MR microscopy on ratsin vivo at 4.7 T using surface coils (original) (raw)
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Solenoid coil for mouse-model MRI with a clinical 3-Tesla imager
Revista Mexicana de Fisica
A solenoid coil was built for magnetic resonance imaging of the mice. A coil prototype composed of 5 turns, with a length of 4 cm and 2.5 cm radius was developed to acquire (whole) body mouse magnetic resonance images at 130 MHz and an insertable gradient coil set. Coil performance was measured using the Q factor for both the loaded and unloaded cases were 161.67 and 178.03, respectively. These Q factors compare very well with those values reported in the literature. The images were acquired with a clinical 3 T system equipped with a custom-built gradient insert coil and gradient echo image sequence. Both phantom and in vivo images showed good signal-to-noise ratio and uniformity. The electromagnetic interaction between the insertable coils and the solenoidal coil is poor, and no image artefacts are present in the whole-body image of the mouse. This preliminary experience has shown that consistent high quality MR images of the mice can be obtained using this particular hardware configuration, making it a promising method for acquisition of high-spatial resolution MR images of mice. Volume coils are still a good choice when combined with high field MR imagers and standard gradient echo sequences for the magnetic resonance imaging of the mouse.
In vivo MR micro imaging with conventional radiofrequency coils cooled to 77�K
Magnetic Resonance in Medicine, 2000
Cryogenically cooled conventional surface coils are shown to provide significant signal-to-noise ratio (SNR) gains for MR micro imaging of tissue structure in vivo. Measurements are described which employ a simple, all-polyvinyl chloride (PVC) vacuum dewar capable of maintaining a bath of liquid nitrogen around the coil, within 5 mm of the tissue to be imaged. Images acquired in vivo at 64 MHz with a 2-cm diameter copper coil cooled to 77 K demonstrated a gain in SNR of approximately 2.7 ؎ 0.3 relative to those obtained with the same coil at room temperature under otherwise identical conditions. This increase is consistent with the reduction in coil resistance and the minor contribution to overall resistance from the imaging object. The performance of the coil is illustrated with images from the human finger and rabbit eye and potential applications are discussed.
Magma: Magnetic Resonance Materials in Physics, Biology, and Medicine, 2000
There is great interest in the non-destructive capabilities of magnetic resonance microscopy for studying murine models of both disease and normal function; however, these studies place extreme demands on the MR hardware, most notably the gradient field system. We designed, using constrained current minimum inductance methods, and fabricated a complete, unshielded three-axis gradient coil set that utilizes interleaved, multilayer axes to achieve maximum gradient strengths of over 2000 mT m-E in rise times of less than 50 I.ts with an inner coil diameter of 5 cm. The coil was wire-wound using a rectangular wire that minimizes the deposited power l\~r a given gradient efficiency. Water cooling was also incorporated into the coil to assist in thermal management. The duty cycle for the most extreme cases of single shot echo planar imaging (EPI) is limited by the thermal response and expressions for maximum rates of image collection are given for burst and continuous modes of operation. The final coil is capable of the collection of single shot EPI images with 6 mm field of view and 94 I.mi isotropic voxels at imaging rates exceeding 50 s ~. <3
Magnetic Resonance Materials in Biology, Physics, and Medicine, 2000
There is great interest in the non-destructive capabilities of magnetic resonance microscopy for studying murine models of both disease and normal function; however, these studies place extreme demands on the MR hardware, most notably the gradient field system. We designed, using constrained current minimum inductance methods, and fabricated a complete, unshielded three-axis gradient coil set that utilizes interleaved, multilayer axes to achieve maximum gradient strengths of over 2000 mT m − 1 in rise times of less than 50 ms with an inner coil diameter of 5 cm. The coil was wire-wound using a rectangular wire that minimizes the deposited power for a given gradient efficiency. Water cooling was also incorporated into the coil to assist in thermal management. The duty cycle for the most extreme cases of single shot echo planar imaging (EPI) is limited by the thermal response and expressions for maximum rates of image collection are given for burst and continuous modes of operation. The final coil is capable of the collection of single shot EPI images with 6 mm field of view and 94 mm isotropic voxels at imaging rates exceeding 50 s − 1 .
Simultaneous image acquisition from the Head (or body) coil and a surface coil
Magnetic Resonance in Medicine, 1988
Any number of coils can in principle be used simultaneously and independently in magnetic resonance imaging if the mutual inductances are sufficiently small. Surface coils and head or body coils have equal sensitivity at some crossover depth of the order of 6 to 10 cm. Using a 7.5-cm-diameter surface coil that was intrinsically isolated from the head coil, images were acquired simultaneously from both coils and combined to improve the signal-to-noise ratio at 6 cm depth by 2'12. A similar experiment with the body coil showed 2"' improvement at about 8 cm depth.
Implanted coil MR microscopy of renal pathology
Magnetic Resonance in Medicine, 1989
Inductively coupled implanted coils have been shown to provide up to a 10-fold increase in signal-to-noise ratio when compared to whole-body imaging of small animals. The current study was designed to extend the implanted coil imaging technique to a rodent model of renal pathology. Resonant radiofrequency (RF) coils were implanted around the left kidney of four rats and inductively coupled from within a birdcage body coil. All images were acquired at 2 T using a T1-weighted spin-echo sequence with TR := SO0 ms and TE = 20 ms. In vivo MR microscopy with voxels of 1 I7 X 1 17 X 2000 pm demonstrated cortex, inner and outer medulla, and major vascular structures on baseline images. Mercuric chloride-induced nephrotoxic acute tubular necrosis (ATN) diminished cortico-medullary contrast at 24 h after dosing with pathologic evaluation demonstrating nephrotoxic changes in the inner cortex. The kidney regained a baseline MR appearance 360 h after dosing and resolution of the damage was confirmed with histology. TI data were gathered on excised kidneys as an adjunct to the images to help correlate the loss and return ofcortico-medullary contrast with the pathology and pathophysiology of nephrotoxic ATN. With implanted RF coils we were able to demonstrate renal pathology and follow its subsequent resolution. Specifically, loss and return of corticomedullary contrast as a result of nephrotoxic ATN were serially documented in four rats. Such serial in vivo studies performed on single animals should further the use of MR microscopy by minimizing the number of animals required for adequate biostatistics.
Magnetic Resonance Imaging, 2006
Purpose: To acquire high-resolution magnetic resonance (MR) images, we developed a new blinking artifact reduced pulse (BARP) sequence with a surface coil specialized for microscopic imaging (47 mm in diameter). Materials and Methods: To reduce eye movement, we ascertained that the subjects' eyes were kept open and fixated to the target in the 1.5-T MR gantry. To reduce motion artifacts from blinking, we inserted rest periods for blinking (1.5 s within every 5 s) during MR scanning (T2-weighted fast spin echo; repetition time, 5 s; echo time, 100 ms; echo train, 11; matrix, 256Â128; field of view, 5 cm; 1-mm thicknessÂ30 slices). Three scans (100 sÂ3) were performed for each normal subject, and they were added together after automatic adjustment for location to reduce quality loss caused by head motion. Results: T2-weighted MR images were acquired with a high resolution and a high signal-to-noise ratio. Motion artifacts were reduced with BARP, as compared with those with random blinking. Intraocular structures such as the iris and ciliary muscles were clearly visualized. Because the whole eye can be covered with a 1-mm thickness by this method, three-dimensional maps can easily be generated from the obtained images. Conclusion: The application of BARP with a surface coil of the human eye might become a useful and widely adopted procedure for MR microimaging. D