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1.
Concepts Magn Reson Part A Bridg Educ Res ; 38A(5): 236-252, 2011 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-23204945

RESUMEN

Multi-turn spiral surface coils are constructed in flat and cylindrical arrangements and used for high field (7.1 T) mouse cardiac MRI. Their electrical and imaging performances, based on experimental measurements, simulations, and MRI experiments in free space, and under phantom, and animal loading conditions, are compared with a commercially available birdcage coil. Results show that the four-turn cylindrical spiral coil exhibits improved relative SNR (rSNR) performance to the flat coil counterpart, and compares fairly well with a commercially available birdcage coil. Phantom experiments indicate a 50% improvement in the SNR for penetration depths ≤ 6.1 mm from the coil surface compared to the birdcage coil, and an increased penetration depth at the half-maximum field response of 8 mm in the 4-spiral cylindrical coil case, in contrast to 2.9 mm in the flat 4-turn spiral case. Quantitative comparison of the performance of the two spiral coil geometries in anterior, lateral, inferior, and septal regions of the murine heart yield maximum mean percentage rSNR increases of the order of 27-167% in vivo post-mortem (cylindrical compared to flat coil). The commercially available birdcage outperforms the cylindrical spiral coil in rSNR by a factor of 3-5 times. The comprehensive approach and methodology adopted to accurately design, simulate, implement, and test radiofrequency coils of any geometry and type, under any loading conditions, can be generalized for any application of high field mouse cardiac MRI.

2.
Artículo en Inglés | MEDLINE | ID: mdl-21096736

RESUMEN

The idea of a novel MR surface coil based on multi-turn spiral geometry is presented for use in mouse cardiac MRI. The benefits from flat, cylindrical arrangement of the coil are compared using computer simulations and MRI experiments in various cases of free space, phantom and animal loading conditions. Results show that the cylindrical case compares well with a commercially available birdcage coil offering a 50% signal intensity improvement for depths of penetration up to 6.1 mm from coil surface. There is also adequate B(1) field penetration that allows visualization of the lateral and inferior walls of the murine heart.


Asunto(s)
Corazón/anatomía & histología , Imagen por Resonancia Magnética/métodos , Ondas de Radio , Animales , Ratones
3.
Magn Reson Med ; 45(3): 365-70, 2001 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-11241691

RESUMEN

Using in vivo magnetic resonance microscopy, registered (1)H and hyperpolarized (3)He images of the rat lung were obtained with a resolution of 0.098 x 0.098 x 0.469 mm (4.5 x 10(-3) mm(3)). The requisite stability and SNR was achieved through an integration of scan-synchronous ventilation, dual-frequency RF coils, anisotropic projection encoding, and variable RF excitation. The total acquisition time was 21 min for the (3)He images and 64 min for the (1)H image. Airways down to the 6th and 7th orders are clearly visible. Magn Reson Med 45:365-370, 2001.


Asunto(s)
Helio , Hidrógeno , Aumento de la Imagen , Pulmón/patología , Imagen por Resonancia Magnética/métodos , Microscopía/métodos , Animales , Anisotropía , Procesamiento de Imagen Asistido por Computador , Imagenología Tridimensional , Isótopos , Masculino , Ratas , Ratas Endogámicas F344 , Sensibilidad y Especificidad
4.
Magn Reson Imaging ; 18(6): 753-9, 2000 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-10930785

RESUMEN

We describe an MR-compatible ventilator that is computer controlled to generate a variety of breathing patterns, to minimize image degrading effects of breathing motion, and to support delivery of gas anesthesia and experimental inhalational gases. A key feature of this ventilator is the breathing valve that attaches directly to the endotracheal tube to reduce dead volume and allows independent control of inspiratory and expiratory phases of ventilation. This ventilator has been used in a wide variety of MR and x-ray microscopy studies of small animals, especially for MR imaging the lungs with hyperpolarized gases ((3)He & (129)Xe).


