Novel RF coil geometry for lower extremity imaging

Brown, Ryan; Mareyam, Azma; Reid, Eric; Wang, Yi

doi:10.1002/mrm.10712

Cited by 6 publications

(5 citation statements)

References 15 publications

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“…Depending upon the specific application the size, geometry and number of receiver coils to yield an "optimum result" whether it be homogeneity, localized SNR or acceleration for parallel imaging will vary, and has been extensively discussed in the literature (1,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) and remains an active area of research. In our case the number of elements in the array was limited by the number of receivers on our system (n=4).…”

Section: Resultsmentioning

confidence: 99%

4T Actively detuneable double-tuned 1H/31P head volume coil and four-channel 31P phased array for human brain spectroscopy

Avdievich

Hetherington

2007

Journal of Magnetic Resonance

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Typically 31 P in vivo magnetic resonance spectroscopic studies are limited by SNR considerations. Although phased arrays can improve the SNR; to date 31 P phased arrays for high-field systems have not been combined with 31 P volume transmit coils. Additionally, to provide anatomical reference for the 31 P studies, without removal of the coil or patient from the magnet, double-tuning ( 31 P/ 1 H) of the volume coil is required. In this work we describe a series of methods for active detuning and decoupling enabling use of phased arrays with double-tuned volume coils. To demonstrate these principles we have built and characterized an actively detuneable 31 P/ 1 H TEM volume transmit/ fourchannel 31 P phased array for 4 T magnetic resonance spectroscopic imaging (MRSI) of the human brain. The coil can be used either in volume-transmit/array-receive mode or in TEM transmit/receive mode with the array detuned. Three-fold SNR improvement was obtained at the periphery of the brain using the phased array as compared to the volume coil.

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Section: Resultsmentioning

confidence: 99%

4T Actively detuneable double-tuned 1H/31P head volume coil and four-channel 31P phased array for human brain spectroscopy

Avdievich

Hetherington

2007

Journal of Magnetic Resonance

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“…However, resolution can be increased by other means. Future high resolution imaging will require surface array coils (Brown et al 2004) with a better signal to noise ratio, rather then the volume coils used in this study. These coils could also be used for parallel acquisition to reduce the number of steps in the phase encoding direction (Griswold et al 2000).…”

Section: Discussionmentioning

confidence: 99%

Magnetic resonance microscopy of the equine hoof wall: a study of resolution and potential

Keller

Galloway

Pollitt

2010

Equine Veterinary Journal

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Summary Reasons for performing study: Obtaining magnetic resonance images of the inner hoof wall tissue at the microscopic level would enable early accurate diagnosis of laminitis and therefore more effective therapy. Objectives: To optimise magnetic resonance imaging (MRI) parameters in order to obtain the highest possible resolution of the structures beneath the equine hoof wall. Methods: Magnetic resonance microscopy (MRM) was performed in front feet from 6 cadaver horses using T2‐weighted fast spin echo (FSE‐T2), and T1‐weighted gradient echo (GRE‐T1) sequences. Results: In T2 weighted FSE images most of the stratum medium showed no signal, however the coronary, terminal and sole papillae were visible. The stratum lamellatum was clearly visible and primary epidermal lamellae could be differentiated from dermal lamellae. Conclusion: Most structures beneath the hoof wall were differentiated. Conventional scanners for diagnostic MRI in horses are low or high field. However this study used ultra‐high field scanners currently not available for clinical use. Signal‐to‐noise ratio (S/N) increases as a function of field strength. An increase of spatial resolution of the image results in a decreased S/N. S/N can also be improved with better coils and the resolution of high field MRI scanners will increase as technology develops and surface array coils become more readily available. Potential relevance: Although MR images with microscopic resolution were obtained ex vivo, this study demonstrates the potential for detection of lamellar pathology as it occurs. Early recognition of the development of laminitis to instigate effective therapy at an earlier stage and may improve the outcome for laminitic horses. Clinical MR is now readily available at 3 T, while 4 T, 7 T and 9 T systems are being used for human whole body applications.

