strengths, of the order of the earth's field (Ϸ50 T). Previous approaches to low-field MRI have relied heavily on techniques such as optical pumping (refs. 5 and 6, and ref. 7 and references therein) or prepolarization of the nuclear spins in a strong transient field (8-10) to generate enhanced, nonequilibrium nuclear magnetization and thereby boost the strength of the NMR signal. Tseng et al. (6) demonstrated MRI of hyperpolarized 3 He gas in a field of 2 mT. In the low-field imaging work of Macovski et al. (8,9), the spins we...

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“…A clear advantage of the combined scheme FFC-MRI resides in the enhancement of T 1 -weigthed (spin-lattice relaxation time) contrasts at low fields. This essential feature is a consequence of enhanced differences between the relaxation times associated to the diverse components of the sample [6]- [8]. Relaxationweighted images obtained by this technique are otherwise impossible [9]- [10].…”

Section: Introductionmentioning

confidence: 99%

Longitudinal gradient-coil with improved uniformity within the volume of interest

Dominguez

Romero

Anoardo

2014

2014 IEEE Biennial Congress of Argentina (ARGENCON)

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We present a longitudinal magnetic field gradient-coil with optimized uniformity within the volume of interest (VOI). The accuracy of the optimization algorithm was confronted with measurements of the spatial dependence of the magnetic field within the VOI in a prototype-coil. The proposed device integrates the gradient-unit of a fast-fieldcycling magnetic resonance imaging (MRI) apparatus of own design.Resumen-Se presenta una bobina de gradiente de campo magnético longitudinal con uniformidad optimizada dentro del volumen de interés (VOI). La precisión del algoritmo de optimización es cotejada con mediciones de la dependencia espacial del campo magnético en un prototipo. Este dispositivo integra la unidad de gradientes de un aparato de imágenes por resonancia magnética (IRM) con ciclado rápido de campo de diseño propio.

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MR relaxometry imaging. Work in progress.

Cited by 25 publications

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Delta relaxation enhanced MR: Improving activation‐specificity of molecular probes through R₁ dispersion imaging

Delta relaxation enhanced MR: Improving activation‐specificity of molecular probes through R₁ dispersion imaging

Microtesla MRI with a superconducting quantum interference device

Longitudinal gradient-coil with improved uniformity within the volume of interest

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MR relaxometry imaging. Work in progress.

Cited by 25 publications

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Delta relaxation enhanced MR: Improving activation‐specificity of molecular probes through R1 dispersion imaging

Delta relaxation enhanced MR: Improving activation‐specificity of molecular probes through R1 dispersion imaging

Microtesla MRI with a superconducting quantum interference device

Longitudinal gradient-coil with improved uniformity within the volume of interest

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Delta relaxation enhanced MR: Improving activation‐specificity of molecular probes through R₁ dispersion imaging

Delta relaxation enhanced MR: Improving activation‐specificity of molecular probes through R₁ dispersion imaging