Asunto(s)
Pulmón/anatomía & histología , Imagen por Resonancia Magnética/métodos , Gases Nobles , Protones , Animales , Cobayas , Helio , Isótopos , Imagen por Resonancia Magnética/instrumentación , Ratones , Gases Nobles/química , Ratas , Roedores , Ventilación , Ventiladores Mecánicos
5.
NMR Biomed ; 13(4): 202-6, 2000 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-10867697

RESUMEN

Hyperpolarized helium (HP (3)He) is useful for direct MR imaging of the gas spaces of small animal lungs. Previously, breaths of 100% HP (3)He were alternated with breaths of air to maximize helium signal in the lungs and to minimize the depolarizing effects of O(2). However, for high-resolution imaging requiring many HP (3)He breaths (hundreds) and for pulmonary disease studies, a method was needed to simultaneously deliver O(2) and HP (3)He with each breath without significant loss of polarization. We modified our existing computer-controlled ventilator by adding a plastic valve, additional relays and a controller. O(2) and HP (3)He are mixed at the beginning of each breath within the body of a breathing valve, which is attached directly to the endotracheal tube. With this mixing method, we found that T(1) relaxation of HP (3)He in the guinea pig lung was about 20 s compared to 30 s with alternate air/HP (3)He breathing. Because imaging times during each breath are short (about 500 ms), the HP (3)He signal loss from O(2) contact is calculated to be less than 5%. We concluded that the advantages of mixing HP (3)He with O(2), such as shorter imaging times (reduced T(1) losses in reservoir) and improved physiologic stability, outweigh the small signal loss from the depolarizing effects of oxygen on HP (3)He.


Asunto(s)
Helio , Pulmón/fisiología , Imagen por Resonancia Magnética/métodos , Oxígeno , Pruebas de Función Respiratoria/métodos , Animales , Animales de Laboratorio , Intubación Intratraqueal , Isótopos , Pulmón/anatomía & histología , Imagen por Resonancia Magnética/instrumentación , Ratas , Pruebas de Función Respiratoria/instrumentación
6.
Magn Reson Med ; 43(3): 440-5, 2000 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-10725887

RESUMEN

Hyperpolarized (HP) 3He can be encapsulated within biologically compatible microspheres while retaining sufficient polarization to be used as a signal source for MRI. Two microsphere sizes were used, with mean diameters of 5.3 +/- 1.3 microm and 10.9 +/- 3.0 microm. These suspensions ranged in concentration from 0.9-7.0% gas by volume. Spectroscopic measurements in phantoms at 2 T yielded 3He relaxation times that varied with gas concentration. At the highest 3He concentration, the spinlattice relaxation time, T1, was 63.8 +/- 9.4 sec, while the transverse magnetization decayed with a time constant of T2* = 11.0 +/- 0.4 msec. In vivo MR images of the pelvic veins in a rat were acquired during intravenous injection of 3He microspheres (SNR approximately equal 15). Advantages such as intravascular confinement, lack of background signal, and limited recirculation indicate quantitative perfusion measurements may be improved using this novel signal source.


Asunto(s)
Helio/química , Angiografía por Resonancia Magnética , Animales , Aumento de la Imagen/métodos , Masculino , Microscopía Electrónica de Rastreo , Microesferas , Pelvis/irrigación sanguínea , Fantasmas de Imagen , Ratas
7.
Magn Reson Med ; 42(4): 721-8, 1999 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-10502761

RESUMEN

In imaging of hyperpolarized noble gases, a knowledge of the diffusion coefficient (D) is important both as a contrast mechanism and in the design of pulse sequences. We have made diffusion coefficient maps of both hyperpolarized (3)He and (129)Xe in guinea pig lungs. Along the length of the trachea, (3)He D values were on average 2.4 cm(2)/sec, closely reproducing calculated values for free gas (2.05 cm(2)/sec). The (3)He D values measured perpendicular to the length of the trachea were approximately a factor of two less, indicating restriction to diffusion. Further evidence of restricted diffusion was seen in the distal pulmonary airspaces as the average (3)He D was 0.16 cm(2)/sec. An additional cause for the smaller (3)He D in the lung was due to the presence of air, which is composed of heavier and larger gases. The (129)Xe results show similar trends, with the trachea D averaging 0.068 cm(2)/sec and the lung D averaging 0.021 cm(2)/sec. Magn Reson Med 42:721-728, 1999.