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“…In those stud-ies, feet were examined at 0.5T (11) and 1.5T (3), and thigh (12) and calf (8) muscles were examined at 1.5T. The design of a lower-extremity coil for 1 H imaging of the lower thighs and calves at 1.5T using a unique phased array has also been reported (13 Adiabatic RF pulses have been used to compensate for the nonuniform B1 field of surface coils (16). However, adiabatic RF pulses have a long duration (typically greater than 16 msec), which makes it difficult to achieve short TEs.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of the RF field uniformity of a double‐tuned ³¹P/¹H birdcage RF coil for spin‐echo MRI/MRS of the diabetic foot

Greenman

Rakow‐Penner

2005

Magnetic Resonance Imaging

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Purpose: To evaluate the B1 field uniformity of a doubletuned birdcage coil designed for 31 P/ 1 H MRI/MRS spinecho (SE) imaging of the metatarsal head region of the foot in neuropathic diabetic patients. Materials and Methods:A low-pass double-tuned 31 P/ 1 H RF birdcage coil was constructed to fit over the adult forefoot. Flip angle (FA) maps were created from B1 data acquired at the 3T 31 P (four normal subjects) and 1 H (five normal subjects) frequencies. T2-weighted (T2-W) 1 H images, 31 P rapid acquisition with relaxation enhancement (RARE) images, and composite SE pulse CSI data were acquired to demonstrate the uniformity of the resulting images and data. Results:The means and standard deviations (SDs) of the range of FAs across the feet of the volunteer subjects indicated good uniformity (the maximum coefficients of variation (CVs) for all of the 31 P and 1 H FA maps were 7.6% and 7.3%, respectively). The FA values across the metatarsal head region indicated a maximum signal intensity variation of Ϯ3% in a RARE image acquired using an echo train length of 32. IN DIABETES, functional abnormalities of the microvasculature in the distal regions of the lower extremities result in polyneuropathy, which causes a loss of sensation, vasodilation, and motor function in the muscle (1). These complications have especially profound effects in the feet. Sensory, motor, and autonomic neuropathies in the distal regions of the extremities predispose many diabetics to traumatic insults leading to superficial ulcerations and osteomyelitis (2,3). These pathologies typically occur at the metatarsal head region of the forefoot. The energy metabolism of the muscles in this region may be a measure of the degree of ischemia and the viability of the affected tissues. Thus, a phosphorus-31/proton ( 31 P/ 1 H) MRI/MRS examination of the forefoot of diabetic patients could be valuable for assessing the severity of polyneuropathy, monitoring therapeutic intervention, and planning surgical procedures. Conclusion:Recently introduced spin-echo (SE) methods offer advantages for 31 P imaging and spectroscopy. Direct imaging of the 31 P metabolites can be accomplished with substantially reduced scan times and improved spatial resolution compared to chemical shift imaging (CSI) MRS techniques using the rapid acquisition with relaxation enhancement (RARE) (4,5) pulse sequence. Also, an SE spectroscopic technique that uses a composite excitation and refocusing pulse to reduce the echo time (TE) has been introduced (6). This technique may have advantages for 31 P spectroscopy of human skeletal muscle. The loss of early data points in the free induction decay (FID) of pulse-and-acquire sequences results in reduced SNR and baseline distortion in 31 P spectroscopy (7). It is also useful to combine SE 1 H imaging with 31 P MRS to acquire SE T2-weighted (T2-W) and proton density (PD)-weighted images (8) for anatomical registration and identification of pathology (2). However, the signal produced by SE sequences is much more susceptible to spatial ...

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Novel RF coil geometry for lower extremity imaging

Cited by 6 publications

References 15 publications

4T Actively detuneable double-tuned 1H/31P head volume coil and four-channel 31P phased array for human brain spectroscopy

4T Actively detuneable double-tuned 1H/31P head volume coil and four-channel 31P phased array for human brain spectroscopy

Magnetic resonance microscopy of the equine hoof wall: a study of resolution and potential

Evaluation of the RF field uniformity of a double‐tuned ³¹P/¹H birdcage RF coil for spin‐echo MRI/MRS of the diabetic foot

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Novel RF coil geometry for lower extremity imaging

Cited by 6 publications

References 15 publications

4T Actively detuneable double-tuned 1H/31P head volume coil and four-channel 31P phased array for human brain spectroscopy

4T Actively detuneable double-tuned 1H/31P head volume coil and four-channel 31P phased array for human brain spectroscopy

Magnetic resonance microscopy of the equine hoof wall: a study of resolution and potential

Evaluation of the RF field uniformity of a double‐tuned 31P/1H birdcage RF coil for spin‐echo MRI/MRS of the diabetic foot

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Evaluation of the RF field uniformity of a double‐tuned ³¹P/¹H birdcage RF coil for spin‐echo MRI/MRS of the diabetic foot