Asunto(s)
Pulmón/anatomía & histología , Imagen por Resonancia Magnética/métodos , Animales , Cobayas , Helio , Isótopos , Capacidad de Difusión Pulmonar , Isótopos de Xenón
8.
Magn Reson Med ; 42(4): 729-37, 1999 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-10502762

RESUMEN

The transverse relaxation time, T *(2), of hyperpolarized (HP) gas in the lung in vivo is an important parameter for pulse sequence optimization and image contrast. We obtained T *(2) maps of HP (3)He and (129)Xe in guinea pig lungs (n = 17) and in human lungs. Eight different sets of (3)He guinea pig studies were acquired, with variation of slice selection, tidal volume, and oxygen level. For example, for a (3)He tidal volume of 3 cm(3) and no slice selection, the average T *(2) in the trachea was 14.7 ms and 8.0 ms in the intrapulmonary airspaces. The equivalent (129)Xe experiment yielded an average T *(2) of 40.8 ms in the trachea and 18.5 ms in the intrapulmonary airspaces. The average (3)He T *(2) in the human intrapulmonary airspaces was 9.4 ms. The relaxation behavior was predicted by treating the lung as a porous medium, resulting in good agreement between estimated and measured T *(2) values in the intrapulmonary airspaces. Magn Reson Med 42:729-737, 1999.


Asunto(s)
Pulmón/anatomía & histología , Imagen por Resonancia Magnética/métodos , Animales , Cobayas , Helio , Humanos , Isótopos , Masculino , Persona de Mediana Edad , Capacidad de Difusión Pulmonar , Tráquea/anatomía & histología , Isótopos de Xenón
9.
Magn Reson Med ; 41(4): 787-92, 1999 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-10332855

RESUMEN

A new strategy designed to provide functional magnetic resonance images of the lung in small animals at microscopic resolution using hyperpolarized 3He is described. The pulse sequence is based on a combination of radial acquisition (RA) and CINE techniques, referred to as RA-CINE, and is designed for use with hyperpolarized 3He to explore lung ventilation with high temporal and spatial resolution in small animal models. Ventilation of the live guinea pig is demonstrated with effective temporal resolution of 50 msec and in-plane spatial resolution of <100 microm using hyperpolarized 3He. The RA-CINE sequence allows one to follow gas inflow and outflow in the airways as well as in the distal part of the lungs. Regional analysis of signal intensity variations can be performed and can help assess functional lung parameters such as residual gas volume and lung compliance to gas inflow.


Asunto(s)
Helio , Pulmón/fisiología , Imagen por Resonancia Cinemagnética/métodos , Animales , Cobayas , Isótopos , Pulmón/citología , Microscopía/métodos
10.
Magn Reson Med ; 41(4): 800-8, 1999 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-10332857

RESUMEN

Three-dimensional magnetic resonance images of the guinea pig lung were acquired in vivo using hyperpolarized (HP) noble gases and radial projection encoding (PE). Results obtained with 3He (voxel size 17 microl) demonstrated high image quality showing airway structure down to the 5th or 6th generations. Signal-to-noise ratios (SNRs) of 129Xe images (voxel size 40 microl) were lower by about 1 order of magnitude as a consequence of the smaller gyromagnetic ratio, a more rapid relaxation in the gas reservoir, and lower polarization and isotope abundance. Comparison between experimentally obtained SNRs and results from calculations based on a model that accounts for the three-dimensional PE acquisition scheme and the non-equilibrium situation in HP gas imaging yielded excellent agreement for small flip angles. A theoretical examination of the potential resolution in HP gas MR microscopy of the lungs suggests that in vivo visualization of alveolar clusters distal to respiratory bronchioles may be possible.


Asunto(s)
Pulmón/citología , Imagen por Resonancia Magnética/métodos , Gases Nobles , Animales , Cobayas , Microscopía , Modelos Teóricos , Sensibilidad y Especificidad
11.
Proc Natl Acad Sci U S A ; 95(18): 10832-5, 1998 Sep 01.
Artículo en Inglés | MEDLINE | ID: mdl-9724790

RESUMEN

Laser-polarized gases (3He and 129Xe) are currently being used in magnetic resonance imaging as strong signal sources that can be safely introduced into the lung. Recently, researchers have been investigating other tissues using 129Xe. These studies use xenon dissolved in a carrier such as lipid vesicles or blood. Since helium is much less soluble than xenon in these materials, 3He has been used exclusively for imaging air spaces. However, considering that the signal of 3He is more than 10 times greater than that of 129Xe for presently attainable polarization levels, this work has focused on generating a method to introduce 3He into the vascular system. We addressed the low solubility issue by producing suspensions of 3He microbubbles. Here, we provide the first vascular images obtained with laser-polarized 3He. The potential increase in signal and absence of background should allow this technique to produce high-resolution angiographic images. In addition, quantitative measurements of blood flow velocity and tissue perfusion will be feasible.


Asunto(s)
Angiografía/métodos , Imagen por Resonancia Magnética/métodos , Animales , Helio , Rayos Láser , Masculino , Ratas , Ratas Sprague-Dawley
12.
Magn Reson Med ; 40(1): 61-5, 1998 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-9660554

RESUMEN

Spatially localized lineshapes of hyperpolarized (HP) 3He in guinea pig lungs have been measured in vivo. Three different axial slice locations, each containing different compositions of airway sizes and orientations, were studied. Gas peaks from major bronchi (2 ppm) and alveoli (-2 ppm) were distinguished. The gas phase spectra show structural features that are a result of frequency shifts caused by bulk magnetic susceptibility. For a given slice, the spectral lineshapes reflect the airway composition within the slice location, according to theory. The peak assignments given here also agree with previous studies done by Wagshul et al. with HP 129Xe. At each of the slice locations, data were acquired during two phases of the breathing cycle, resulting in a relative frequency shift of approximately 0.3 ppm in the superior slices. Spectra obtained over a number of breaths show the dynamics of the gas buildup in the lung and provide further evidence supporting the peak assignments.


Asunto(s)
Helio , Pulmón/anatomía & histología , Espectroscopía de Resonancia Magnética/métodos , Animales , Cobayas , Isótopos , Intercambio Gaseoso Pulmonar , Valores de Referencia , Mecánica Respiratoria , Sensibilidad y Especificidad
13.
IEEE Trans Biomed Eng ; 45(7): 921-7, 1998 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-9644901

RESUMEN

We used in vivo magnetic resonance (MR) microscopy to follow the growth of fibrous capsule as a foreign body reaction to silicone implants in rats. Anesthetized rats were imaged 1, 7, 14, and 28 days after silicone-coated MR imaging coils were sutured to their neck muscles. On the twenty-eighth day, rats were sacrificed and coils and adjacent tissues were removed en bloc and fixed in formalin, reimaged with MR, and sectioned for conventional histology. Three-dimensional (3-D) spin-echo [3DFT] acquisition gave in-plane resolution of 32 x 32 microns in vivo and 16 x 16 microns ex vivo. All MR images showed a diffuse band of elevated signal intensity between the silicone of the coil and adjacent tissue. The border of the hyperintense band was thin and not well defined at seven days post-implantation. From 7-28 days, the band showed relatively homogeneous signal intensity and its thickness increased 44% on the rectus muscle side and 78% on the subcutaneous side. The capsule thickness determined either by MR in vivo and ex vivo microscopy or conventional histology was not significantly different, and there was a significant correlation between thickness measurements among those methods. MR in vivo microscopy provides sufficient resolution and spatial information to serially evaluate the growth of the foreign body fibrous capsule over time, thus achieving greater accuracy and consistency in measurements.


Asunto(s)
Reacción a Cuerpo Extraño/patología , Imagen por Resonancia Magnética , Prótesis e Implantes/efectos adversos , Siliconas/efectos adversos , Animales , Femenino , Reacción a Cuerpo Extraño/etiología , Microscopía/métodos , Cuello/cirugía , Ratas , Ratas Sprague-Dawley
14.
Magn Reson Med ; 39(1): 23-7, 1998 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-9438433

RESUMEN

This paper presents a fast spin echo (FSE) imaging method that employs circular sampling of k-space. The technique has been implemented on a 2 Tesla imaging system and validated on both phantoms and living animals. Experimental studies have shown that circular sampling can produce artifact-free FSE images without the need of phase correction. Although not fully explored, preliminary results also show that circular sampling may have advantages over the conventional rectilinear FSE in signal-to-noise ratio and imaging efficiency. A major disadvantage is the increased sensitivity to off-resonance effects. The authors expect that the FSE technique with circular sampling will find its applications in magnetic resonance microscopy, neuro-functional imaging, and real-time dynamic studies.


Asunto(s)
Encéfalo/anatomía & histología , Imagen Eco-Planar/métodos , Fantasmas de Imagen , Animales , Imagen Eco-Planar/instrumentación , Procesamiento de Imagen Asistido por Computador/métodos , Imagen por Resonancia Magnética/métodos , Modelos Teóricos , Ratas , Sensibilidad y Especificidad
15.
IEEE Trans Biomed Eng ; 44(11): 1107-13, 1997 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-9353990

RESUMEN

A temperature control system consisting of a thermistor, signal processor, and computer algorithm was developed for magnetic resonance (MR) microscopy of small live animals. With control of body temperature within +/- 0.2 degree C of the set point, heart rate is stabilized and, in turn, repetition time (TR) during cardiac-gated studies is less variable. Thus, image quality and resolution are improved.


Asunto(s)
Temperatura Corporal/fisiología , Retroalimentación/fisiología , Procesamiento de Señales Asistido por Computador , Termómetros , Animales , Diseño de Equipo , Hurones , Cobayas , Imagen por Resonancia Magnética , Ratones , Microscopía , Modelos Biológicos , Monitoreo Fisiológico/instrumentación , Monitoreo Fisiológico/métodos , Ratas , Respiración Artificial
16.
Magn Reson Med ; 38(1): 66-71, 1997 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-9211381

RESUMEN

The magnetization in hyperpolarized gas (HP) MRI is generated by laser polarization that is independent of the magnet and imaging process. As a consequence, there is no equilibrium magnetization during the image acquisition. The competing processes of gas inflow and depolarization of the spins lead to large changes in signal as one samples k-space. A model is developed of dynamic changes in polarization of hyperpolarized 3He during infusion and in vivo imaging of the lung and verified experimentally in a live guinea pig. Projection encoding is used to measure the view-to-view variation with temporal resolution < 4 ms. Large excitation angles effectively sample the magnetization in the early stages of inflow, highlighting larger airways, while smaller excitation angles produce images of the more distal spaces. The work provides a basis for pulse sequences designed to effectively exploit HP MRI in the lung.


Asunto(s)
Helio , Pulmón/anatomía & histología , Imagen por Resonancia Magnética/métodos , Animales , Cobayas , Isótopos , Masculino , Respiración
17.
Radiology ; 199(3): 867-70, 1996 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-8638019

RESUMEN

The authors imaged the lungs of live guinea pigs with hyperpolarized (HP) helium-3 as a magnetic resonance (MR) signal source. HP He-3 gas produced through spin exchange with rubidium metal vapor was delivered through an MR-compatible, small-animal ventilator. Two- and three-dimensional lung images acquired with ventilation-gated, radial k-space sampling showed complete ventilation of both lungs. All images were of high quality, demonstrating that HP He-3 allows high-signal-intensity MR imaging in living systems.


Asunto(s)
Pulmón/anatomía & histología , Imagen por Resonancia Magnética/métodos , Animales , Cobayas , Helio , Imagen por Resonancia Magnética/instrumentación , Imagen por Resonancia Magnética/estadística & datos numéricos , Masculino , Radioisótopos
18.
Magn Reson Med ; 34(6): 853-7, 1995 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-8598812

RESUMEN

The authors used magnetic resonance (MR) microscopy to assess hepatic tissue damage induced by bromobenzene both in living rats and in fixed rat liver tissues. Experiments were conducted at 7 Tesla on three groups of Fisher rats treated with bromobenzene at a single dose of 68, 135, and 269 mg/kg, respectively. Optical microscopy of hematoxylin and eosin stained sections showed liver damage only at the highest dose, whereas with MR microscopy, tissue alterations were detected at all three doses both in vivo and ex vivo. The contrast mechanism of the superior sensitivity of MR microscopy is believed to be related to the changes in local diffusion coefficients that accompany cellular degeneration and death, although other contrast mechanisms may also be involved. The superior sensitivity of MR microscopy, as demonstrated in this study, has many implications for potential use of MR techniques to perform in vivo histology.


Asunto(s)
Bromobencenos/toxicidad , Hígado/efectos de los fármacos , Espectroscopía de Resonancia Magnética , Animales , Relación Dosis-Respuesta a Droga , Femenino , Procesamiento de Imagen Asistido por Computador , Hígado/patología , Espectroscopía de Resonancia Magnética/métodos , Necrosis , Ratas , Ratas Endogámicas F344 , Sensibilidad y Especificidad
19.
Magn Reson Med ; 33(6): 785-9, 1995 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-7651114

RESUMEN

Neointimal hyperplasia after angioplasty was followed in vivo in rats by using MR microscopy and surgically implanted RF imaging coils. By using an inductively coupled pick-up coil, the arteries were imaged 4 days before and 3, 7, and 14 days after angioplasty with a 3DFT spin echo sequence. Eight of 10 angioplastied rats showed moderate to severe stensois based MR measures of lumen diameter reduction from baseline images. There was a good correlation between total wall thickness between MR and hematoxylin and eosin (H&E)-stained sections obtained on the last day. Arteries in the intact and sham groups remained unchanged from baseline measurements. Because this imaging technique examines the artery under in vivo conditions of arterial pressure and flow, it promises to be a useful tool for evaluating pharmacological and mechanical methods of reducing the incidence of vascular stenosis.


Asunto(s)
Angioplastia de Balón/efectos adversos , Arteria Carótida Externa/patología , Imagen por Resonancia Magnética , Animales , Traumatismos de las Arterias Carótidas , Estenosis Carotídea/patología , Estenosis Carotídea/terapia , Femenino , Hiperplasia , Microscopía , Ratas , Ratas Sprague-Dawley , Túnica Íntima/patología
20.
Magn Reson Med ; 33(2): 271-5, 1995 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-7707920

RESUMEN

Magnetic resonance images of the lungs of a guinea pig have been produced using hyperpolarized helium as the source of the MR signal. The resulting images are not yet sufficiently optimized to reveal fine structural detail within the lung, but the spectacular signal from this normally signal-deficient organ system offers great promise for eventual in vivo imaging experiments. Fast 2D and 3D GRASS sequences with very small flip angles were employed to conserve the norenewable longitudinal magnetization. We discuss various unique features associated with performing MRI with hyperpolarized gases, such as the selection of the noble gas species, polarization technique, and constraints on the MR pulse sequence.


Asunto(s)
Helio , Pulmón/anatomía & histología , Imagen por Resonancia Magnética , Animales , Cobayas , Helio/química , Helio/metabolismo , Helio/efectos de la radiación , Aumento de la Imagen/métodos , Rayos Láser , Pulmón/metabolismo , Espectroscopía de Resonancia Magnética , Rubidio/química , Rubidio/efectos de la radiación , Factores de Tiempo
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